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  • 51. Hobara, Y.
    et al.
    Walker, S. N.
    Balikhin, M.
    Pokhotelov, O. A.
    Gedalin, M.
    Krasnoselskikh, V.
    Hayakawa, M.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dunlop, M.
    Reme, H.
    Fazakerley, A.
    Cluster observations of electrostatic solitary waves near the Earth's bow shock2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A5, p. A05211-Article in journal (Refereed)
    Abstract [en]

    Using a period of internal burst mode data from the Cluster Electric Field and Wave instrument a number of electrostatic solitary structures have been identified in the foot region of Earth's quasi-perpendicular bow shock. The four individual probe potential measurements are utilized to investigate the fundamental characteristics of the solitary wave structures such as wave propagation vector, propagation velocity, scale-size and potential amplitude. Two classes of waves are observed. Bipolar solitary waves typically propagate in the solar wind direction toward the shock but at a significant angle from the ambient magnetic field. Unipolar/tripolar solitary waves tend to propagate along the ambient magnetic field. The wave amplitude-scale size relation is similar to that obtained for similar structures observed in the auroral zone. The structures lie in the theoretically allowed region in width-amplitude space to be consistent with the BGK ion holes. Using a period of internal burst mode data from the Cluster Electric Field and Wave instrument a number of electrostatic solitary structures have been identified in the foot region of Earth's quasi-perpendicular bow shock. The four individual probe potential measurements are utilized to investigate the fundamental characteristics of the solitary wave structures such as wave propagation vector, propagation velocity, scale-size and potential amplitude. Two classes of waves are observed. Bipolar solitary waves typically propagate in the solar wind direction toward the shock but at a significant angle to the ambient magnetic field in contrast to most previous studies which assume parallel propagation to the ambient magnetic field. In contrast, unipolar/tripolar solitary waves tend to propagate along the ambient magnetic field. The wave amplitude-scale size relation is similar to that obtained for structures observed in the auroral zone. The structures lie in the theoretically allowed region in width-amplitude space to be consistent with the BGK (Bernstein-Greene-Kruskal) ion holes. The two classes of observed solitary waves may greatly influence the ambient plasma dynamics around the shock. The bipolar solitary waves do not exhibit a large net potential difference but may still play an important role in plasma thermalisation by particle scattering. Unipolar/tripolar solitary waves exhibit a remarkable net potential difference that may be responsible for the plasma energisation along the ambient magnetic field.

  • 52.
    Hole, Lars Robert
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Mohr, Hans Matthias
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Modeling of Sound Propagation in the Atmospheric Boundary Layer: Application of the MIUU Mesoscale Model1999In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 104, no D10, p. 11891-11901Article in journal (Refereed)
    Abstract [en]

    A mesoscale atmospheric model, the Meteorological Institute of Uppsala University model, has been used to simulate local wind and temperature profiles in an area with hilly terrain in eastern Norway. Simulated wind and temperature profiles (up to 250 m height above ground) have been used as input to an acoustical model, called Oases. In this way, sound propagation out to 1.4 km distance along ground has been determined for a site situated in a valley bottom in the center of the model domain. Measured ground conditions are also included in the acoustical model. During the investigated period, meteorological measurements were carried out in conjunction with measurements of low-frequency (≲100 Hz) impulse sound propagation out to a range of 1400 m along a flat, uniform, and snow-covered ground. For a case with geostrophic winds of the order of 25 m s-1 the predicted profiles are compared with profiles measured by meteorological towers and a tethered balloon launched at the site. Acoustic predictions based on both measured and simulated atmospheric profiles agree well with measured single-frequency sound levels in most cases. This suggests that forecasts of sound propagation using both a nested mesoscale atmospheric model and an acoustical model should be possible in future.

  • 53. Holohan, E.P.
    et al.
    Walter, T.R.
    Schöpfer, M.P.J.
    Walsh, J.J.
    van Wyk de Vries, B.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Origins of oblique-slip faulting during caldera subsidence2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 4, p. 1778-1794Article in journal (Refereed)
    Abstract [en]

    Although conventionally described as purely dip-slip, faults at caldera volcanoes may have a strike-slip displacement component. Examples occur in the calderas of Olympus Mons (Mars), Miyakejima (Japan) and Dolomieu (La Reunion). To investigate this phenomenon, we ran numerical and analog simulations of caldera subsidence caused by magma reservoir deflation. The numerical models constrain mechanical causes of oblique-slip faulting from the three-dimensional stress field in the initial elastic phase of subsidence. The analog experiments directly characterize the development of oblique-slip faulting, especially in the later, non-elastic phases of subsidence. The combined results of both approaches can account for the orientation, mode and location of oblique-slip faulting at natural calderas. Kinematically, oblique-slip faulting originates to resolve: (1) horizontal components of displacement that are directed radially toward the caldera centre; and (2) horizontal translation arising from off-centered or ‘asymmetric’ subsidence. We informally call these two origins the “camera iris” and “sliding trapdoor” effects, respectively. Our findings emphasize the fundamentally three-dimensional nature of deformation during caldera subsidence. They hence provide an improved basis for analyzing structural, geodetic and geophysical data from calderas, as well as analogous systems, such as mines and producing hydrocarbon reservoirs.

  • 54. Huss, M.
    et al.
    Bauder, A.
    Funk, M.
    Hock, Regine
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Environment and Landscape Dynamics.
    Determination of the seasonal mass balance of four Alpine glaciers since 18652008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no F1, p. F01015-Article in journal (Refereed)
    Abstract [en]

    Alpine glaciers have suffered major losses of ice in the last century. We compute spatially distributed seasonal mass balances of four glaciers in the Swiss Alps (Grosser Aletschgletscher, Rhonegletscher, Griesgletscher and Silvrettagletscher) for the period 1865 to 2006. The mass balance model is forced by daily air temperature and precipitation data compiled from various long-term data series. The model is calibrated using ice volume changes derived from five to nine high-resolution digital elevation models, annual discharge data and a newly compiled data set of more than 4000 in situ measurements of mass balance covering different subperiods. The cumulative mass balances over the 142 year period vary between -35 and -97 m revealing a considerable mass loss. There is no significant trend in winter balances, whereas summer balances display important fluctuations. The rate of mass loss in the 1940s was higher than in the last decade. Our approach combines different types of field data with mass balance modeling to resolve decadal scale ice volume change observations to seasonal and spatially distributed mass balance series. The results contribute to a better understanding of the climatic forcing on Alpine glaciers in the last century.

  • 55. Ivandic, Monika
    et al.
    Grevemeyer, Ingo
    Berhorst, Arnim
    Flueh, Ernst R.
    McIntosh, Kirk
    Impact of bending related faulting on the seismic properties of the incoming oceanic plate offshore of Nicaragua2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202Article in journal (Refereed)
  • 56.
    Jevrejeva, S
    et al.
    Beijing Normal University.
    Moore, John C
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Grinsted, A.
    Potential for bias in 21st century semiempirical sea level projections2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. D20116-Article in journal (Refereed)
    Abstract [en]

    We examine the limitations of a semiempirical model characterized by a sea level projection of 73 cm with RCP4.5 scenario by 2100. Calibrating the model with data to 1990 and then simulating the period 1993–2009 produces sea level in close agreement with acceleration in sea level rise observed by satellite altimetry. Nonradiative forcing contributors, such as long-term adjustment of Greenland and Antarctica ice sheets since Last Glacial Maximum, abyssal ocean warming, and terrestrial water storage, may bias model calibration which, if corrected for, tend to reduce median sea level projections at 2100 by 2–10 cm, though this is within the confidence interval. We apply the semiempirical approach to simulate individual contributions from thermal expansion and small glacier melting. Steric sea level projections agree within 3 cm of output from process-based climate models. In contrast, semiempirical simulation of melting from glaciers is 26 cm, which is twice large as estimates from some process-based models; however, all process models lack simulation of calving, which likely accounts for 50% of small glacier mass loss worldwide. Furthermore, we suggest that changes in surface mass balance and dynamics of Greenland ice sheet made contributions to the sea level rise in the early 20th century and therefore are included within the semiempirical model calibration period and hence are included in semiempirical sea level projections by 2100. Antarctic response is probably absent from semiempirical models, which will lead to a underestimate in sea level rise if, as is probable, Antarctica loses mass by 2100.

