Open AccessCorrelation of solar wind entropy and oxygen ion charge state ratio
Author(s) -
Pagel A. C.,
Crooker N. U.,
Zurbuchen T. H.,
Gosling J. T.
Publication year - 2004
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2003ja010010
Subject(s) - solar wind , physics , interplanetary medium , coronal mass ejection , heliosphere , interplanetary spaceflight , astrophysics , atmospheric sciences , entropy (arrow of time) , computational physics , plasma , thermodynamics , quantum mechanics
Both proton specific entropy and solar wind composition have been recognized in the past as markers of boundaries between what was originally slow and fast solar wind during the declining phase of the solar cycle, when the solar wind alternates between the two regimes. During the rising phase, when boundaries between regimes are not apparent, ACE SWICS and SWEPAM data from 1998–1999 show that O 7+ /O 6+ and proton specific entropy are well‐correlated over the full range of complicated time variations. The correlation holds in spite of the fact that unlike O 7+ /O 6+ , entropy is not a constant of the solar wind flow. At solar maximum however, particularly in 2000, the correlation between entropy and O 7+ /O 6+ degrades. While the correlation inside known interplanetary coronal mass ejections (ICMEs) is much worse throughout 1998–2001, the correlation outside ICMEs also worsens at solar maximum, possibly owing to unidentified transient outflows. Outside ICMEs and shocks, entropy structures have decorrelation times of 5–40 hours and both ln(O 7+ /O 6+ ) and entropy have Gaussian distributions, consistent with their correlation. We conclude that except at solar maximum, the processes affecting entropy in nontransient solar wind act at time scales much smaller than the scales found here and that entropy is a good a proxy for O 7+ /O 6+ .