Energy Cascade Rate Measured in a Collisionless Space Plasma with MMS Data and Compressible Hall Magnetohydrodynamic Turbulence Theory

NAHUEL ANDRÉS; FOUAD SAHRAOUI; SEBASTIEN GALTIER; LINA Z. HADID; RENAUD FERRAND; SHIYONG HUANG

Washington DC

Congreso; AGU Meeting; 2018

AGU

The first complete estimation of the compressible energy cascade rate jε C j at magnetohydrodynamic(MHD) and subion scales is obtained in Earth?s magnetosheath using Magnetospheric MultiScalespacecraft data and an exact law derived recently for compressible Hall MHD turbulence. A multispacecrafttechnique is used to compute the velocity and magnetic gradients, and then all the correlation functionsinvolved in the exact relation. It is shown that when the density fluctuations are relatively small, jε C jidentifies well with its incompressible analog jε I j at MHD scales but becomes much larger than jε I j atsubion scales. For larger density fluctuations, jε C j is larger than jε I j at every scale with a value significantlyhigher than for smaller density fluctuations. Our study reveals also that for both small and large densityfluctuations, the nonflux terms remain always negligible with respect to the flux terms and that the majorcontribution to jε C j at subion scales comes from the compressible Hall flux.