Magnetosheath High Speed Jets: Towards Comprehensive Understanding

High Speed Jets (HSJs) are temporally and spatially localised regions of magnetosheath plasma which exhibit high dynamic pressure, sometimes up to x15 the surrounding magnetosheath pressure. Penetrating from the bow shock through the magnetosheath, they can locally distort the magnetopause upon impact, generating both magnetopause surface waves and/or inner-magnetospheric compressional waves. As such, the effects of the jets have been seen in the magnetosphere all the way to the ground.

Here we review the recent progress in studying these jets that can couple bow shock and magnetopause dynamics. Large statistical datasets of in situ observations have revealed the HSJ occurrence rates and properties. Most importantly, HSJs are found more often downstream of the quasi-parallel shock, and thus occur on the dayside predominantly during intervals of quasi-radial interplanetary magnetic field. Combining the observational datasets with modeling and large scale kinetic simulations has made it possible to systematically address their formation. The main source of HSJs is not solar wind discontinuities. Instead, mounting evidence points to ripples on the bow shock itself, induced by large scale foreshock processes. Thanks to this joint effort we are moving towards comprehensive understanding of the formation, properties and dynamics of the jets as well as their effects.