|
|
 |
|
|
Ann. Geophys., 23, 2599-2604, 2005
www.ann-geophys.net/23/2599/2005/
© European Geosciences Union 2005
The accuracy of using the spectral width boundary measured in off-meridional SuperDARN HF radar beams as a proxy for the open-closed field line boundary
G. Chisham1, M. P. Freeman1, T. Sotirelis2, and R. A. Greenwald2
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
Abstract. Determining reliable proxies for the ionospheric signature of the open-closed field line boundary (OCB) is crucial
for making accurate measurements of magnetic reconnection.
This study compares the latitudes of spectral width boundaries (SWBs) measured by different beams of the Goose Bay
radar of the Super Dual Auroral Radar Network (SuperDARN), with the latitudes of OCBs determined using the
low-altitude Defense Meteorological Satellite Program (DMSP) spacecraft, in order to determine whether the
accuracy of the SWB as a proxy for the ionospheric projection of the OCB depends on the line-of-sight direction
of the radar beam.
The latitudes of SWBs and OCBs were identified using automated algorithms applied to 5 years (1997–2001) of data
measured in the 1000–1400 magnetic local time (MLT) range.
Six different Goose Bay radar beams were used, ranging from those aligned in the geomagnetic meridional
direction to those aligned in an almost zonal direction.
The results show that the SWB is a good proxy for the OCB in near-meridionally-aligned beams but becomes progressively
more unreliable for beams greater than 4 beams away from the meridional direction.
We propose that SWBs are identified at latitudes lower than the OCB in the off-meridional beams due to the presence of
high spectral width values that result from changes in the orientation of the beams with respect to the
gradient in the large-scale ionospheric convection pattern.
Keywords. Ionosphere (Instruments and techniques;
Plasma convection) – Magnetospheric physics (Magnetopause,
cusp and boundary layers)
Full Article in PDF (268 KB) |
|
|
