High-Latitude Plasma Convection Based on SuperDARN Observations and the Locally Divergence-Free Condition

A new technique for estimating the global-scale pattern of magnetospheric convection in the ionosphere is presented. The technique uses the SuperDARN line-of-sight velocity observations combined with an empirical convection model and the assumption that the resulting velocity field is divergence free. In contrast to other techniques for convection estimation, it does not express the velocity field in terms of known basis vectors and it does not assume that the velocity can be determined from a static potential. The velocity is estimated by applying Bayesian inverse theory to the input data, model, and constraints. Linear equations for the plasma velocity at every point in the domain are solved simultaneously in a least-squares sense. Application of the technique results in convection patterns with spatial resolution equal to the calculation grid. The technique builds on previous work that provided regional patterns to provide patterns over the entire high-latitude region. It has the ability to provide a moderate resolution (

\sim 100\times 100

\,km for example) over the majority of the domain of consideration and higher resolution (

\sim 50\times 50

\,km for example) in a nested region. Examples of patterns will be presented along with overlays of the velocities on auroral images from the THEMIS All-Sky Imagers. The patterns conform with expectations based on the observed IMF conditions and display features that show close correspondence to simultaneously observed features in the auroral luminosity. Finally the technique for using the velocity pattern to estimate an electrostatic potential pattern will be presented along with example results.