Variations of ionospheric slab thickness over the magnetic equator of Southeast Asia

In this paper, the diurnal and seasonal variations of the ionospheric slab thickness in an ionosonde chain over magnetic equator of Southeast Asia are studied. Three ionosonde stations of SEALION project located along the magnetic meridian of 100°E are selected to investigate, including two stations in Thailand, namely Chumphon and Chiang Mai, and one station in Indonesia, namely Kototabang. The monthly hourly medians of the foF2 from three ionosonde stations in 2010 are used to compute the observed NmF2. Refer to the TEC data; it can be obtained directly from GPS receiver at Chumphon station since the TEC data in 2010 were observed completely. In contrast, the TEC data at Chiang Mai station lost extremely and those at Kototabang station were unavailable. Hence, the TEC data used for these two stations are obtained from the International GNSS service (IGS). Our results show that 1) for all seasons, the NmF2 values during daytime have the successive decreasing values from Chiang Mai, Kototabang, and Chumphon. While the NmF2 values at three stations are almost identical during nighttime; 2) for all seasons at these three stations, the TEC values in the daytime are larger than those in the nighttime and their maximum values in the equinox and winter are higher than those in the summer; 3) the slab thickness values in all seasons during nighttime are generally larger than those during daytime for all three stations. Meanwhile, during daytime for all seasons, the slab thickness at Chumphon station is the highest among these three stations due to the fountain effect over magnetic equator.