Features of the Structure of the Winter Morning High- and Mid-Latitude Ionosphere

The structure of the winter morning (0500–0900 LT) ionosphere in the Northern and Southern hemispheres is studied in detail. For this, CHAMP satellite data for quiet conditions during the period of high solar activity of 2000–2002 are used. Careful analysis is used to identify electron concentration troughs: the high-latitude ionospheric trough; subauroral, or main, ionospheric trough; and mid-latitude ring ionospheric trough. In order to identify and separate the high-latitude and main ionospheric troughs, the model of auroral diffuse precipitation of the Polar Geophysical Institute is used, which describes the boundaries of low-latitude zone I and high-latitude zone II of auroral diffuse precipitation. The longitudinal variations of the precipitation boundaries are corrected using the DMSP satellite data. The problem of separating the troughs becomes more complicated with the passage of local time, because the main ionospheric trough is more strongly displaced to the pole than the auroral oval; therefore, its area of existence begins to overlap the area of existence of the high-latitude trough. In order to identify and separate the main and ring troughs, all, even weak, geomagnetic disturbances for the observation period are analyzed in detail. The asymmetry of the Northern and Southern hemispheres is considered, and similar and different characteristics are identified. Therefore, a more complete and accurate pattern of the structure of the morning ionosphere is obtained.