Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm21b0263p&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM21B-0263
Physics
2740 Magnetospheric Configuration And Dynamics, 2760 Plasma Convection (2463), 2776 Polar Cap Phenomena, 2794 Instruments And Techniques
Scientific paper
Intervals of Steady Magnetospheric Convection (SMC) are loosely defined as times when convection is enhanced and no substorm signatures are observed. Several quantitative definitions have been developed to detect SMC events. These methods make use of AE indices, IMF conditions, in situ magnetotail observations, and the size of the auroral oval. None of these methods, however, relies on directly measured convection, and SMC events are, by definition, a convection phenomena. The SuperDARN radar network is an ideal tool with which to study SMC intervals because it gives a direct measurment of convection on a global scale. In this study we assess previous definitions of SMC using the SuperDARN global convection maps, and we present a modified method of SMC selection, using AE indices. O'Brien et. al. (GRL, 2002) presented a technique using the AE and AL indices to identify SMC intervals. Enhanced convection was quantified by a constant miminum AE cutoff value. Global SuperDARN convection maps for SMC events based on the O'Brien at al. technique revealed a seasonal dependence of the polar cap voltage for these SMC events, with lower voltages measured in the summer months. It is believed to be due to increased ionospheric conductivity in the summer, since AE is derived from ionospheric currents. Thus, equilavent AE values in winter and summer correspond to different levels of convection. Using a method that has a constant minimum AE cutoff therefore results in the selection of intervals that may not satisfy the qualitative criterion of enchanced convection, typical of SMC events. We found an optimal function to quantify enhanced convection, and this function varies throughout the year. By using this function, the seasonal dependance of conductivity on SMC interval selection is minimized. In doing so, the SMC event selection then becomes based primarily on convection.
McPherron Robert L.
McWilliams Kathryn A.
Pfeifer J.
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