On the determination of K-indices by computer

Abstract

At a magnetic observatory, a 'K-index' is assigned to each 3 h interval of recording to be a measure of whether conditions were quiet or active during this time. A K-index measures the maximum amplitude or disturbance variations, independent of the regular daily (or solar diurnal) variation. The numbers used for K-indices are the digits from 0 to 9, with higher numbers corresponding to greater magnetic activity. The K-index scale is quasi-logarithmic, and may be thought of as being like the magnitude scale for earthquakes in seismology. Thus K = 0 means very quiet magnetic conditions and K = 9 means a very strong magnetic storm. More information on K-index scales is given in Parkinson (1983).