Structure of the High-Latitude Noon Ionosphere of the Southern Hemisphere

Abstract

The structure of the winter noon ionosphere of the southern hemisphere was studied. This structure includes the dayside cusp, associated high-latitude ionospheric trough (HLT), main ionospheric trough (MIT), electron density (Ne) peak at latitudes about 70°, mid-latitude ring ionospheric trough (RIT), and low-latitude quasi-trough. Data from the CHAMP satellite in the southern hemisphere for quiet geomagnetic conditions under high solar activity were selected for analysis. The DMSP satellite data and a model of auroral diffuse precipitation were also used. This model represents two zones of auroral diffuse precipitation on the equatorward and poleward edges of the auroral oval. It is shown that the situation in the winter noon ionosphere of the southern hemisphere depends cardinally on longitude. At sunlit longitudes, only the HLT is observed, and MIT is formed in the shadow region. At intermediate longitudes, both troughs can be observed and, therefore, there is a problem of their separation. The positions of all structures of the ionosphere depend on the longitude; in particular, the positions of the daytime MIT are changed by 6°−7°. At latitudes of the dayside cusp, both the peak and the minimum of Ne can be observed. A high and narrow peak of Ne is regularly recorded in the CHAMP data at latitudes of the equatorward zone of diffuse precipitation (68°−72°). In the shadow region, this peak forms the MIT poleward wall, and at sunlit longitudes a quasi-trough equatorward of this peak is sometimes observed. The RIT is rarely formed during the day, only at the American and Atlantic longitudes.

Observational Characteristics of High‐Latitude Ionization Trough Seen by Swarm

“…One of the distinguishing characteristics of an auroral oval is the presence of strong currents, and the auroral boundary has been determined from the measurements of currents (Chen et al, 2003;Milan et al, 2017). Karpachev (2019Karpachev ( , 2022aKarpachev ( , 2022bKarpachev ( , 2023 classified troughs into mid-and high-latitude troughs from satellite observations using the auroral boundary obtained from an empirical model. However, the auroral boundary is variable with geomagnetic activity.…”

“…However, the formation of sharp boundaries of high-latitude troughs required an additional process, and Grebowsky et al (1983) suggested the trough formation by the enhanced dissociative recombination rate associated with high-speed plasma convection. Recent studies (Karpachev, 2022a(Karpachev, , 2022b(Karpachev, , 2023, investigated the conditions for the development of high-latitude troughs under midnight, morning, evening, and noon conditions using the electron concentration data from the Challenging Minisatellite Payload (CHAMP) satellite. Following these studies, two types of high-latitude troughs develop.…”