Interplanetary Coronal Mass Ejection speeds and temperatures relative to the background solar wind observed at ACE, WIND, and STEREO

Details Interplanetary Coronal Mass Ejection speeds and temperatures relative to the background solar wind observed at ACE, WIND, and STEREO Interplanetary Coronal Mass Ejection speeds and temperatures relative to the background solar wind observed at ACE, WIND, and STEREO

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh12a..08e&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH12A-08

Physics

2100 Interplanetary Physics, 2101 Coronal Mass Ejections (7513), 2164 Solar Wind Plasma

Scientific paper

When examining ACE ICMEs compared to the background solar wind conditions over the solar cycle, we found 2 key results: 1) Most ICMEs have speeds within the one standard deviation of the background wind speed, and ICME speeds generally track the variations in the background wind speed. 2) Even though the proton temperature and proton speed in the background wind are well correlated and the ICME speed generally follows the background wind speed, the ICME temperature does not follow the ICME speed. Instead the temperature of most of the ICMEs is low and has no significant trend with time. Three possibilities to explain the correlation between the ICME and background wind speed are: 1) The CME launch speeds change over the solar cycle as the solar wind speed changes; 2) The speed is closer to the background speed when ACE crosses on the edge of a CME; 3) As CMEs propagate their interaction with the background wind causes fast CMEs to slow and slow ones to speed up. These possibilities can be tested by comparing ACE, WIND, and STEREO in situ measurements, and by comparing the trend in the published speeds determined from remote observations of CMEs with the trend in the ICME speeds. Although fully understanding how the low ICME temperatures develop, and why the temperatures are uncorrelated with the background wind conditions is not straightforward, we will develop expected temperature formulas to assist in identify ICMES in the STEREO data and explore how much the temperature relative to the expected temperature varies across the ICME to determine if the anomalously low temperatures are spatially confined within the ICMEs. Our initial comparisons between ACE and STEREO ICME data indicate the ratio of the temperature to the expected temperature and the proton beta can be significantly different from one spacecraft to another across a given ICME.

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