All Physics Faculty Publications

Document Type

Article

Journal/Book Title/Conference

Journal of Geophysical Research: Space Physics

Volume

100

Issue

A5

Publisher

American Geophysical Union

Publication Date

1995

First Page

8013

Last Page

8020

Abstract

Plasmaspheric densities have been observed previously to be higher in December than in June, with the ratio varying between 1.5 and 3.0 and with larger variations at lower L shells. In order to search for the cause of the observed annual variations, we have modeled plasmaspheric density, using a time-dependent hydrodynamic model. On an L = 2 field line with geomagnetic longitude equal to 300°, the modeled plasmaspheric densities were a factor of 1.5 times higher in December than in June. The modeled December to June density ratio was found to increase slightly with L shell, in contrast to observations; this discrepancy may be due to the fact that outer plasmaspheric flux tubes are never completely full. In addition, for an L = 2 field line with geomagnetic longitude equal to 120°, the modeled plasmaspheric density was higher in June than in December by a factor of about 1.2. Various numerical tests were also performed in order to examine the sensitivity of plasmaspheric density to various parameters. In particular, a large vertical neutral wind was applied in order to raise the O+ profile, which had the effect of raising plasmaspheric density by a factor of 6. This in conjunction with a theoretical analysis suggests that plasmaspheric density levels are very sensitive to O+ levels in the upper ionosphere. We conclude that annual variations in plasmaspheric density are due to similar variations in ionospheric O+.

Comments

Originally published by the American Geophysical Union. Abstract available online through the Journal of Geophysical Research: Space Physics.

Download

Included in

Physics Commons

Share

COinS