Dynamics of the earth's bow shock position

Abstract

The paper deals with a study of the variations in the Earth's bow shock position based on simultaneous measurements by the Prognoz 10 and IMP-8 satellites. Abrupt variations of solar wind parameters that have been registered by one apparatus are identified with shock crossings as seen by the other one. In the cases of solar wind - magnetosheath crossings the velocity has been calculated also from the data obtained by only one apparatus (the one observing the crossing). Assuming the velocity of discontinuity propagation the same as the velocity of the solar wind, we can calculate the mean shock velocity from the time interval between these events. The shock model proposed by Formisano has been used for the calculations of the bow shock position. Experimental data indicates that the bow shock position depends on the magnetic field more strongly than is usually supposed. On the other hand, the dependence on the solar wind dynamic pressure seems to be weaker than expected. Calculated velocities of the shock front motion lie in the interval of 2 to 60 km/s. For small variations of the solar wind dynamic pressure the calculated velocity is roughly proportional to the magnitude of the variation.