Interpretation of the HeII (304 angstrom) EUV image of the inner magnetosphere by using empirical models

The visualization of the inner magnetosphere is a long-cherished goal in ma gnetospheric physics. This goal was recently achieved with the He II (304 A ngstrom) image of the inner magnetosphere by using the EUV scanner on board the Planet-B spacecraft (Nakamura et al., 2000). However, our understandin g of the inner magnetosphere in relation to these images has not been asses sed. The two-dimensional (2-D) EUV image is difficult to interpret, as it i s necessary to infer the three-dimensional (3-D) spatial information of the inner magnetosphere from the 2-D remote sensing data. We examine our prese nt knowledge of the inner magnetosphere and compare simulated 2-D images wi th the real EUV image. We conclude that an empirical model that assumes con ventional E x B flows and combines the diffusive equilibrium model of Chin et al. (1979) and the Weimer (1995) electric potential and Tsyganenko (1989 ) magnetic field models is in good agreement with the EUV image only within the Earth-dominated flow regime. Furthermore, the model gives a better fit to the EUV image data, by assuming the convection-dominated flow regime to be filled with ionospheric He+ at a filling rate of 1.2(.)(6.6/L)-3.0 (He( +)ions cm(-3) d(-1)), instead of the well-known L-4 density dependence on f lux tube volume.