Generation of Pc 1 waves by the ion temperature anisotropy associated with fast shocks caused by sudden impulses

Abstract

Observations have reported on the high correlation of Pc 1 events with magnetospheric compressions. A number of mechanisms have been suggested for the generation of the Pc 1 waves. In this paper, we propose a new mechanism which leads to the generation of Pc 1 waves. The interaction of a dynamic pressure pulse (Δρυ²) with the Earth's bow shock leads to the formation of a weak fast mode shock propagating into the magnetosheath. The shock wave can pass right through a tangential discontinuity (magnetopause) and into the magnetosphere, without disturbing either of the structures. In a quasi‐perpendicular geometry, the shock wave exhibits anisotropic heating with T⊥ > T∥. This anisotropy drives unstable ion cyclotron waves which we believe can contribute to the generation of the Pc 1 waves which are detected. The viability of the mechanism is demonstrated with simulations. This mechanism could explain peak in the occurrence of observed Pc 1 waves in the postnoon sector where a field‐aligned discontinuity in the solar wind would most often be parallel to the magnetopause surface due to the average Parker spiral magnetic field configuration.