Solar cycle variation of the GPS cycle slip occurrence in China low-latitude region

Using the Global Positioning System (GPS) cycle slip data detected from the observations of two GPS stations over China low-latitude region from 1999 to 2005, the solar cycle variation of cycle slip occurrence is studied. It is found that the cycle slip occurrence in these two stations varies with solar cycle and shows good temporal correlation; the cycle slip occurs in solar maximum years (1999-2002) much more frequently than that in solar minimum years (2003-2005). In solar maximum years, the seasonal and diurnal dependences of cycle slip occurrence are obvious as shown by previous studies; that is, for seasonal dependence cycle slip mainly occurs in the equinox months and for diurnal dependence cycle slip mainly occurs from 1900 LT to midnight. In solar minimum years, the similar diurnal dependence of cycle slip still exists, nevertheless, the seasonal dependence of cycle slip is not obvious due to small cycle slip occurrence. In the meantime, the spread F occurrence also shows seasonal and diurnal dependence, but there are some differences compared with cycle slip occurrence. During the period from 2000 to 2002, the Q-type spread F mainly occurs in the equinox months; from 2003 to 2005, the Q-type spread F occurs mainly in summer months. As for the diurnal distribution, the Q-type spread F mainly occurs from 2000 LT to sunrise time and lasts much longer than the cycle slip does, and the F-type spread F mainly occurs after midnight and is very different with the cycle slip occurrence. Considering the reasons for cycle slip phenomenon in GPS observations, it is thought that the statistical results of cycle slip occurrence with solar cycle, season, and local time just reflect the temporal distribution of the ionospheric irregularities above a certain intense level over the observing region.