The Ionosphere at Middle and Low Latitudes Under Geomagnetic Quiet Time of December 2019

The ionospheric electron density shows remarkable day-to-day variability due to solar radiance, geomagnetic activity and lower atmosphere forcing. In this report, we investigated the ionospheric variations at middle and low latitudes during a period under geomagnetic quiet time (Kpmax = 1.7) from November 30 to December 8, 2019. During the quiescent period, the ionosphere is not undisturbed as expected in the Asian-Australian and the American sectors. Total electron content (TEC) has multiple prominent enhancements at middle and low latitudes in the two sectors, and TEC depletions also occur repeatedly in the Asian-Australian sector. The low-latitude electric fields vary significantly, which is likely to be modulated by the notably changing tides in the mesosphere and lower thermosphere region. It is worth noting that the variations of TEC and the electric fields are not consistent in the two sectors, particularly on December 4–6. Further investigation reveals that the increase in TEC depends on altitude. The TEC enhancements are mainly contributed by the altitude below 500 km in both two sectors, which indirectly reflects that the driving sources may come from the lower atmosphere. Especially, a mid-latitude band structure continuously appears at all local times in the North American sector on December 6–8, which is also mainly contributed by the altitude below 500 km.