Sporadic E at cusp latitudes

This is a study of the sporadic E (Es) that is observed over a 'cusp latitude' station, Cambridge Bay (77° CGM lat.). Es is extremely common in late evening hours at this location, reaching ∼80% occurrence rate in some months. The Es appears to form near the time when the convection reversal passes over the station. We explain our observations by a two-step formation mechanism involving horizontal convergence of ionization by the electric fields of the afternoon convection reversal, and then vertical convergence of this ionization by the electric fields in the polar cap. We show that several properties of the Es are consistent with this two-step mechanism.