Experimental study of nonlinear interaction of plasma flow with charged thin current sheets: 2. Hall dynamics, mass and momentum transfer

Abstract

Abstract.Proceeding with the analysis of Amata et al. (2005), we suggest that the general feature for the local transport at a thin magnetopause (MP) consists of the penetration of ions from the magnetosheath with gyroradius larger than the MP width, and that, in crossing it, the transverse potential difference at the thin current sheet (TCS) is acquired by these ions, providing a field-particle energy exchange without parallel electric fields. It is suggested that a part of the surface charge is self-consistently produced by deflection of ions in the course of inertial drift in the nonuniform electric field at MP.Consideration of the partial moments of ions with different energies demonstrates that the protons having gyroradii of roughly the same size or larger than the MP width carry fluxes normal to MP that are about 20% of the total flow in the plasma jet under MP. This is close to the excess of the ion transverse velocity over the cross-field drift speed in the plasma flow just inside MP (Amata et al., 2005), which conforms to the contribution of the finite-gyroradius inflow across MP. A linkage through the TCS between different plasmas results from the momentum conservation of the Correspondence to: S. Savin (ssavin@iki.rssi.ru) higher-energy ions. If the finite-gyroradius penetration occurs along the MP over ∼1.5 R E from the observation site, then it can completely account for the formation of the jet under the MP. To provide the downstream acceleration of the flow near the MP via the cross-field drift, the weak magnetic field is suggested to rotate from its nearly parallel direction to the unperturbed flow toward being almost perpendicular to the accelerated flow near the MP.We discuss a deceleration of the higher-energy ions in the MP normal direction due to the interaction with finite-scale electric field bursts in the magnetosheath flow frame, equivalent to collisions, providing a charge separation. These effective collisions, with a nonlinear frequency proxy of the order of the proton cyclotron one, in extended turbulent zones are a promising alternative in place of the usual parallel electric fields invoked in the macro-reconnection scenarios. Further cascading towards electron scales is supposed to be due to unstable parallel electron currents, which neutralize the potential differences, either resulted from the ion-burst interactions or from the inertial drift.The complicated MP shape suggests its systematic velocity departure from the local normal towards the average one, inferring domination for the MP movement of the non-local processes over the small-scale local ones.Published by Copernicus GmbH on behalf of the European Geosciences Union and the American Geophysical Union. The measured Poynting vector indicates energy transmission from the MP into the upstream region with the waves triggering impulsive downstream flows, providing an input into the local flow balance and the outward movement of the MP.Equating the transverse electric field inside the MP TCS by the Hall term in the Ohm's law ...

Super fast plasma streams as drivers of transient and anomalous magnetospheric dynamics

“…Hietala et al, 2009;Savin et al, 2011). However, as mentioned above, HFA's and SW current sheets are not the only sources of SPS's (Nemecek et al, 1998;Savin et al, 2006Savin et al, , 2008Savin et al, , 2010Amata et al, 2011;Hietala et al, 2009). Savin et al (2008Savin et al ( , 2011 outline that MSH and boundary resonances at a few mHz can substantially affect the SPS appearance and boundary dynamics.…”

“…As for the previous suggestions for the SPS generation mechanisms, sonic (at maximum) jets could be generated in the MSH either by flow self-focusing, or by surface charge at moving magnetospheric boundaries (see Savin et al, 2006Savin et al, , 2008Savin et al, , 2011, and references therein). The Laval-nozzle effect was believed to accelerate the "super-jets" (cf.…”

“…Probably, the SPS's move fast past Interball-1 in their transverse direction, giving much larger input to the total flux balance between MP and BS as compared with time-averaging along the orbit (cf. Savin et al, 2006Savin et al, , 2008Savin et al, , 2011. In any case, the SPS input to the flux balance should be rather substantial (∼30 %, see Savin et al, 2008Savin et al, , 2011, and references therein).…”

“…Recent observations by the Cluster, THEMIS and Interball-1 spacecraft (see Savin et al, 2006Savin et al, , 2008Savin et al, , 2010Savin et al, , 2011Amata et al, 2006Amata et al, , 2011Hietala et al, 2009;Jacobsen et al, 2009;Zhang et al, 2009, and references therein) indicate the presence of very fast plasma streams inside the MSH. In the spacecraft frame these streams, which we will call SPS's, can last for several tens of seconds and have an extremely high ram pressure.…”

“…It has been suggested that the SW is not the only direct driver of the jets (cf. Nemecek et al, 1998;Savin et al, 2006Savin et al, , 2008Savin et al, , 2011Amata et al, 2011;Hietala et al, 2009). Flow stratification and turbulence development are rather common phenomena for dissipation of kinetic energy.…”