Statistical evidence for O+ energization and outflow caused by wave-particle interaction in the high altitude cusp and mantle
2011 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 29, no 5, 945-954 p.Article in journal (Refereed) Published
We present a statistical study of the low (<1 Hz) frequency electric and magnetic field spectral densities observed by Cluster spacecraft in the high altitude cusp and mantle region. At the O+ gyrofrequency (0.02-0.5 Hz) for this region the electric field spectral density is on average 0.2-2.2 (mV m(-1))(2) Hz(-1), implying that resonant heating at the gyrofrequency can be intense enough to explain the observed O+ energies of 20-1400 eV. The relation between the electric and magnetic field spectral densities results in a large span of phase velocities, from a few hundred km s(-1) up to a few thousand km s(-1). In spite of the large span of phase velocity, the ratio between the calculated local Alfven velocity and the estimated phase velocity is close to unity. We provide average values of a coefficient describing diffusion in ion velocity space at different altitudes, which can be used in studies of ion energization and outflow. The observed average waves can explain the average O+ energies measured in the high altitude (8-15 R-E) cusp/mantle region of the terrestrial magnetosphere according to our test particle calculations.
Place, publisher, year, edition, pages
2011. Vol. 29, no 5, 945-954 p.
Magnetospheric physics, Magnetosphere-ionosphere interactions
IdentifiersURN: urn:nbn:se:uu:diva-155400DOI: 10.5194/angeo-29-945-2011ISI: 000291092600022OAI: oai:DiVA.org:uu-155400DiVA: diva2:425832