3.1 Theory The integration of theory and modeling with spacecraft and ground-based observations represents a new approach to space physics missions. The mission-oriented models developed as part of this program are designed to accept inputs and provide outputs comp atible with the ISTP/GGS measurements, with emphasis on providing a global context for the ISTP/GGS spacecraft and ground-based measurements. In constructing a theoretical framework for the widely separated spacecraft observations, not only are global sim ulations used, but also micro and mesoscale simulations which have global implications. A hierarchy of computational physics models and submodels has been developed. These models are dynamic and tightly coupled where appropriate. At the global level are t hree-dimensional magnetohydrodynamic (MHD) codes that simulate the interaction of the incoming solar wind with the magnetosphere, and its coupling to the ionosphere. The ionospheric response enters as a dynamically coupled electrostatic two-dimensional su bmodel that serves as the inner boundary to the MHD code. The global responses of the thermosphere and ionosphere are simulated with the MAMI (Modeling of the Atmosphere-Magnetosphere-Ionosphere) system, based on a theoretical model that combines an electron transport code with an ionospheric chemistry and dyna mics code. The input to MAMI is provided by ground-based magnetometer and radar observations and POLAR images. Computational submodels have also been developed to couple a global MHD code to a relativistic guiding center test particle code to model the dynamic response of the radiation belt particles to variability in the upstream conditions. A global MHD code ha s also been coupled to test particle codes in the large scale kinetics approach that reconstructs distribution functions for comparison with satellite measurements. Finally, a submodel based on non-linear dynamics techniques has been developed to accept i nput from WIND or other upstream spacecraft, and predict the expected values for several commonly used magnetospheric indices. Radiation belt enhancements caused by dramatic changes in the space weather environment can also be realistically simulated using the global magnetospheric model response to solar wind input and the resulting radiation belt modifications calculated from a submodel.

Figure 1.5. Theory and Modeling Efforts.

3.2 Ground-Based The spaceborne observations of the ISTP/GGS satellites are complemented by ground-based observations that remotely sense the ionospheric base of the magnetosphere, thus providing ground-truth for the spacecraft measurements, and coverage of regions inacc essible to satellites. Ground-based experiments have helped to fill the gap left by the lack of a low-altitude orbiter in ISTP/GGS. They provide the observational signature of the final link in the Sun-Earth connection chain, the flow of mass and momentum , and energy dissipation in the Earth’s atmosphere. This capability of continuous monitoring of the flow into the terrestrial atmosphere is an essential contribution. Four separate investigations constitute the set of ground-based instruments in the GGS program. The Sondrestrom incoherent scatter radar is located in Greenland. The Super Dual Auroral Radar Network (SuperDARN) of high-latitude HF radars has been develop ed and operated with funding from Britain, Canada, Finland, France, Japan, South Africa, Sweden and the US. The ISTP/GGS ground system routinely recovers well above 95% of data transmissions from the Deep Space Network. From August 1996 through March 1997, the ISTP/GGS Ground System created 27,203 data products; 99.73% of these products were error-free and delivered on schedule. Also included is the Canadian Auroral Network for the Origin of Plasmas in the Earth’s Neighborhood Program Unified Study (CANOPUS), comprised of magnetometers, riometers, meridian photometers and all-sky imagers. Finally, the SESAME project operated by the British Antarctic Survey, contributes ionospheric sounder, VLF, Fabry-Perot interferometer, magnetometer and riometer measurements from its station in the Antarctic.

Figure 1.6. Ground-Based Investigations. Figure 1.7. GGS Ground-Based observations cover both hemispheres. Figure 1.8. ISTP/GGS Ground Data System.