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Ann. Geophys., 20, 1905-1920, 2002
www.ann-geophys.net/20/1905/2002/
© European Geosciences Union 2002
A multi-instrument approach to mapping the global dayside merging rate
G. Provan, T. K. Yeoman, M. Lester, and S. E. Milan
Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
Correspondence to: G. Provan (gp3@ion.le.ac.uk)
Abstract. For the first time three
different methods have been used to calculate the global merging rate during
the same substorm growth phase. The ionospheric plasma drift was monitored by
six of the Northern Hemisphere SuperDARN radars, allowing the convection
pattern to be studied over 12 h of magnetic local time. The radars observed
reconnection signatures on the dayside simultaneously with substorm signatures
on the nightside. The three methods to calculate the global merging rate are: (i)
the equatorward expansion of radar backscatter on the nightside, which provides
an estimate of the rate of polar cap expansion, while upstream WIND
measurements gave an estimate of the reconnection electric fields; (ii) the
derivation of the dayside boundary normal plasma flow velocity and an estimate
of the extent of the ionospheric merging gap, from radar observation of dayside
reconnection; (iii) utilizing the map-potential technique to map the
high-latitude plasma flow and cross polar cap potential (Ruohoniemi and Baker,
1998), allowing the global dayside merging rate to be calculated. The three
methods support an extensive magnetopause X-line length of between 30 ± 12RE
and 35 ± 15 RE (assuming a single X-line and constant merging
rate). Such close agreement between the different methods of calculation are
unexpected, especially as the length of the magnetopause X-line is not well
known.
Key words. Magnetospheric physics
(magnetopause, cusp and boundary layers; magnetosphere – ionosphere
interactions; solar-wind magnetosphere interactions)
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