Abstract

We investigate the seasonal variation of the ionospheric F2-layer intensity at midlatitudes during the solar cycle 23. The occurrence of larger daytime electron density in winter than in summer is called as seasonal anomaly or winter anomaly. The seasonal anomaly occurs mainly at midlatitudes and... Show moreWe investigate the seasonal variation of the ionospheric F2-layer intensity at midlatitudes during the solar cycle 23. The occurrence of larger daytime electron density in winter than in summer is called as seasonal anomaly or winter anomaly. The seasonal anomaly occurs mainly at midlatitudes and is more pronounced in the northern hemisphere than in the southern hemisphere. We investigate the variation of the seasonal anomaly with solar cycle and local time by analyzing the radio occultation measurements from FORMOSAT-3/COSMIC satellites during the solar minimum period (2007-2008) and from the CHAMP satellite during the solar maximum period (2001-2002). The vertical electron density profiles obtained from COSMIC and CHAMP will be compared with those observed by the Incoherent Scatter Radar at Millstone Hill. The hemispheric difference in the seasonal anomaly will also be investigated by using the ionosonde measurements of the F-peak electron density at Osan in Korea and Darwin in Australia. We discuss the combined effects of the neutral composition and the global annual asymmetry on the creation of the seasonal anomaly. Show less