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Cluster and DMSP observations of SAID electric fields

Cluster and DMSP observations of SAID electric fields

Publication date: 25 May 2007

Authors: Puhl-Quinn, P.A. et al.

Journal: Journal of Geophysical Research
Volume: 112
Issue: A5
Page: A05219
Year: 2007

Copyright: American Geophysical Union

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 EM of 25 mV/m in situ and latitudinal extent DeltaLambda ~ 0.5° in the southern and northern hemispheres near 07:00 and 07:30 UT, respectively. Cluster was near perigee (R ~ 4 RE) 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 EM from Cluster exceeded 300 mV/m, a magnitude comparison of EM 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.

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