Variations in the Winter Troughs' Position With Local Time, Longitude, and Solar Activity in the Northern and Southern Hemispheres

摘要

Comprehensive pattern of ionospheric troughs' location in winter for all local times, longitudes, high (HSA), and low (LSA) solar activity, in both hemispheres, is at first investigated. Statistical analysis based on a large dataset of Interkosmos-19, CHAMP, and Kosmos-900 satellites was performed for quiet geomagnetic conditions Kp = 1-3. Three troughs were considered: high-latitude trough (HLT) located inside the auroral oval, main ionospheric trough (MIT) located equatorward from the auroral oval, that is, at subauroral latitudes, and mid-latitude ring ionospheric trough (RIT). The main purpose was to study the formation of the troughs' diurnal pattern in different conditions. The main problem was to distinguish MIT from RIT and MIT from HLT. For this purpose, early morning hours (04-06 LT), late morning hours (07-10 LT), day, evening, and night conditions were examined. In the early morning sector, RIT was separated from MIT and eliminated from the dataset. In the late morning sector, MIT and HLT were first clearly divided, although only for HSA. During the day, in the Northern Hemisphere under all conditions, HLT is mainly observed, in the Southern Hemisphere at poorly lit longitudes only the daytime MIT, and at well-lit longitudes only the HLT is observed. The division of MIT and HLT was carried out according to the (statistical) position of the equatorial boundary of the auroral oval precipitation. At night, longitudinal variations in the MIT position determine the asymmetry of the hemispheres. Thus, the occurrence and position of MIT and HLT depend on the hemisphere, longitude, and solar activity.