An image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low-light-level television camera. The discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher. The image, which had a duration of less than 30 milliseconds,resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops. Large upward discharges may create a hazard for aircraft and rocket launches and, by penetrating into the ionosphere, may initiate whistler waves and other effects on a magnetospheric scale. Such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud-to-earth lightning strokes. An unusually high rate of such photometric events was recorded during the night of 22 to 23 September 1989 during a storm associated with hurricane Hugo.

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We discuss two phases of the substorm-associated magnetospheric dynamics in terms of the particles and fields at synchronous orbit. The first phase corresponds to the 'decreases' of energetic particle flux first identified by Erickson and Winckler (1973) and discussed by Walker et al. (1976) and Erickson et al. (1979). This phase begins one-half hour to one hour before the substorm onset and is characterized by (1) a distortion of the magnetosphere to a more taillike configuration caused by (2) an intensification and/or motion toward the earth of the cross-taft current and of its earthward part, the partial ring current, (3) a shift of trapped particle trajectories closer to the earth on the nightside following contours of constant B causing the particle 'decreases,' accompanied by a change in the pitch angle distributions from 'pancake' to 'butterfly' as observed at geostationary orbit, (4) an initiation of a response of the auroral electrojet (AL e) index. The decreases of energetic particle flux can correspond to the substorm growth phase as defined initially by McPherron (1970) or the growth or precursor phase of Erickson et al. (1979). Plasma motions and currents during decreases tend to be variable, but the description above nevertheless characterizes the large-scale trend. It is suggested that the electric field induced by the increasing tail current near the earth acts opposite to the cross-taft convection field and can temporarily inhibit convection near the geostationary orbit. The second phase ;s the conventional expansion phase that begins with the 'onset,' characterized in our study by (1) a sudden decrease in the tail current and a return of the inflated magnetosphere to a dipolelike configuration, (2) a sudden shift of trapped high-energy particles toward the tail again following contours of constant B, and at the same time (3) a surge of tail plasma toward th6 earth as the induced electric field now increases the total convection field. Separate effects thus result in the dramatic increases of both high energy and plasma particles seen at sUbstorm expansion phase onset, (4) an AE index response and the appearance of bays at stations near midnight local time accompanied by very active aurora as well as the precipitation of high-energy part, icles. The different appearance of the responses at ATS I (on the magnetic equator) and ATS 6 (off the magnetic equator) can be well explained by the above description. True diamagnetic effects of the particle population are clearly evident at the ATS 6 region and must be carefully distinguished from the effects of distant currents. The use of oppositely directed detectors on ATS 6 that permit the evaluation of the guiding center particle density gradients has been of great use in this analysis. • On leave fromCentre d'Etude Spatiale des Rayonnements, Uni-versit6 Paul Sabatier, two opposite directions carried out on board ATS 6 have shown that during these flux decreases the outer radiation belts are actually observed to retract toward the earth in a region loc...

From a statistical study of 500‐ to 1000‐kev electrons at synchronous orbit, it is concluded that near local midnight there exists a ‘fault line,’ west of which substorms are accompanied by geomagnetic inflation and east of which they are accompanied by collapse. Published studies have shown that the large, transient, substorm‐associated fluxes of 50‐ to 150‐kev electrons observed at synchronous orbit are produced near local midnight and subsequently drift longitudinally to other local times. A study of these lower‐energy electron spikes and the concurrent geomagnetic data indicates that the electrons are produced during and within the geomagnetic collapse. Using measured magnetic data, it is concluded that the collapse is an inward convective surge of field lines with an average convective velocity estimated at 0.5 RE/min. Magnetotail plasma particles of initial energies up to 10‐20 kev are convected inward and energized tenfold; protons drift longitudinally westward (producing the observed evening inflation, and perhaps establishing a partial ring current), and electrons drift eastward. The model proposed is similar in many respects to others already proposed. However, our model exhibits the asymmetric inflation and collapse behavior about the fault line shown by observations at synchronous orbit.

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