PFISR observations of the nightside Region-2 electrodynamics during substorm growth and expansion phases: preliminary results

The nightside Region-2 (R2) electrodynamics, including the Harang reversal, has been shown recently to be closely related with substorm dynamics. The newly available Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) is able to measure the ionospheric convection, as well as electron density and some other important plasma parameters, and thus can provide some new aspects to this problem. In the past one and a half years, more than 60 runs have been conducted when PFISR was on the nightside. By taking advantage of the THEMIS ground based all-sky camera array, substorm events, for which good all-sky camera measurements are available during the runs, have been selected and categorized by the location of the radar at the time of onset relative to that of the auroral onset. Preliminary results show consistency with our previous SuperDARN observations, that is the convection flows at nightside change significantly at onset and the way they evolve highly depends on their location relative to that of substorm onset. The electron density profiles measured by PFISR enable us to study the characteristics of the substorm arc brightening and the associated field-aligned current system. Preliminary results show evidence that the onset arc may be Alfvénic. Other ground based instruments, such as magnetometers and SuperDARN, are also studied as complementary to PFISR. These observations provide a unique ionospheric perspective on substorm process and can contribute to an integral understanding of the substorm dynamics.