Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm21c..07s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SM21C-07
Physics
[2463] Ionosphere / Plasma Convection, [2704] Magnetospheric Physics / Auroral Phenomena, [2721] Magnetospheric Physics / Field-Aligned Currents And Current Systems, [2776] Magnetospheric Physics / Polar Cap Phenomena
Scientific paper
We describe the ionospheric manifestations of the temporal-spatial evolution of open magnetic field lines during the first 20 min after the onset of pulsed magnetopause reconnectionevents, appearing in the form of aurora and convection channel events. We then discuss their relevance to our understanding of temporal-spatial structure in the reconnecting magnetosphere. We first distinguish between two consecutive phases of this evolution, depending on time elapsed since reconnection (``newly open''and "old open" field lines). Phase 1 consists of the auroral brightening events appearing on the pre- and postnoon sides of the ``midday gap aurora'' and associated flow channels (FC 1 in our terminology; originally known as pulsed ionospheric flows; PIFs) as described by Southwood (1987). The auroral brightenings in both sectors expand noonward and poleward, followed by a fading phase in the regime of mantle precipitation after appr. 10 min. The later phase 2 (time since reconnection appr. 10-20 min) is characterized by the appearance of a 200-300 km wide channel of enhanced (> 1 km/s) antisunward convection located on the dusk - or dawn side of the polar cap, the location depending on the IMF By polarity. This fast flow appears within the regime of polar rain precipitation. This is our flow channel FC 2. In the case of a By - dominated IMF orientation (|By/Bz| > 1) flow channel FC 2 contributes to extending the dawn-dusk convection asymmetry of polar cap flows tailward of the cusp region. The momentum transfer from high magnetospheric altitudes (cusp dynamo) to the ionosphere is attributed to a system of C1-C2 Birkeland currents (HCC-LCC currents of Taguchi et al., 1993) located poleward of the R1-R2 currents. In many instances a considerable fraction of the CPCP potential is associated with these flow channels. In the case of strongly south IMF orientation (|By/Bz| < 1) a different, more symmetric FC 2 configuration appears, characterized by flow channels on both sides of the polar cap. The FC 2 flow channels appear in the form of events ``directly driven'' by IMF southward turnings or as a sequence of appr. 10 min long ``spontaneous events'' during intervals of quasi-steady IMF orientation. The two phases of the flow evolution (the FC 1 and FC 2 events) in the convection cycle are clearly manifest in ground magnetic deflections. In particular, the Svalgaard-Mansurov effect appearing at longitudes tailward of the cusp is due to Hall currents in FC 2.
Farrugia Charles J.
Sandholt Per Even
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