Geomagnetic activity at the time of heliospheric current sheet crossings

Geomagnetic activity during three days before and after heliospheric current sheet crossings is examined. It is shown that the expression for the index , obtained by Murayama [1979], is applicable to such geomagnetic activity, where (in nT) and V (in km/sec) stand for the southward component of the interplanetary magnetic field and solar wind bulk velocity, respectively. The effects of and V on AL are also examined separately. It is found that short term (∼hours) variations of AL are controlled by fluctuations of while long term (∼days) variations of AL are controlled by V.