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We report in-situ detection by two spacecraft of oppositely directed jets of plasma emanating from a magnetic reconnection site at the Earth’s dayside magnetopause, confirming a key element inherent in all reconnection scenarios. The dual-spacecraft (Equator-S and Geotail) observations at the flank magnetopause, together with SuperDARNHalley radar observations of the subsolar cusp region, reveal the presence of a rather stable and extended reconnection line which lies along the equatorial magnetopause. These observations were made under persistent southward interplanetary magnetic field (IMF) conditions, implying that under these conditions the reconnection sites are determined by the large-scale interactions between the solar wind magnetic field and the dayside magnetosphere, rather than by local conditions at the magnetopause. Control by local conditionswould result in patchy reconnection, distributed in a less well-organized fashion over the magnetopause surface.

Geotail magnetometer observations from 1995-97 were used to identify 1369 dayside magnetospheric boundary crossings. Statistical properties of this set of multiple crossings are presented and discussed in terms of models for magnetopause motion. Our results indicate that equatorial boundary crossings are caused by north-south aligned ridges propagating azimuthally around the magnetosphere. Perpendicular orientations of the magnetospheric and magnetosheath magnetic fields inhibit the boundary motion. For the garden hose orientations of the interplanetary magnetic field (IMF), magnetospheric boundary motion is favoured in the dawn sector, while orthospiral orientations favour motion in the dusk sector. These results suggest that pressure pulses generated at the quasi-parallel bow shock drive the boundary motion., QC 20100525

Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensifications on 25 April 1998, when both spacecraft were located in the early morning sector (03-04 MLT) at a radial distance o, Addresses: Nakamura R, Max Planck Inst Extraterr Phys, D-8046 Garching, Germany. Max Planck Inst Extraterr Phys, D-8046 Garching, Germany. Inst Space Sci, Bucharest, Romania. Univ Calif Los Alamos Natl Lab, Los Alamos, NM 87545 USA. Univ New Hampshire, Ct. QCR 20190618

Based on fine-resolution Geotail magnetometer data, a set of 5-min magnetic field averages was compiled for the period 1993-1997 and merged with 5-min average solar wind parameters, measured by IMP 8 and Wind spacecraft. Using this data set, the shape of, Addresses: Tsyganenko NA, NASA, Goddard Space Flight Ctr, Hughes STX Corp, Extraterr Phys Lab, Code 695, Greenbelt, MD 20771 USA. NASA, Goddard Space Flight Ctr, Hughes STX Corp, Extraterr Phys Lab, Greenbelt, MD 20771 USA. Swedish Inst Space Phys, S-7559

An extended interval of strong northward interplanetary magnetic field (IMF) was observed by the Wind spacecraft located at an upstream distance of ∼193 RE from February 8–10, 1995, with a brief break of southward IMF from 0200 to 0400 UT on February 9. This brief interval of southward IMF led to an isolated substorm of moderate intensity (∼500 nT) with expansion phase starting at ∼0431 UT. This substorm may be triggered by the northward turning of the IMF since its onset time matched well with the time expected for the arrival of the northward turning of the IMF at Earth. The substorm activities were monitored by 11 spacecraft in space (Wind, IMP 8, Geotail, six geosynchronous satellites, one DMSP satellite, and Freja) and two networks of ground stations (Canopus and SuperDARN) covering both the northern and southern hemispheres. The extensive coverage of this event provides us with results (1) showing some unusual characteristics possibly related to the isolated nature of the substorm and (2) revealing some surprising features difficult to reconcile with the traditional substorm model. In the first category is unusually long duration of the growth phase and the long time delay between substorm expansion onset and particle injection onset at the geosynchronous orbit. In the second category is new evidence for multiple particle acceleration sites during substorm expansion and for sunward flow during the late expansion phase of a substorm being unrelated to a single acceleration site (X line) moving from the near-Earth tail to the more distant tail. We also present observations which show the possible optical signature on the ground of bursty bulk flows in the magnetotail.

On February 21, 1994, both Geotail and LMP 8 satellites detected an interplanetary plasma cloud with intense interplanetary magnetic field (IMF>50 nT) and high dynamic pressure (> 50 nPa). During this interval the Freja satellite detected intense cusp-like plasma injections in four out of six dayside traversals. The first two traversals are carefully studied, During the first traversal the overall morphology of the ion injection is characterized by a ''multiple-injection'' signature over a wide magnetic local time (MLT) range, whereas it is characterized by a ''single-injection'' signature with narrow injection region at 8 MLT in the second traversal, The solar wind conditions were also quite different between these two periods: while both dynamic and magnetic pressures stayed high during entire period, the dynamic beta was much higher during the first Freja traversal than during the second traversal. Between these two traversals, the cusp plasma injection is detected by the Sondre Stromfjord radar. The radar signature of the plasma injection is identified using the satellite particle data when the satellite and the radar were conjugate (the satellite's footprint was in the radar's field of view.) The cusp position and dynamics observed by the Sondre Stromfjord radar again show a very good correlation to the solar wind condition, especially to the dynamic pressure. The result indicates the following. (1) During southward IMF the cusp morphology differs for conditions of high or low solar wind dynamic pressure. High dynamic pressure widens the cusp (with multiple injections), whereas high magnetic pressure narrows it (with single injection), The effect of the IMF on the cusp locations and morphology becomes dominant only when the dynamic pressure is not very high, (2) Such a morphological difference reflects dynamic pressure more than dynamic beta during southward IMF at least during times of high solar wind dynamic pressure. (3) The cusp morphology responds ve, NR 20140805