Systematics of K $K$ 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 (\(K=0\mbox{--}9\)) 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 \(K \geq 4\) (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.