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Tail reconnection during IMF-northward non-substorm intervals

Dr. Adrian Grocott (University of Leicester)

During the “Dungey-cycle” of magnetospheric convection, reconnection at the dayside low-latitude magnetopause causes closed terrestrial field lines to become connected into the solar wind, adding open flux to the polar caps.  This flux is transported anti-sunward at high-latitudes over the northern and southern polar caps by the flow of the solar wind, into the tail lobes.  Here it convects equatorwards, ultimately reconnecting again in the central plasma sheet, becoming closed once again.  This newly closed flux then convects back to the dayside at lower-latitudes via dawn and dusk completing the twin-vortex convection pattern with which we are familiar.  The physical process by which the tail component of this reconnection cycle occurs is often associated with magnetospheric substorms.  However, a new mode of large-scale magnetotail flux transport which appears to dominate during intervals of northward, but BY-dominated IMF, has been observed in HF ionospheric radar data.  This takes the form of highly asymmetric Dungey-cycle twin-vortex convection, with bursts of fast azimuthal flow in the midnight sector accompanying intervals of modest flux closure.  We suggest that dayside reconnection equatorward of the cusp persists during such intervals of intermediate IMF clock angle (in addition, perhaps, to high-latitude reconnection usually associated with northward IMF), and that this drives a moderate convection cycle which is not sufficient to trigger magnetospheric substorms, but still involves reconnection in the tail.  We coin the term ‘tail reconnection during IMF-northward, non-substorm intervals’ (TRINNIs) to describe this phenomenon, which recurs on timescales of tens of minutes, and acts to balance the low-level open flux creation at the dayside.  The dependence of the orientation of TRINNI flows on IMF BY, as well as the interhemispheric asymmetry which they display, and the nature of their magnetospheric counterpart, will be discussed.
[Presentation (PPT)]


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