Systematics of K index in the geomagnetic field

In this paper we study the systematics of K index in fourteen Chinese stations in the 2009–2017 time interval. We find that the frequency distribution of K index ( K=09 ) follows a Gaussian function with K values, while its rank-ordered frequency distribution follows a modified power function of the rank. We investigate empirical correlation between the annual frequency of K ≥ 4 (denoted by M ) and that of geomagnetic storm (denoted by m ), and predict ( M , m ) values in 2018 and 2019, respectively. We find that M follows a mixture of several Gaussian functions of year, and predict the 24th solar cycle length to be 11.4 years, which is consistent with the prediction of the auto-regressive processes (AR) model.