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Aol, S., Buchert, S. & Jurua, E. (2020). Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites. Annales Geophysicae, 38(1), 243-261
Open this publication in new window or tab >>Traits of sub-kilometre F-region irregularities as seen with the Swarm satellites
2020 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 38, no 1, p. 243-261Article in journal (Refereed) Published
Abstract [en]

During the night, in the F-region, equatorial ionospheric irregularities manifest as plasma depletions observed by satellites, and they may cause radio signals to fluctuate. In this study, the distribution characteristics of ionospheric F-region irregularities in the low latitudes were investigated using 16 Hz electron density observations made by a faceplate which is a component of the electric field instrument (EFI) onboard Swarm satellites of the European Space Agency (ESA). The study covers the period from October 2014 to October 2018 when the 16 Hz electron density data were available. For comparison, both the absolute (dN(e)) and relative (dN(e)/N-e) density perturbations were used to quantify the level of ionospheric irregularities. The two methods generally reproduced the local-time (LT), seasonal and longitudinal distribution of equatorial ionospheric irregularities as shown in earlier studies, demonstrating the ability of Swarm 16 Hz electron density data. A difference between the two methods was observed based on the latitudinal distribution of ionospheric irregularities where (dNe) showed a symmetrical distribution about the magnetic equator, while dN(e)/N-e showed a magnetic-equator-centred Gaussian distribution. High values of dNe and dN(e)/N-e were observed in spatial bins with steep gradients of electron density from a longitudinal and seasonal perspective. The response of ionospheric irregularities to geomagnetic and solar activities was also investigated using Kp index and solar radio flux index (F10.7), respectively. The reliance of dN(e)/N-e on solar and magnetic activity showed little distinction in the correlation between equatorial and off-equatorial latitudes, whereas dNe showed significant differences. With regard to seasonal and longitudinal distribution, high dNe and dN(e)/N-e values were often found during quiet magnetic periods compared to magnetically disturbed periods. The dNe increased approximately linearly from low to moderate solar activity. Using the high-resolution faceplate data, we were able to identify ionospheric irregularities on the scale of only a few hundred of metres.

Place, publisher, year, edition, pages
COPERNICUS GESELLSCHAFT MBH, 2020
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-407632 (URN)10.5194/angeo-38-243-2020 (DOI)000516603400002 ()
Available from: 2020-03-31 Created: 2020-03-31 Last updated: 2020-03-31Bibliographically approved
Archer, W. E., Gallardo-Lacourt, B., Perry, G. W., St-Maurice, J. P., Buchert, S. & Donovan, E. (2019). Steve: The Optical Signature of Intense Subauroral Ion Drifts. Geophysical Research Letters, 46(12), 6279-6286
Open this publication in new window or tab >>Steve: The Optical Signature of Intense Subauroral Ion Drifts
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2019 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 12, p. 6279-6286Article in journal (Refereed) Published
Abstract [en]

Little is currently known about the optical phenomenon known as Steve. The first scientific publication on the subject suggests that Steve is associated with an intense subauroral ion drift (SAID). However, additional inquiry is warranted as this suggested relationship as it is based on a single case study. Here we present eight occurrences of Steve with coincident or near-coincident measurements from the European Space Agency's Swarm satellites and show that Steve is consistently associated with SAID. When satellite observations coincident with Steve are compared to that of typical SAID, we find the SAID associated with Steve to have above average peak ion velocities and electron temperatures, as well as extremely low plasma densities.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2019
Keywords
ionosphere, Swarm satellites, SAID, Steve
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-392879 (URN)10.1029/2019GL082687 (DOI)000477616300014 ()
Available from: 2019-09-24 Created: 2019-09-24 Last updated: 2019-09-24Bibliographically approved
Lomidze, L., Knudsen, D. J., Burchill, J., Kouznetsov, A. & Buchert, S. (2018). Calibration and Validation of Swarm Plasma Densities and Electron Temperatures Using Ground-Based Radars and Satellite Radio Occultation Measurements. Radio Science, 53(1), 15-36
Open this publication in new window or tab >>Calibration and Validation of Swarm Plasma Densities and Electron Temperatures Using Ground-Based Radars and Satellite Radio Occultation Measurements
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2018 (English)In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 53, no 1, p. 15-36Article in journal (Refereed) Published
Abstract [en]

