Mirror Mode Waves Immersed in Magnetic Reconnection

Mirror mode waves with anticorrelated density and magnetic field are widely observed in the heliosphere. This paper presents the first evidence of mirror mode waves occurring in the vicinity of a magnetic reconnection site (X-line) at the interface between the solar wind and Earth’s magnetosphere based on the analyses of two Magnetospheric Multiscale (MMS) crossing events along with the Grad–Shafranov (GS) reconstruction model with temperature anisotropy. The GS scheme solves the steady two-dimensional MHD equations in the frame of references moving with the plasma by using the spacecraft measurements. Both events have mirror type of pressure anisotropy and correspond, respectively, to the symmetric and asymmetric Harris type current sheets with the total thermal and magnetic field pressures being approximately constant. The GS reconstruction results show the magnetic reconnection with X line geometry associated with the mirror mode structures on the spatial lengths of 170 ∼ 370 km or 1.3 ∼ 3 ion gyroradius. The coexistence of mirror waves and magnetic reconnection provides the first observational evidence for the prior theoretical prediction of mixed tearing and mirror instabilities in plasma current sheets with temperature anisotropy.