Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sm61a08s&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SM61A-08 INVITED
Physics
2704 Auroral Phenomena (2407), 2724 Magnetopause, Cusp, And Boundary Layers, 2760 Plasma Convection, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
We report four classes (categories) of typical dayside auroral transients all of which can be explained as signatures of electron precipitation from different modes/configurations of magnetopause reconnection. We supplement the ground-based optical auroral observations with radar data on ionospheric convection and particle precipitation obtained from satellites in polar orbit. Class 1, corresponding to strongly southward IMF orientation, is characterized by a sequence of auroral equatorward boundary intensifications (EBIs), observed in the vicinity of the open-closed field line boundary, where a clear low-energy cutoff is observed in the ion precipitation flux. EBIs are followed by poleward moving/expanding auroral forms (PMAFs) in the region of cusp/mantle precipitation. PMAFs are observed in conjunction with a staircase ion energy-latitude dispersion. Class 1 observations result from pulsed reconnection at sub-cusp latitudes. In class 2, corresponding to northward IMF Bz with a significant By component, the aurora is characterized by east-west expanding forms which are accompanied by activations of lobe cell convection. In our view, this is the auroral response to bursts of high-latitude reconnection in one single hemisphere. Class 3 is an extension of class 2 and constitutes the signature of high-latitude reconnection taking place near-simultaneously in both hemispheres. It occurs when the IMF points strongly north. The cusp aurora shows a sharp, contracting poleward boundary which is subject to sequential brightenings/poleward expansions at times of ``reverse'' 2-cell convection. These observations may be explained in terms of episodes of capture by the magnetosphere of magnetosheath flux tubes, thereby increasing the amount of closed flux on the dayside. Finally, class 4 auroral activity is restricted to an IMF pointing predominantly east-west. The cusp aurora bifurcates in a sequence of activations of two latitudinally separated forms (bifurcation events). Both merging and lobe convection cells are present and, correspondingly, the energy-latitude ion dispersion of a hybrid, V-shaped form (Woch and Lundin, 1992).
Farrugia Charles
Sandholt Per Even
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