Energy deposition by precipitating particles and Joule dissipation in the auroral ionosphere

Eight days of synoptic data from the Chatanika incoherent scatter radar have been analyzed in an attempt to determine the characteristic morphology of auroral zone energy deposition by Joule heating and precipitating particles. The observations cover invariant latitudes between ∼62° and 68°. The composite spatial morphology derived from these eight days of data shows that morning sector particle precipitation deposits energy into the thermosphere at a faster rate and at lower altitudes than evening sector precipitation. The Joule heating rate has the opposite asymmetry about midnight, i.e., more Joule heating results for a given premidnight eastward electrojet current than for the same morning sector westward electrojet current intensity. This complementary asymmetry about midnight between the Joule and particle precipitation heating rates is consistent with the changes in ionospheric conductivity implied by the local time variation of precipitating particle hardness. The Joule heating rate generally dominates particle energy deposition in the premidnight sector. However, the daily averages of the two energy sources are roughly equal.