Solar wind control of plasma irregularity production at high latitudes

The magnetic-field-aligned irregularities in the ionospheric plasma density is a phenomenon regularly occurring during geomagnetic disturbances. Plasma irregularity structures are responsible for scattering of radio signals propagating through the ionosphere and for producing strong coherent returns or backscatter routinely observed by coherent radars operating at various frequencies. The global factors controlling production rates of E-region irregularities at high latitudes are investigated using observations of coherent radar backscatter in both hemispheres with the global Super Dual Auroral Radar Network (SuperDARN) and the ACE satellite measurements in the solar wind. It is shown that the Interplanetary Magnetic Field (IMF) Bz component effects dominate at Bz<0, while IMF By effects become noticeable at Bz>0. The occurrence strongly increases as Bz becomes more negative and minimizes at small negative By and positive Bz values. The Bz effects are stronger by a factor of ~2 than those of By. The extent of magnetic conjugacy is considerable, with an overall correlation between conjugate occurrences of 0.7. The backscatter is most conjugate at large negative Bz and generally at large IMF values. The correlations are higher on the dayside and during the equinoxes, indicating a preference for both conjugate locations to be sunlit. Finally, correlations of occurrences with solar wind coupling functions are higher on the dayside, with some evidence of the response time increasing away from magnetic noon, implying more direct IMF control near noon. The overall predictability of the E-region backscatter occurrence from the solar wind inputs is considerable, with correlations being higher than those reported previously for the F-region backscatter.