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

Abstract

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.

A Statistical Study of the Subauroral Polarization Stream Over North American Sector Using the Millstone Hill Incoherent Scatter Radar 1979–2019 Measurements

“…Moreover, He et al (2014) indicated that the narrow SAID channel moves equatorward during high solar activity periods. This is in agreement with that mentioned in Le et al (2017) and Karpachev (2019) that the position of midlatitude trough will move slightly equatorward from low solar activity to high solar activity periods. In our results, the SAPS‐related midlatitude trough exhibits almost identical percentile depletion among low and high solar activity periods.…”

Discovery of a low-latitude ionospheric trough associated with the inner radiation belt

“…The MIT is usually understood as a trough located equatorward of the auroral oval, i.e. it is a subauroral trough by definition 13 , 35 . This trough tracks, with a certain delay, variations in the Kp index according to the MIT model.…”

“…This model considers changes in the position of the MIT regarding Kp and local time. A recently revealed dependence on hemisphere 13 has also been considered. In Fig.…”

Discovering the Low-Latitude Ionospheric Trough Associated With the Inner Radiation Belt

“…The MIT is usually understood as a trough that is located equatorward of the auroral oval, i.e. it is a subauroral trough by de nition 13,35 . This trough tracks, with a certain delay, the variations in the Kp-index according to the MIT model.…”

“…This model takes into account the changes in the MIT position with Kp and local time. The recently revealed dependence on the hemisphere 13 , has been considered, too. In Fig.…”