HF radar observations of the high-latitude ionospheric convection pattern in the morning sector for northward IMF and motion of the convection reversal boundary

Observations of plasma convection in the morning sector (0000 to 0600 magnetic local time (MLT)) during a period of northward IMF (B-z = +5 to +10 nT) on September 11, 1991, made with the conjugate HF radars at Goose Bay and Halley and supplemented by DMSP plasma flow data, are described. There are several interesting features of the data: the period over which large (>500 m/s) plasma flow velocities are maintained while the IMF is northward; the range of latitudes over which the convection is observed; and the short timescale responses to changes in IMF conditions. The period was characterized by several strong (+/-10 nT) reversals of IMF B-y and an absence of substorm activity, as seen in geostationary satellite particle data. The effects of these B-y reversals and the motion of the convection reversal boundary (CRB, the boundary between eastward flow at lower latitudes and westward flow at higher latitudes) are examined. A significant crosscorrelation is found between IMF B-y and the latitude of the CRB. The observed short time delays and other features are consistent with convection driven by lobe cell merging.