CDC’s as Global Diagnostics

• CDC’s are macroscopic objects that respond to plasma forces, enabling us to treat them as tracers of quite global MHD equilibria.

• CDC’s should rapidly move to the cusp field line where there exists a force-free location. The radial coordinates of this force-free location depend on the strength of the magnetopause current system as well as the macroscopic size of the cavity.

• The location and distribution of these cavities provide global diagnostics of the Earth’s magnetic equilibrium over quite large length scales. (2 Re)