IMF and geomagnetic activity during the solar wind disappearance event

Abstract

There was a very peculiar situation reported during 11-12 May 1999, that the "solar wind disappeared". This was one of the long lasting, low velocity and low density solar wind events and was caused by the passage of a “void” around the earth and its environment. The interplanetary magnetic field (IMF), especially, the north-south component (<i style="">B_z</i>) remained quiet during the event. However, it showed a fast and intense fluctuation after the passage of this low solar wind region or “void”. The equatorial <i style="">D</i>_st and <i style="">A</i>_p variations indicate a mild geomagnetic storm after the passage of void. This mild geomagnetic storm is probably due to fluctuations in <i style="">B</i>_z whose value varies from –12 to 9 nT.