MAPPING IONOSPHERIC CONVECTION PATTERNS TO THE MAGNETOSPHERE

While convection patterns in the high-latitude ionosphere are usually presented in a corotating frame of reference, those of the magnetosphe re are given in inertial coordinates. In the corotating representation the convection throat, which is frequently associated with the cusp, opens between 1000 and 1100 MLT. Cusp precipitation, however, centers about noon. We find that transforming the convection patterns of Heppn er and Maynard (1987) (hereinafter H-M) into inertial coordinates alig ns the throat region with local noon. We present projections of the H- M patterns to the magnetosphere in both corotating and inertial coordi nates using the magnetic field model of Tsyganenko (1989). In inertial coordinates the mapped H-M convection throat opens at noon. Consisten t with predictions of the Rice convection model for magnetospheric ele ctric fields late in the substorm cycle, only a small fraction of the equipotential contours penetrate to the subsolar region. This suggests that a significant portion of flux tube merging occurs on magnetic fi eld lines whose equatorial mapping is on the flanks of the magnetosphe re. Nonconjugacy between the mapping of H-M patterns for both positive and negative interplanetary magnetic field By, especially in the 1400 -1600 LT sector, may explain the By dependence of the electron precipi tation ''hot spot'' discovered by Evans (1985). A separate lobe cell i s not required to explain the central, equipotential contours of the l arge convection cell.