Dynamics of the Weddel Sea anomaly and main ionospheric trough in the Southern Summer hemisphere

The impact of the Weddell Sea Anomaly on the structure of the nighttime ionosphere in the Southern summer hemisphere is considered in detail. For this purpose, data from the CHAMP satellite were used in January 2003 under high solar activity and in January 2008 under low solar activity. The data relate to the local time interval 02-04 LT, when the increase in electron density due to the formation of an anomaly is the strongest. At longitudes of 60-180° E under high solar activity and 0–210° E at low solar activity, where there is no anomaly, the main ionospheric trough is observed. The plasma peak in the nighttime ionosphere associated with the anomaly formation reaches 6 MHz under low solar activity, and 10 MHz under high solar activity. The strongly developed plasma peak decreases sharply to high latitudes at the equatorward border of auroral diffuse precipitation, which corresponds to the plasmapause. When the anomaly is weakly developed, the contribution of diffuse precipitation becomes noticeable, so that the plasma peak expands towards the pole due to this precipitation. Poleward of anomaly, the high-latitude trough is usually observed at latitudes of the auroral oval. A well-defined minimum of the electron density is often formed equatorward of Weddell Sea Anomaly, which can be defined as a sub-trough. Sometimes the sub-trough is created by the escape of ionospheric plasma from the summer hemisphere to the winter hemisphere. Then a density maximum is formed in the winter hemisphere at conjugate latitudes. Sub-trough is much more common under low solar activity than under high activity.