Modeling study of nighttime enhancements in F region electron density at low latitudes

摘要

In this paper we carry out case-control simulations to examine the mechanisms of the nighttime anomalous enhancements in electron density in the ionosphere at low latitudes, which were studied earlier in another research. The results confirm the earlier conclusion that the downward E × B plasma drift due to westward electric field at night is the main driving force for the nighttime enhancement. In addition, the phase of the electric field is found important in forming the enhancement. Delayed westward electric field can produce significant postmidnight enhancement as observed at Sanya (geomagnetic latitude: 8.2°N). In addition, the equatorward neutral wind at night is found to modulate the formation of the nighttime enhancement at geomagnetic latitudes below 15°N. The combined effects of the two drivers cause significant equatorward/downward plasma flux, which results in the enhancement of electron density as well as the drop in ionospheric peak height.