Magnetic-reconnection exhausts in the sheath of magnetic clouds

Abstract

Context. Reconnection exhausts are a common phenomenon in the solar wind. Many exhausts were observed between an interplanetary coronal mass ejection (ICME) and the ambient solar wind, or between two ICMEs, or within the interior of a single ICME. Observed exhausts are almost exclusively associated with ICMEs with low (often much lower than 1) proton beta. Aims. Often the sheath regions of ICMEs have a high level of plasma beta. Therefore we aim to find out whether the reconnection exhausts occur frequently in the sheath regions of ICMEs. Methods. We examined the plasma and magnetic-field data in the sheath of the magnetic cloud (i.e., ICME) observed on 18-20 October 1995, and identified six reconnection exhausts. Results. The six reconnection exhausts occured within regions of proton beta that was higher than unity. Five of them occurred on a high level (>2.2) of proton beta. Conclusions. Low proton beta is no exclusive condition for magnetic reconnection. Reconnection may occur frequently in the sheath of ICMEs when magnetic fields from different source regions, that is, from diffident orientations, are pushed together.