In this study we calibrate and validate in situ ionospheric electron density (N-e) and temperature (T-e) measured with Langmuir probes (LPs) on the three Swarm satellites orbiting the Earth in circular, nearly polar orbits at similar to 500km altitude. We assess the accuracy and reliability of the LP data (December 2013 to June 2016) by using nearly coincident measurements from low- and middle-latitude incoherent scatter radars (ISRs), low-latitude ionosondes, and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites, covering all latitudes. The comparison results for plasma frequency (f alpha root Ne) for each Swarm satellite are consistent across these three, principally different measurement techniques. It shows that the Swarm LPs systematically underestimate plasma frequency by about 10% (0.5-0.6MHz). The correlation coefficients are high (0.97), indicating accurate relative variation in the Swarm LP densities. The comparison of T-e from high-gain LPs and those from ISRs reveals that all three satellites overestimate it by 300-400K but exhibit high correlations (0.92-0.97) against the validation data. The low-gain LP T-e data show larger overestimation (similar to 700K) and lower correlation (0.86-0.90). The adjustment of the Swarm LP data based on Swarm-ISR comparison results removes the systematic biases in the Swarm data and gives plasma frequencies and high- and low-gain electron temperatures that are precise within about 0.4MHz (8%), 150-230K, and 260-360K, respectively. We demonstrate that the applied correction significantly improves the agreement between (1) the plasma densities from Swarm, and from ionosondes and COSMIC, and (2) the T-e from Swarm LPs and International Reference Ionosphere 2016.

Keywords
Swarm, Langmuir probe, electron density, electron temperature, validation, calibration
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-348796 (URN)10.1002/2017RS006415 (DOI)000425595100002 ()
Available from: 2018-04-24 Created: 2018-04-24 Last updated: 2018-04-24Bibliographically approved
Andrews, D. J., Opgenoorth, H. J., Leyser, T. B., Buchert, S., Edberg, N. J. T., Morgan, D. D., . . . Withers, P. (2018). MARSIS Observations of Field-Aligned Irregularities and Ducted Radio Propagation in the Martian Ionosphere. Journal of Geophysical Research - Space Physics, 123(8), 6251-6263
Open this publication in new window or tab >>MARSIS Observations of Field-Aligned Irregularities and Ducted Radio Propagation in the Martian Ionosphere
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 8, p. 6251-6263Article in journal (Refereed) Published
Abstract [en]

Knowledge of Mars's ionosphere has been significantly advanced in recent years by observations from Mars Express and lately Mars Atmosphere and Volatile EvolutioN. A topic of particular interest are the interactions between the planet's ionospheric plasma and its highly structured crustal magnetic fields and how these lead to the redistribution of plasma and affect the propagation of radio waves in the system. In this paper, we elucidate a possible relationship between two anomalous radar signatures previously reported in observations from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on Mars Express. Relatively uncommon observations of localized, extreme increases in the ionospheric peak density in regions of radial (cusp-like) magnetic fields and spread echo radar signatures are shown to be coincident with ducting of the same radar pulses at higher altitudes on the same field lines. We suggest that these two observations are both caused by a high electric field (perpendicular to B) having distinctly different effects in two altitude regimes. At lower altitudes, where ions are demagnetized and electrons magnetized, and recombination dominantes, a high electric field causes irregularities, plasma turbulence, electron heating, slower recombination, and ultimately enhanced plasma densities. However, at higher altitudes, where both ions and electrons are magnetized and atomic oxygen ions cannot recombine directly, the high electric field instead causes frictional heating, a faster production of molecular ions by charge exchange, and so a density decrease. The latter enables ducting of radar pulses on closed field lines, in an analogous fashion to interhemispheric ducting in the Earth's ionosphere.

Keywords
Mars, ionosphere, irregularities, MARSIS, crustal fields, plasma
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368054 (URN)10.1029/2018JA025663 (DOI)000445731300011 ()
Funder
Swedish Research Council, 621-2014-5526Swedish National Space Board, 162/14
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07Bibliographically approved
Marque, C., Klein, K.-L., Monstein, C., Opgenoorth, H. J., Pulkkinen, A., Buchert, S., . . . Thulesen, P. (2018). Solar radio emission as a disturbance of aeronautical radionavigation. Journal of Space Weather and Space Climate, 8, Article ID A42.
Open this publication in new window or tab >>Solar radio emission as a disturbance of aeronautical radionavigation
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2018 (English)In: Journal of Space Weather and Space Climate, ISSN 2115-7251, E-ISSN 2115-7251, Vol. 8, article id A42Article in journal (Refereed) Published
Abstract [en]

