scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
Equatorial-to-Middle Latitude Ionospheric Irregularities: Studies Using ROCSAT Data
Su Shin-Yi 1 , Chao Chi-Kwan 1 , Liu Chao-Han 2
1 National Central University, 2 Academia Sinica
Equatorial-to-middle latitude topside ionospheric ion density variations observed by
ROCSAT-1 at the 600-km altitude have been studied to construct the global/seasonal/localtime
distributions of the equatorial plasma depletion (plasma bubble) occurrence rates, and the
low-to-middle latitude plasma enhancement (plasma blob) occurrence rates from 1999 to
2004 when the solar activities were moderate to high. The occurrence distributions of the two
contrasting density irregularity structures indicate some complementary pattern in the
latitudinal distribution. The seasonal/longitudinal (s/l) distributions of the equatorial density
depletions have been studied extensively in the past and the causes of such distributions have
been proposed due to (1) the magnetic declination angle to affect the longitudinal gradient of
the ionospheric conductivity across the sunset terminator, (2) the geographic location of the
dip equator to affect the ionospheric seasonal density variation, and (3) the strength of the
geomagnetic field at the dip equator to drive the over-all electrodynamics. In contrast, the
study of the low-to-middle latitude density enhancements has just been started and the
occurrence distribution only indicates that the maximum occurrence rates appear during the
June solstice in both northern and southern hemispheres. Some occurrence dependence is
noticed at longitude of large magnetic declination region, but the causal relationship between
the equatorial density depletion and the density enhancement irregularities needs further
investigation. Details of the global/seasonal/local-time distributions between the two different
density irregularities are compared and the causes of the plasma enhancement irregularity
structures are discussed.