A New Approach to the Ionosphere at Middle and Low Latitudes under the Geomagnetic Quiet Time of December 2019 by ICON and GOLD Observations

It has been found that the total electron content (TEC) and the ionospheric electric fields indicated by the geomagnetic data showed inconsistent changes with each other at the mid- and low latitudes in both the American and the Asian–Australian sectors during geomagnetic quiet time (GQT) from 30 November to 8 December 2019 (Kpmax = 1.7). Meanwhile, the effects of thermospheric compositions are still indistinct. In this work, we analyze the mid/low-latitude ionospheric variations during this period, utilizing multi-instrument observations. The vertical drift velocities from the Ionospheric Connection Explorer (ICON) show significant variations and are in line with the changes in TEC at low latitudes in both of the two sectors. The zonal electric fields are supposed to play the main role in the TEC changes. This is also confirmed by the ionospheric F2 layer parameters data from the ionosonde stations at Sanya in the Asian–Australian sectors. The correlation between the variations in the geomagnetic H component (ΔH) and ionospheric F-layer electric fields can be affected by solar activity levels. The geomagnetic data ΔH sometimes may not indicate the magnitude of the electric fields in the F-region ionosphere under geomagnetic quiet conditions. The column density ratio of atomic oxygen (O) to molecular nitrogen (N2) (∑O/N2) from the Global Scale Observations of the Limb and Disk (GOLD) showed a strong enhancement at mid-latitudes in the American sector on 30 November. It is speculated that the neutral compositions should make a minor contribution to the changes in TEC during this event, compared with the electric fields.