Ponderomotive Disturbance of the Solar Wind Velocity before the Fronts of Shock Waves

The solar wind speed perturbation before the fronts of shock waves is theoretically investigated. It is shown that there is a small, but quite detectable deceleration in front of the Earth’s bow shock in the Earth-bound frame of reference. The perturbation is caused by the ponderomotive Abraham force. The Abraham force results from the excitation of fast magnetosonic waves in the foreshock region. The theoretical estimate of the solar wind deceleration by ~10 km/s agrees with measurements of the directional plasma flow velocity on the spacecraft in the foreshock region of the Earth’s bow shock. The use of the velocity addition theorem for interplanetary foreshocks with a structure similar to Earth’s foreshock allows to predict acceleration rather than deceleration of the solar wind in front of interplanetary shocks in the Earth-bound reference frame. The main conclusion is that the theory of ponderomotive plasma modification is of undoubted interest for the interpretation of in situ measurements in the interplanetary environment.