In contrast with a bursty reconnection scenario that typically is associated with magnetic reconnection occurring at the Sun during solar flares and in the Earth’s magnetosphere during magnetospheric substorms, releasing free magnetic energy explosively, it has been commonly regarded that magnetic reconnection at current sheets in the solar wind seems to have typically a quasi-steady state behavior, thus without a localized energy being released explosively.
In spite of such an expectation, the recent paper by Wang et al. (2022) shows 76 bursty reconnection events in the solar wind observed by the Magnetospheric Multiscale (MMS) mission during the time interval of October 2017-May 2019, thus suggesting that bursty reconnection in the solar wind is more common than previously thought. This paper also shows that the observed plasma was more efficiently heated in the magnetic reconnection-diffusion region than at its external slow shocks, and that flow enhancements are much higher in the reconnection external (outflow) region than at the diffusion region.
By examining the solar wind data collected during the time interval of October 2017 to May 2019, many solar wind-current sheet crossings were observed with most of them associated with enhanced plasma flows. Based on accepted criteria to distinguish the magnetic reconnection- diffusion region from the external outflow region, a total of 76 diffusion region events where recognized from the observed MMS- current sheet crossings. The location of those reconnection diffusion-region events were distributed widely in the observed solar wind region, up to distances of about 27 Earth radii, and occurred in a variety of solar wind conditions.
The MMS mission, launched in 2015, was designed to fulfil an advanced exploration of electron-scale kinetic physics in the observed plasmas . The “fast plasma investigation” onboard the MMS can provide plasma measurements with an unprecedentedly high resolution, both for ions and for electrons. Similarly, the magnetic and electric field data can be sampled at very high rates., which enabled an advanced investigation of kinetic physics in the solar wind as that presented in this paper. Moreover, since the duration of the diffusion region was observed to last typically only a few seconds, one can argue that it is only possible to clearly discern the diffusion region when the plasma data has a time resolution as high as that provided by the MMS measurements . This could have been one of the main reasons for the rare existing reports on magnetic reconnection- diffusion region events in the solar wind.
In summary, this paper shows that reconnection can frequently be fast and bursty in the solar wind. Thus, the knowledge obtained and accumulated in the past from the bursty character of reconnection during solar flares and during magnetospheric substorms should be applicable in the solar wind as well. Further, an important consequence of this study is that reconnection can efficiently energize plasma in the solar wind, thus probably playing a key role in solar wind heating and acceleration.
Therefore, based on these accomplishments, we believe that the results presented in the paper by Wang et al. can be regarded as an important contribution toward a more advanced understanding of magnetic reconnection in space plasmas .
Wang R., S. Wang, Q. Lu, X. Li, S.Lu & W.Gonzalez , "Direct observation of turbulent magnetic reconnection in the solar wind ", Nature Astronomy, https://doi.org/10.1038/s41550-022-01818-5 , 2022 .
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