  • 57.
    Jones, A
    et al.
    Met Office Hadley Centre, Exeter, UK.
    Moore, John
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    et, al
    UX.
    The impact of abrupt suspension of solar radiation management (termination effect) in experiment G2 of the Geoengineering Model Intercomparison Project (GeoMIP)2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118Article in journal (Refereed)
  • 58.
    Jonsell, Ulf
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Hansson, Margareta E.
    Siggard-Andresen, Marie-Louise
    Steffensen,, Jörgen-Peder
    Comparison of northern and central Greenland ice core records of methanesulfonate covering the last glacial period2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no D14, p. D14313-D14313.11Article in journal (Refereed)
    Abstract [en]

    Methanesulfonate (MS-) is measured in ice cores with the objective to obtain a proxy record of marine phytoplankton production of dimethylsulfide (DMS). We present a continuous MS- record covering the last glacial period from the North Greenland Ice Core Project (NGRIP) ice core and compare this record with the corresponding records previously presented from Greenland and, in particular, with the GISP2 ice core located 320 km south of NGRIP. Despite that the records have similar mean concentrations, their responses to climatic changes during the last glacial period are slightly different. NGRIP MS- concentrations were higher during the cold marine isotopic stages (MIS) 2 and 4 and lower during the warm MIS 5. This long-term trend in MS-, which is similar to the inverse of the corresponding trend in δ 18O, is not detected in the GISP2 MS- record. A systematic response in MS- concentrations to changes between Greenland stadials and interstadials is only detected in the GISP2 record. The different responses of the MS- signals to climate change during the last glacial period are possibly related to the partitioning of air masses reaching the two sites. In contrast to observations from Antarctic records, dust concentrations do not affect the MS- concentrations in the ice, whereas the deposition of sulfate probably is enhanced by high dust concentrations in the atmosphere. The MS- signal has a higher potential of being a proxy record of DMS production changes in Greenlandic compared to Antarctic ice cores.

  • 59.
    Juhlin, Christopher
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Stephens, Michael
    Gently dipping fracture zones in Paleoproterozoic metagranite, Sweden: Evidence from reflection seismic and cored borehole data and implications for the disposal of nuclear waste2006In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 111, no B9, p. B09302-Article in journal (Refereed)
    Abstract [en]

    The Svecokarelian orogen in the coastal area north of Stockholm, central Sweden, is characterized by a complex deformation belt. In this belt, bedrock domains strike WNW-NW, dip steeply, and are affected by high ductile strain. These domains anastomose around tectonic lenses that are up to a few tens of kilometers in length and are a few kilometers wide. The bedrock within the lenses is folded and, in general, affected by lower ductile strain. Site investigations for the disposal of highly radioactive nuclear waste are presently in progress within one of these lenses. Approximately 16 km of high-resolution ( 10 m source and receiver spacing, 100 channels) seismic data were acquired in 2002 along five separate profiles ( 2 to 5 km in length) within this lens. In the southeast, reflection orientations are well determined where profiles cross one another. Here, there is a nearly one to one correlation of distinct reflections on the seismic sections with hydraulically conductive fracture zones in cored boreholes, indicating that these fracture zones control the reflectivity. However, smaller lenses of amphibolite within the fracture zones may enhance the reflectivity. The reflections dip gently to the SSE and SE, and the zones in the boreholes are dominated by fractures that show the same dip direction or are subhorizontal. A working hypothesis for the gently dipping fracture zones suggests that these structures formed as minor thrust faults during the later stages of the Svecokarelian orogeny. Mineral fillings and coatings along fractures in these zones indicate later reactivation. The current stress field, a high intensity of fractures in the zones at a high angle to sigma(3), high in situ stresses in the bedrock, and rapid glacial unloading with the development of high differential stresses may explain the large volume of groundwater in these zones. The reflection seismic data, in combination with the verifying work presented in the cored borehole data, have steered the subsequent focus in geoscientific studies to the northwestern part of the candidate area.

  • 60. Keiding, M
    et al.
    Lund, B
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Arnadottir, T
    Earthquakes, stress, and strain along an obliquely divergent plate boundary: Reykjanes Peninsula, southwest Iceland2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, p. B09306-Article in journal (Refereed)
    Abstract [en]

    We investigate the seismicity and the state of stress along the obliquely divergent Reykjanes Peninsula plate boundary and compare the directions of stress from inversion of earthquake focal mechanisms with the directions of strain rate from GPS data. The seismicity on the peninsula since early instrumental recordings in 1926 shows a systematic change from primarily earthquake swarms in the west to main shock-aftershock sequences in the east. The largest earthquakes on the Reykjanes Peninsula typically occur by right-lateral slip on N-S faults and reach magnitude 6 on the eastern part of the peninsula. During 1997-2006 most earthquakes on the Reykjanes Peninsula were located in two areas, Fagradalsfjall and Krisuvik on the central part of the peninsula, as recorded by the South Iceland Lowland (SIL) seismic network. The state of stress estimated by inversion of microearthquake focal mechanisms from the SIL catalogue is mainly oblique strike slip, with a tendency toward a normal stress state. Mapping the directions of the least compressive horizontal stress (S-hmin) shows an average Shmin direction of N(120 +/- 6)degrees E and a remarkable agreement with the directions of greatest extensional strain rate ((epsilon) over dot(Hmax)) derived from GPS velocities during 2000-2006. The agreement between the directions of stress at depth and strain rate observed at the surface indicate that the earthquakes are primarily driven by plate motion.

  • 61. Keika, K.
    et al.
    Nakamura, R.
    Baumjohann, W.
    Runov, A.
    Takada, T.
    Volwerk, M.
    Zhang, T. L.
    Klecker, B.
    Lucek, E. A.
    Carr, C.
    Reme, H.
    Dandouras, I.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Frey, H.
    Response of the inner magnetosphere and the plasma sheet to a sudden impulse2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A7, p. A07S35-Article in journal (Refereed)
    Abstract [en]

    [1] The passage of an interplanetary shock caused a sudden compression of the magnetosphere between 0900 UT and 0915 UT on 24 August 2005. An estimate of the shock normal from solar wind data obtained by Geotail upstream of the bow shock indicates symmetric compression with respect to the noon-midnight meridian. Compression-related disturbances of the magnetic and electric field and plasma motion were observed by Double Star Program (DSP) Tan Ce 1 (TC1) and Tan Ce 2 (TC2) in the inner magnetosphere and by the Cluster spacecraft in the dawnside plasma sheet. DSP/TC1 and TC2 observations suggest that the disturbances in the inner magnetosphere are propagating from the dayside magnetopause. Cluster S/C 4 observations indicate that the front normal of the disturbances in the dawnside plasma sheet is phi similar to 180 degrees at 0902: 50 UT and phi = 107 degrees at 0904: 34 UT, where phi is the longitude in GSM coordinates, if we assume that the measured electric field is on the front plane and the normal lies on the X-Y plane. The timing analysis applied to magnetic field data from the four Cluster spacecraft independently gives a front normal, which is calculated to be phi =131 degrees at about 0904: 20 UT. Shock-associated magnetic and electric field disturbances propagating from both the dayside and flank magnetopauses are detected in the plasma sheet; the latter makes the dominant contribution. Substorms are, however, not triggered at the passage of the disturbances.

  • 62. Kekonen, Teija
    et al.
    Moore, John
    Perämäki, Pekka
    Mulvaney, Rob
    Pohjola, Veijo
    miljö- och landskapsdynamik. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Environment and Landscape Dynamics. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Isaksson, Elisabeth
    van de Wal, Roderik S. W.
    800 year long ion record from the Lomonosovfonna (Svalbard) ice core2005In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 110, no D7Article in journal (Refereed)
    Abstract [en]

    We present a high-resolution record of water-soluble ion chemistry from a 121 m ice core spanning about 800 years. The core is well dated to 2/3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1/3 of the core. This core suffers from modest seasonal melt, and so we present concentration data in decadal running means to minimize percolation effects. Sea-salt ions (Na+, Cl, Mg2+, and K+) account for more than 70% of all ions. In general, sea-salt ion concentrations are rather variable and have no clear association with climatic variations. Sulfate, with 74% being from non-sea-salt sources, has higher concentrations than seen on Vestfonna ice cap but lower than in Ny-Ålesund aerosols, suggesting central Spitsbergen receives more marine (westerly) air masses than Ny-Ålesund but more sulfate enriched (easterly) air masses than Nordaustlandet. Clear anthropogenic impacts are found for sulfate, nitrate, and ammonium (and probably excess chloride) after the mid twentieth century, with sulfate showing a significant rise by the end of the nineteenth century. Sulfate and methanesulfonate concentrations correlate well during the twentieth century, and it is clear that most of the preindustrial sulfate is of biogenic origin. Terrestrial component (Ca2+) has the highest concentrations in the coldest part of the Little Ice Age, suggesting more windy conditions, transporting local terrestrial dust to the ice cap. All ion concentrations decrease at the end of the twentieth century, which reflects loss of ions by runoff, with non-sea-salt magnesium being particularly sensitive to melting.

  • 63. Korovinskiy, D. B.
    et al.
    Divin, Andrey
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Erkaev, N. V.
    Ivanova, V. V.
    Ivanov, I. B.
    Semenov, V. S.
    Lapenta, G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Markidis, S.
    Biernat, H. K.
    Zellinger, M.
    MHD modeling of the double-gradient (kink) magnetic instability2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 3, p. 1146-1158Article in journal (Refereed)
    Abstract [en]

    The paper presents the detailed numerical investigation of the "double-gradient mode," which is believed to be responsible for the magnetotail flapping oscillations-the fast vertical (normal to the layer) oscillations of the Earth's magnetotail plasma sheet with a quasiperiod similar to 100-200 s. The instability is studied using the magnetotail near-equilibrium configuration. For the first time, linear three-dimensional numerical analysis is complemented with full 3-D MHD simulations. It is known that the "double-gradient mode" has unstable solutions in the region of the tailward growth of the magnetic field component, normal to the current sheet. The unstable kink branch of the mode is the focus of our study. Linear MHD code results agree with the theory, and the growth rate is found to be close to the peak value, provided by the analytical estimates. Full 3-D simulations are initialized with the numerically relaxed magnetotail equilibrium, similar to the linear code initial condition. The calculations show that current layer with tailward gradient of the normal component of the magnetic field is unstable to wavelengths longer than the curvature radius of the field line. The segment of the current sheet with the earthward gradient of the normal component makes some stabilizing effect (the same effect is registered in the linearized MHD simulations) due to the minimum of the total pressure localized in the center of the sheet. The overall growth rate is close to the theoretical double-gradient estimate averaged over the computational domain.

