SHINE Campaign: May 12, 1997

May 12, 1997

Introduction
The May 12, 1997 halo CME occurred shortly after solar minimum when activity was low and the structure of the corona and solar wind was relatively simple. It was associated with the only active region on the solar disk [NOAA AR 8038], which was located north of the equator near central meridian. The active region was rapidly evolving, of new cycle polarity, and generated the only major flare of the day, which began at 04:42 UT and peaked around 04:55 UT. The flare was first visible in Ha and was associated with a filamaent that erupted soon thereafter followed by a pair of expanding Ha ribbons. The subsequent X-ray flare emission came from a small arcade that had formed over the region where the filament erupted. Twin dimming regions (positioned North-East and South-East) flanked the filament eruption. A classic EIT wave occurred during this event [Thompson et al., 1998].

The halo CME was observed in SOHO/LASCO C2 instrument at 06:30 UT with an estimated frontal speed of ~600 km/s [Plunkett et al., 1998] and onset time between 04:30-05:00 UT. For about 10 days before the event, the Earthward directed solar wind consisted of relatively slow (i.e., bulk flow speed less than 400 km/s) dense ambient material. The shock produced by the interplanetary coronal mass ejection (ICME) arrived at L1 early on the 15th followed by a magnetic cloud and then a high-speed stream, which is speculated [Webb et al., 2000] to have compressed the cloud from behind. The ICME produced a moderate geomagnetic storm with a maximum Dst of -115nT. Figure 1 summarizes the key solar wind plasma parameters from the WIND satellite for the nine-day period centered on the May 15th ICME arrival at L1, as well as the Dst geomagnetic index as provided by Kyoto University ( http://swdcdb.kugi.kyoto-u.ac.jp/dstdir/). More comprehensive summaries of the event can be found in papers by Webb et al. [2000], Thompson et al. [1998], and Plunkett [1998] along with the references found therein.

Figure 1 * Solar wind key plasma parameters from the WIND satellite (a-h) and the Dst geomagnetic index (i) as provided by Kyoto University (http://swdcdb.kugi.kyoto-u.ac.jp/dstdir/) for the nine-day period May 11-20, 1997. a) Proton temperature (K), b) Proton number density (cm-3), c) Vx (km s-1) , d) Dynamic Pressure (nPa), e) Bx(GSM) (nT), f) By(GSM) (nT), g) Bz(GSM) (nT), h) |B| (nT), i) Dst (nT). The red vertical lines separate the different types of solar wind plasma labeled at the bottom of the plot. (Plot courtesy of Dr. Yan Li.)

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