Simulated midlatitude summer nighttime anomaly in realistic geomagnetic fields

Abstract

In the present work, using the three‐dimensional theoretical ionospheric model of the Earth in Institute of Geology and Geophysics, Chinese Academy of Sciences (TIME3D‐IGGCAS), we simulate the temporal‐spatial distribution of the midlatitude summer nighttime anomaly (MSNA) and the influences of thermospheric meridional and zonal winds on the formation of MSNA. MSNA mainly appears in three distinct regions, the East Asian region, the northern Atlantic‐Europe region and the South Pacific region. MSNA in the South Pacific region is obviously stronger than that in the other two regions. In these three regions, MSNA not only occurs in local summer, but also often occurs in Equinox. Through lifting up or lowering the F region ionization, thermospheric winds mainly drive the formation of MSNA. In the East Asian region and the northern Atlantic‐Europe region, MSNA are mainly driven by the thermospheric meridional wind, and the influence of the thermospheric zonal wind can be neglected. However, although MSNA in the South Pacific region (or Weddell Sea Anomaly) are mainly driven by the thermospheric meridional wind, the thermospheric zonal wind also plays an important role in the formation of MSNA.