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Ann. Geophys., 23, 2687-2704, 2005
www.ann-geophys.net/23/2687/2005/
© European Geosciences Union 2005
Automatic identification of magnetic clouds and cloud-like regions at 1 AU: occurrence rate and other properties
R. P. Lepping1, C.-C. Wu1,2, and D. B. Berdichevsky1,3
1Laboratory for Extraterrestrial Physics, NASA/GSFC, Greenbelt, MD 20771, USA
2CSPAR/The University of Alabama in Huntsville, Huntsville, AL 35889, USA
3L-3 Communications EER Systems Inc., 1801 Mc Cormick Dr., Suite 170, Largo, MD 20774, USA
Abstract. A scheme is presented whose purpose is twofold: (1) to
enable the automatic identification of an interplanetary magnetic cloud (MC)
passing Earth from real-time measurements of solar wind magnetic field and
plasma quantities or (2) for on-ground post-data collection MC
identification ("detection" mode). In the real-time ("prediction") mode
the scheme should be applicable to data from a spacecraft upstream of Earth,
such as ACE, or to that of any near real-time field and plasma monitoring
platform in the solar wind at/near 1AU. The initial identification of a
candidate MC-complex is carried out by examining proton plasma beta, degree
of small-scale smoothness of the magnetic field's directional change,
duration of a candidate structure, thermal speed, and field strength. In a
final stage, there is a test for large-scale B-field smoothness within the
candidate regions that were identified in the first stage. The scheme was
applied to WIND data over the period 1995 through mid-August of 2003 (i.e.
over 8.6 years), in order to determine its effectiveness in identifying MC
passages of any type (i.e. N S, SN, all S, all N, etc.
types). (NS refers to the B component of the magnetic field going from north (+)
to south (-) in GSE coordinates.) The distribution of these MC types for
WIND is provided. The results of the scheme are compared to WIND MCs
previously identified by visual inspection (called MFI MCs) with relatively
good agreement, in the sense of capturing a large percentage of MFI MCs, but
at the expense of finding a large percentage of "false positives". The
scheme is shown to be able to find some previously ignored MCs among the
false positives. It should be effective in helping to identify in real time
most NS MCs for magnetic storm forecasting. The NS type
of MC is expected to be most prevalent in solar cycle 24, which should start
around 2007. The scheme is likely to be applicable to solar wind
measurements taken well within 1 AU to well beyond it.
Keywords. Interplanetary physics (Interplanetary magnetic
fields; Solar wind plasma) – Magnetospheric physics (Solar
wind-magnetosphere interactions)
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