The Propagation and Evolution of Polar Cap Patches During Auroral Substorm Activity

Polar cap patches are islands of enhanced plasma density formed during intervals of southward interplanetary magnetic field (IMF). The present study examines the observations of polar cap patches during sequential auroral substorms that occurred on 9 September 2011. The propagation and evolution of large-scale polar cap patches were monitored by three SuperDARN radars (MCM, ZHO, and SYE) located in the Southern Hemisphere. During the substorm periods, MCM radar observed periodic blobs of anti-sunward propagating HF backscatter echoes. By examining the 2-D scan plots, there were the dawn-dusk elongated radar patches moving across the magnetic pole and eventually merging into the nightside auroral zone. Simultaneous ZHO and SYE radars recorded consecutive ionospheric plasma blobs and moderate Doppler negative velocity near the poleward boundary of the nightside auroral oval. Coordinated GPS observations in ZHO showed pulsed increases in total electron content (TEC) and scintillations. Due to the high values in the TEC data, such radar patches are suggested to result from the transportation of high-density plasma from the dayside sunlit ionosphere during sequential auroral substorms. The in situ observations by the DMSP satellite suggested re-structuring of plasma patches near the poleward boundary of the auroral oval by pulsed flow bursts.