On the generation of magnetosheath high speed jets by bow shock ripples (Invited)

The terrestrial magnetosheath is embedded with coherent high speed jets of about 1 R_E in scale, predominantly during quasi-radial interplanetary magnetic field (IMF). When these high dynamic pressure (P_dyn) jets hit the magnetopause, they cause large indentations and further magnetospheric effects. The source of these jets has remained controversial. One of the proposed mechanisms is based on ripples of the quasi-parallel bow shock. In this paper, we combine for the first time four years of subsolar magnetosheath observations from the THEMIS mission and corresponding NASA/OMNI solar wind conditions with model calculations of a rippled bow shock. Concentrating on the magnetosheath close to the shock during low IMF cone-angles, we find that (1) 97% of the observed jets can be produced by local ripples of the shock under the observed upstream conditions; (2) the coherent jets form a significant fraction of the high P_dyn tail of the magnetosheath flow distribution; (3) the magnetosheath P_dyn distribution matches the flow from a bow shock with ripples that have a dominant amplitude to wavelength ratio of about 9% (~ 0.1 R_E/1 R_E) and are present ~12% of the time at any given location.