Solar Wind - Ionosphere Coupling Times from the Dayside to the Nightside as Observed by AMPERE

Abstract:

We have examined the solar wind - ionosphere coupling by comparing magnetic field measurements at the top of the ionosphere with solar wind measurements at the bow shock nose. The AMPERE data products derived from the Iridium constellation provide global maps of magnetic field perturbations with an integration time of ten minutes. By dividing the maps into sectors, the response times at different magnetic local times and inside and outside the polar cap, can be compared. Forward regression is used to determine the past solar wind samples which best can explain the magnetic field perturbations. The main results are as follows. The full response near noon to the solar wind reconnection electric field occurs 10-20 minutes after the solar wind reaches the bow shock nose, and the midnight response is only 20 minutes later. An additional delayed response is usually observed after 60 to 90 minutes at the night side. No direct response to the reconnection electric field is seen closest to midnight inside the polar cap. As expected, the dayside response in the sunlit hemisphere is much stronger than in the dark hemisphere. But no difference in the response times between the hemispheres were found. The IMF B_Y exerts a strong influence on the direction of the magnetic field in the polar cap in the sunlit hemisphere. The response is within 20 minutes in all of the polar cap. In the dark hemisphere there is barely any response to IMF B_Y.