Refractive index effects on the scatter volume location and Doppler velocity estimates of ionospheric HF backscatter echoes

摘要

Ionospheric E×B plasma drift velocities derived from the SuperDual Auroral Radar Network (SuperDARN) Doppler data exhibit systematicallysmaller (by 20–30%) magnitudes than those measured by the DefenceMeteorological Satellites Program (DMSP) satellites. A part of thedisagreement was previously attributed to the change in the E/B ratio dueto the altitude difference between the satellite orbit and the location ofthe effective scatter volume for the radar signals. Another important factorarises from the free-space propagation assumption used in converting themeasured Doppler frequency shift into the line-of-sight velocity. In thiswork, we have applied numerical ray-tracing to identify the location of theeffective scattering volume of the ionosphere and to estimate the ionosphericrefractive index. The simulations show that the major contribution to theradar echoes should be provided by the Pedersen and/or escaping rays that arescattered in the vicinity of the F-layer maximum. This conclusion issupported by a statistical analysis of the experimental elevation angle data,which have a signature consistent with scattering from the F-region peak. Adetailed analysis of the simulations has allowed us to propose a simplevelocity correction procedure, which we have successfully tested against theSuperDARN/DMSP comparison data set.