This is a report of a program to study the magnetic connectivity between the auroral region of the ionosphere and the equatorial geosynchronous region of the magnetosphere. The program uses plasma measurements made with polar orbiting Defense Meteorological Satellite Program (DMSP) satellites and several geosynchronous satellites, seeking time intervals when nearly identical plasma electron spectra (32 eV to 30 keV) indicate magnetic connectivity between a polar/geosynchronous satellite pair. When such signatures of connectivity are found, the locations of the relevant satellite pair are compared with the locations that would be predicted by a magnetospheric model. Here we report results from the initial application of this program that uses data from DMSP F-8, F-9 and F-10 polar satellites and the synchronous satellites 1989-046 and 1990-095 acquired in the 6-day interval March 7--12, 1991. The results are compared with predictions of the T89a model [Tsyganenko, 1989; Peredo et al., 1993>. Orbital calculations predicted 96 close conjunctions among these satellites during the interval. Of those we have made spectral comparisons for 47, finding 20 for which close spectral similarity occurred during few-second intervals. Ionospheric footpoints of the satellite pairs calculated by the T89a model for these intervals revealed eight for which the discrepancy between the DMSP latitude at ''best spectral match'' and the model projection of the synchronous satellite was smaller than 1¿. However, there were five intervals for which the discrepancy was greater than 6¿. The latter were all found in the local time interval 0700--0900, perhaps indicating a particular inadequacy of the T89a model in that region. This initial work also supports the view that the auroral oval of discrete arcs is an ionospheric mapping of the full thickness of the plasma sheet (e.g., Feldstein and Galperin, 1985) and not just of the plasma sheet boundary layer (e.g., Eastman et al., 1985). During just its first few years of concurrent operation this constellation of well-instrumented synchronous and polar-orbiting satellites has provided data for literally thousands of close conjunctions such as we analyze in this report. Thus an algorithm is developed enabling the verification and testing of proposed mappings between the ionosphere and magnetosphere (such as T89a). ¿ American Geophysical Union 1996