[1] We present coordinated ground satellite observations of solar wind compressionrelated dayside electromagnetic ion cyclotron (EMIC) waves from 25 September 2005. On the ground, dayside structured EMIC wave activity was observed by the CARISMA and STEP magnetometer arrays for several hours during the period of maximum compression. The EMIC waves were also registered by the Cluster satellites for half an hour, as they consecutively crossed the conjugate equatorial plasmasphere on their perigee passes at L ∼ 5. Simultaneously, conjugate to Cluster, NOAA 17 passed through field lines supporting EMIC wave activity and registered a localized enhancement of precipitating protons with energies >30 keV. Our observations suggest that generation of the EMIC waves and consequent loss of energetic protons may last for several hours while the magnetosphere remains compressed. The EMIC waves were confined to the outer plasmasphere region, just inside the plasmapause. Analysis of lower-frequency Pc5 waves observed both by the Cluster electron drift instrument (EDI) and fluxgate magnetometer (FGM) instruments and by the ground magnetometers show that the repetitive structure of EMIC wave packets observed on the ground cannot be explained by the ultra low frequency (ULF) wave modulation theory. However, the EMIC wave repetition period on the ground was close to the estimated field-aligned Alfvénic travel time. For a short interval of time, there was some evidence that EMIC wave packet repetition period in the source region was half of that on the ground, which further suggests bidirectional propagation of wave packets.Citation: Usanova, M. E., et al. (2010), Conjugate ground and multisatellite observations of compression-related EMIC Pc1 waves and associated proton precipitation,
Abstract. EDI measures the drift velocity of artificially injected electron beams. From this drift velocity, the perpendicular electric field and the local magnetic field gradients can be deduced when employing different electron energies. The technique requires the injection of two electron beams at right angles to the magnetic field and the search for those directions within the plane that return the beams to their associated detectors after one or more gyrations. The drift velocity is then derived from the directions of the two beams and/or from the difference in their times-of-flight, measured via amplitude-modulation and coding of the emitted electron beams and correlation with the signal from the returning electrons. After careful adjustment of the control parameters, the beam recognition algorithms, and the onboard magnetometer calibrations during the commissioning phase, EDI is providing excellent data over a wide range of conditions. In this paper, we present first results in a variety of regions ranging from the polar cap, across the magnetopause, and well into the magnetosheath.
[1] We report on magnetically conjugate Cluster and the Defense Meteorological Satellite Program (DMSP) satellite observations of subauroral ion drifts (SAID) during moderate geomagnetic activity levels on 8 April 2004. To our knowledge, the field-aligned separation of DMSP and Cluster (%28,000 km) is the largest separation ever analyzed with respect to the SAID phenomenon. Nonetheless, we show coherent, subauroral magnetosphere-ionosphere (MI) coupling along an entire field line in the post-dusk sector. The four Cluster satellites crossed SAID electric field channels with meridional magnitude E M of 25 mV/m in situ and latitudinal extent DL % 0.5°in the southern and northern hemispheres near 07:00 and 07:30 UT, respectively. Cluster was near perigee (R % 4 R E ) and within 5°(15°) of the magnetic equator for the southern (northern) crossing. The SAID were located near the plasmapause-within the ring current-plasmasphere overlap region. Downward field-aligned current signatures were observed across both SAID crossings. The most magnetically and temporally conjugate SAID field from DMSP F16A at 07:12 UT was practically identical in latitudinal size to that mapped from Cluster. Since the DMSP ion drift meter saturated at 3000 m/s (or $114 mV/m) and the electrostatically mapped value for E M from Cluster exceeded 300 mV/m, a magnitude comparison of E M was not possible. Although the conjugate measurements show similar large-scale SAID features, the differences in substructure highlight the physical and chemical diversity of the conjugate regions.
[1] The 'whistler critical Mach number', M crit w , is one of the dimensionless parameters that characterizes collisionless shocks. Originally, it was introduced to indicate the critical point above which whistler waves do not propagate upstream. Indeed our analysis of Geotail data at the Earth's bow shock shows intense whistler waves in the sub-critical regime, M A < M crit w , but not in the super-critical regime. In this paper, we further report that M crit w seems to regulate the electron acceleration efficiency at the shocks. At the shock transition layer it is found that the spectral index G of electron energy spectra defined by f(E) / E ÀG is distributed between 3.5 and 5.0 in the sub-critical regime, while the hardest energy spectra with G = 3-3.5 are detected in the super-critical regime. We discuss a possible relationship between M crit w and the electron acceleration.
Abstract. Plasmaspheric plumes have been routinely observed by CLUSTER and IMAGE. The CLUSTER mission provides high time resolution four-point measurements of the plasmasphere near perigee. Total electron density profiles have been derived from the electron plasma frequency identified by the WHISPER sounder supplemented, in-between soundings, by relative variations of the spacecraft potential measured by the electric field instrument EFW; ion velocity is also measured onboard these satellites. The EUV imager onboard the IMAGE spacecraft provides global images of the plasmasphere with a spatial resolution of 0.1 R E every 10 min; such images acquired near apogee from high above the pole show the geometry of plasmaspheric plumes, their evolution and motion. We present coordinated observations of three plume events and compare CLUSTER in-situ data with global images of the plasmasphere obtained by IMAGE. In particular, we study the geometry and the orientation of plasmaspheric plumes by using four-point analysis methods. We compare several aspects of plume motion as determined by different methods: (i) inner and outer plume boundary velocity calculated from time delays of this boundary as observed by the wave experiment WHISPER on the four spacecraft, (ii) drift velocity measured by the electron drift instrument EDI onboard CLUSTER and (iii) global velocity determined from successive EUV images. These different techniques consistently indicate that plasmaspheric plumes rotate Correspondence to: F. Darrouzet (fabien.darrouzet@oma.be) around the Earth, with their foot fully co-rotating, but with their tip rotating slower and moving farther out.
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