Cluster Observations of Channels of Enhanced Convection Velocity in the Ring Current Region

Details Cluster Observations of Channels of Enhanced Convection Velocity in the Ring Current Region Cluster Observations of Channels of Enhanced Convection Velocity in the Ring Current Region

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm52e..06p&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SM52E-06

Physics

2712 Electric Fields (2411), 2760 Plasma Convection, 2778 Ring Current

Scientific paper

For decades, spacecraft-borne instruments have detected enhanced convection features in the duskside and premidnight subauroral region, variously known as polarization jet [Galperin et al., 1973] or subauroral ion drifts (SAID) [Spiro et al., 1979]. We report Cluster observations of this phenomenon, detected with the electron drift instrument (EDI) which uses a novel particle-detection method to measure electric fields in the plane perpendicular to the magnetic field. We have identified enhanced convection velocity striations within the dusk-side ring current region. Such striations with durations 1-5 minutes were observed in AMPTE/IRM data [LaBelle et al., 1988] and also may be the source of fine features observed recently in ground-based radar observations of SAID [Erickson et al., 2002]. Cluster, due to its more polar orbit, finds them on time scales of tens of minutes implying that the channels are extended along magnetic flux tubes. A survey of Cluster/EDI data from February, 2001 until July, 2003 was performed, using data from 14 to 24 hours local time, from 60-69 degrees invariant latitude, and for Kp > 4. Enhanced electric fields were defined as those in the anti-corotation direction (westward) with amplitude exceeding twice the corotation speed. The data show a tendency for the enhanced electric fields to occur at lower latitudes in premidnight/midnight local time than on the duskside, consistent with previous observations. Many previous observations report widths as narrow as 0.1 degrees for SAID events, and for example the 1-5 minute crossing times at IRM imply striation widths on the order of 1000-2000 km. The variable separations of the Cluster spacecraft over the multi-year data set provides a unique opportunity to improve the determination of this width. In this paper, we elaborate about statistical properties, theoretical implications, and association with the SAPS (sub-auroral polarization streams) and SAID phenomena. Erickson, P.J., et al., Inferred electric field variability in the polarization jet from Millstone Hill E-region coherent scatter observations, Radio Sci., 37, 10.1029/2000RS002531, 2002. Galperin, Yu., et al., Direct measurements of ion drift velocity in the upper ionosphere during a magnetic storm, Cosmicheskie Issled., 11, 273, 1973. LaBelle, J., et al., The duskside plasmapause/ring current interface: Convection and plasma wave observations, J. Geophys. Res., 93, 2573, 1988. Spiro, R.W., et al., Rapid subauroral ion drifts observed by Atmosphere Explorer C, Geophys. Res. Lett., 6, 660, 1979.

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