The ionospheric midlatitude trough observed by FORMOSAT-3/COSMIC during solar minimum

Results show that the midlatitude trough extends from dusk to dawn in all four seasons and is most pronounced in the winter hemisphere.

The troughs in the two hemispheres are asymmetric, where the trough in the Northern Hemisphere is more evident and stronger than that in the Southern Hemisphere during the equinoctial seasons. In general, the trough minimum position shows a high-low-high latitudinal variation with magnetic local time and occurs at lower latitudes under higher magnetic activity. On the other hand, the midlatitude trough structures become more complex in the Southern Hemisphere because of the nighttime plasma density enhancement of the Weddell Sea Anomaly.