Radar studies of natural and artificial waves and instabilities in the auroral ionosphere
2014-12-15T10:41:02Z (GMT) by
The electron Pedersen conductivity instability (EPCI) was proposed by Dimant and Sudan (1995a, 1995b, 1995c) as an extension to accepted Farley-Buneman instability theory and was predicted to give rise to D-region radar echoes. Theoretical modelling of its growth rate and threshold velocity for varying flow and aspect angles is presented, together with evidence for a two-layer structure where the growth rate is maximised. Backscatter parameters obtained by two coherent radar systems, CUTLASS and STARE, are presented for two case studies where the data are consistent with an electrojet flow whose velocity exceeds the threshold value for EPCI excitation.;Backscatter parameters obtained from artificially generated FAIs for spatial sweeping and preconditioning experiments are also presented. Varying the illumination time of part of the heated patch affects the CUTLASS backscatter power corresponding to that patch. The variation in backscatter over CUTLASS range gates, for a heater beam with varying pointing direction, is shown to agree closely with the expected results obtained by modelling the heater beam intensity. It is shown that the CUTLASS backscatter power, for a given heater power, is dependent upon whether the ionosphere has previously been excited at a higher heater power.;A new longer-lag mode was run on CUTLASS for the October 1999 heating campaign and the ACF decorrelation and backscatter power decay time constants obtained from data collected when this mode was running were different by an order of magnitude. Turbulence characteristics were obtained from the artificial irregularity distribution. These are compared to a study preferred by Villain et al. (1996) and the results are consistent with an artificial irregularity distribution that remained correlated for longer times than naturally occurring irregularity distributions.