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Comparison of the Characteristics of Magnetic Clouds and Magnetic Cloud-Like Structures for the Events of 1995 – 2003

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Abstract

Using nine years of solar wind plasma and magnetic field data from the Wind mission, we investigated the characteristics of both magnetic clouds (MCs) and magnetic cloud-like structures (MCLs) during 1995 – 2003. A MCL structure is an event that is identified by an automatic scheme (Lepping, Wu, and Berdichevsky, Ann. Geophys. 23, 2687, 2005) with the same criteria as for a MC, but it is not usually identifiable as a flux rope by using the MC (Burlaga et al., J. Geophys. Res. 86, 6673, 1981) fitting model developed by Lepping, Jones, and Burlaga (Geophys. Res. Lett. 95(11), 957, 1990). The average occurrence rate is 9.5 for MCs and 13.6 for MCLs per year for the overall period of interest, and there were 82 MCs and 122 MCLs identified during this period. The characteristics of MCs and MCL structures are as follows: (1) The average duration, Δt, of MCs is 21.1 h, which is 40% longer than that for MCLs (Δt=15 h); (2) the average \(B_{z_{\min}}\) (minimum B z found in MC/MCL measured in geocentric solar ecliptic coordinates) is −10.2 nT for MCs and −6 nT for MCLs; (3) the average Dstmin  (minimum Dst caused by MCs/MCLs) is −82 nT for MCs and −37 nT for MCLs; (4) the average solar wind velocity is 453 km s−1 for MCs and 413 km s−1 for MCLs; (5) the average thermal speed is 24.6 km s−1 for MCs and 27.7 km s−1 for MCLs; (6) the average magnetic field intensity is 12.7 nT for MCs and 9.8 nT for MCLs; (7) the average solar wind density is 9.4 cm−3 for MCs and 6.3 cm−3 for MCLs; and (8) a MC is one of the most important interplanetary structures capable of causing severe geomagnetic storms. The longer duration, more intense magnetic field and higher solar wind speed of MCs, compared to those properties of the MCLs, are very likely the major reasons for MCs generally causing more severe geomagnetic storms than MCLs. But the fact that a MC is an important interplanetary structure with respect to geomagnetic storms is not new (e.g., Zhang and Burlaga, J. Geophys. Res. 93, 2511, 1988; Bothmer, ESA SP-535, 419, 2003).

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Authors and Affiliations

  1. CSPAR/The University of Alabama in Huntsville, Huntsville, AL, 35899, USA

    Chin-Chun Wu

  2. Key State of Laboratory for Space Weather, Chinese Academy of Sciences, Beijing, 100080, China

    Chin-Chun Wu

  3. Heliophysics Science Division, NASA/GSFC, Greenbelt, MD, 20771, USA

    Chin-Chun Wu & R. P. Lepping

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  1. Chin-Chun Wu
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  2. R. P. Lepping
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Correspondence to Chin-Chun Wu.

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Wu, CC., Lepping, R.P. Comparison of the Characteristics of Magnetic Clouds and Magnetic Cloud-Like Structures for the Events of 1995 – 2003. Sol Phys 242, 159–165 (2007). https://doi.org/10.1007/s11207-007-0323-6

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  • DOI: https://doi.org/10.1007/s11207-007-0323-6

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