High Latitude Energy Deposition During Geomagnetic Storms Determined from AMPERE Observations

Data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) have been used to characterize the Birkeland currents and corresponding electric fields, precipitating energy flux, and Joule heat for 24 magnetic storms in the 2010 to 2015 time period.  The calculation uses a high latitude conductivity model derived from incoherent scatter radar observations of ionospheric electron densities in correlation analysis with the field-aligned currents measured by AMPERE.  The derivation of conductivities from field-aligned currents ensures spatial and temporal consistency in the calculated electrodynamic parameters and allows evaluation of the full electrodynamics given the observations of Birkeland currents from AMPERE.  Here we use this approach to estimate the energetics of ionospheric energy dissipation during geomagnetic storms. For all of the magnetic storms studied, the combined energy input from precipitating particles and Joule heating exhibits sharply-peaked maxima at the times of local minima in Dst, suggesting a close coupling between the ring current and the high latitude currents driven by the Region 2 field-aligned currents.  The average width of these features is about five hours.  The relatively rapid increase and decrease of the high latitude energy deposition suggests burst-like transfer of energy from the magnetosphere to the ionosphere just prior to storm recovery.  Within these enhancements, the Joule heating rate typically exceeds the energy flux from precipitating particles by a factor of two to four, indicating that enhanced electric fields are present within the high latitude electrojets. These transient events represent important features of the high latitude ionosphere during the recovery phase of magnetic storms.