Statistic analysis of the ionospheric topside scale height based on COSMIC RO measurements

The ionospheric topside basis scale height, Hsc, presents the height range above the F2 layer peak height at which the peak electron density (NmF2) decays by a factor of an exponent (~2.718). The data periods of Hsc derived from the COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) RO (Radio Occultation) are from 1st January 2007 to 31st December 2011. Time series of Hsc during these five years in specified regions are analyzed. The most significant finding in this study is that the Hsc variations in a relatively small region demonstrate annual periodicities but do not last the whole day. The variation fluctuation is related to the geomagnetic latitudes and presents a good symmetry in two geomagnetic hemispheres. A novel phenomenon is that scale height and peak height also reveal the geomagnetic equator ionosphere anomaly as well as peak density. The peak density anomaly presents two crests along the geomagnetic equator while the scale height and peak height exhibit single-line distribution. Diurnal variation of Hsc is also investigated in this study. There is a deep valley at 08:00 LT and the peak is at around 12:00 LT. The high values last the whole afternoon.