  • 64.
    Kravitz, B
    et al.
    Pacific Northwest National Laboratory, Richland, Washington, USA.
    Moore, John C
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    et, al
    UX.
    Robust climate response from the Geoengineering Model Intercomparison Project (GeoMIP)2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118Article in journal (Refereed)
  • 65.
    Kullen, Anita
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ohtani, S.
    Karlsson, T.
    Geomagnetic signatures of auroral substorms preceded by pseudobreakups2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, p. A04201-Article in journal (Refereed)
    Abstract [en]

    The evolution of ten growth-phase pseudobreakups and subsequent substorms, identified in Northern Hemisphere Polar UV images during winter 1998-1999, are compared to the AE index, the unified PC indices, and GOES B field data. Comparing substorm onset (auroral breakup) with GOES data and AE and PC indices, it is found that an exact onset determination from these parameters is in most cases not possible. The three weakest substorms leave no clear signatures in the auxiliary parameters. For the other events, the AE increase appears with a time delay of 5-15 min after onset. The PC indices increase, as expected, before the AE index. The time span between PC increase and onset varies widely (-26 to 5 min). A tail dipolarization is seen in GOES data with a time delay of 2-31 min after onset. The dipolarization delay at geosynchronous orbit appears because of the GOES displacement from the tail onset region. Using the mapped GOES distance from the auroral breakup region as an estimate of GOES displacement from the breakup source region, we find that the tail dipolarization region expands in average with an azimuthal speed of 0.22 MLT min(-1) and an equatorward speed of 0.09 degrees min(-1). Pseudobreakups leave hardly any signature in AE or PC index data except in the four strongest substorm cases. In these cases, a bump appears in the PC indices during the pseudobreakup. A bump in geosynchronous B field data is found only in those two cases where GOES is located very close to the pseudobreakup tail source region.

  • 66.
    Kullén, Anita
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cumnock, J. A.
    Karlsson, T.
    Seasonal dependence and solar wind control of transpolar arc luminosity2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A8, p. A08316-Article in journal (Refereed)
    Abstract [en]

    The influence of the solar wind and the interplanetary magnetic field (IMF) on the luminosity of transpolar arcs (TPAs) is examined by taking into account seasonal effects. The study focuses on those transpolar arcs that appear after an IMF By sign change during steady northward IMF. It includes 21 northern hemisphere events identified in a previous study from global UV images taken by the Polar spacecraft between 1996 and 2000. Sorting the TPA events by sign of the Earth dipole tilt we find that the TPAs which appear in the dark hemisphere are on average much weaker than TPAs in the sunlit hemisphere. For the dark hemisphere events, no clear correlation between solar wind parameters and TPA luminosity is found. However, in the sunlit hemisphere, a clear dependence on solar wind and IMF conditions is seen. The TPA brightness is strongly influenced by IMF magnitude, northward IMF Bz and solar wind speed. A weak, negative correlation with the ion density is found. The TPA luminosity in the sunlit hemisphere is much more strongly controlled by the magnetic energy flux than by the kinetic energy flux of the solar wind. This explains the absence of transpolar arcs for the two By sign change cases for positive dipole tilts with lowest magnetic energy flux values. The strong influence of the Earth dipole tilt on the transpolar arc luminosity appears due to the dependence of the ionospheric conductivity on solar EUV emissions.

  • 67. Kurita, S.
    et al.
    Katoh, Y.
    Omura, Y.
    Angelopoulos, V.
    Cully, C. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Le Contel, O.
    Misawa, H.
    THEMIS observation of chorus elements without a gap at half the gyrofrequency2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. A11223-Article in journal (Refereed)
    Abstract [en]

    Using waveform data obtained by one of the THEMIS satellites, we report properties of rising tone chorus elements without a gap at half the gyrofrequency in a region close to the magnetic equator. The wave normal angle of the chorus elements is typically field-aligned in the entire frequency range of both upper-band and lower-band chorus emissions. We find that the observed frequency sweep rates are consistent with the estimation based on the nonlinear wave growth theory of Omura et al. (2008). In addition, we compare the frequency profiles of the chorus wave amplitudes with those of the optimum and threshold wave amplitudes derived from the nonlinear wave growth theory for triggering rising tone chorus emissions. The results of the comparison show a reasonable agreement, indicating that rising tone chorus elements are continually generated through a triggering process which generates elements with the optimum amplitudes for nonlinear growth.

  • 68.
    Köhler, Birgit
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    von Wachenfeldt, Eddie
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Kothawala, Dolly
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Tranvik, Lars J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Reactivity continuum of dissolved organic carbon decomposition in lake water2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. G01024-Article in journal (Refereed)
    Abstract [en]

    We determined microbial decomposition of dissolved organic carbon (DOC) over 3.7-year long dark bioassays of six Swedish lake waters. The overall lost DOC fraction was similar in clearwater lakes (34.8 {plus minus} 2.4%) and brownwater lakes (37.8 {plus minus} 1.9%). Reactivity continuum modeling revealed that the most labile DOC fraction, degrading at rates >0.01 day-1, was larger in the clearwater (11.1 {plus minus} 1.2%) than the brownwater lakes (0.8 {plus minus} 0.1%). The initial apparent first-order decay coefficients k was fivefold larger in the clearwater (0.0043 {plus minus} 0.0012 day-1) than the brownwater lakes (0.0009 {plus minus} 0.0003 day-1). Over time, k decreased more steeply in the clearwater than the brownwater lakes, reaching the k of the brownwater lakes within five months. Finally, k averaged 0.0001 day-1 in both lake categories. In the brownwater lakes, CDOM absorption decayed with an initial k twice as large (0.0018 {plus minus} 0.0008 day-1) as that of DOC. The initial k was inversely correlated with initial specific UV absorption and colored dissolved organic matter (CDOM) absorption, and positively correlated with initial tryptophan-like fluorescence as proxy for autochthonous DOC. Exposure to simulated sunlight at the end of the incubations caused loss of color in the clearwater lakes and loss of DOC in the brownwater lakes, where subsequent mineralization was also stimulated. The DOC lost in the absence of photochemical processes fell below previously reported watershed-scale losses in Sweden by 25% at most. This suggests that a major part of the in situ DOC loss could potentially be attributed to dark reactions alone.

  • 69. Liu, W. L.
    et al.
    Li, X.
    Sarris, T.
    Cully, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ergun, R.
    Angelopoulos, V.
    Larson, D.
    Keiling, A.
    Glassmeier, K. H.
    Auster, H. U.
    Observation and modeling of the injection observed by THEMIS and LANL satellites during the 23 March 2007 substorm event2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 2, p. A00C18-Article in journal (Refereed)
    Abstract [en]

    During the encounter of a substorm on 23 March 2007, the THEMIS constellation observed energetic particle injections and dipolarizations in the premidnight sector. Clear injection and dipolarization signatures were observed during the main intensification by three probes ( A, B, and D) in the region around 11 R-E and 2100 local time ( LT). THEMIS C, which was leading in the constellation at 8.3 R-E, also observed a clear injection signature, but the dipolarization was not so clear. From the timing based on these observations, a fast westward expanding ion injection and dipolarization front was identified. In combination with the energetic particle observations from Los Alamos National Laboratory (LANL) geosynchronous satellites, the particle injection seemed to initiate between 2100 and 0100 LT. This event provides an excellent opportunity to examine the dipolarization and particle injection processes beyond geosynchronous orbit and over a wide LT range. We model this injection event by means of test particle simulation, setting up an initial particle distribution and sending an earthward dipolarization-like pulse from the tail that also expands azimuthally, then recording the ions and electrons at the various satellite locations. Most features of the injected particles are reproduced by the test particle simulation. These include not only the earthward injections but also the fast westward expansion of the injection, as well as the timing of the injections as observed among different satellites that made the observations. On the basis of the observations and the simulation results, we suggest that this substorm injection was initiated around 2300 LT, farther down the tail, and propagated radially inward and expanded azimuthally.

