Publication Date:
2015-04-26
Description:
The nature of the transition that high-latitude reverse convection makes in response to fast IMF changes is investigated using observations from multiple spacecraft and a ground magnetometer array. We focused on two fast IMF-transition events on 22 April 2006. Immediately after the first event, three ST5 spacecraft identified a clear change in the distribution of the polar cap field-aligned current. Coordinate observations with the Greenland magnetometer chain showed that the near-noon Hall current distribution, which is closely related to the polar cap field-aligned current or reverse convection, was in a transition state for about 10 min. For the second event, the Greenland magnetic perturbations also showed that a transition state occurred in the near-noon sector for 10 – 15 min. Three DMSP spacecraft that traversed the polar cap provided evidence showing that variations of the ground magnetic perturbations were produced by the transition from clockwise plasma circulation to the anti-clockwise circulation over the polar cap. A simple calculation based on the Biot-Savart law shows that the near-noon transition state is consistent with the approach of a new convection region to the near-noon sector at the speed of 0.5 – 1 km s −1 , which is coupled with the moving away of the old convection region at a similar speed. For the higher-latitude sunward flow region, it is found that the convection takes a transition state almost simultaneously (within 1 min) with that in the near-noon sector, i . e ., quasi-instantaneous response.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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