Department of Astronomy, Harvard University, Cambridge, Massachusetts 02138, USA.
Phys Rev Lett. 2011 Nov 11;107(20):201101. doi: 10.1103/PhysRevLett.107.201101.
Temperature anisotropy in the solar wind results from a combination of mechanisms of anisotropic heating (e.g., cyclotron-resonant heating and dissipation of kinetic Alfvén waves) and cooling (e.g., Chew-Goldberger-Low double-adiabatic expansion). In contrast, anisotropy-driven instabilities such as the cyclotron, mirror, and firehose instabilities limit the allowable departure of the plasma from isotropy. This study used data from the Faraday cups on the Wind spacecraft to examine scalar temperature and temperature components of protons. Plasma unstable to the mirror or firehose instability was found to be about 3-4 times hotter than stable plasma. Since anisotropy-driven instabilities are not understood to heat the plasma, these results suggest that heating processes are more effective than cooling processes at creating and maintaining proton temperature anisotropy in the solar wind.
太阳风中的温度各向异性是由各向异性加热机制（例如回旋共振加热和动理学阿尔文波的耗散）和冷却机制（例如切夫-戈德伯格-洛双绝热膨胀）共同作用的结果。相比之下，各向异性驱动的不稳定性，如回旋、镜像和火棒不稳定性，限制了等离子体从各向同性的允许偏离。本研究使用 Wind 航天器上的法拉第杯的数据来检查质子的标量温度和温度分量。发现对镜像或火棒不稳定性不稳定的等离子体比稳定等离子体热约 3-4 倍。由于各向异性驱动的不稳定性不会使等离子体升温，因此这些结果表明，在太阳风中，加热过程比冷却过程更有效地产生和维持质子温度各向异性。