  • 70. Longpré, M.A.
    et al.
    Troll, V.R.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Hansteen, T.H.
    Upper mantle magma storage under a Canarian shield volcano: Teno massif, Tenerife, Spain2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, p. 11-Article in journal (Refereed)
  • 71.
    Longpré, Marc-Antoine
    et al.
    Department of Geology, Trinity College Dublin, Dublin, Ireland.
    Troll, Valentin
    Hansteen, Thor H.
    IFM-GEOMAR, Wischhofstrasse 1-3, D-24148 Kiel, Germany.
    Upper mantle magma storage and transport under a Canarian shield-volcano, Teno, Tenerife (Spain)2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, article id B08203Article in journal (Refereed)
    Abstract [en]

    We use clinopyroxene-liquid thermobarometry, aided by petrography and mineral major element chemistry, to reconstruct the magma plumbing system of the late Miocene, largely mafic Teno shield-volcano on the island of Tenerife. Outer rims of clinopyroxene and olivine phenocrysts show patterns best explained by decompression-induced crystallization upon rapid ascent of magmas from depth. The last equilibrium crystallization of clinopyroxene occurred in the uppermost mantle, from ∼20 to 45 km depth. We propose that flexural stresses or, alternatively, thermomechanical contrasts create a magma trap that largely confines magma storage to an interval roughly coinciding with the Moho at ∼15 km and the base of the long-term elastic lithosphere at ∼40 km below sea level. Evidence for shallow magma storage is restricted to the occurrence of a thick vitric tuff of trachytic composition emplaced before the Teno shield-volcano suffered large-scale flank collapses. The scenario developed in this study may help shed light on some unresolved issues of magma supply to intraplate oceanic volcanoes characterized by relatively low magma fluxes, such as those of the Canary, Madeira and Cape Verde archipelagoes, as well as Hawaiian volcanoes in their postshield stage. The data presented also support the importance of progressive magmatic underplating in the Canary Islands.

  • 72. Lu, Quanming
    et al.
    Huang, Can
    Xie, Jinlin
    Wang, Rongsheng
    Wu, Mingyu
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wang, Shui
    Features of separatrix regions in magnetic reconnection: Comparison of 2-D particle-in-cell simulations and Cluster observations2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, p. A11208-Article in journal (Refereed)
    Abstract [en]

    In collisionless magnetic reconnection, the in-plane Hall currents are carried mainly by the magnetized electrons. The in-plane Hall currents are directed toward the X line along the magnetic field lines just inside the separatrices and away from the X line along the separatrices. Such a current system leads to the quadrupole out-of-plane magnetic field with the peaks between the regions carrying the in-plane currents. Simultaneously, the electron flow toward the X line along the separatrices causes electron density depletions along the separatrices. In this paper, the features of separatrix regions in magnetic reconnection and the relations between the electron density depletions and the out-of-plane magnetic field are investigated with both two-dimensional particle-in-cell simulations and Cluster observations. We conclude that the electron density depletions are formed because of the magnetic mirror, and they are outside the peaks of the out-of-plane magnetic field. Such a theoretical prediction is confirmed by both simulations and observations.

  • 73. Lui, A. T. Y.
    et al.
    Zheng, Y.
    Rème, H.
    Dunlop, M. W.
    Gustafsson, Georg
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Owen, C. J.
    Breakdown of the frozen-in condition in the Earth's magnetotail2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no A4, p. A04215-Article in journal (Refereed)
    Abstract [en]

    [1] We investigate in detail the breakdown of the frozen-in condition detected by Cluster at the downstream distance of similar to 19 R-E in the midnight sector of the magnetotail during a substorm expansion on 22 August 2001. It is found that the breakdown occurred ( 1) in a low-density environment with moderate to large proton plasma flow and significant fluctuations in electric and magnetic fields, ( 2) in regions with predominantly dissipation but occasionally dynamo effect, and ( 3) at times simultaneously at two Cluster satellites separated by more than 1000 km in both X- and Z-directions. Evaluation of the terms in the generalized Ohm's law indicates that the anomalous resistivity contribution arising from field fluctuations during this event is the most significant, followed by the Hall, electron viscosity, and inertial contributions in descending order of importance. This result demonstrates for the first time from observations that anomalous resistivity from field fluctuations ( implying kinetic instabilities) can play a substantial role in the breakdown of the frozen-in condition in the magnetotail during substorm expansions. Consideration of several observed features in the breakdown regions indicates that the breakdown occurs in a turbulent site resembling observed features found in current disruption and dipolarization sites.

  • 74.
    Lyon, S. W.
    et al.
    Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden.
    Grabs, T.
    Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden.
    Laudon, H.
    Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden.
    Bishop, K. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Seibert, J.
    Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden.
    Variability of groundwater levels and total organic carbon in the riparian zone of a boreal catchment2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no G1Article in journal (Refereed)
    Abstract [en]

    The riparian zone is a narrow corridor where hillslopes (and their associated hydrobiogeochemical processes) interface with the river system. As such, the riparian zone serves as the last piece of landscape with which water interacts as it transitions from being water flowing primarily through the landscape (i.e., shallow groundwater) to water flowing primarily on the landscape (i.e., stream water). This study investigates the spatiotemporal variability in riparian-zone soil water total organic carbon (TOC) and its relation to the shallow groundwater table using observations from the recently instrumented riparian observatory in the Krycklan catchment study area located in boreal northern Sweden. In general, there is a decrease in TOC concentration with depth down through the soil profile. The rate of this decrease was variable among the six monthly samplings used in this study. The spatial variability of soil water TOC in the riparian zone was connected to the spatial variability of the shallow groundwater levels. This demonstrated the importance of the temporal variation of flow pathways and the mixing of waters from different sources of TOC moving into and through the riparian zone. The coupled variation of the hydrologic and biogeochemical systems raised questions about the ability of simple lumped approaches to accurately predict how in-stream TOC concentrations will change with climate and/or land use. The integrated sampling approach in the riparian observatory covers both hydrologic and biogeochemical aspects of soil water TOC and provides a basis for development and testing of distributed, physically based transport models.

  • 75. Ma, Y. J.
    et al.
    Russell, C. T.
    Nagy, A. F.
    Toth, G.
    Bertucci, C.
    Dougherty, M. K.
    Neubauer, F. M.
    Wellbrock, A.
    Coates, A. J.
    Garnier, P.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cravens, T. E.
    Crary, F. J.
    Time-dependent global MHD simulations of Cassini T32 flyby: From magnetosphere to magnetosheath2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 3, p. A03204-Article in journal (Refereed)
    Abstract [en]

    When the Cassini spacecraft flew by Titan on 13 June 2007, at 13.6 Saturn local time, Titan was directly observed to be outside Saturn's magnetopause. Cassini observations showed dramatic changes of magnetic field orientation as well as other plasma flow parameters during the inbound and outbound segments. In this paper, we study Titan's ionospheric responses to such a sudden change in the upstream plasma conditions using a sophisticated multispecies global MHD model. Simulation results of three different cases (steady state, simple current sheet crossing, and magnetopause crossing) are presented and compared against Cassini Magnetometer, Langmuir Probe, and Cassini Plasma Spectrometer observations. The simulation results provide clear evidence for the existence of a fossil field that was induced in the ionosphere. The main interaction features, as observed by the Cassini spacecraft, are well reproduced by the time-dependent simulation cases. Simulation also reveals how the fossil field was trapped during the interaction and shows the coexistence of two pileup regions with opposite magnetic orientation, as well as the formation of a pair of new Alfven wings and tail disconnection during the magnetopause crossing process.

  • 76. Ma, Y. J.
    et al.
    Russell, C. T.
    Nagy, A. F.
    Toth, G.
    Dougherty, M. K.
    Wellbrock, A.
    Coates, A. J.
    Garnier, P.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cravens, T. E.
    Richard, M. S.
    Crary, F. J.
    The importance of thermal electron heating in Titan's ionosphere: Comparison with Cassini T34 flyby2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A10213-Article in journal (Refereed)
    Abstract [en]

    We use a new magnetohydrodynamic (MHD) model to study the effects of thermal-electron heating in Titan's ionosphere. This model improves the previously used multispecies MHD model by solving both the electron and ion pressure equations instead of a single plasma pressure equation. This improvement enables a more accurate evaluation of ion and electron temperatures inside Titan's ionosphere. The model is first applied to an idealized case, and the results are compared in detail with those of the single-pressure MHD model to illustrate the effects of the improvement. Simulation results show that the dayside ionosphere thermal pressure is larger than the upstream pressure during normal conditions, when Titan is located in the dusk region; thus Saturn's magnetic field is shielded by the highly conducting ionosphere, similar to the interaction of Venus during solar maximum conditions. This model is also applied to a special flyby of Titan, the T34 flyby, which occurred near the dusk region. It is shown that better agreement with the magnetometer data can be achieved using the two-fluid MHD model with the inclusion of the effects of thermal electron heating. The model results clearly demonstrate the importance of thermal-electron heating in Titan's ionosphere.

