Impulsive Energy Transfer from the Magnetosphere to the Ionosphere during Geomagnetic Storms

Data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) have been used to study electric fields and currents for multiple magnetic storms.The calculation uses a high latitude conductivity model based on the field-aligned currents measured by AMPERE compared to measurements from the Poker Flat Incoherent Scatter Radar.The derivation of conductivities from field-aligned currents ensures spatial and temporal consistency in the calculated electrodynamic parameters.For all of the magnetic storms studied, the combined energy input from precipitating particles exhibits sharply-peaked maxima for small scale structures at the times of local minima in DsT, suggesting a close coupling between magnetospheric and/or ring current energy content and the high latitude currents driven by field-aligned currents.We speculate that these relatively rapid increases and decreases of the high latitude energy deposition may be a result of the variation of ionospheric conductance with field-aligned current strength, leading to a nonlinear relation between current and voltage, and impulsive transfer of energy from the magnetosphere to the ionosphere.