The regional characteristics of the occurrence rate of ionospheric anomalies in 2011–2018

This paper presents the regional characteristics of the occurrence rate of ionospheric anomalies of total electron content derived from global position system (GPS) observations. The area of concern spans 70° of longitude, from 70° E to 140° E, and 40° of latitude, from 15° N to 55° N. We introduced the 27 days moving window method to automatically detect anomalies that are caused by various sources. The spatial, diurnal, seasonal, and yearly distribution of the occurrence rate of extreme anomalies in 2011–2018 were provided. The spatial distribution of the occurrence rates of positive and negative anomalies had clear patterns in latitude and it did not change much in longitude at a certain local time over this area. The occurrence rates of positive and negative anomalies at the middle latitudes had significantly different diurnal variations from those at low latitudes. The maximum and minimum of the occurrence rates of positive anomalies occurred at about 17:00 local time (LT) and about 13:00 LT over the region from 36° N to 45° N. The maximum and minimum of the occurrence rates of negative anomalies in the same area occurred at about 07:00 LT and 18:00 LT over the region from 36° N to 45° N. There was no clear pattern in the seasonal variations of occurrence rates of positive and negative anomalies over [70° E-140° E, 15° N-55° N] in 2011–2018. The mean O/N2 had low values in summer and comparable high values in other seasons in 2015, and the O/N2 may not be the main reason for irregular seasonal characteristics of occurrence rate of anomalies. The occurrence rates of positive and negative anomaly in the year when the F10.7 index is relatively low, such as 2018, may be larger than the occurrence rates in the year with relatively large F10.7 index, such as 2014.