Lobe cell convection and polar cap precipitation

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Read Full Article (file size: 4473884 bytes) Cited by JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. A5, 1198, doi:10.1029/2002JA009725, 2003 Lobe cell convection and polar cap precipitation S. Eriksson Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA W. J. Peria Department of Earth and Space Sciences, University of Washington, Seattle, Washington, USA J. W. Bonnell Space Sciences Laboratory, University of California, Berkeley, California, USA Y.-J. Su Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA R. E. Ergun Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA Y.-K. Tung Space Sciences Laboratory, University of California, Berkeley, California, USA G. K. Parks Space Sciences Laboratory, University of California, Berkeley, California, USA C. W. Carlson Space Sciences Laboratory, University of California, Berkeley, California, USA Abstract The characteristic electric and magnetic field signature of lobe cells as observed by the low-altitude FAST satellite in 55 dawn-dusk passes are compared with Polar ultraviolet images of polar cap auroral activity. Initial results from 34 events of UV image coverage suggest that there is an intimate coupling between the sunward convection flow of the lobe cell and transpolar auroral arcs or diffuse polar cap precipitation in ∼62% of these cases. However, in some cases where the field signatures are suggestive of lobe cell convection, there is no detectable particle precipitation either in Polar UVI or the FAST data sets. Moreover, the presence of lobe cells coincide with UV data intensifications in the premidnight 2000–2400 MLT sector and/or the postnoon 1500 MLT region in ∼59% of all cases with UVI coverage. The magnetic local time dependence of the lobe cells and polar cap precipitation on the interplanetary magnetic field (IMF) are examined using the upstream Wind monitor. The relative importance of the IMF B _y and B _z components are investigated and compared with the predictions of the antiparallel merging model and strongly suggests a connection with the magnetospheric sash, as is further implied by the mapping of magnetic field lines using the Tsyganenko [2002] (T01) model. It was also noted that a majority of lobe cell events occurred during enhanced AE index substorm-like conditions and that generally stronger AE indices are measured for stronger IMF B _y magnitudes during these events. Received 4 October 2002; accepted 7 January 2003; published 17 May 2003. Index Terms: 2760 Magnetospheric Physics: Plasma convection; 2776 Magnetospheric Physics: Polar cap phenomena; 2455 Ionosphere: Particle precipitation; 2431 Ionosphere: Ionosphere/magnetosphere interactions (2736); 2788 Magnetospheric Physics: Storms and substorms. Read Full Article (file size: 4473884 bytes) Cited by Citation: Eriksson, S., W. J. Peria, J. W. Bonnell, Y.-J. Su, R. E. Ergun, Y.-K. Tung, G. K. Parks, and C. W. Carlson (2003), Lobe cell convection and polar cap precipitation, J. Geophys. Res., 108(A5), 1198, doi:10.1029/2002JA009725. Copyright 2003 by the American Geophysical Union.

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