No abstract

From the comparison of the worldwide geomagnetic data with IMP 1 magnetic records obtained in the interplanetary space, it is found that the DP 2 fluctuations, which are thought to be the geomagnetic counterpart of intensity fluctuations of the magnetospheric convective system, are coherent with variations in the north-south component of the interplanetary magnetic field. This coherence is observed irrespective of whether this component is directed northward or southward. Average time delay between the crossing of an interplantary magnetic structure across the nose of the bow shock and the associated magnetic variation on the ground is 7 minutes at the pole and 9 minutes at the midday equator. Applicability of the proposed models of the magnetospheric electric field to this phenomenon is critically examined, and the penetration of the interplanetary electric field into the magnetosphere is suggested as the origin of the DP 2 phenomenon.

The low energy particle (LEP) instrument onboard GEOTAIL is designed to make comprehensive observations of plasma and energetic electrons and ions with fine temporal resolution in the terrestrial magnetosphere (mainly magnetotail) and in the interplanetary medium. It consists of three units of sensors (LEP-EA, LEP-SW and LEP-MS) and a common electronics (LEP-E). The Energy-per-charge Analyzers (EA) measure three-dimensional velocity distributions of electrons (with EA-e) and ions (with EA-i), simultaneously and separately, over the. energy-per-charge range of several eV/q to 43 keV/q. Emphasis in the EA design is laid on the large geometrical factor to measure tenuous plasma in the magnetotail with sufficient counting statistics in the high-time-resolution measurement. On the other hand, the Solar Wind ion analyzer (SW) has smaller geometrical factor, but fine angular and energy resolutions, to measure energy-per-charge spectra of the solar wind ions. In both EA and S W sensors, the complete three-dimensional velocity distributions can only be obtained in a period of four spins, while the velocity moments up to the third order are calculated onboard every spin period (nominally, 3 sec). The energetic-ion Mass Spectrometer (MS) can provide three-dimensional determinations of the ion composition. In this paper, we describe the instrumentation and present some examples of the inflight measurements.

Abstract. Poleward boundary intensifications are nightside geomagnetic disturbances that have an auroral signature that moves equatorward from the poleward boundary of the auroral zone. They occur repetitively, so that many individual disturbances can occur during time intervals of-1 hour, and they appear to be the most intense auroral disturbance at times other than the expansion phase of substorms. We have used data from three nightside conjunctions of the Geotail spacecraft in the magnetotail with the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) ground-based array in central Canada to investigate the relation between the poleward boundary intensifications and bursty plasma sheet flows and to characterize the bursty flows associated with the disturbances. We have found a distinct difference in plasma sheet dynamics between periods with, and periods without, poleward boundary intensifications. During periods with identifiable poleward boundary intensifications, the plasma sheet has considerable structure and bursty flow activity. During periods without such poleward boundary intensifications, the plasma sheet was found to be far more stable with fewer and weaker bursty flows. This is consistent with the intensifications being the result of the mapping to the ionosphere of the electric fields that give rise to bursty flows within the plasma sheet. Two different types of plasma sheet disturbance have been found to be associated with the poleward boundary intensifications. The first consists of plasma sheet flows that appear to be the result of Speiser motion of particles in a localized region of thin current sheet. The second, seen primarily in our nearest-to-the-Earth example, consists of energy-dispersed ion structures that culminate in bursts of low-energy ions and isotropic low-energy electrons and are associated with minima in magnetic field and temperature and maxima in ion density and pressure. Both types of plasma sheet disturbance are associated with localized regions of enhanced dawn-to-dusk electric fields and appear to be associated with localized enhanced reconnection. Our analysis has shown that poleward boundary intensifications are an important aspect of geomagnetic activity that is distinct from substorms. In addition to their very distinct auroral signature, we have found them to be associated with a prolonged series of ground magnetic Pi 2 pulsations and ground X component perturbations, which peak at latitudes near the ionospheric mapping of the magnetic separatrix, and with a series of magnetic B z oscillations near synchronous orbit. Like substorms, the tail dynamics associated with the poleward boundary intensifications can apparently extend throughout the entire radial extent of the plasma sheet. Color versions of figures are available at http ://www' atmøs'ucla'edu/-larry/geøtail'html'

Magnetospheric convective system proposed by Axford and Hines is revised and made compatible with the view, based on the recently obtained geomagnetic data, that (1) the convective motion induced by the solar wind would penetrate to the innermost part of the magnetosphere, if it were not for the superposed effect of the earth's rotation, and the fact that (2) the earth's magnetosphere has an essentially open tail. Magnetic lines of force in the magnetosphere are then found separated into two groups: those that travel across the tail during the convective motion and those that are never transported to the tail. On field lines of the former group, the plasma density would be less than the value expected on the basis of the equilibrium theory, since the plasma along these field lines can escape to the outer space while the field line travels across the open magnetospheric tail and since the rate of plasma replenishment from lower levels is low. On field lines of the latter group, plasma escape is always prevented by closed field lines, so that the diffusive equilibrium would prevail. Hence at the boundary between these two groups of field lines, the plasma density is expected to show discontinuity. This boundary surface is suggested to be the plasmapause, and various observed features of the plasmapause are explained.