Interplanetary magnetic field control and magnetic conjugacy of auroral E region backscatter

The interplanetary magnetic field (IMF) control and magnetic conjugacy of the auroral E region backscatter are assessed using observations by the nominally conjugate Super Dual Auroral Radar Network (SuperDARN) Syowa East and Pykkvibaer HF radars at ∼69° magnetic latitude and the ACE satellite measurements in the solar wind. A common‐mode radar data set comprising 118 days in January–December 2000 is considered, and the E region echo occurrence rates are calculated for each 10 min interval. The occurrence variations are adjusted for the magnetic local time and seasonal dependencies by subtracting the reference daily trends for low IMF magnitudes. The Bz effects dominate at Bz < 0, while 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. Key Points IMF conditions control occurrence of auroral E region irregularities Auroral E region backscatter is highly magnetically conjugate High predictability of E region echo occurrence, particularly on the dayside