SIMULATION OF CONVECTION FLOW ESTIMATION ERRORS IN VHF BISTATIC AURORAL RADAR SYSTEMS

The results of model calculations are presented which simulate the err ors in the estimation of plasma drift velocities measured by coherent VHF bistatic auroral radar systems sensitive to E-region plasma irregu larities. The Doppler velocity data from such radars is commonly analy sed by utilising a cosine rule reduction technique. There is now a con siderable amount of evidence to suggest that the cosine rule is, in ge neral, not valid for E-region backscatter. The strongest E-region rada r backscatter signals are thought to be caused by modified two stream instability waves which propagate at speeds close to the local ion aco ustic speed and not, as was previously believed, at speeds close to th e component of the flow velocity in the direction of the beam. As a re sult of the breakdown of the cosine rule, systematic errors arise in t he estimation of both how speeds and flow angles, by coherent VHF bist atic radar systems. The model presented here incorporates a nonlinear theory of radar auroral backscatter from which backscatter irregularit y phase speeds may be calculated for a variety of dow conditions. This allows radar Doppler velocities and corresponding cosine rub estimate s to be simulated. In this way, the effects of beam geometry, flow spe ed and backscatter altitudes and aspect angles on the errors which ari se in flow estimation based on the cosine rule are evaluated theoretic ally.