Statistical Modeling He+ Density Troughs with respect to Longitude: Northern and Southern Hemispheres

Statistics of the light ion trough (LIT) in He+ density with respect to longitude are considered under nighttime conditions (when the LITs mostly occur) for winter and summer seasons in the Northern and Southern hemispheres. Study based on the ISS-b satellite observations during a high solar activity period 1978-79 (F10.7=200) in the topside ionosphere (1000-1200 km). It is revealed that the statistics of the LIT longitudinal occurrence is more significant in winter than in summer. Moreover, the statistics differs in the amplitude behavior for the different hemispheres. The obtained results, indicated the strong asymmetry between the Northern and Southern hemisphere, are discussed.