Study of SAPS-like flows with the King Salmon SuperDARN radar

This thesis has two focuses. The major focus is an investigation of the nature of high-velocity ~2 km/s)ionospheric flows occasionally detected by the King Salmon SuperDARN radar at relatively low magnetic latitudes of 65^0. The second focus is a validation work on the quality of SuperDARN convection measurements. As an alternative convection-monitoring instrument, an ion drift meter onboard the DMSP satellite was chosen for comparison with SuperDARN. This study includes a broad range of velocities of up to ~1.5 km/s. Consideration of very large velocities is fundamentally important for successful research on the major topic of the thesis.The validation work is performed first. Two approaches are undertaken. The first approach considers data at the raw level. SuperDARN F region line-of-sight velocities are directly compared with DMSP cross-track ion drifts in approximately the same directions. More than 200 satellite passes over the fields of view of five Northern Hemisphere and four Southern Hemisphere radars are considered. It is shown that all radars exhibit overall consistency with DMSP measurements and a linear fit line to the data has a slope of 0.8 with a tendency for SuperDARN velocities to be smaller. Radar echo range effects and the role of spatial inhomogeneity and temporal variations of the convection pattern are investigated. SuperDARN convection maps were generated for select events for which SuperDARN l-o-s data agree almost ideally with DMSP measurements.Convection maps were obtained using all Northern Hemisphere SuperDARN radars. The full convection vectors were found to be in reasonable agreement with the DMSP ion drifts, although a small deterioration (~10%) was noticed. The overall agreement between SuperDARN and DMSP measurements implies SuperDARN observations are reliable for velocity magnitudes of up to ~1.5 km/s, and SuperDARN radars are suitable instruments for studying extremely fast ionospheric flows. These results also imply that radar measurements can be merged with DMSP measurements into a common data set to provide more reliable convection maps.For the main focus of the thesis, a statistical investigation of the King Salmon radar echoes was performed to determine typical echo characteristics and compare them with data from other SuperDARN radars. It is shown that King Salmon regularly observes high-velocity echoes in the dusk sector at ~21:00 MLT and ~65^0 MLat. Individual events are presented with line-of-sight velocities (observed with the L-shell aligned beams) as high as 2 km/s. Statistically, the enhanced flows are the largest and cover the greatest area in the winter and are the smallest and cover the least area in the summer. Similar fast flows were discovered in the Unwin radar data (in the Southern Hemisphere, lowest magnetic latitude ~57^0) that became available near the completion time of this thesis. It is also shown that statistically, the Stokkseyri radar, which observes in the auroral zone and has a similar azimuthal orientation as King Salmon, does not observe similar high-velocity echoes. Geophysical conditions for the onset of high-velocity King Salmon flows in several individual events are then investigated. It is shown that fast flows are excited in close association with substorm progression near the King Salmon field of view. By comparing SuperDARN data with optical images obtained from the IMAGE satellite and particle data from the DMSP satellites it is shown that velocity enhancement begins at substorm onset and peaks 20-50 minutes later over a range of latitudes including the auroral and sub-auroral regions. During the substorm recovery phase, as bright aurora shifts poleward, exceptionally fast flows can be excited at the equatorial edge of the electron auroral oval and these flows can be classified as sub-auroral polarization stream (SAPS) flows. Variability of SAPS flows and their relationship to auroral oval processes are discussed. Finally, several suggestions for further research are presented