  • 77.
    Malehmir, Alireza
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dahlin, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Lundberg, Emil
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Sjöström, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Högdahl, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    Reflection seismic investigations in the Dannemora area, central Sweden: insights into the geometry of polyphase deformation zones and magnetite-skarn deposits2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. B11307-Article in journal (Refereed)
    Abstract [en]

    The Bergslagen region is one of the most ore prospective districts in Sweden. Presented here are results from two nearly 25 km long reflection seismic profiles crossing this region in the Dannemora mining area. The interpretations are constrained by seismic wave velocity measurements on a series of rock samples, cross-dip analysis, prestack time migration, and swath 3-D imaging, as well as by other available geophysical and geological observations. A series of major fault zones is imaged by the seismic data, as is a large mafic intrusion. However, the most prominent feature is a package of east-dipping reflectors found east of the Dannemora area that extend down to at least 3 km depth. This package is associated with a polyphase, ductile-brittle deformation zone with the latest ductile movement showing east-side-up or reverse kinematics. Its total vertical displacement is estimated to be in the order of 2.5 km. Also clearly imaged in the seismic data is a steeply dipping reflector near the Dannemora mine that extends down to a depth of at least 2.2 km. The geological nature of this reflector is not known, but it could represent either a fluid-bearing fault zone or a deep-seated iron deposit, making it an important target for further detailed geophysical and geological investigations.                   

  • 78. Mandt, Kathleen E.
    et al.
    Gell, David A.
    Perry, Mark
    Waite, J. Hunter, Jr.
    Crary, Frank A.
    Young, David
    Magee, Brian A.
    Westlake, Joseph H.
    Cravens, Thomas
    Kasprzak, Wayne
    Miller, Greg
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ågren, Karin
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Edberg, Niklas J. T.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Heays, Alan N.
    Lewis, Brenton R.
    Gibson, Stephen T.
    de la Haye, V.
    Liang, Mao-Chang
    Ion densities and composition of Titan's upper atmosphere derived from the Cassini Ion Neutral Mass Spectrometer: Analysis methods and comparison of measured ion densities to photochemical model simulations2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. E10006-Article in journal (Refereed)
    Abstract [en]

    The Cassini Ion Neutral Mass Spectrometer (INMS) has measured both neutral and ion species in Titan's upper atmosphere and ionosphere and the Enceladus plumes. Ion densities derived from INMS measurements are essential data for constraining photochemical models of Titan's ionosphere. The objective of this paper is to present an optimized method for converting raw data measured by INMS to ion densities. To do this, we conduct a detailed analysis of ground and in-flight calibration to constrain the instrument response to ion energy, the critical parameter on which the calibration is based. Data taken by the Cassini Radio Plasma Wave Science Langmuir Probe and the Cassini Plasma Spectrometer Ion Beam Spectrometer are used as independent measurement constraints in this analysis. Total ion densities derived with this method show good agreement with these data sets in the altitude region (similar to 1100-1400 km) where ion drift velocities are low and the mass of the ions is within the measurement range of the INMS (1-99 Daltons). Although ion densities calculated by the method presented here differ slightly from those presented in previous INMS publications, we find that the implications for the science presented in previous publications is mostly negligible. We demonstrate the role of the INMS ion densities in constraining photochemical models and find that (1) cross sections having high resolution as a function of wavelength are necessary for calculating the initial photoionization products and (2) there are disagreements between the measured ion densities representative of the initial steps in Titan photochemistry that require further investigation.

  • 79. Marcucci, M. F.
    et al.
    Coco, I.
    Ambrosino, D.
    Amata, E.
    Milan, S. E.
    Cattaneo, M. B. Bavassano
    Retinò, Alessandro
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Extended SuperDARN and IMAGE observations for northward IMF: Evidence for dual lobe reconnection2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A2, p. A02204-Article in journal (Refereed)
    Abstract [en]

    We present observations of ionospheric convection in the Northern Hemisphere made by the SuperDARN radar network during a 3 h period on 3 December 2001. The interplanetary magnetic field (IMF) during the time of observations is predominately northward with the By component changing from positive to slightly negative. During this period Cluster is skimming the southern high latitude dusk magnetopause and reveals that reconnection is going on quasi-continuously with the reconnection site being most of the time tailward of the southern cusp and always near the satellite location (Retino, et al., 2005). Detailed analysis of the three dimensional distribution function indicates that Cluster samples magnetosheath lines connected with geomagnetic field lines tailward of the cusps in both hemispheres (Bavassano Cattaneo et al., 2006). The evolution of the ionospheric convection measured by SuperDARN, together with IMAGE FUV observations of aurorae and DMSP particle precipitation data, confirms Cluster observations and shows that simultaneous reconnection poleward of both the northern and southern cusps occurs at a variable rate on the dusk part of the magnetosphere when the IMF clock angle is small.

  • 80.
    Martensson, E M
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.
    Nilsson, E D
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.
    de Leeuw, G
    TNO, Phys & Elect Lab, NL-2509 JG The Hague, Netherlands.
    Cohen, L H
    TNO, Phys & Elect Lab, NL-2509 JG The Hague, Netherlands.
    Hansson, H C
    Stockholm Univ, Inst Appl Environm Res, Air Pollut Lab, ITM, SE-10691 Stockholm, Sweden.
    Laboratory simulations and parameterization of the primary marine aerosol production2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no D9, p. 4297-Article in journal (Refereed)
  • 81. Matsui, H.
    et al.
    Puhl-Quinn, P. A.
    Bonnell, J. W.
    Farrugia, C. J.
    Jordanova, V. K.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Lindqvist, P. -A
    Georgescu, E.
    Torbert, R. B.
    Characteristics of storm time electric fields in the inner magnetosphere derived from Cluster data2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, p. A11215-Article in journal (Refereed)
    Abstract [en]

    Storm-time electric fields in the inner magnetosphere measured by Cluster are reported in this study. First, we show two events around the time when Dst index is at a minimum. The electric field possibly related to subauroral ion drifts and/or undershielding is measured inside the inner edge of the electron plasma sheet in the eveningside. For the second event observed in the nightside, the electric field is partly related to dipolarization and is considered as inductive. An electric field without coincident magnetic signatures is also observed. Spatial coherence of the electric field is not large when we check multispacecraft data. It is inferred that the electric field in the magnetotail penetrates inside the region 1 current, while it is not clear about the electric field within the region 2 current from our data. Then superposed epoch analyses using 71 storms are performed. Electric fields at R = 3.5-6R(E) and less than 25 degrees of magnetic latitudes are enhanced around the minimum Dst at all magnetic local times. Electric fields during the recovery phase decay on a time scale shorter than that of Dst index, which could be interpreted in terms of the relation between electric field and ring current during that storm phase. AC electric fields are generally larger than DC electric fields, indicating that the former component might play some role in accelerating ring current particles. These results will be useful to update our empirical electric field model.

  • 82. Mitchell, Stephen
    et al.
    Beven, Keith
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Freer, Jim
    Law, Beverly
    Processes influencing model-data mismatch in drought-stressed, fire-disturbed eddy flux sites2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. G02008-Article in journal (Refereed)
    Abstract [en]

    Semiarid forests are very sensitive to climatic change and among the most difficult ecosystems to accurately model. We tested the performance of the Biome-BGC model against eddy flux data taken from young (years 2004-2008), mature (years 2002-2008), and old-growth (year 2000) ponderosa pine stands at Metolius, Oregon, and subsequently examined several potential causes for model-data mismatch. We used the Generalized Likelihood Uncertainty Estimation methodology, which involved 500,000 model runs for each stand (1,500,000 total). Each simulation was run with randomly generated parameter values from a uniform distribution based on published parameter ranges, resulting in modeled estimates of net ecosystem CO2 exchange (NEE) that were compared to measured eddy flux data. Simulations for the young stand exhibited the highest level of performance, though they overestimated ecosystem C accumulation (-NEE) 99% of the time. Among the simulations for the mature and old-growth stands, 100% and 99% of the simulations underestimated ecosystem C accumulation. One obvious area of model-data mismatch is soil moisture, which was overestimated by the model in the young and old-growth stands yet underestimated in the mature stand. However, modeled estimates of soil water content and associated water deficits did not appear to be the primary cause of model-data mismatch; our analysis indicated that gross primary production can be accurately modeled even if soil moisture content is not. Instead, difficulties in adequately modeling ecosystem respiration, mainly autotrophic respiration, appeared to be the fundamental cause of model-data mismatch.

  • 83.
    Modolo, Ronan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Chanteur, G. M.
    A global hybrid model for Titan's interaction with the Kronian plasma: Application to the Cassini Ta flyby2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A1, p. A01317-Article in journal (Refereed)
    Abstract [en]

    The interaction between the corotating magnetospheric plasma of Saturn and the exosphere of Titan is investigated by means of a three-dimensional and multispecies hybrid simulation model coupling charged and neutral species via three ionizing mechanisms: the absorption of extreme ultraviolet solar photons, the impacts of magnetospheric electrons, and the charge exchange reactions between ions and neutral atoms or molecules. The simulation model includes the low and energetic components of the magnetospheric plasma, the main exospheric neutral species (molecular hydrogen and nitrogen and methane), and the atmospheric slowing down of charged particles penetrating below the exobase. Ionization rates of the exospheric species are computed as consistently as possible for each of the three ionizing mechanisms by making use of the relevant local number densities and cross sections or ionization frequencies. This model is thus able to provide a priori estimates of the escaping fluxes of exospheric ionic species and to separate for the contributions of the different ionization sources. A simulation run has been made for the conditions encountered by spacecraft Cassini during flyby Ta of Titan on 26 October 2004. Results are presented to characterize the main features of the simulated plasma environment of Titan: the induced magnetic tail and the flow of magnetospheric plasma around Titan, as well as the wake and the acceleration of the planetary plasma. Considering the coarse spatial resolution of the present simulation, these features are in reasonable agreement with in situ plasma measurements made by spacecraft Cassini.

