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Wind/SWE observations of firehose constraint on solar wind proton temperature anisotropy
Author(s) -
Kasper Justin C.,
Lazarus Alan J.,
Gary S. Peter
Publication year - 2002
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 - 10.1029/2002gl015128
Subject(s) - physics , solar wind , proton , anisotropy , plasma , magnetic field , instability , computational physics , atomic physics , mechanics , nuclear physics , quantum mechanics
The proton resonant firehose 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 ○ . Linear theory and one‐dimensional simulations predict that enhanced field fluctuations from the proton resonant firehose instability impose a constraint on proton temperature anisotropies of the form 1 − T ⊥ p / T ∥ p = S p /β ∥ p α p where β ∥ p ≡ 8π n p k B T ∥ p / B ○ 2 , and the fitting parameters S p ∼ 1 and α p ≃ 0.7. Observations from the Wind spacecraft are reported here. These measurements show for the first time with a comprehensive plasma and magnetic field data set that this constraint is statistically satisfied in the solar wind near 1 AU, with best‐fit values of S p = 1.21 ± 0.26 and α p = 0.76 ± 0.14.