Modulation of Dayside Reconnection During Northward IMF

On 17 September 2000 the IMF was directed continuously northward for more than three hours. Density fluctuations in the solar wind resulted in quasi-periodic variations in the solar wind dynamic pressure, and correlated fluctuations also occurred in the IMF Bz component. The Northern hemisphere SuperDARN radars observed bursts of high-latitude high-velocity plasma flow during this northward IMF interval, both when ionospheric signatures consistent with low-latitude merging were observed, and when lobe merging was occurring. On average the recurrence period of these flow bursts was ~22 min. During this time the SI-12 spectrographic imager channel on the IMAGE spacecraft observed the dayside proton auroral spot continuously (Frey et al., 2003). The brightness of the auroral spot varied over time. Here we find a direct correlation between the occurrence of bursts of plasma flow and periodic fluctuations in the brightness of the proton auroral spot. Our results suggest that correlated fluctuations in the solar wind dynamic pressure and IMF Bz component modulated ionospheric precipitation and dayside reconnection, resulting in fluctuations in the brightness of the proton auroral spot and periodic variations in the dayside high-latitude plasma flow.