Observations of Topside Ionospheric Responses at 600 km Altitude During the April 17, 2002 Storm Period

Details Observations of Topside Ionospheric Responses at 600 km Altitude During the April 17, 2002 Storm Period Observations of Topside Ionospheric Responses at 600 km Altitude During the April 17, 2002 Storm Period

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsa21b0458s&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SA21B-0458

Physics

2435 Ionospheric Disturbances, 2437 Ionospheric Dynamics, 2439 Ionospheric Irregularities, 2481 Topside Ionosphere

Scientific paper

The ROCSAT-1 orbiting at 600 km altitude observes a textbook-like response of the plasma flow variations in the topside ionosphere during the April 17, 2002 magnetic storm. At the impingement of the interplanetary shock, low frequency Pi-1 plasma flow oscillations at the noon sector have been observed for more than two minutes. The storm induced disturbance dynamo effect begins an hour later with the post-midnight enhancement of the upward flow pattern described in the model of Scherliess and Fejer [1997], and the enhanced zonal flow pattern described in the model of Heelis and Coley [1992]. However, the dynamo induced vertical electric field is noticed to decay at a faster rate than the induced eastward electric field in the post-midnight sector. A unusually large density depletion is then observed at the end of this disturbance dynamo effect. It occurs at the mid-latitude of 34o (27o dip latitude) at the sunrise terminator. The density decreases more than two orders of magnitude from the background level and the depletion width is about 500 km wide. An upward flow of 750 m/s is found inside the depletion. The NO ions found inside the depletion region implies that the depletion has been raised from the bottom-side ionosphere in accordance with the large upward flow observed. Large and rapid east-west reversing flows up to 300 m/s are also observed together with large parallel flow variations of similar magnitudes. The temperature inside the depletion is found to increase to 2400 K from the background temperature of 1400 K outside the depletion. The temperature variation inside the depletion indicates a good correlation with the parallel flow variation but fails to anti-correlate with the density variation. This implies that the model of energy deposit by the photoelectrons that are produced at the sunshine apex height at the equatorial region [Oyama et al., 1988] can not explain the observation because the highest temperature does not occur at the deepest density depletion region. Instead, the temperature increase could be resulted from the adiabatic heating of compressing ions along the field lines from the equatorial region to high latitude region in the model of Bailey and Heelis [1980].

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