GEM: Correlative Ground Based and Satellite Investigations of the Dynamics of the Nightside Open/Closed Magnetic Field Line Boundary

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The GEM program's second major observational and analysis campaign will be on the physics of the magnetotail and substorms. A critical question for magnetosphere-ionosphere coupling is to determine from where in the magnetosphere do magnetic field lines map to connect to the nighttime auroral ionosphere. This question becomes even more important for understanding substorm dynamics when significant changes to the magnetospheric configuration occur during this episodic release of energy. A recent study by Burke et al. 1993a has identified the high latitude boundary of the nighttime auroral region as magnetically connecting to the distant x-line in the geomagnetic tail. This identifies the open/closed boundary for magnetotail magnetic field lines. We propose a correlative analysis effort using DMSP satellite data and ground- based data from Svalbard and Sondrestrom to determine the characteristics of this boundary as seen jointly in both data sets, to confirm the magnetospheric interpretation of the boundary where possible using GEOTAIL data, and to resolve the spatial and temporal variations of this boundary. Optical data from a network or auroral TV and meridian scanning photometers in Svalbard and Greenland will be combined with radar data from Sondrestrom to compare with DMSP satellite data. Three DMSP satellites measuring ion drift, plasma characteristics and energetic particle precipitation currently monitor the high latitude ionosphere continuously. Directly overhead passes will establish critical signatures. The spatial and temporal dynamics of this boundary can then be determined with spatially separated data sets. Application of these results will place constraints on the geotail configuration during substorms and will aid in the development of a model of the substorm process. We plan two observation periods: January 1994 and December 1994 through January 1995. The first coincides with the planned GEM World Day period and when GEOTAIL is at an apogee of 100 R near midnight. The second corresponds to special observation periods for additional ground-based data. We proposed to collaborate with other GEM investigators to jointly define and analyze special campaign events for elucidation of substorm and geotail physics.