On November 4th, 2015 secondary air traffic control radar was strongly disturbed in Sweden and some other European countries. The disturbances occurred when the radar antennas were pointing at the Sun. In this paper, we show that the disturbances coincided with the time of peaks of an exceptionally strong (similar to 10(5) Solar Flux Units) solar radio burst in a relatively narrow frequency range around 1 GHz. This indicates that this radio burst is the most probable space weather candidate for explaining the radar disturbances. The dynamic radio spectrum shows that the high flux densities are not due to synchrotron emission of energetic electrons, but to coherent emission processes, which produce a large variety of rapidly varying short bursts (such as pulsations, fiber bursts, and zebra patterns). The radio burst occurs outside the impulsive phase of the associated flare, about 30 min after the soft X-ray peak, and it is temporarily associated with fast evolving activity occurring in strong solar magnetic fields. While the relationship with strong magnetic fields and the coherent spectral nature of the radio burst provide hints towards the physical processes which generate such disturbances, we have so far no means to forecast them. Well-calibrated monitoring instruments of whole Sun radio fluxes covering the UHF band could at least provide a real-time identification of the origin of such disturbances, which reports in the literature show to also affect GPS signal reception.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
Sun: radio radiation, Sun: flares, Sun: solar-terrestrial relations
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-367389 (URN)10.1051/swsc/2018029 (DOI)000446555400002 ()
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2018-12-04Bibliographically approved
Aikio, A. T., Vanhamaeki, H., Workayehu, A. B., Virtanen, I. I., Kauristie, K., Juusola, L., . . . Knudsen, D. (2018). Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight. Journal of Geophysical Research - Space Physics, 123(6), 5140-5158
Open this publication in new window or tab >>Swarm Satellite and EISCAT Radar Observations of a Plasma Flow Channel in the Auroral Oval Near Magnetic Midnight
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2018 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, no 6, p. 5140-5158Article in journal (Refereed) Published
Abstract [en]

We present Swarm satellite and EISCAT radar observations of electrodynamical parameters in the midnight sector at high latitudes. The most striking feature is a plasma flow channel located equatorward of the polar cap boundary within the dawn convection cell. The flow channel is 1.5 degrees wide in latitude and contains southward electric field of 150 mV/m, corresponding to eastward plasma velocities of 3,300 m/s in the F-region ionosphere. The theoretically computed ion temperature enhancement produced by the observed ion velocity is in accordance with the measured one by the EISCAT radar. The total width of the auroral oval is about 10 degrees in latitude. While the poleward part is electric field dominant with low conductivity and the flow channel, the equatorward part is conductivity dominant with at least five auroral arcs. The main part of the westward electrojet flows in the conductivity dominant part, but it extends to the electric field dominant part. According to Kamide and Kokubun (1996), the whole midnight sector westward electrojet is expected to be conductivity dominant, so the studied event challenges the traditional view. The flow channel is observed after substorm onset. We suggest that the observed flow channel, which is associated with a 13-kV horizontal potential difference, accommodates increased nightside plasma flows during the substorm expansion phase as a result of reconnection in the near-Earth magnetotail.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2018
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-362178 (URN)10.1029/2018JA025409 (DOI)000439803100044 ()
Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2018-10-04Bibliographically approved
Knudsen, D. J., Burchill, J. K., Buchert, S., Eriksson, A., Gill, R., Wahlund, J.-E., . . . Moffat, B. (2017). Thermal ion imagers and Langmuir probes in the Swarm electric field instruments. Journal of Geophysical Research - Space Physics, 122(2), 2655-2673
Open this publication in new window or tab >>Thermal ion imagers and Langmuir probes in the Swarm electric field instruments
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 2, p. 2655-2673Article in journal (Refereed) Published
Abstract [en]

The European Space Agency's three Swarm satellites were launched on 22 November 2013 into nearly polar, circular orbits, eventually reaching altitudes of 460 km (Swarm A and C) and 510 km (Swarm B). Swarm's multiyear mission is to make precision, multipoint measurements of low-frequency magnetic and electric fields in Earth's ionosphere for the purpose of characterizing magnetic fields generated both inside and external to the Earth, along with the electric fields and other plasma parameters associated with electric current systems in the ionosphere and magnetosphere. Electric fields perpendicular to the magnetic field.B are determined through ion drift velocity v(i) and magnetic field measurements via the relation.E. = -.vi x.B. Ion drift is derived from two-dimensional images of low-energy ion distribution functions provided by two Thermal Ion Imager (TII) sensors viewing in the horizontal and vertical planes;v(i) is corrected for spacecraft potential as determined by two Langmuir probes (LPs) which also measure plasma density ne and electron temperature T-e. The TII sensors use a microchannel-plate-intensified phosphor screen imaged by a charge-coupled device to generate high-resolution distribution images (66 x 40 pixels) at a rate of 16 s(-1). Images are partially processed on board and further on the ground to generate calibrated data products at a rate of 2 s(-1); these include.vi,.E., and ion temperature T-i in addition to electron temperature Te and plasma density n(e) from the LPs.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-359803 (URN)10.1002/2016JA022571 (DOI)000397022900083 ()
Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2018-09-24Bibliographically approved
Zou, Y., Nishimura, Y., Burchill, J. K., Knudsen, D. J., Lyons, L. R., Shiokawa, K., . . . Nishitani, N. (2016). Localized field-aligned currents in the polar cap associated with airglow patches. Journal of Geophysical Research - Space Physics, 121(10), 10172-10189
Open this publication in new window or tab >>Localized field-aligned currents in the polar cap associated with airglow patches
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2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 10, p. 10172-10189Article in journal (Refereed) Published
Abstract [en]

