Large‐scale imaging of high‐latitude convection with Super Dual Auroral Radar Network HF radar observations

TLDR

SuperDARN HF radars measure E×B drift of ionospheric plasma across high‑latitude regions, and two‑dimensional convection velocity has been mapped by combining line‑of‑sight velocity measurements from radar pairs in overlapping volumes. The authors present a new method for deriving large‑scale convection maps from all available velocity data, and discuss processing, conditioning factors, and result reliability. They determine electrostatic potential via a spherical‑harmonic series expansion, constrain the solution with a statistical model where data are missing, and process radar velocity data with conditioning factors to produce the maps. The expanded six‑radar network now images about one‑third of the convection zone in ~2 min, low‑order expansions give a gross global convection picture, and imaging shows rapid (<6 min) global reconfiguration of convection in response to IMF polarity changes.

Abstract

The HF radars of the Super Dual Auroral Radar Network (SuperDARN) provide measurements of the E × B drift of ionospheric plasma over extended regions of the high‐latitude ionosphere. With the recent augmentation of the northern hemisphere component to six radars, a sizable fraction of the entire convection zone (approximately one‐third) can be imaged nearly instantaneously (∼2 min). To date, the two‐dimensional convection velocity has been mapped by combining line‐of‐sight velocity measurements obtained from pairs of radars within common‐volume areas. We describe a new method of deriving large‐scale convection maps based on all the available velocity data. The measurements are used to determine a solution for the distribution of electrostatic potential, Φ, expressed as a series expansion in spherical harmonics. The addition of data from a statistical model constrains the solution in regions of no data coverage. For low‐order expansions the results provide a gross characterization of the global convection. We discuss the processing of the radar velocity data, the factors that condition the fitting, and the reliability of the results. We present examples of imaging that demonstrate the response of the global convection to variations in the interplanetary magnetic field (IMF). In the case of a sudden polarity change from northward to southward IMF, the convection is seen to reconfigure globally on very short (&lt;6 min) timescales.