Characteristics of Magnetic Clouds and Interplanetary Coronal Mass Ejections which Cause Intense Geomagnetic Storms


We present the results of a statistical data analysis of the geo-effectiveness of non-magnetic-cloud interplanetary coronal mass ejections (ICMEs) and compare them with those of magnetic-cloud (MC) interplanetary coronal mass ejections observed during solar cycle 23. (The term ICME as used here will refer to a non-MC ICME.) The starting point of this investigation is the set of intense geomagnetic storms (Dstmin ≤ -100 nT) of solar cycle 23 between 1996 and 2005. We also compare the solar source locations of the ICMEs with those of the MCs. The source locations of the solar disturbances are, on average, closer to the Sun-Earth line for the MCs than for the ICMEs. There is an anomaly for the location of the related solar sources: no event came from the region between the solar equator plane and 10°S (south) of that plane. The primary results are listed as follows. The average duration of these MCs is slightly longer (~7%) than that of ICMEs. The average geomagnetic storm intensity for the MCs is higher than that for the ICMEs and CIRs formed by high-speed streams from coronal holes, especially for the events associated with X class flares. The relevant average magnetic field component, i.e., |Bzmin|, is more intense within the MCs than within the ICMEs. The average solar wind speed is similar for both MCs and ICMEs. Maximum solar wind speed is higher within ICMEs than within MCs. Maximum solar wind proton density is higher for MCs than for ICMEs.

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