The relationship between electron density and temperature inside coronal mass ejections

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Abstract
Osherovich et al. (1993a) have shown convincing evidence that electron density and temperature are inversely correlated within coronal mass ejections with magnetic cloud structure based on observations of two clouds. We extend this study by calculating the electron polytropic index inside five magnetic clouds which were observed by Ulysses during the in-ecliptic portion of its mission from November 1991 through January 1992. As in the previous work we find that the electron temperature and density are inversely correlated inside the magnetic clouds. However, we attribute this to the fact that denser plasma cools faster than less dense plasma. We show that, in general, inside magnetic clouds the denser plasma is more isotropic supporting our hypothesis of greater collisional cooling of denser plasma. We find that the same inverse relationship between temperature and density is also observed in non-cloud CMEs where one might expect a polytropic index to be impossible to calculate because of the variations in the streamline constant through the CME. We conclude that the observed relationship between electron temperature and density inside CMEs results from differences in collisional histories of the electrons and does not provide a meaningful value for the polytropic index.

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