Automatic identification of magnetic clouds and cloud-like regions at 1 AU: occurrence rate and other properties

Lepping, R. P., and C.-C. Wu, and D.B. Berdichevsky

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 1 AU. The initial identification of a candidate MC-complex is carried out by examinig 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, S=>N, all S, all N, etc. types). N=>S refers to the B_z 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 indentified 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 albe to find some previously ignored MCs among the false positives. It should be effective in helping to identify in real time most N=>S MCs for magnetic storm forecastin. The N=>S 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.

Ann. Geophysicae, 2005