Airglow patches have been recently associated with channels of enhanced antisunward ionospheric flows propagating across the polar cap from the dayside to nightside auroral ovals. However, how these flows maintain their localized nature without diffusing away remains unsolved. We examine whether patches and collocated flows are associated with localized field-aligned currents (FACs) in the polar cap by using coordinated observations of the Swarm spacecraft, a polar cap all-sky imager, and Super Dual Auroral Radar Network (SuperDARN) radars. We commonly (66% of cases) identify substantial FAC enhancements around patches, particularly near the patches' leading edge and center, in contrast to what is seen in the otherwise quiet polar cap. These FACs have densities of 0.1-0.2 mu A/m(-2) and have a distribution of width peaking at similar to 75 km. They can be approximated as infinite current sheets that are orientated roughly parallel to patches. They usually exhibit a Region 1 sense, i.e., a downward FAC lying eastward of an upward FAC. With the addition of Resolute Bay Incoherent Scatter radar data, we find that the FACs can close through Pedersen currents in the ionosphere, consistent with the locally enhanced dawn-dusk electric field across the patch. Our results suggest that ionospheric polar cap flow channels are imposed by structures in the magnetospheric lobe via FACs, and thus manifest mesoscale magnetosphere-ionosphere coupling embedded in large-scale convection.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-312119 (URN)10.1002/2016JA022665 (DOI)000388965900056 ()
Available from: 2017-01-09 Created: 2017-01-04 Last updated: 2017-11-29Bibliographically approved
Park, J., Stolle, C., Xiong, C., Luehr, H., Pfaff, R. F., Buchert, S. & Martinis, C. R. (2015). A dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions. Geophysical Research Letters, 42(4), 967-974
Open this publication in new window or tab >>A dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions
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2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 4, p. 967-974Article in journal (Refereed) Published
Abstract [en]

In this study we investigate a dayside, midlatitude plasma depletion (DMLPD) encountered on 22 May 2014 by the Swarm and GRACE satellites, as well as ground-based instruments. The DMLPD was observed near Puerto Rico by Swarm near 10 LT under quiet geomagnetic conditions at altitudes of 475-520 km and magnetic latitudes of similar to 25 degrees-30 degrees. The DMLPD was also revealed in total electron content observations by the Saint Croix station and by the GRACE satellites (430 km) near 16 LT and near the same geographic location. The unique Swarm constellation enables the horizontal tilt of the DMLPD to be measured (35 degrees clockwise from the geomagnetic east-west direction). Ground-based airglow images at Arecibo showed no evidence for plasma density depletions during the night prior to this dayside event. The C/NOFS equatorial satellite showed evidence for very modest plasma density depletions that had rotated into the morningside from nightside. However, the equatorial depletions do not appear related to the DMLPD, for which the magnetic apex height is about 2500 km. The origins of the DMLPD are unknown, but may be related to gravity waves.

National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-252033 (URN)10.1002/2014GL062655 (DOI)000351851900001 ()
Available from: 2015-04-30 Created: 2015-04-28 Last updated: 2017-12-04Bibliographically approved
Park, J., Luehr, H., Stolle, C., Malhotra, G., Baker, J. B., Buchert, S. & Gill, R. (2015). Estimating along-track plasma drift speed from electron density measurements by the three Swarm satellites. Annales Geophysicae, 33(7), 829-835
Open this publication in new window or tab >>Estimating along-track plasma drift speed from electron density measurements by the three Swarm satellites
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2015 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 33, no 7, p. 829-835Article in journal (Refereed) Published
Abstract [en]

Plasma convection in the high-latitude ionosphere provides important information about magnetosphere-ionosphere-thermosphere coupling. In this study we estimate the along-track component of plasma convection within and around the polar cap, using electron density profiles measured by the three Swarm satellites. The velocity values estimated from the two different satellite pairs agree with each other. In both hemispheres the estimated velocity is generally anti-sunward, especially for higher speeds. The obtained velocity is in qualitative agreement with Super Dual Auroral Radar Network data. Our method can supplement currently available instruments for ionospheric plasma velocity measurements, especially in cases where these traditional instruments suffer from their inherent limitations. Also, the method can be generalized to other satellite constellations carrying electron density probes.

Keywords
Ionosphere, Plasma convection
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-261328 (URN)10.5194/angeo-33-829-2015 (DOI)000358800400003 ()
Available from: 2015-09-01 Created: 2015-09-01 Last updated: 2017-12-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2158-6074

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