ACE News #15:
May 8, 1998

Correlated Heavy Ion Intensity Variations Contained Within a CME:


Stacked ion spectra measured using SWEPAM during the CME observed on Feb. 4 and 5, 1998 were examined to determine the relative uniformity of the plasma state within and near the CME. Ion energy per charge spectra measured on Feb. 5 are shown at the right. As shown in ACE News #11, a slow-moving CME consisting of a large magnetic cloud started in the late morning on Feb. 4 and lasted until nearly the end of Feb. 5. As is often observed, the ion temperatures were very cold throughout most of this CME. This condition allowed SWEPAM to resolve individual heavy ions using the solar wind as a velocity filter.

Inspection of the spectra at the right, shows several resolved peaks in the E/Q spectra other than those for protons (located at ~ 0.5 keV/Q with M/Q = 1) and alpha particles (located at ~ 1 keV/Q with M/Q = 2). Just to the right of the alpha peak is a relatively broad peak centered at about M/Q=2.4, which may contain both O7+ and C5+, and a relatively narrow peak at M/Q=2.66, which is probably due to O6+. Also seen are three, and sometimes four peaks above O6+ that intensify and wane twice during the day. Preliminary analysis places these peaks at about M/Q = 3.1, 3.5, and 4.0. Within the uncertainties of our analysis, the identities of these peaks could be C4+ and Si9+, Si8+, and Si7+ and He+, respectively. Their intensities appear to be correlated with that of a peak at M/Q=1.5, seen between the proton and alpha-particle peaks. This peak, no doubt, corresponds to 3He+.

These striking correlated enhancements in the heavy ions, all having close to normal coronal abundances relative to He, indicate a source in the corona that has He and heavier ions uniformly enhanced relative to hydrogen. This observation appears to run contrary to the standard model of heavy ion fractionation in the corona.

Contributed by D.J. McComas and W.C. Feldman, Los Alamos National Laboratory.

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Last modified 21 May 1998, Steve Sears
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