Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm11d..05m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM11D-05
Physics
2723 Magnetic Reconnection (7526, 7835), 2736 Magnetosphere/Ionosphere Interactions (2431), 2760 Plasma Convection (2463), 2776 Polar Cap Phenomena
Scientific paper
The opening and closing of magnetic flux by reconnection at the dayside magnetopause and in the magnetotail is the primary driver of convection in the magnetosphere and polar ionospheres. It is not the existence of open flux that excites convection; rather it is the creation or destruction of open flux that excites convection. These flows persist until a new equilibrium condition is reached, assuming no further reconnection occurs. The time scale for the excitation and decay of ionospheric flows depends on the time necessary for the polar cap to reconfigure following reconnection. The consequence of this zero-flow equilibrium concept (Cowley and Lockwood, 1992) has a powerful consequence when considering both bursty and steady-state reconnection. Newly created regions of open flux are appended contiguously to the polar cap adjacent to the previously reconnected region of open flux. Similarly, newly closed flux regions are appended contiguously to the closed field line region outside the polar cap on the nightside. The opening or closing of magnetic flux will create a perturbation of the polar cap boundary, and convection cells develop at the ends of the reconnection X-line. Convection is excited such that the newly created open flux is incorporated into the polar cap on the dayside or the newly closed flux is excluded from the polar cap on the nightside. The observation of the nightside convection response to reconnection has been very difficult to accomplish because (a) the nightside has a far more dynamic and complex response to reconnection, and (b) radar observations of convection in the midnight sector are difficult to achieve due to absorption of the radio waves during active conditions. The newest SuperDARN radar at Rankin Inlet is located at very high latitudes (73.2 magnetic), and it offers extensive and nearly continual observations of plasma convection in the poleward part of the nightside auroral region. Because of its high latitude, the Rankin Inlet radar effectively does not experience signal absorption, compared with the auroral SuperDARN radars. The Rankin Inlet radar often detects plasma convection into the polar cap on the nightside, as expected for the reconnection-induced convection vortices. Similar flows are only very rarely seen by the auroral SuperDARN radars, and this requires extremely disturbed conditions when the polar cap is extremely large and equatorward of the SuperDARN auroral radars. Examples of the nightside reconnection response observed by the Rankin Inlet radar and the auroral SuperDARN radars will be presented.
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