Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm42a03o&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM42A-03
Physics
2407 Auroral Ionosphere (2704), 2431 Ionosphere/Magnetosphere Interactions (2736)
Scientific paper
In order to understand the mechanisms of the ion heating associated with ion upflow in the topside ionosphere, we have investigated events with significant anisotropy of ion temperature measured with the EISCAT Svalbard radar and the EISCAT VHF radar. The data were obtained from November 25 to December 4, 2000. In previous studies anisotropy of ion temperature at about 300 km altitude has been found to be well correlated with strong enhancements of the electric field. This type of anisotropy is explained by ion-neutral interaction when ions and neutrals have a large relative drift velocity. Although theoretical predictions indicate that at 700 km height where our data are taken, these ion-neutral collisions are less important compared to ion-ion collisions, we have occasionally found significant correlations between anisotropy of ion temperature and perpendicular E x B drift velocity even at this high altitude. We have found that the anisotropy of ion temperature is also associated with electron density enhancements caused by precipitation, isotropic increases of electron temperature and frequent occurrence of naturally enhanced ion acoustic lines in the radar spectra. These lines are possibly related to a plasma instability. The present study indicates that at 700 km height around the cusp not only ion-neutral collision processes but also micro processes such as heating by waves play a role in heating ions and hence causing anisotropy.
Buchert Stephan C.
Fujii Ryoichi
Nozawa Satoshi
Ogawa Yasumasa
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