The dependence of high-latitude dayside ionospheric flows on the north-south component of the IMF: a high time resolution correlation analysis using EISCAT Polar and AMPTE UKS and IRM data

In 1984 and 1985 a series of experiments was undertaken in which dayside ionospheric flows were measured by the EISCAT Polar experiment, while observations of the solar wind and interplanetary magnetic field (IMF) were made by the AMPTE UKS and IRM spacecraft upstream from the Earth's bow shock. As a result, 40 h of simultaneous data were acquired, which are analysed in this paper to investigate the relationship between the ionospheric flow and the North-South (Bsub(z)) component of the IMF. Using cross-correlation analysis it is shown that clear relationships do exist between the ionospheric flow and IMF Bsub(z), but that the form of the relations depends strongly on latitude and local time. These dependences are readily interpreted in terms of a twin-vortex flow pattern in which the magnitude and latitudinal extent of the flows become successively larger as Bsub(z) becomes successively more negative. The data also suggest that the morning reversal in the East-West component of flow moves to earlier local times as Bsub(z) declines in value and becomes negative. The correlation analysis also provides information on the ionospheric response time to changes in IMF Bsub(z), it being found that the response is very rapid indeed. No evidence is found for a latitudinal gradient in response time; changes in flow take place coherently in time across the entire radar field-of-view. (author)