Variations of magnetic clouds and CMEs with solar activity cycle

C.-C. Wu, R. P. Lepping, and N. Gopalswamy

The University of Alabama in Huntsville, CSPAR, Huntsville, AL 35899, also Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771


Sixty-eight magnetic clouds observed by Wind during November 1994 - May 2002.  The average occurrence rate is ~9 magnetic clouds per year for the overall period (68 events/7.6 years).  It is found that some of the frequency of occurrence anomalies were during the early part of solar cycle 23:  (i) only 4 clouds were observed in 1999, (ii) an unusually large number of clouds (16 events) were observed in 1997 in which the Sun was starting to leave solar minimum.  During the period of 1996-2001, the results also show: (1) the occurrence frequency of magnetic cloud appears to be related neither to the occurrence of solar coronal mass ejections (CMEs) as observed by SOHO nor to solar activity cycle, (2) the intensity of geomagnetic storms related to magnetic clouds is affected by both solar activity and the occurrence frequency of CMEs, and (3) ~91% of magnetic clouds induced geomagnetic storms.

Proceedings of International Solar Cycle Studies Symposium 2003: Solar Variability as an Input to the Earth's Environment, Tatranska Lomnica, Slovakia, June 23-28, in press, 2003