Pattern of Latitudinal Distribution of Ionospheric Irregularities in the African Region and the Effect of March 2015 St. Patrick's Day Storm

摘要

This paper investigates the latitudinal distribution of quiet and storm time irregularities over the African ionosphere in the month of March 2015. The average rate of change in total electron content (TEC) index (ROTI_(ave)) calculated from Global Positioning System data is used as a proxy for the irregularities. The result during the quiet condition shows that irregularities are mostly observed between 19:00 and 00:00 LT regardless of the hemisphere. Its appearance in the Southern Hemisphere is earlier, though with less severity mainly around the equatorward edge of the equatorial anomaly peak. The peak of its development occurred at 21:00 LT, as it is observed in all the latitudes except those outside the equatorial region. The strength is found to be most severe at ～12° magnetic latitude (up to 1.10 TECU/min.) in the south. Beyond ～18° magnetic latitude, it is rarely noticed in the south. However, it is not observed around this latitude in the north, indicating a major hemispheric asymmetry in terms of the latitudinal boundary between the Northern and Southern Hemispheres. Furthermore, its disappearance is found to be most rapid around the poleward verge of the equatorial anomaly region particularly in the Southern Hemisphere. In contrast to quiet time observations, irregularities were absent in all latitudes during the storm days considered. This can be attributed to the local time of the storm's onset and the possible imposition of westward electric fields in the dusk period.