Adiabatic vs. non‐adiabatic particle distributions during convection surges

The convection surge is a mechanism whereby a temporary intensification and subsequent relaxation of the east‐west electric field coexists with an earthward displacement of the nightside curved magnetospheric field lines. Calculations of single particle trajectories for H+ and O+ during convection surges have found that the first adiabatic invariant µ = E⟂/B (where E⟂ is the energy contributed by the motion of the particle perpendicular to the magnetic field and B is the magnitude of the ambient magnetic field) may break down, depending on the particle's species and location. Applying this property to a collection of single particle trajectories, it has been suggested that the boundary between the adiabatic and non‐adiabatic regimes could be interpreted as the injection boundary formed in the middle magnetosphere during substorm expansions. Under this interpretation, the non‐adiabatic conditions establish the character of the populations tailward of the injection boundary. To investigate the behavior of the full particle distributions, we have modified the convection surge numerical code of Mauk [1986] to approximate the breakdown of the adiabaticity. In this report we present simulated results for various parameter conditions. Contrary to the adiabatic results, the non‐adiabatic conditions do not yield the magnetic‐field‐aligned distributions that are commonly observed tailward of the injection boundary.