The Nighttime Winter Anomaly Phenomenon observed by the in situ Electron Density Measurements from the CSES satellite

Abstract The nighttime winter anomaly (NWA) phenomenon is studied using the in situ electron density measurements from the CSES (China Seismo-Electronmagnetic Satellite) satellite orbiting above the F2 layer peak height (hmF2) region. Observations in the present study indicates that: (1) The NWA phenomenon can appear at mid-latitudes in large longitude ranges above the hmF2 region during low solar activity period, with the most obvious part being located at the American longitude sector during northern winter time and at the Asian longitude sector during the southern winter time as mention in previous studies. (2) The NWA phenomenon can also appear in the equatorial region. The equatorial NWA is located at the American to Eurasian longitude sectors during northern winter time and at the eastern Pacific longitude sector during southern winter time, and its occurrence and distribution vary with solar activity, which is similar to that of the mid-latitude NWA. (3) The formation mechanism for the mid-latitude NWA can be explained by the ionosphere-plasmasphere coupling process, and the formation mechanism for the equatorial NWA can be explained by the wind-driven plasma transporting process. These results are helpful for the in-depth understanding of the topside ionosphere, and the in situ electron density measurements from the CSES satellite provide us good opportunities to study the ionospheric climatological phenomena due to its special and unified observation local times.