A Statistical Study of Interplanetary Shocks and Pressure Pulses Internal to Magnetic Clouds

Michael R. Collier, Ronald P. Lepping, and Daniel B. Bierdichevsky
NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA

date: 27 November 2005 -version: 3.0

Abstract:

We have examined all cases of magnetic clouds observed by Wind over the time period from November of 1994 through August of 2003 to find cases of interplanetary shocks and pressure pulses internal to magnetic clouds for which we could determine accurate normal directions. We have found eight cases in 82 clouds, so that these shocks and pressure pulses occurred approx. 10% of the Wind magnetic clouds. Of the eight cases, five occured during the 1995-1998 and 2003 period when the average sunspot number was less than 90 and three occurred during the 1999-2002 period when the average sunspot number was greater than 90, although roughly equal numbers of magnetic clouds were observed over the two time periods (44 versus 38). Of the eight cases, six were forward shocks and two were pressure pulses. The internal shocks and pressure pulses tend to occur in the latter half of the clouds, i.e. time-wise, about two-thirds of the way through. In every case, the magnetic field change is highly compressive at the shock showing little or no change (< 10^o) in angle during or after the magnitude jump.

Annales Geophysicae, J. Geophys. Res, submitted, 2006