Examination of the absence of noontime bite-out in equatorial total electron content

摘要

This study examines the absence of noontime bite-out in the total electron content (TEC) near the geomagnetic equator, using the data of observation and simulation. The results show that the noontime bite-out is absent not only in TEC, but in the bottomside and topside TECs. In the bottomside ionosphere, the ionizations below about 200 km increase with an increasing solar production from 10:00 to 12:00 LT. Meanwhile, the ionizations between hmF2 and an altitude of about 200 km are removed by the upward E × B drifts. Moreover, because hmF2 is uplifted, there are other increasing ionizations in the bottomside ionosphere. These increasing ionizations are much greater than the former increasing ionizations, and the uplifted hmF2 is caused by the upward E × B drifts. Since the sum of the increasing ionizations is slightly greater than the decreasing ones, the bottomside TEC does not have the noontime bite-out. In the topside ionosphere, the transport processes dominate. The upward E × B drifts would move ionizations from altitudes near the F2-peak to the topside ionosphere during noontime. Accordingly, the noontime bite-out is absent in the topside TEC. Overall, the absent noontime bite-out in TEC is mainly formed by the upward E × B drifts.