A statistical analysis of SuperDARN scattering volume electron densities and velocity corrections using a radar frequency shifting technique

摘要

Ionospheric plasma drift velocities measured by High Frequency (HF) coherent scatter radars, such as the Super Dual Auroral Radar Network (SuperDARN), are typically underestimated, sometimes significantly, because the refractive index in the scattering volume is not known. Large-scale or background estimates of ionospheric electron density and refractive index can be made by other instruments; however, these instruments both do not cover the large field-of-view of the SuperDARN radars and do not provide information about the small-scale structures which may be very important for the scattering process. A method has been developed to use different operating frequencies of the SuperDARN radars to obtain the average scattering volume electron density. These electron density measurements provide an estimate of refractive index and allow for corrections to the SuperDARN velocity data to be made. A comprehensive analysis of all SuperDARN data since its inception almost 20 years ago has provided estimates of average electron density in the scattering volume of the radars for various magnetic latitudes, solar activities, local times, and seasons. The analysis indicates that the average electron density, and therefore refractive index, in the scattering volume can vary significantly with the various parameters. Densities ranging from less than 2 × 10 ~(11) m ~(-3) to more than 8 × 10 ~(11) m ~(-3), result in refractive index corrections from less than 5% (not very significant) to more than 50% (extremely significant). These results provide estimates of appropriate adjustments to the drift velocities assumed by SuperDARN for various conditions. Further, this research has provided substantial insight into the physics of the coherent scattering process and provides a method by which electron density of the scattering structures can be monitored. This will be tested using in situ high-latitude ionospheric measurements from the upcoming enhanced Polar Outflow Probe (ePOP) satellite mission.