  • 84.
    Moore, John C.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Beaudon, E.
    Kang, Shichang
    Divine, D.
    Isaksson, E.
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    van de Wal, R. S. W.
    Statistical extraction of volcanic sulphate from nonpolar ice cores2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. D03306-Article in journal (Refereed)
    Abstract [en]

    Ice cores from outside the Greenland and Antarctic ice sheets are difficult to date because of seasonal melting and multiple sources (terrestrial, marine, biogenic and anthropogenic) of sulfates deposited onto the ice. Here we present a method of volcanic sulfate extraction that relies on fitting sulfate profiles to other ion species measured along the cores in moving windows in log space. We verify the method with a well dated section of the Belukha ice core from central Eurasia. There are excellent matches to volcanoes in the preindustrial, and clear extraction of volcanic peaks in the post-1940 period when a simple method based on calcium as a proxy for terrestrial sulfate fails due to anthropogenic sulfate deposition. We then attempt to use the same statistical scheme to locate volcanic sulfate horizons within three ice cores from Svalbard and a core from Mount Everest. Volcanic sulfate is < 5% of the sulfate budget in every core, and differences in eruption signals extracted reflect the large differences in environment between western, northern and central regions of Svalbard. The Lomonosovfonna and Vestfonna cores span about the last 1000 years, with good extraction of volcanic signals, while Holtedahlfonna which extends to about AD1700 appears to lack a clear record. The Mount Everest core allows clean volcanic signal extraction and the core extends back to about AD700, slightly older than a previous flow model has suggested. The method may thus be used to extract historical volcanic records from a more diverse geographical range than hitherto.

  • 85.
    Morooka, Michiko W.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wahlund, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Farrell, W. M.
    Gurnett, D. A.
    Kurth, W. S.
    Persoon, A. M.
    Shafiq, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Andre, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Holmberg, Madeleine K. G.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Dusty plasma in the vicinity of Enceladus2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A12221-Article in journal (Refereed)
    Abstract [en]

    We present in situ Cassini Radio Plasma Wave Science observations in the vicinity of Enceladus and in the E ring of Saturn that indicate the presence of dusty plasma. The four flybys of Enceladus in 2008 revealed the following cold plasma characteristics: (1) there is a large plasma density (both ions and electrons) within the Enceladus plume region, (2) no plasma wake effect behind Enceladus was detected, (3) electron densities are generally much lower than the ion densities in the E ring (n(e)/n(i) < 0.5) as well as in the plume (n(e)/n(i) < 0.01), and (4) the average bulk ion drift speed is significantly less than the corotation speed and is instead close to the Keplerian speed. These signatures result from half or more of the electrons being attached to dust grains and by the interaction between the surrounding cold plasma and the predominantly negatively charged submicrometer-sized dust grains. The dust and plasma properties estimated from the observations clearly show that the dust-plasma interaction is collective. This strong dust-plasma coupling appears not only in the Enceladus plume but also in the Enceladus torus, typically from about 20 R(E) (similar to 5000 km) north and about 60 R(E) (similar to 15,000 km) south of Enceladus. We also suggest that the dust-plasma interaction in the E ring is the cause of the planetary spin-modulated dynamics of Saturn's magnetosphere at large.

  • 86. Motoba, T.
    et al.
    Hosokawa, K.
    Ogawa, Y.
    Sato, N.
    Kadokura, A.
    Buchert, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Reme, H.
    In situ evidence for interplanetary magnetic field induced tail twisting associated with relative displacement of conjugate auroral features2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A04209-Article in journal (Refereed)
    Abstract [en]

    We provide in situ evidence for a twisted near-Earth tail configuration that is responsible for the time sequence of conjugate auroral features associated with relative interhemispheric displacement during a weak substorm, as reported by Motoba et al. (2010). We analyzed the magnetic field data observed using four Cluster satellites in the vicinity of 11-14 R-E central downtail, in close conjunction with the Iceland-Syowa conjugate optical auroral features. Interestingly, we found that the variations in the magnetic field y component (B-y) at all satellites correlated moderately well with the variations in the time-shifted interplanetary magnetic field (IMF) clock angle (theta(CA)). The correlation coefficients (0.56 similar to 0.61) between the B-y field at Cluster and IMF theta(CA) peaked at a time delay of 52 +/- 1 min from the dayside magnetopause, probably corresponding to the time scale for the reconfiguration of the IMF theta(CA) related B-y field in the near-Earth tail. The IMF theta(CA) related B-y variation at Cluster, regarded as a manifestation of the twisting magnetotail configuration, also roughly coincided with the relative magnetic local time displacement of nightside conjugate auroral forms. These results provide strong evidence that the reconfiguration (twisting) process of the near-Earth tail on a relatively longer time scale controls the nightside conjugate auroral locations in both ionospheres.

  • 87. Mozer, F.S.
    et al.
    Retino, Alessandro
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Quantitative estimates of magnetic field reconnection properties from electric and magnetic field measurements2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no A10, p. A10206-Article in journal (Refereed)
    Abstract [en]

    Reconnection occurs in a reconnection magnetic field geometry when there are positive electric field components tangential to the magnetopause and a magnetic field component normal to it. Because these three components are the smallest of the six electric and magnetic fields, their magnitudes are difficult to determine because of errors in, or oscillations of, the assumed constant direction normal to the current sheet. A method is described for minimizing these errors by appropriate selection of the normal direction and by analyzing the correlations between the large normal electric field and the large tangential magnetic field. The correlation coefficients are equal to ratios of the small fields, which are combined with the less accurate measurements of the averages of the small fields to produce best estimates of the small fields. For more than 120 magnetopause crossings, about 40% had such correlations that signify static conditions during those crossings. This method is applied to 22 polar subsolar magnetopause crossings to show that most were located in the ion diffusion region, as defined by the change of the total magnetic field, and that 14 had a large and steady reconnection rate with a zero parallel electric field. In these events the reconnection rate decreased with increasing guide magnetic field.

  • 88.
    Mård Karlsson, Johanna
    et al.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Skelton, Alasdair
    Stockholms universitet, Institutionen för geologi och geokemi.
    Sandén, Michael
    Stockholms universitet, Institutionen för geologi och geokemi.
    Ioualalen, Mansour
    Kaewbanjak, Narngrit
    Pophet, Nuttita
    Asavanant, Jack
    von Matern, Axel
    Stockholms universitet, Institutionen för geologi och geokemi.
    Reconstructions of the coastal impact of the 2004 Indian Ocean tsunami in the Khao Lak area, Thailand2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, p. C10023-Article in journal (Refereed)
    Abstract [en]

    Khao Lak, SW Thailand was severely affected by the tsunami on 26 December 2004. Here we present reconstructions of its coastal impact in this area. These are based on (1) eyewitness reports alone and (2) eyewitness reports supported by videos and photos of the tsunami and the damage it caused, field measurements, and satellite imagery. On the basis of eyewitness reports, we estimated that the sea began retreating at 1000 local time (LT) and, based also on photos, that the tsunami arrived at 1026-1029 LT. On the basis of videos of the tsunami, we estimated an offshore wave direction of 083 +/- 3 degrees and on the basis of the paths by which eyewitnesses were carried, we estimated an onshore direction of 088 +/- 6 degrees. On the basis of videos, we calculated that the velocity of the wavefront on its final approach was 33 +/- 4 km/h. We obtained tsunami heights of 7.3 +/- 0.8 m (relative to ground level) on the basis of eyewitness reports and 8.0 +/- 0.6 m (relative to mean sea level) on the basis of field and photographic data. On the basis of eyewitness reports and photos, we concluded that Khao Lak experienced at least two main waves with a period >40 min. From eyewitness reports and satellite imagery, we measured maximum inundation <= 0.5 km in the southern part of the area, which is confined by a steeply sloping hinterland, and <= 1.5 km in the more gently sloping northern part. Comparison between these reconstructions supports the reliability of eyewitness reports as a source of quantitative data, and comparison with the numerical simulation by Ioualalen et al. (2007) supports the validity of the simulation.

