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Ann. Geophys., 23, 733-743, 2005
www.ann-geophys.net/23/733/2005/
© European Geosciences Union 2005
A statistical comparison of SuperDARN spectral width boundaries and DMSP particle precipitation boundaries in the morning sector ionosphere
G. Chisham1, M. P. Freeman1, T. Sotirelis2, R. A. Greenwald2, M. Lester3, and J.-P. Villain4
1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK
2Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
3Radio and Space Plasma Physics Group, University of Leicester, Leicester, LE1 7RH, UK
4LPCE/CNRS, 3A Avenue de la Recherche Scientifique, 45071 Orleans Cedex 2, France
Abstract. Determining reliable proxies for the ionospheric signature of the open-closed field line boundary (OCB) is crucial
for making accurate ionospheric measurements of many magnetospheric processes (e.g. magnetic reconnection).
This study compares the latitudes of Spectral Width Boundaries (SWBs), identified in the morning sector ionosphere
using the Super Dual Auroral Radar Network (SuperDARN), with Particle Precipitation Boundaries (PPBs) determined
using the low-altitude Defense Meteorological Satellite Program (DMSP) spacecraft, in order to determine whether the
SWB represents a good proxy for the ionospheric projection of the OCB.
The latitudes of SWBs and PPBs were identified using automated algorithms applied to 5 years (1997-2001) of data
measured in the 00:00-12:00 Magnetic Local Time (MLT) range.
A latitudinal difference was measured between each PPB and the nearest SWB within a ±10min Universal Time (UT)
window and within a ±1h MLT window.
The results show that the SWB represents a good proxy for the OCB close to midnight (~00:00-02:00 MLT) and
noon (~08:00-12:00 MLT), but is located some distance (~2°-4°) equatorward of the OCB across much
of the morning sector ionosphere (~02:00-08:00 MLT).
On the basis of this and other studies we deduce that the SWB is correlated with the poleward boundary of
auroral emissions in the Lyman-Birge-Hopfield ``Long" (LBHL) UV emission range and hence, that spectral width
is inversely correlated with the energy flux of precipitating electrons.
We further conclude that the combination of two factors may explain the spatial distribution of spectral width
values in the polar ionospheres.
The small-scale structure of the convection electric field leads to an enhancement in spectral width in regions
close to the OCB, whereas increases in ionospheric conductivity (relating to the level of incident electron energy
flux) lead to a reduction in spectral width in regions just equatorward of the OCB.
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