Latitudinal variations of nighttime enhancements in total electron content

Latitudinal variations of the various characteristics of nighttime anomalous enhancements in total electron content (TEC) are presented by considering TEC data from the ATS series of satellites for a 2‐month period from a number of stations in the northern hemisphere extending from 2° to 63° dip latitude. The latitudinal variations of the various TEC enhancement characteristics are found to be strikingly similar, and they reveal a pattern of cyclic variation with two distinct minima, one at 30°N and the other at 60°N (dip latitude). The TEC enhancements show a strong positive correlation with geomagnetic activity at middle and high latitudes and no significant correlation at low latitudes. The observed pattern of the latitudinal vaiations of the TEC enhancements is discussed in the light of the potential source mechanisms.