Research on the ionospheric diurnal Double-Maxima patterns in Asia-Australian area based on the VTEC observations of BDS geostationary satellites

Abstract

Ionospheric diurnal double-maxima (DDM) pattern is a special phenomenon of the ionosphere, which shows that the ionospheric electron density/total electron content (TEC) presents a two-peak structure during the daytime. This paper uses the Beidou geostationary (GEO) vertical total electron content (VTEC) data from the MGEX tracking stations in the Asian-Australian area from 2019 to 2020 to study the ionospheric DDM phenomenon. The results show that the occurrence rate of ionospheric DDM is roughly symmetrical about the magnetic equator, with a “W”-shaped distribution. With decreasing latitude, the occurrence of DDM first decreases from 58%/73% to 7%/17% and then increases in the equatorial region to 30%. Minimum occurrence occurs near ± 20°. The occurrence rate of DDM in different latitude regions varies with longitude. There is no significant variation at low-latitudes (magnetic latitude 15°N ∼ 15°S), while in the northern hemisphere mid-latitudes (regions north of magnetic latitude 15°N), the occurrence of DDM first decreases and then increases with longitude in the area of observation. The southern hemisphere’s mid-latitudes (regions south of magnetic latitude 15°S) east of 90°E show an increasing trend with longitude. The two peaks and one valley of DDM mainly occur in 10:00–13:00 LT, 14:00–18:00 LT, and 12:00–15:00 LT, respectively. As the latitude decreases, the occurrence time of the DDM structures tends to be delayed, but there is no significant variation with an increase in longitude. The DDM phenomenon in the southern hemisphere usually occurs earlier than in the northern hemisphere. The occurrence time of the DDM structures in different months shows an inverted “U” shape in the mid-latitudes of the northern hemisphere and a “U” shape in the mid-latitudes of the southern hemisphere. DDM structures appear the latest in the local summer and the earliest in the winter. There is no significant variation in the low-latitude regions.