  • 89. Möller, Marco
    et al.
    Finkelnburg, Roman
    Braun, Matthias
    Hock, Regine
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Jonsell, Ulf
    Pohjola, Veijo A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Scherer, Dieter
    Schneider, Christoph
    Climatic mass balance of the ice cap Vestfonna, Svalbard: A spatially distributed assessment using ERA-Interim and MODIS data2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no F3Article in journal (Refereed)
    Abstract [en]

    The ice cap Vestfonna in the northern Svalbard archipelago is one of the largest ice bodies of the European Arctic (similar to 2400 km(2)), but little is known about its mass balance. We model the climatic mass balance of the ice cap for the period September 2000 to August 2009 on a daily basis. Ablation is calculated by a spatially distributed temperature-radiation-index melt model. Air temperature forcing is provided by ERA-Interim data that is downscaled using data from an automatic weather station operated on the ice cap. Spatially distributed net shortwave radiation fluxes are obtained from standard trigonometric techniques combined with Moderate Resolution Imaging Spectroradiometer-based cloud cover and surface albedo information. Accumulation is derived from ERA-Interim precipitation data that are bias corrected and spatially distributed as a function of elevation. Refreezing is incorporated using the P(max) approach. Results indicate that mass balance years are characterized by short ablation seasons (June to August) and correspondingly longer accumulation periods (September to May). The modeled, annual climatic mass balance rate shows an almost balanced mean of -0.02 +/- 0.20 m w.e. yr(-1) (meters water equivalent per year) with an associated equilibrium line altitude of 383 +/- 54 m above sea level (mean +/- one standard deviation). The mean winter balance is +0.32 +/- 0.06 m w.e. yr(-1), and the mean summer balance -0.35 +/- 0.17 m w.e. yr(-1). Roughly one fourth of total surface ablation is retained by refreezing indicating that refreezing is an important component of the mass budget of Vestfonna.

  • 90. Nag, Amitabh
    et al.
    Rakov, Vladimir A.
    Schulz, Wolfgang
    Saba, Marcelo M. F.
    Thottappillil, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Biagi, Christopher J.
    Oliveira Filho, Alcides
    Kafri, Ahmad
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Theethayi, Nelson
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Götschl, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    First versus subsequent return-stroke current and field peaks in negative cloud-to-ground lightning discharges2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no D19, p. D19112-Article in journal (Refereed)
    Abstract [en]

    We examine relative magnitudes of electric field peaks of first and subsequent return strokes in negative cloud-to-ground lightning flashes recorded in Florida, Austria, Brazil, and Sweden. On average, the electric field peak of the first stroke is appreciably, 1.7 to 2.4 times, larger than the field peak of the subsequent stroke ( except for studies in Austria where the ratio varies from 1.0 to 2.3, depending on methodology and instrumentation). Similar results were previously reported from electric field studies in Florida, Sweden, and Sri Lanka. For comparison, directly measured peak currents for first strokes are, on average, a factor of 2.3 to 2.5 larger than those for subsequent strokes. There are some discrepancies between first versus subsequent stroke intensities reported from different studies based on data reported by lightning locating systems (LLS). The ratio of LLS-reported peak currents for first and subsequent strokes confirmed by video records is 1.7 to 2.1 in Brazil, while in the United States ( Arizona, Texas, Oklahoma, and the Great Plains) it varies from 1.1 to 1.6, depending on methodology used. The smaller ratios derived from the LLS studies are likely to be due to poor detection of relatively small subsequent strokes. The smaller values in Austria are possibly related ( at least in part) to the higher percentage ( about 50% versus 24-38% in other studies) of flashes with at least one subsequent stroke greater than the first. The effects of excluding single-stroke flashes or subsequent strokes in newly formed channels appear to be relatively small.

  • 91. Nakamura, R.
    et al.
    Baumjohann, W.
    Fujimoto, M.
    Asano, Y.
    Runov, A.
    Owen, C. J.
    Fazakerley, A. N.
    Klecker, B.
    Reme, H.
    Lucek, E. A.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cluster observations of an ion-scale current sheet in the magnetotail under the presence of a guide field2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A7, p. A07S16-Article in journal (Refereed)
    Abstract [en]

    We report on Cluster observations of a thin current sheet interval under the presence of a strong vertical bar B-Y vertical bar during a fast earthward flow interval between 1655 UT and 1703 UT on 17 August 2003. The strong vertical bar B-Y vertical bar in the tail could be associated with a strong IMF vertical bar B-Y vertical bar, but the large fluctuations in B-Y, not seen in the IMF, suggest that a varying reconnection rate causes a varying transport of B-Y-dominated magnetic flux and/or a change in B-Y due to the Hall-current system. During the encounter of the high-speed flow, an intense current layer was observed around 1655: 53 UT with a peak current density of 182 nA/m(2), the largest current density observed by the Cluster four-spacecraft magnetic field measurement in the magnetotail. The half width of this current layer was estimated to be similar to 290 km, which was comparable to the ion-inertia length. Its unique signature is that the strong current is mainly field-aligned current flowing close to the center of the plasma sheet. The event was associated with parallel heating of electrons with asymmetries, which suggests that electrons moving along the field lines can contribute to a strong dawn-to-dusk current when the magnetotail current sheet becomes sufficiently thin and active in a strong guide field case.

  • 92. Nilsson, H.
    et al.
    Barghouthi, I. A.
    Slapak, R.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hot and cold ion outflow: Observations and implications for numerical models2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, p. 105-117Article in journal (Refereed)
    Abstract [en]

    Cluster observations of oxygen ion outflow and low-frequency waves at high altitude above the polar cap and cold ion outflow in the lobes are used to determine ion heating rates and low-altitude boundary conditions suitable for use in numerical models of ion outflow. Using our results, it is possible to simultaneously reproduce observations of high-energy O+ ions in the high-altitude cusp and mantle and cold H+ ions in the magnetotail lobes. To put the Cluster data in a broader context, we first compare the average observed oxygen temperatures and parallel velocities in the high-altitude polar cap with the idealized cases of auroral (cusp) and polar wind (polar cap) ion outflow obtained from a model based on other data sets. A cyclotron resonance model using average observed electric field spectral densities as input fairly well reproduces the observed velocities and perpendicular temperatures of both hot O+ and cold H+, if we allow the fraction of the observed waves, which is efficient in heating the ions to increase with altitude and decrease toward the nightside. Suitable values for this fraction are discussed based on the results of the cyclotron resonance model. Low-altitude boundary conditions, ion heating rates, and centrifugal acceleration are presented in a format suitable as input for models aiming to reproduce the observations.

  • 93. Nilsson, H.
    et al.
    Barghouthi, I. A.
    Slapak, R.
    Eriksson, Anders I.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    André, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hot and cold ion outflow: Spatial distribution of ion heating2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, no 11, p. A11201-Article in journal (Refereed)
    Abstract [en]

    Ions apparently emanating from the same source, the ionospheric polar cap, can either end up as energized to keV energies in the high-altitude cusp/mantle, or appear as cold ions in the magnetotail lobes. We use Cluster observations of ions and wave electric fields to study the spatial variation of ion heating in the cusp/mantle and polar cap. The average flow direction in a simplified cylindrical coordinate system is used to show approximate average ion flight trajectories, and discuss the temperatures, fluxes and wave activity along some typical trajectories. It is found that it is suitable to distinguish between cusp, central and nightside polar cap ion outflow trajectories, though O + heating is mainly a function of altitude. Furthermore we use typical cold ion parallel velocities and the observed average perpendicular drift to obtain average cold ion flight trajectories. The data show that the cusp is the main source of oxygen ion outflow, whereas a polar cap source would be consistent with our average outflow paths for cold ions observed in the lobes. A majority of the cusp O + flux is sufficiently accelerated to escape into interplanetary space. A scenario with significant oxygen ion heating in regions with strong magnetosheath origin ion fluxes, cold proton plasma dominating at altitudes below about 8 R E in the polar cap, and most of the cusp oxygen outflow overcoming gravity and flowing out in the cusp and mantle is consistent with our observations.

  • 94. Nishimura, Y.
    et al.
    Bortnik, J.
    Li, W.
    Thorne, R. M.
    Chen, L.
    Lyons, L. R.
    Angelopoulos, V.
    Mende, S. B.
    Bonnell, J.
    Le Contel, O.
    Cully, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ergun, R.
    Auster, U.
    Multievent study of the correlation between pulsating aurora and whistler mode chorus emissions2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A11221-Article in journal (Refereed)
    Abstract [en]

    A multievent study was performed using conjugate measurements of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and an all-sky imager during periods of intense lower-band chorus waves. The thirteen identified cases support our previous finding, based on two events, that the intensity modulation of lower-band chorus near the magnetic equator is highly correlated with quasiperiodic pulsating auroral emissions near the spacecraft's magnetic footprint, indicating that lower-band chorus is the driver of the pulsating aurora. Furthermore, we identified a fortuitous measurement made simultaneously by two THEMIS spacecraft with small spatial separation. The two spacecraft were found to be located in a single pulsating chorus patch and the spacecraft footprints were in the same pulsating auroral patch when intense chorus bursts were measured simultaneously, whereas only one of the spacecraft's footprints was in a patch when the other spacecraft did not detect intense chorus. On the basis of this event, we can estimate the pulsating chorus patch size by mapping the pulsating auroral patches from the ionosphere toward the magnetic equator, giving a roughly circular region of similar to 5000 km diameter for corresponding azimuthally elongated patches with similar to 100 km size in the ionosphere. Using a ray-tracing-based calculation of the divergence of chorus raypaths from a point source, together with the corresponding resonant energies, we found that the chorus patch size is most probably not a result of ray divergence but a property of the wave excitation region.

