3-D mesoscale MHD simulations of magnetospheric cusp-like configurations: cusp diamagnetic cavities and boundary structure

Abstract

Abstract. We present results from mesoscale simulations of the magnetospheric cusp region for both strongly northward and strongly southward interplanetary magnetic field (IMF). Simulation results indicate an extended region of depressed magnetic field and strongly enhanced plasma β which exhibits a strong dependence on IMF orientation. These structures correspond to the Cusp Diamagnetic Cavities (CDC's). The typical features of these CDC's are generally well reproduced by the simulation. The inner boundaries between the CDC and the magnetosphere are gradual transitions which form a clear funnel shape, regardless of IMF orientation. The outer CDC/magnetosheath boundary exhibits a clear indentation in both the x-z and y-z planes for southward IMF, while it is only indented in the x-z plane for northward, with a convex geometry in the y-z plane. The outer boundary represents an Alfvénic transition, mostly consistent with a slow-shock, indicating that reconnection plays an important role in structuring the high-altitude cusp region.

First MMS Observation of Energetic Particles Trapped in High‐Latitude Magnetic Field Depressions

“…However the total pressure is still lower than outside of the cavity (i). Reduced magnetic pressure, balanced by the increased thermal pressure is a typical signature of the diamagnetic cusp cavities created by reconnection in MHD (Adamson et al, ). Here the plasma pressure calculation does not include the high‐energy particles, which is why the plasma pressure does not balance the magnetic pressure.…”

“…Figure 6 shows the plasma and field properties of the dayside magnetosphere at 09:24 UT from high-resolution MHD global simulation results, with the MMS1 location projected in each plane as well as the cartoon of the expected DMC locations based on the maximum shear of the draped IMF field around the geomagnetic field in the vicinity of the cusps. The DMCs are directly generated by reconnection in maximum magnetic shear regions in a similar manner described by Nykyri, Otto, Adamson, Dougal, and Mumme (2011) and Adamson et al (2011Adamson et al ( , 2012. These cavities are indicated by a strongly enhanced plasma beta (color scale is saturated at beta = 38 in order to better see the northern hemisphere DMC in the same plane) tailward of the MMS at x = 5 R E (panel a) in the expected regions in Southern (region iv in panels b and g) and Northern Hemispheres (region iv in panels c and h).…”

“…The DMCs, characterized by extended regions of decreased magnetic field and high plasma beta surrounding the high‐altitude cusp funnel, are mainly formed by magnetic reconnection between the IMF and Earth's magnetic field surrounding the magnetospheric cusps (Adamson et al, , ; Nykyri, Otto, Adamson, Dougal, & Mumme, ; Nykyri, Otto, Adamson, & Tjulin, ; Zhang et al, ). Cusps are a funnel‐like, basic topological features of the magnetosphere, and were first predicted by Chapman and Ferraro () using the image dipole model.…”

Diamagnetic depression observations at Saturn's magnetospheric cusp by the Cassini spacecraft

“…However, the differing spacecraft velocities at high altitudes (∼10 R E ) affect the observations; Clusters larger velocity (than Polar) results in a smoothing effect of the observed diamagnetic depression, and therefore, it is only measured during enhanced (>2 nPa) solar wind dynamic pressures [Nykyri et al, 2011b]. Modeling by Adamson et al [2011Adamson et al [ , 2012 showed that the location and size of the cusp diamagnetic depression is strongly dependent on the IMF orientation, and that it is mainly structured by reconnection processes.…”

IMF dependence of energetic oxygen and hydrogen ion distributions in the near‐Earth magnetosphere

“…The diamagnetic cavity in the high‐latitude cusp region is also thought to be a possible source of energetic ions in the dayside magnetosphere and near‐Earth plasma sheet [e.g., Chen and Fritz , ; Fritz et al , ; Fritz et al , ]. The diamagnetic cavity is a region with enhanced plasma pressure and decreased magnetic field strengths formed by the magnetic reconnection in the high‐latitude magnetopause [e.g., Nykyri et al , , Adamson et al ., ]. This region is able to trap charged particles.…”