SuperDARN-derived plasma convection: Comparison with other data and application to field -aligned current measurements

In this thesis, several aspects of the SuperDARN HF radar observations at high latitudes are investigated in cooperation with measurements performed by three other instruments, the Sondrestrom incoherent scatter radar, the ion drift meter onboard of the DMSP satellite and the CADI ionosonde.

The first issue under investigation was consistency of plasma convection data provided by these instruments. First, routine measurements by the Goose Bay and Stokkseyri SuperDARN radar pair (“merge” velocity estimates) were compared with the Sondrestrom incoherent scatter radar data. Three different levels of assessment were used; by looking at the line-of-sight velocities, by comparing the SuperDARN vectors and corresponding Sondrestrom line-of-sight velocities and by comparing the end products of the instruments, the convection maps. All three comparisons showed overall reasonable agreement of the convection measurements though the data spread was significant and for some points a strong disagreement was obvious. Importantly, the convection map comparison showed a tendency for the SuperDARN velocities to be often less than the Sondrestrom drifts for strong flows (velocities > 1000 m/s) and larger for weak flows (velocities < 500 m/s). </p>

The second issue under investigation was the configuration of the ionospheric plasma convection and field-aligned currents (FACs) in the dayside ionosphere at small IMF B₂ and B_y. By merging SuperDARN convection data for a number of events, it was found that convection tends to be compressed to the poleward edge of the polar cap with a noticeable decrease of the flow velociity inside the central polar cap for this condition. Also, for individual events, existence of three sheets of FACs was illustrated. FACs had similar appearance as region 1, region 2, and region 0 currents known from satellite magnetometer observations for the disturbed magnetosphere. Spatially, sheets of region 1 FACs were co-located with a line separating the plasma flow of different directions (shear) in a convection patterns. Region 2 and region 0 currents were observed equatorward and northward of region 1 currents, respectively. (Abstract shortened by UMI.)