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Ann. Geophys., 22, 1973-1987, 2004
www.ann-geophys.net/22/1973/2004/
© European Geosciences Union 2004
The dynamics and relationships of precipitation, temperature and convection boundaries in the dayside auroral ionosphere
J. Moen1,2, M. Lockwood3, K. Oksavik1, H. C. Carlson4, W. F. Denig5, A. P. van Eyken6, and I. W. McCrea3
1Department of Physics, University of Oslo, P.O. Box 1048, Blindern, N-0316 Oslo, Norway
2Arctic Geophysics, University Centre in Svalbard, N-9170 Longyearbyen, Norway
3Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, UK
4Air Force Research Laboratory, AFOSR, 801 Stafford St., Arlington, VA 22203, USA
5Air Force Research Laboratory, VSBXP, 29 Randolph Rd, Hanscom AFB, MA 01731-3010, USA
6EISCAT Scientific Association, P.O. Box 164, Kiruna, Sweden
Abstract. A continuous band of high ion temperature, which
persisted for about 8h and zigzagged north-south across more than five
degrees in latitude in the dayside (07:00-15:00MLT) auroral ionosphere, was
observed by the EISCAT VHF radar on 23 November 1999. Latitudinal gradients
in the temperature of the F-region electron and ion gases (Te and
Ti, respectively) have been compared with concurrent observations of
particle precipitation and field-perpendicular convection by DMSP
satellites, in order to reveal a physical explanation for the
persistent band of high Ti, and to test the potential role of Ti
and Te gradients as possible markers for the open-closed field line
boundary. The north/south movement of the equatorward Ti boundary was
found to be consistent with the contraction/expansion of the polar cap due to
an unbalanced dayside and nightside reconnection. Sporadic intensifications in
Ti, recurring on ~10-min time scales, indicate that frictional
heating was modulated by time-varying reconnection, and the band of high
Ti was located on open flux. However, the equatorward Ti boundary
was not found to be a close proxy of the open-closed boundary. The closest
definable proxy of the open-closed boundary is the magnetosheath electron
edge observed by DMSP. Although Te appears to be sensitive to magnetosheath
electron fluxes, it is not found to be a suitable parameter for routine
tracking of the open-closed boundary, as it involves case dependent analysis
of the thermal balance. Finally, we have documented a region of newly-opened
sunward convecting flux. This region is situated between the convection
reversal boundary and the magnetosheath electron edge defining the
open-closed boundary. This is consistent with a delay of several minutes
between the arrival of the first (super-Alfvénic) magnetosheath
electrons and the response in the ionospheric convection, conveyed to the
ionosphere by the interior Alfvén wave. It represents a candidate
footprint of the low-latitude boundary mixing layer on sunward convecting
open flux.
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