Effect of the ns component of the interplanetary magnetic field on geomagnetic storms

Summary The individual storm-time variations of the geomagnetic field were compared with the variations of the B_z-component of the interplanetary magnetic field over 24 and 48-hour intervals of storm time. Good correlation between B_z and Dst was observed in about one half of the 166 cases analysed (1965–72), the time lag of the manifestations of the interplanetary field at the Earth's surface having been taken into account. The effect of the B_z-field is reflected to a considerably larger extent in intense storms (Dst –80 nT). Good correlation was observed in 80% of the total number of 35 intense storms. Preliminary investigations have shown that Dst-variations, constructed from B_z-data using the relations derived herein, are quite close to the observed, particularly as regards the main phase (3 examples are given).