Energy Cascade Rate in Compressible Hall-MHD: Theory vs. MMS Observations

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

San Francisco

Congreso; AGU Meeting; 2019

Energy cascade rate derived from Incompressible MHD theory (IMHD) has been widely used to studyinertial range solar wind (SW) turbulence in view of better understanding the longstanding problem of SWheating. In recent years the IMHD theory was extended to compressible flows described within theisothermal approximation [1,2] and applied to investigate the role of density fluctuations in inertial range SWand magnetosheath turbulence [3]. Here we discuss the extension of those theoretical and observationalmodels to describe sub-ion scale cascade using new incompressible and compressible Hall-MHD models(resp. IHMHD and CHMHD) [4,5]. We will discuss the application of these new models to the MMS in-situobservations in the magnetosheath and the SW. Comparing the results obtained from IHMHD and CHMHDhighlights the importance of density fluctuations at the sub-ion scale, even when the inertial range is nearlyincompressible, in agreement with theoretical expectation. We will discuss other features such as the linkbetween the fluid sub-ion cascade and kinetic features like plasma instabilities and kinetic damping processes.