Diurnal and Longitudinal Variations in the Equatorial Anomaly for Winter Solstice According to Interkosmos-19 Satellite Data

Abstract

The equatorial anomaly dynamics in the winter solstice is studied based on data from topside sounding of the ionosphere from the Interkosmos-19 satellite for high solar activity. This is the final study on the construction of the pattern of equatorial anomaly variations under conditions of high solar activity. Changes in the equatorial anomaly structure with local time and longitude are considered in detail. It is shown that the anomaly begins to form at ~0800 LT during the creation of the winter northern crest, but the well-developed equatorial anomaly is formed only by 1000–1100 LT. The daytime maximum of the equatorial anomaly development is reached at 1200 LT. The foF2 value above the equator and the degree of the equatorial anomaly development (equatorial anomaly intensity, EAI) at 1200 LT vary with longitude according to changes in the vertical plasma drift velocity W. Three harmonics are observed in the longitudinal variations in W, foF2, and EAI at this time. The EAI increases up to the diurnal maximum 1.5−2.0 h after the evening W burst. Longitudinal variations in foF2 at 2000 LT are also associated with the relevant variations in W, in which two harmonics are revealed. The degree of equatorial anomaly development drops after the evening peak but equatorial anomaly is still well-developed at midnight and is completely absent at 0500–0700 LT. The EAI at different moments of local time differs rather strongly for different longitudinal sectors. The average position of northern crest is ~25° of the geomagnetic inclination I, and the southern crest is at ~–30° I. During the day, the winter crest is higher than the summer crest; by night-time, it is quite the opposite. Thus, a well-expressed equatorial anomaly is observed from 1000–1100 to 0000–0200 LT during the winter solstice.