No abstract

This study statistically investigated the seasonal variation, magnetic local time (MLT) variation, geomagnetic activity dependence, and solar activity dependence of the mid-latitude trough using GPS total electron content (TEC) data from 2000 to 2014. The daily median Kp index was used to characterize the daily geomagnetic activity level. The results showed that the trough minimum position depended primarily on the geomagnetic activity, MLT, and the season. The trough depth depended primarily on the solar flux index (F107) and, to a lesser degree, on MLT. The trough depth increased as F107 increased and as the incidence angle of solar flux decreased. The trough equatorward half-width decreased as the geomagnetic activity increased. These variations in the GPS-TEC trough minimum position were compared with the variations in the TEC trough derived from the International Reference Ionosphere (IRI)-2007 model. The GPS-TEC trough minimum position changed little with respect to F107, whereas the IRI-TEC trough minimum position showed a strong F107 dependence.

We collected total electron content (TEC) data in the longitudinal sector of 60°W–90°W during 1999–2015 to investigate the latitudinal variation of nighttime middle‐ and high‐latitude ionosphere. The midlatitude trough is one of the important features of the nighttime ionosphere. The statistical analysis provides unprecedented detail of the local time, seasonal, solar activity, and geomagnetic activity variations of the total electron content in the latitude range of 40°N–75°N, focusing on the variation of midlatitude trough. The results show that the trough minimum position has significant local time, seasonal, and geomagnetic activity dependences but slight solar activity dependence. In addition, an empirical model of the TEC in the middle to high latitudes was constructed by empirical orthogonal function analysis. The empirical model can reconstruct latitudinal profiles of TEC and well reproduce the dependence of the midlatitude trough on local time, seasonal, solar cycle, and geomagnetic activity. In addition, we also analyzed the geomagnetic activity dependence of TEC at different latitudes and different local time sectors.