Energy analysis of substorms based on remote sensing techniques, solar wind measurements, and geomagnetic indices

[1] Observations from the Polar Ionospheric X-ray Imaging Experiment (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to examine the energy deposition in the Northern Hemisphere by precipitating electrons for seven substorms during 1997. By combining the results from these two remote sensing techniques we derive the 5 min average electron energy distributions from 100 eV to 100 keV with a spatial resolution of similar to700 km. During growth phase we find that most of the energy is carried by electrons below 10 keV. The study shows that the maximum intensity of the substorm is mostly defined by the flux of electrons below 10 keV. In contrast, the electrons above 10 keV show a greater intensification at substorm onset and are more confined azimuthally during the expansion phase. By using the most appropriate parameterized methods to estimate the energy increase of the ring current (U-R) and the Joule heating rate in both hemispheres (U-J) and by adding the rate of energy deposition in both hemispheres by precipitating electrons (U-A), we estimate the total energy dissipation rate during substorms (U-T). Our estimate of U-A is a factor 2-4 larger than that reported in earlier studies. We find that the contributions to the total time-integrated energy dissipation over the duration of the substorm, W(U-T), from W(U-R), W(U-J), and W(U-A) on average are 15%, 56%, and 29%. Comparing W(U-T) and the time-integrated epsilon parameter, W(epsilon), which approximates the solar wind input due to dayside reconnection, we find that the parameter does not always provide enough energy into the magnetosphere to balance W(U-T). An additional energy transfer mechanism is needed to balance the energy budget. We find that a viscous interaction that transfers 0.17% of the solar wind kinetic energy in addition to the energy transfer due to dayside reconnection, estimated by the epsilon parameter, is sufficient to balance the total energy dissipation U-T.