  • 95.
    Norin, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Grach, S. M.
    Leyser, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Thidé, Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sergeev, E. N.
    Berlin, M.
    Ionospheric plasma density irregularities measured by stimulated electromagnetic emission2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A9, p. A09314-Article in journal (Refereed)
    Abstract [en]

    It is well known that ionospheric plasma turbulence can be conveniently generated by controlled injection of powerful high-frequency radio beams from the ground. Irradiation of the ionosphere with such radio waves leads to the formation of plasma density structures, striations, and the generation of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission (SEE). In this paper we present experimental results of the dependence of SEE on decreasing excitation levels of the striations. In the experiments the frequency of the injected radio beam was varied near the fifth harmonic of the local ionospheric electron gyro frequency. We use the SEE measurements to obtain transverse length scales of the striations involved in the generation of the SEE. Our results show that different spectral features of the SEE display different temporal dynamics, suggesting that they are related to striations with different transverse length scales (1 less than or similar to L-perpendicular to less than or similar to 25 m).

  • 96.
    Norin, Lars
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Astronomy and Space Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Grach, S. M.
    Thidé, Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sergeev, E. N.
    Leyser, T. B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Transient dynamics of secondary radiation from an HF pumped magnetized space plasma2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no A9, p. A09303-Article in journal (Refereed)
    Abstract [en]

    In order to systematically analyze the transient wave and radiation processes that are excited when a high-frequency (HF) radio wave is injected into a magnetized space plasma, we have measured the secondary radiation, or stimulated electromagnetic emission (SEE), from the ionosphere, preconditioned such that geomagnetic field-aligned plasma irregularities are already present. The transient dynamics experiments were made using a duty cycle of the HF radio wave of 200 ms (180 ms on and 20 ms off) and 100 ms (80 ms on and 20 ms off) for various frequencies near the fifth harmonic of the local ionospheric electron cyclotron frequency. Within the first 10 ms after the radio pulse turn-on, frequency downshifted structures of the SEE exhibit an overshoot with a maximum at 3 ms < t < 8 ms, whereas the upshifted spectral components do not exhibit this feature. The relative magnitude of the overshoot is strongly dependent on the frequency offset of the pump from the harmonic of the electron cyclotron frequency. A transient blue-shifted frequency component is identified. This component is upshifted from the pump by 14 kHz < Δ f< 55 kHz and exists only within the first 10 ms after the radio pulse turn-on. On a longer time scale we analyze the amplitude modulation, or "ringing," of the reflected radio wave, (also known as "quasi-periodic oscillations" or "spikes"). The ringing has a frequency of the order 15-20 Hz and we show that this phenomenon is also present in the SEE sidebands and is synchronized with the ringing of the reflected HF wave itself.

  • 97. Ogawa, Y.
    et al.
    Buchert, Stephan C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Fujii, R.
    Nozawa, S.
    van Eyken, A. P.
    Characteristics of ion upflow and downflow observed with the European Incoherent Scatter Svalbard radar2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, no 5, p. A05305-Article in journal (Refereed)
    Abstract [en]

    We have investigated how geomagnetic activity, the solar wind (SW), and the interplanetary magnetic field (IMF) influence the occurrence of the F-region/topside ionospheric ion upflow and downflow. Occurrence of dayside ion upflow observed with the European Incoherent Scatter Svalbard radar (ESR) at 75.2 degrees magnetic latitude is highly correlated with the SW density, as well as with the strength of the IMF By component. We suggest that this correlation exists because the region where ion upflow occurs is enlarged owing to SW density and IMF By magnitude, but it does not move significantly in geomagnetic latitude. The occurrence frequency of dayside ion upflow displays peaks versus the geomagnetic activity index (Kp), SW velocity, and negative IMF Bz component; that is, ion upflow is less frequently seen at the highest values of these parameters. Dayside ion downflow in the F-region/topside ionosphere occurs only when the Kp index and/or SW velocity are high or when IMF Bz is largely negative. The ion downflow is likely due to ballistic return of the ion upflow. We suggest that the region of ion upflow not only becomes larger but also moves equatorward with increasing Kp, SW velocity, and negative IMF Bz. The ESR can so be poleward of the upflow region and observe ions convecting poleward and returning ballistically downward.

  • 98. Ogawa, Y.
    et al.
    Buchert, Stephan C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Hoggstrom, I.
    Rietveld, M. T.
    Fujii, R.
    Nozawa, S.
    Miyaoka, H.
    On the statistical relation between ion upflow and naturally enhanced ion-acoustic lines observed with the EISCAT Svalbard radar2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, p. A03313-Article in journal (Refereed)
    Abstract [en]

    We have investigated characteristics of ion upflow and naturally enhanced ion-acoustic lines (NEIALs) based on the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) data continuously obtained between March 2007 and February 2008. For the ion upflow study we have used approximately 78,000 field-aligned profiles obtained with the ESR. For the NEIAL study we have identified approximately 1500 NEIALs in the ESR data at altitudes between 100 and 500 km. The occurrence frequency of ion upflow shows two peaks, at about 0800 and 1300 magnetic local time (MLT), while only one strong peak is seen around 0900 MLT for NEIALs. The upward ion flux also has only one peak around 1100-1300 MLT. The occurrence frequency of ion upflow varies strongly over season. It is higher in winter than in summer, whereas NEIALs are more frequent in summer than in winter. NEIALs frequently occur under high geomagnetic activity and also high solar activity conditions. Approximately 10% of NEIALs in the F region ionosphere were accompanied by NEIALs in the E region (occurred at altitudes below 200 km). About half of the E region enhanced echoes did not have an F region counterpart. Upshifted NEIALs dominate in the E region whereas downshifted NEIALs are usually stronger above an altitude of 300 km. The high occurrence frequency of NEIALs in the prenoon region (0800-1000 MLT) might be associated with acceleration of thermal ions to suprathermal ones. At the same MLT and geomagnetic latitude suprathermal ions and broadband extremely low frequency (BBELF) wave activity have been observed, according to previous studies.

  • 99. Ogawa, Y.
    et al.
    Buchert, Stephan C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Sakurai, A.
    Nozawa, S.
    Fujii, R.
    Solar activity dependence of ion upflow in the polar ionosphere observed with the European Incoherent Scatter (EISCAT) Tromso UHF radar2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, p. A07310-Article in journal (Refereed)
    Abstract [en]

    The influence of solar activity upon ion upflow in the polar ionosphere was investigated using data obtained by the European Incoherent Scatter (EISCAT) Tromso UHF radar between 1984 and 2008. In agreement with other work we find that the upward ion flux is generally higher when solar activity is high than when it is low. Ion upflow events and also the upward velocity behave the opposite: they are more frequently seen and higher, respectively, at times of low solar activity. In any year about 30-40% ion upflow is accompanied by similar to 500 K higher electron temperature than the background temperature at 400 km altitude. Electron and ion heating in connection with upflow is nearly twice as prevalent during high solar activity as it is at low activity. The acceleration of ions by pressure gradients and ambipolar electric field becomes larger when solar activity is low than when it is high. This variation of the average acceleration is caused by the different shapes of electron density profiles for low and high solar activities. Ions start to flow up at above 450 km altitude when solar activity was high, and lower, at 300-500 km altitude, at low solar activity. It is suggested that the solar activity influences long-term variations of the ion upflow occurrence because it modulates the density of neutral particles, the formation of the F2 density peak, and ion-neutral collision frequencies in the thermosphere and ionosphere.

  • 100. Ogawa, Y.
    et al.
    Seki, K.
    Hirahara, M.
    Asamura, K.
    Sakanoi, T.
    Buchert, Stephan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Ebihara, Y.
    Obuchi, Y.
    Yamazaki, A.
    Sandahl, I.
    Nozawa, S.
    Fujii, R.
    Coordinated EISCAT Svalbard radar and Reimei satellite observations of ion upflows and suprathermal ions2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A5, p. A05306-Article in journal (Refereed)
    Abstract [en]

    The relationship between bulk ion upflows and suprathermal ions was investigated using data simultaneously obtained from the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Reimei satellite. Simultaneous observations were conducted in November 2005 and August 2006, and 14 conjunction data sets have been obtained at approximately 630 km in the dayside ionosphere. Suprathermal ions with energies of a few eV were present in the dayside cusp region, and the ion velocity distribution changed from an isotropic Maxwellian near the cusp region to tail heating at energies above a few eV in the cusp region. The velocity distribution of the suprathermal ions has a peak perpendicular or oblique to the geomagnetic field, and the temperature of the suprathermal ions was 0.9-1.4 eV. An increase in the phase space density (PSD) of the suprathermal ions, measured with the Reimei, was correlated with bulk ion upflow observed at the same altitude using EISCAT, and with the energy flux of precipitating electrons with energies of 50-500 eV. The PSD also has a good correlation with the electron temperature, which was increased by precipitation, but not with the ion temperature (0.1-0.3 eV) at the same altitude measured with EISCAT. These results suggest that plasma waves such as broadband extremely low frequency (BBELF) wavefields associated with precipitation are connected to the bulk ion upflows in the cusp and effectively cause the heating of suprathermal ions. The heating of suprathermal ions disagrees with anisotropic heating due to O+-O resonant charge exchange.

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