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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.
STP12 Abstracts Berlin, 12 - 16 July 2010 SCOSTEP Symposium 2010 Modeling of 630.0 nm dayglow under varying solar activity conditions Sunil Krishna M.V. Indian Institute of Technology Roorkee The atomic oxygen airglow emission at 630.0 nm emission is the most extensively observed emission feature in the dayglow and twilight glow. This emission is prominent feature in the thermosphere between 150-300 km. This paper presents the model resutls of the atomic oxygen redline dayglow emission. The solar Extreme Ultra Violet (EUV) radiation flux plays a very important role in the production of airglow emission. To study the redline emission a comprehensive model is developed including all the possible source and loss mechanisms. This model uses solar EUV flux from Solar2000 model. The model results are tested by comparing with the observations of Wind Imaging Interferometer (WINDII). It has been observed that the model produces a fairly good agreement with the observed results in comparison to the earlier model studies. Zhang and Shepherd (2004) have proposed an empirical formula for the calculation of peak emission rate and the intensity of redline emission based on the entire set of WiNDII observations during 1991-1995. These empirical formulae can calculate the peak emission rate and intensity as a function of the solar activity expressed in terms of the F10.7 solar index and solar zenith angle. The present model is used to obtain peak emission rates during the period of 2001-2005 on a fixed date. A comparative study is presented between the results obtained from the empirical formula and the model. It has been observed that the empirical formula produces low emission rates at high solar activity conditions in comparison to the model results and the agreement between the two is better during the low solar activity period. The possible reasons for the lower estimation of peak emission rate by the empirical formula during the peak activity conditions along with a correction factor to the empirical formula is presented in this paper.
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scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

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