MIDLATITUDE PARTICLE AND ELECTRIC FIELD EFFECTS AT THE ONSET OF THE NOVEMBER 1993 GEOMAGNETIC STORM

Millstone Hill incoherent scatter radar elevation scans across midlati tudes captured the ionospheric response to storm-induced electric fiel d and precipitation-induced changes near the equatorward extent of the expanding auroral region during the early phases of the November 3-4, 1993, magnetic storm. Solar wind-induced magnetospheric compression w as observed at similar to 2307 UT [Borovsky et al., this issue] and a prompt, short-duration (10 min) increase in the upward plasma velocity to > 100 mis at similar to 2319 UT on November 3, 1993 signaled the o nset of the storm-induced enhancement of the eastward electric field o ver Millstone Hill in the premidnight sector at 54 degrees invariant l atitude (Lambda). This resulted in an uplifting of the F region ionosp here above the site by similar to 80 km by 2330 UT. Formation of a nar row ionospheric trough poleward of the Millstone site accompanied the auroral convection enhancement at somewhat later times while plasmashe et precipitation produced the ionization at altitudes between 200 and 300 km at Lambda < 60 degrees observed by the radar. Strong precipitat ion of energetic particles from the outer radiation belt was observed by SAMPEX at 58.5 degrees Lambda, near the equatorward limit of the pl asmasheet precipitation observed by DMSP and Millstone Hill. Amplitude perturbations of VLF signals propagating in the Earth-ionosphere wave guide serve to localize the energetic radiation belt precipitation to latitudes between 56 degrees Lambda and 58.5 degrees Lambda and provid e accurate timing of storm-induced energetic precipitation, whose onse t was at similar to 2332 UT in the premidnight sector. A later enhance ment of the eastward electric field at latitudes equatorward of Millst one Hill and the storm-induced trough led to a perturbation of the mid latitude ionosphere to Lambda <40 degrees and is the subject of a comp anion paper [Foster and Rich, this issue].