Abstract
The terrestrial foreshock as a region permeated by different types of plasma waves, various particle populations, and strong wave activity is a subject of intensive investigations. Our statistical study of the solar wind proton velocity deceleration in the foreshock uses multipoint observations of the THEMIS mission and compare them with the Wind solar wind monitor with a motivation to estimate the factors influencing evolution/modification of the solar wind speed.
In order to follow changes of the solar wind proton speed, our moment calculations do not include the reflected particles as well as heavier ions. We have found a systematic deceleration of the solar wind protons with a decreasing distance to the bow shock that is correlated with the flux of reflected and accelerated particles, with the level of magnetic field fluctuations in the ultralow frequency range, and with their compressibility.
We can conclude that the reflected particles excite waves of large amplitudes and, as a consequence, modify median values of the velocity measured in an unperturbed solar wind. The deceleration is as high as 3% in front of the quasi-parallel bow shock and decreases with the distance being observable up to 50 R-E.
We found similar effects in front of the Moon and attributed them to an influence of the solar wind ions reflected from the lunar surface.