On the generation of magnetosheath high‒speed jets by bow shock ripples

The terrestrial magnetosheath is embedded with coherent high‒speed jets of about 1RE in scale, predominantly during quasi‒radial interplanetary magnetic field (IMF). When these high dynamic pressure (Pdyn) 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, 4 years of subsolar magnetosheath observations from the Time History of Events and Macroscale Interactions during Substorms 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 intervals when the angle between the IMF and the Sun‒Earth line was small, 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 Pdyn tail of the magnetosheath flow distribution; (3) the magnetosheath Pdyn distribution matches the flow from a bow shock with ripples that have a dominant amplitude to wavelength ratio of about 9% (∼0.1RE/1RE) and are present ∼12% of the time at any given location. Key Points First quantitative study on the connection between jets and bow shock ripples 97% of the studied high speed jets can be produced by ripples Main ripple size found to be amplitude/wavelength ~9%, i.e., ~0.1Re/1Re