Nature of temperature intermittency in the solar wind turbulence

Abstract

In the solar wind turbulence, proton temperature fluctuations are highly intermittent, especially at small scales in the inertial range. This phenomenon may contain information about solar wind intermittent heating. However, the physical nature of the temperature intermittency is not yet clear. Based on the measurements from Solar Orbiter between 2020 and 2023, we identify temperature intermittent structures in the fast and slow solar wind, respectively. We compare the nature and kinetic effects of them. According to the variations of proton temperature and magnetic field when the temperature intermittency occurs, we classify the temperature intermittency in the fast wind into the following five categories: (1) 20% of the cases are identified as linear magnetic holes with local temperature enhancement, and a majority of them are unstable to mirror-mode (MM) instability. (2) 18% are related to tangential current sheets also with local temperature enhancement. (3) 9% are tangential discontinuities with a temperature interface, which could separate two different parcels of plasma. (4) 15% of the cases are accompanies by local temperature decrease that may be also due to MM instability. (5) 25% of the cases show a chain of magnetic field variations probably related to Alfven vortices. In the slow wind, the situation is different. The temperature intermittent structures are mainly associated with firehose instability. These results will help to further understand the intermittent dissipation process in the solar wind turbulence.