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Title: On the determination of electron polytrope indices within coronal mass ejections in the solar wind

Abstract

Electron temperature and density often appear to be negatively correlated with one another as a coronal mass ejection, CME, in the solar wind passes over a spacecraft at 1 AU and beyond. It has been suggested that this negative correlation within magnetic clouds, which form a subset of all CMEs, implies that the electron polytropic index for the plasma within the clouds is significantly less than 1.0. We argue that single-point measurements of density and temperature within clouds do not speak to the issue of the coupled evolution of density and temperature that occurs as the clouds expand out into the heliosphere, and thus do not provide a measure of the polytropic index within them. Moreover, we show that observed electron temperatures within magnetic clouds and CMEs close to the Sun, at 1 AU, and at large heliocentric distances do not agree with predictions based upon electron polytropic indices significantly less than 1.0. We suggest that the negative correlation between electron temperature and density often observed within CMEs and magnetic clouds at 1 AU and beyond simply reflects the presence of structure within the CMEs and the plasma{close_quote}s tendency to achieve local pressure balance as it evolves outward from themore » Sun. Our results indicate that self-similar models that require the electron polytrope index to be less than 1.0 in order for a magnetic cloud to expand are physically unrealistic. {copyright} 1999 American Geophysical Union« less

Authors:
 [1]
  1. Los Alamos National Laboratory, Los Alamos, New Mexico (United States)
Publication Date:
OSTI Identifier:
688002
Resource Type:
Journal Article
Journal Name:
Journal of Geophysical Research
Additional Journal Information:
Journal Volume: 104; Journal Issue: A9; Other Information: PBD: Sep 1999
Country of Publication:
United States
Language:
English
Subject:
66 PHYSICS; SUN; SOLAR CORONA; MASS TRANSFER; SOLAR WIND; SOLAR PROMINENCES; ELECTRON DENSITY; ELECTRON TEMPERATURE; STELLAR MAGNETOSPHERES; PLASMA INSTABILITY

Citation Formats

Gosling, J.T. On the determination of electron polytrope indices within coronal mass ejections in the solar wind. United States: N. p., 1999. Web. doi:10.1029/1999JA900254.
Gosling, J.T. On the determination of electron polytrope indices within coronal mass ejections in the solar wind. United States. doi:10.1029/1999JA900254.
Gosling, J.T. Wed . "On the determination of electron polytrope indices within coronal mass ejections in the solar wind". United States. doi:10.1029/1999JA900254.
@article{osti_688002,
title = {On the determination of electron polytrope indices within coronal mass ejections in the solar wind},
author = {Gosling, J.T.},
abstractNote = {Electron temperature and density often appear to be negatively correlated with one another as a coronal mass ejection, CME, in the solar wind passes over a spacecraft at 1 AU and beyond. It has been suggested that this negative correlation within magnetic clouds, which form a subset of all CMEs, implies that the electron polytropic index for the plasma within the clouds is significantly less than 1.0. We argue that single-point measurements of density and temperature within clouds do not speak to the issue of the coupled evolution of density and temperature that occurs as the clouds expand out into the heliosphere, and thus do not provide a measure of the polytropic index within them. Moreover, we show that observed electron temperatures within magnetic clouds and CMEs close to the Sun, at 1 AU, and at large heliocentric distances do not agree with predictions based upon electron polytropic indices significantly less than 1.0. We suggest that the negative correlation between electron temperature and density often observed within CMEs and magnetic clouds at 1 AU and beyond simply reflects the presence of structure within the CMEs and the plasma{close_quote}s tendency to achieve local pressure balance as it evolves outward from the Sun. Our results indicate that self-similar models that require the electron polytrope index to be less than 1.0 in order for a magnetic cloud to expand are physically unrealistic. {copyright} 1999 American Geophysical Union},
doi = {10.1029/1999JA900254},
journal = {Journal of Geophysical Research},
number = A9,
volume = 104,
place = {United States},
year = {1999},
month = {9}
}