Statistical patterns of high-latitude convection obtained from Goose Bay HF radar observations

We have derived patterns that describe the statistical interplanetary magnetic field (IMF) dependencies of ionospheric convection in the high-latitude region of the northern hemisphere. The observations of plasma motion were made with the HF coherent backscatter radar located at Goose Bay, Labrador, over the period September 1987 to June 1993. The area covered by the measurements extended poleward of 65 degrees Lambda to a working limit of about 85 degrees Lambda. Distributions of electrostatic potential have been derived and expressed as series expansions in spherical harmonics. The patterns are the first derived from direct ground-based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent satellite studies [Rich and Hairston, 1994; Weimer, 1995]. We show the dependence of the convection on IMF angle in the GSM y-z plane for three intervals of IMF magnitude in this plane. Except for predominantly northward IMF, the convection is primarily two-cell. The dusk cell is larger in terms of both spatial extent and potential variation. The effect of IMF B-y is apparent in the global shaping of the cells and the orientation of the overall pattern in MLT; for B-y + (B-y-) the dusk (dawn) cell is more round (crescent-shaped) and the pattern more rotated toward earlier MLTs. The B-y effect on the nightside convection is pronounced and is hemispherically antisymmetric, like the well-known dayside B-y effect. For IMF increasingly northward, the convection trajectories on the dayside become increasingly distorted, evolving through a three-cell to a four-cell circulation. The additional cells appear on either Side of the noon merdian and result in sunward flow. The overall agreement with the results of the satellite studies is good and extends to quite fine detail in the case of the comparison with Weimer [1995]. There are significant differences with the statistical patterns derived from magnetometer measurements, which tend to show domination by the dawn rather than the dusk cell.