The Speed of Interplanetary Shocks Through the Magnetosheath: A Toy Model

Abstract

Before interacting with the magnetosphere, an interplanetary shock travels through the magnetosheath where its speed and shape are modified. Previous studies have reported widely different answers to the question of the speed of an interplanetary shock in the magnetosheath. Observational studies generally answer this question “macroscopically”, by measuring the time delay between detections of the interplanetary shock at two or more locations and inferring its average speed. In this letter, we instead propose a local predictive model for the velocity and show that paradoxical results from previous authors arise naturally from their use of different detection methods. Our model can be used to predict the propagation of an interplanetary shock in the magnetosheath with a simple laptop, yet provides results which are in broad agreement with much heavier magnetohydrodynamics and hybrid particle-in-cell simulations.