Premium
Proton temperature anisotropy constraint in the solar wind: ACE observations
Author(s) -
Gary S. Peter,
Skoug Ruth M.,
Steinberg John T.,
Smith Charles W.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013165
Subject(s) - physics , solar wind , proton , anisotropy , instability , plasma , magnetic field , computational physics , cyclotron , spectral line , atomic physics , nuclear physics , mechanics , optics , quantum mechanics
The electromagnetic proton cyclotron anisotropy instability may arise in collisionless plasmas in which the proton velocity distribution is approximately bi‐Maxwellian with T ⟂p / T ∥p > 1, where ⟂ and ∥ denote directions relative to the background magnetic field B o . Theory and simulations predict that enhanced field fluctuations from this instability impose a constraint on proton temperature anisotropies of the form where , and the fitting parameters S p ≲ 1 and α p ≃ 0.4. Plasma and magnetic field observations from the ACE spacecraft reported here show for the first time that this constraint is statistically satisfied in the high speed solar wind near 1 AU, and magnetic power spectra provide evidence that this instability is the source of the constraint.