Observational evidence for solar wind proton heating by ion-scale turbulence
Abstract
The solar wind is a tenuous magnetized plasma that serves as a natural laboratory of nearly collisionless turbulence. It is streaming outward from the Sun and has temperatures much higher than those from a spherically expanding ideal gas, implying a heating process must occur. The heating has been extensively discussed in past decades, but still not well understood. Based on in-situ measurements of 11 years, we investigate the solar wind turbulence at proton scales. It is shown that the majority of nearly collisionless solar wind turbulence is characterized by non-zero magnetic helicity and steep energy spectrum at proton scales. Two correlations between the spectral index and magnetic helicity, and between the proton temperature and turbulent energy are revealed. The turbulence with a higher helicity has a steeper energy spectrum statistically. A high helicity also favors a positive correlation between the proton perpendicular temperature and the turbulent magnetic energy. This positive correlation exists particularly at scales 0.3 < kρi < 1, with k being the wavenumber and ρi being the proton gyroradius, and can be described by a power law with a slope about 0.4. In addition, our examination on the nature of the solar wind turbulence supports the model of Kinetic Alfvén wave (KAW) turbulence at proton scales. We interpret these results as evidence of solar wind heating by the proton-scale KAW turbulence. A scenario for the solar wind turbulence and heating is proposed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSH022..04Z
- Keywords:
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- 2134 Interplanetary magnetic fields;
- INTERPLANETARY PHYSICS;
- 2149 MHD waves and turbulence;
- INTERPLANETARY PHYSICS;
- 2164 Solar wind plasma;
- INTERPLANETARY PHYSICS;
- 7827 Kinetic and MHD theory;
- SPACE PLASMA PHYSICS;
- 7839 Nonlinear phenomena;
- SPACE PLASMA PHYSICS;
- 7863 Turbulence;
- SPACE PLASMA PHYSICS