Direct Observation of Short Large-Amplitude Magnetic Field Structures from Formation to Destruction

Abstract

Short large-amplitude magnetic field structures (SLAMSs) are often seen upstream of quasi-parallel shocks. They play vital roles near the quasi-parallel shock, such as decelerating solar wind ions and contributing to the dissipation and reformation of the shock. The formation process of these structures has attracted great attention and has long been realized in simulation. However, their formation mechanism is still full of mysteries. Here, using magnetospheric multiscale mission (MMS) observation, we provide direct observations of the SLAMS formation and destruction processes. SLAMS growth is powered by solar wind ions and shock-reflected ions through the ion-ion non-resonant mode. Reconnection occurs between and inside SLAMSs during their growth; however, these cumulative changes in magnetic field topology and the dissipation of the magnetic field energy contribute to the destruction of the SLAMS. These observations shed new light on the dissipation and reformation of the shock both in space physics and astrophysics.