Assessing auroral electric field variance with coherent and incoherent scatter radar

Line-of-sight F region plasma drifts measured with the Poker Flat Incoherent Scatter Radar (PFISR) during the NASA JOULE II experiment period are compared with estimates derived from E region coherent scatter spectra observed with a 30 MHz imaging radar on common magnetic field lines. The estimates are based on empirical formulas determined through earlier comparisons between in situ and ground-based measurements. Good agreement is found in the current study when the radar measurements are sufficiently well collocated and the convection is sufficiently homogeneous for meaningful comparison. The mean and variance of the background electric field are also estimated from the coherent scatter data and used to assess the contribution of fine structure in the convection pattern to Joule heating. Fine structure in the scale size regime between ∼2∼2 and 200 km is found to increase the second moment of the electric field by up to 50% for intervals of a few minutes during a substorm when the flow was highly irregular. The average contribution to the net Joule heating rate is generally likely to be modest, however.