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Riley et al. 2001
Riley, P., Gosling, J.T. and Pizzo, V.J. (2001). Investigation of the polytropic relationship between density and temperature within interplanetary coronal mass ejections using numerical simulations. Journal of Geophysical Research 106. doi: 10.1029/2000JA000276. issn: 0148-0227.

Single-point spacecraft measurements within coronal mass ejections (CMEs) often exhibit a negative correlation between electron density and temperature. At least two opposing interpretations have been suggested for this relationship. If, on one hand, these single spacecraft observations provide direct measures of the polytropic properties of the plasma, then they imply that the polytropic index for the electrons &ggr;e is often 1. In this study we simulate the evolution of a variety of CME-like disturbances in the solar wind using a one-dimensional, single-fluid model, to address the interpretation of the relationship between electron density and temperature within CMEs at fixed locations in space. Although we strictly impose a polytropic relationship (with &ggr;=constant) throughout our simulations, we demonstrate that a variety of correlations can exist between density and temperature at fixed points. Furthermore, we demonstrate that the presence of only local uncorrelated random fluctuations in density and temperature can produce a negative correlation. Consequently, we conclude that these single-point observations of negative correlations between electron density and temperature cannot be used to infer the value of &ggr;e. Instead, we suggest that entropy variations, together with the plasma's tendency to achieve pressure balance with its surroundings, are responsible for the observed profiles. ¿ 2001 American Geophysical Union

BACKGROUND DATA FILES

Abstract

Keywords
Solar Physics, Astrophysics, and Astronomy, Coronal mass ejections, Space Plasma Physics, Numerical simulation studies, Space Plasma Physics, Shock waves
Journal
Journal of Geophysical Research
http://www.agu.org/journals/jb/
Publisher
American Geophysical Union
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