Abstract

Intermittency is an important part of the solar wind turbulence. In hydrodynamic turbulence, intermittency is caused by the nonuniform cascade, and corresponds to the area where the cascade process gathers. In the solar wind turbulence, people have studied the nature of magnetic intermittent structures using in-situ measurements. At large scales (about 30 minutes), intermittent structures in the solar wind may correspond to the interface of adjacent flux tubes. At smaller scales around the ion inertial length, the magnetic intermittent structures are identified into different families, including discontinuities, magnetic holes, solitons, shocks, CSs, and vortices. Through numerical simulation, the intermittent current sheet (CS)-like structures are found to correspond to active reconnection regions.

Intermittent structures with large-amplitude fluctuations make a substantial contribution to the shape and power level of magnetic field spectra, which are directly related to the physical nature of the energy cascade and dissipation taking place in the solar wind. They often make the magnetic spectra become steeper at both inertial and kinetic scales. Intermittent structures also influence the magnetic spectral anisotropy of fluctuations in the solar wind turbulence. We suggest that the observed magnetic spectral anisotropy could result from intermittency, and the magnetic spectral anisotropy is dependent on the fluctuation amplitude. Accordingly, an empirical relation is established between the magnetic spectral index and the level of intermittency. We also investigate the angular dependence of the influence of waves on the magnetic spectral index around the ion kinetic scales. Therefore, interpretations of the dynamics or evolution of the solar wind turbulence could account for the contribution of strong discontinuities in the measurements.

In the solar wind turbulence, the relation between intermittent structures and local proton temperature enhancement is also a hot topic. Recently, there is a debate on the heating effect of the magnetic intermittency. It was suggested that the intermittency could be a significant source of coronal and solar wind heating, since the number density of intermittent structures was observed to be proportional to the mean proton temperature. However, the entropy inside and outside the intermittent structures were reported to be not significantly different. We find that only 2% of the structures, known as tangential-type intermittency, are accompanied by local temperature enhancement. Besides the plasma heating, proton temperature anisotropy is also found to be concentrated near the magnetic intermittent structures. The magnetic intermittent structures preferentially appear in plasma with a high value of temperature anisotropy, which is unstable to the mirror and firehose instabilities. The unstable plasma are also found to be significantly hotter than stable plasma. Previous works mentioned above mostly focus on the magnetic intermittency and its kinetic effect. In our work, we directly investigate the physical nature and kinetic effect of the temperature intermittency. These results will help to further understand the intermittent dissipation process in the solar wind turbulence.