Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109

ISEE-3 Geotail observations are used to investigate the relationship between the interplanetary magnetic field, substorm activity, and the distant magnetotail. Magnetic field and plasma observations are used to present evidence for the existence of a quasi-permanent, curved reconnection neutral line in the distant tail. The distance to the neutral line varies from | X | = 120 - 140 R_e near the center of the tail to beyond | X | = 200 R_e at the flanks. Downstream of the neutral line the plasma sheet magnetic field is shown to be negative and directly proportional to negative B_Z in the solar wind as observed by IMP-8. V_x in the distant plasma sheet is also found to be proportional to IMF B_Z with southward IMF producing the highest anti-solar flow velocities. A global dayside reconnection efficiency of 20 ± 5 % is derived from the ISEE-3/IMP-8 magnetic field comparisons. Substorm activity, as measured by the AL index, produces enhanced negative B_Z and tailward V_x in the distant plasma sheet in agreement with the basic predictions of the reconnection-based models of substorms. The rate of magnetic flux transfer out of the tail as a function of AL is found to be consistent with previous near-earth studies. Similarly, the mass and energy fluxes carried by plasma sheet flow down the tail are consistent with theoretical mass and energy budgets for an open magnetosphere. In summary, the ISEE-3 Geotail observations appear to provide good support for reconnection models of solar wind-magnetosphere coupling and substorm energy rates.

in Solar Wind-Magnetosphere Coupling, edited by Y. Kamide and J. A. Slavin, pp. 717-730, Terra Sci. Publ. Co., Tokyo, 1986