Under steady-state conditions the magnetopause location is described as a pressure balance between internal magnetic pressures and the external dynamic pressure of the solar wind. Under more extreme solar wind driving, such as high solar wind pressures or strong southward-directed interplanetary magnetic fields, this boundary is significantly more compressed than in steady-state, playing a significant role in the depletion of magnetospheric plasma from the Van Allen Radiation Belts, via magnetopause shadowing.

We use a database of >42,000 spacecraft magnetopause crossings, to determine how the magnetopause position differs from a statistical model, and under which conditions. The role of magnetopause compressions in creating radial gradients of electron phase space densities are further investigated by comparing electron measurements from the Van Allen Probes to our database of magnetopause crossings.

We find that the observed magnetopause is on average 6 % closer to the radiation belts than the model during periods of sudden dynamic pressure enhancement, such as during storm sudden commencement, with a maximum of 42% closer. This demonstrates that large step-changes in solar wind conditions enable the magnetopause to have a significant time-dependence which empirical models cannot capture. Therefore empirical magnetopause models such as the Shue et al. [1998] model should be used cautiously to interpret energetic electron losses by magnetopause shadowing.