Abstract
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.
Highlights
A magnetic cloud (MC) is defined as a region of a high strength magnetic-field, low proton temperature, low proton β, and smoothly-changing magnetic field (Burlaga et al 1981)
For solar sources located in the northern hemisphere, the average latitudes are 8°N for magnetic clouds (MCs) and 14°N for interplanetary coronal mass ejections (ICMEs), and the average longitudes are 4°W for MCs and 12°W for ICMEs
For solar sources located in the southern hemisphere, the average latitudes are 21°S (MCs) and 14°S (ICMEs), and the average longitudes are 15°W (MCs) and 10°W (ICMEs)
Summary
A magnetic cloud (MC) is defined as a region of a high strength magnetic-field, low proton temperature, low proton β, and smoothly-changing (rotating) magnetic field (Burlaga et al 1981). Magnetic clouds are often preceded by upstream sheaths in which the plasma is usually hot and dense and the magnetic field is extremely turbulent (e.g., Tsurutani and Gonzalez 1997, and reference therein). The front “boundary” of the sheath may be a shock, a shock-like structure, a pressure pulse or a sharp rise in density, temperature, or velocity. About 1/4 of observed MCs have no upstream pressure pulse/shock, but all have a density increase (e.g., Wu and Lepping 2002). It is generally believed that MCs are an important subset of ICMEs We attempt to compare MCs-associated with non-MC-associated ICMEs for cases that cause strong geomagnetic storms. The term ICME as used will refer to a nonMC-associated ICME; and the term MC as used will refer to a MC-associated ICME
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