A CASE-STUDY OF STORM COMMENCEMENT AND RECOVERY PLASMASPHERIC ELECTRIC-FIELDS NEAR L=2.5 AT EQUINOX

Data from the VLF Doppler experiment at Faraday, Antarctica (65 degree s S, 64 degrees W) are used to study the penetration of the high-latit ude convection electric field to lower latitudes during severely distu rbed conditions. Alterations of the electric field at L-values within the range 2.0-2.7 an studied for two cases at equinox (10-12 September 1986 and 1-3 May 1986). The recovery of the electric field is found t o be approximately an exponential function of time. Values for the equ atorial meridional E x B drift velocity, inferred from the data, are u sed as inputs to a model of the plasmasphere and ionosphere. The model and experimental results are used to investigate the post-storm alter ation of ionospheric coupling processes. The magnitude of the effect o f ionosphere-plasmasphere coupling fluxes on N(m)F2 values and the O+- H+ transition height is dependent on the local time of storm commencem ent, and on the orientation of the electric field. The coupling fluxes appear to have a maximum influence on ionospheric content during the main phase of geomagnetic activity that produces outward motion of pla smaspheric whistler ducts.