Magnetosheath kinetic structure: Mirror mode and jets during southward IP magnetic field

Earth's magnetosheath is permeated by a variety of plasma waves, nonlinear structures and ion distributions.  Understanding solar wind interaction with Earth's magnetic field requires a detailed knowledge of the magnetosheath as the interface between both regions, including its kinetic micro-structure. In this work we study an extended interval (45 min) with southward magnetic field (B_z< 0) observed by MMS in the dayside magnetosheath. We use magnetic field and plasma data to study the properties of three transient enhancements in dynamic pressure identified as jets. We also calculate instability thresholds and investigate wave characteristics inside and outside of the jets. The characteristics of these jets are variable, which suggest different origins. While two of them can be classified as V-jets with large increment in velocity with almost no density increment the third one is an N-jet showing large enhancements in density with almost no velocity increment. The N-jet lasts seven times longer than the V-jets and occurs just at the region where the negative B_z becomes positive. Ion distributions inside the jets are more isotropic (T_perp ≈T_parallel) compared with the surrounding plasma where T_perp > T_parallel. FFT and minimum variance analysis show that fluctuations inside the N-jet tend to have larger transversal components, although they propagate at large angles to the background field. In contrast, waves in regions surrounding the jets are compressive and can be identified as elliptically polarized mirror mode waves. We have also show that the mirror instability threshold C_M is positive inside these intervals.