Abstract. The Equator-S magnetometer is very sensitive and has a sampling rate of normally 128 Hz. The high sampling rate allows for the ®rst time¯uxgate magnetometer measurements of ELF waves between the ion cyclotron and the lower hybrid frequencies in the equatorial dayside magnetosheath. The so-called lion roars, typically seen by the Equator-S magnetometer at the bottom of the magnetic troughs of magnetosheath mirror waves, are near-monochromatic packets of electron whistler waves lasting for a few wave cycles only, typically 0.25 s. They are right-hand circularly polarized waves with typical amplitudes of 0.5±1 nT at around one tenth of the electron gyrofrequency. The cone angle between wave vector and ambient ®eld is usually smaller than 1X5 .
No abstract
Using the EquatorS spacecraft and Super-DARN HF radars an extensive survey of bursty reconnection at the magnetopause and associated¯ows in the polar ionosphere has been conducted. Flux transfer event (FTE) signatures were identi®ed in the EquatorS magnetometer data during periods of magnetopause contact in January and February 1998. Assuming the eects of the FTEs propagate to the polar ionosphere as geomagnetic ®eld-aligned-currents and associated Alfve n-waves, appropriate ®eld mappings to the ®eldsof-view of SuperDARN radars were performed. The radars observed discrete ionospheric¯ow channel events (FCEs) of the type previously assumed to be related to pulse reconnection. Such FCEs were associated with 80% of the FTEs and the two signatures are shown to be statistically associated with greater than 99% con®dence. Exemplary case studies highlight the nature of the ionospheric¯ows and their relation to the high latitude convection pattern, the association methodology, and the problems caused by instrument limitations.
Abstract. Magnetic ®eld measurements, taken by the magnetometer experiment (MAM) on board the German Equator-S spacecraft, have been used to identify and categorise 131 crossings of the dawn-side magnetopause at low latitude, providing unusual, long duration coverage of the adjacent magnetospheric regions and near magnetosheath. The crossings occurred on 31 orbits, providing unbiased coverage over the full range of local magnetic shear from 06:00 to 10:40 LT. Apogee extent places the spacecraft in conditions associated with intermediate, rather than low, solar wind dynamic pressure, as it processes into the¯ank region. The apogee of the spacecraft remains close to the magnetopause for mean solar wind pressure. The occurrence of the magnetopause encounters are summarised and are found to compare well with predicted boundary location, where solar wind conditions are known. Most scale with solar wind pressure. Magnetopause shape is also documented and we ®nd that the magnetopause orientation is consistently sunward of a model boundary and is not accounted for by IMF or local magnetic shear conditions. A number of well-established crossings, particularly those at high magnetic shear, or exhibiting unusually high-pressure states, were observed and have been analysed for their boundary characteristics and some details of their boundary and near magnetosheath properties are discussed. Of particular note are the occurrence of mirror-like signatures in the adjacent magnetosheath during a signi®cant fraction of the encounters and a high number of multiple crossings over a long time period. The latter is facilitated by the spacecraft orbit which is designed to remain in the near magnetosheath for average solar wind pressure. For most encounters, a well-ordered, tangential (draped) magnetosheath ®eld is observed and there is little evidence of large deviations in local boundary orientations. Two passes corresponding to close conjunctions of the Geotail spacecraft are analysed to con®rm boundary orientation and motion. These further show evidence of an anti-sunward moving depression on the magnetopause (which is much smaller at Equator-S). The Tsyganenko model ®eld is used routinely to assist in categorising the crossings and some comparison of models is carried out. We note that typically the T87 model ®ts the data better than the T89 model during conditions of low to intermediate u index near the magnetopause and also near the dawn-side tail current sheet in the dawnside region.
Abstract. Data from Equator-S and Geotail are used to study the dynamics of the plasma sheet observed during a substorm with multiple intensi®cations on 25 April 1998, when both spacecraft were located in the early morning sector (03±04 MLT) at a radial distance of 10± 11 R E . In association with the onset of a poleward expansion of the aurora and the westward electrojet in the premidnight and midnight sector, both satellites in the morning sector observed plasma sheet thinning and changes toward a more tail-like ®eld con®guration. During the subsequent poleward expansion in a wider local time sector (20±04 MLT), on the other hand, the magnetic ®eld con®guration at both satellites changed into a more dipolar con®guration and both satellites encountered again the hot plasma sheet. High-speed plasma¯ows with velocities of up to 600 km/s and lasting 2±5 min were observed in the plasma sheet and near its boundary during this plasma sheet expansion. These high-speed¯ows included signi®cant dawn±dusk ows and had a shear structure. They may have been produced by an induced electric ®eld at the local dipolarization region and/or by an enhanced pressure gradient associated with the injection in the midnight plasma sheet.
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