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 hig h-latitude region of the northern hemisphere. The observations of plas ma 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 Lambd a to a working limit of about 85 degrees Lambda. Distributions of elec trostatic potential have been derived and expressed as series expansio ns in spherical harmonics. The patterns are the first derived from dir ect ground-based observations of ionospheric convection that approach in completeness and level of detail the patterns derived in recent sat ellite studies [Rich and Hairston, 1994; Weimer, 1995]. We show the de pendence of the convection on IMF angle in the GSM y-z plane for three intervals of IMF magnitude in this plane. Except for predominantly no rthward IMF, the convection is primarily two-cell. The dusk cell is la rger in terms of both spatial extent and potential variation. The effe ct of IMF B-y is apparent in the global shaping of the cells and the o rientation of the overall pattern in MLT; for B-y + (B-y-) the dusk (d awn) cell is more round (crescent-shaped) and the pattern more rotated toward earlier MLTs. The B-y effect on the nightside convection is pr onounced and is hemispherically antisymmetric, like the well-known day side B-y effect. For IMF increasingly northward, the convection trajec tories on the dayside become increasingly distorted, evolving through a three-cell to a four-cell circulation. The additional cells appear o n either Side of the noon merdian and result in sunward flow. The over all agreement with the results of the satellite studies is good and ex tends 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.