THE WIND MAGNETIC CLOUD AND EVENTS OF OCTOBER 18-20, 1995 - INTERPLANETARY PROPERTIES AND AS TRIGGERS FOR GEOMAGNETIC-ACTIVITY

Late on October 18, 1995, a magnetic cloud arrived at the Wind spacecr aft approximate to 175 R-E upstream of the Earth. The cloud had an int ense interplanetary magnetic field that varied slowly in direction, fr om being strongly southward to strongly northward during its approxima te to 30 hours duration, and a low proton temperature throughout. From a linear force free field model the cloud was shown to have a flux ro pe magnetic field line geometry, an estimated diameter of about 0.27 A U, and an axis that was aligned with the Y axis(GSE) within about 25 d egrees. A corotating stream, in which large amplitude Alfven waves of about 0.5 hour period were observed, was overtaking the cloud and inte nsifying the fields in the rear of the cloud. The prolonged southward magnetic field observed in the early part of the cloud produced a geom agnetic storm of K-p = 7(-) and considerable auroral activity late on October 18. About 8 hours in front of the cloud an interplanetary shoc k occurred. About three-fourths the way into the cloud another apparen t interplanetary shock was observed. It had an unusual propagation dir ection, differing by only 21 degrees from alignment with the cloud axi s. It may have been the result of the interaction with the postcloud s tream, compressing the cloud, or was possibly due to an independent so lar event. It is shown that the front and rear boundaries of the cloud and the upstream driven shock had surface normals in,good agreement w ith the cloud axis in the ecliptic plane. The integrated Poynting flux into the magnetosphere, which correlated well with geomagnetic indice s, jumped abruptly to a high value upon entry into the magnetic cloud, slowly decreased to zero near its middle, and again reached substanti al but sporadic values in the cloud-stream interface region. This repo rt aims to support a variety of ISTP studies ranging from the solar or igins of these events to resulting magnetospheric responses.