Seasonal difference in ionization and height of F2-layer caused by neutrals at low latitudes

Abstract

Simulation of seasonal anomaly based on a morphological study has been carried out for low latitudes. In the morphological study, summer-winter differences have been studied in the diurnal behaviour of foF2, hpF2 and in the strength of the equatorial electrojet for three low-latitude stations and for three different solar activity periods. Simultaneous examination of the equatorial electrojet strength, foF2 and hpF2 show that the seasonal differences cannot be ascribed to the corresponding differences in the magnitude of the electromagnetic drift. Solving the continuity equation at low latitudes for a high solar activity period and assuming increased atomic oxygen in winter (1.15 times) and increased molecular oxygen and nitrogen in summer (1.15 times), it is concluded that the seasonal differences in the calculated foF2 are of the order of the observed seasonal differences (1–1.5 MHz), with the height of the F2-layer showing a trend similar to the observations. Furthermore, the observations from Alouette II as well as the theoretical studies show that seasonal anomaly is dominant only around the F2-peak. Inclusion of a model neutral wind shows that the neutral wind opposes the formation of the seasonal anomaly.