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Ann. Geophys., 23, 1763-1770, 2005
www.ann-geophys.net/23/1763/2005/
© European Geosciences Union 2005
Interhemispheric observations of the ionospheric signature of tail reconnection during IMF-northward non-substorm intervals
A. Grocott, T. K. Yeoman, S. E. Milan, and S. W. H. Cowley
Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
Abstract. This paper presents the first interhemispheric radar observations
interpreted as the ionospheric response to tail reconnection during
IMF-northward non-substorm intervals. SuperDARN measurements of plasma
convection in the nightside ionospheres of both hemispheres, taken on
21–22 February and 26–27 April 2000, show bursts of flow in the midnight sector
which are understood to be characteristic of such phenomena. Upstream
interplanetary magnetic field data confirm that the field orientation at the
dayside magnetopause was northwards, but with a significant IMF By
component (negative during the first interval, positive during the second),
for many hours prior to the bursts being observed. During the
By-negative interval the bursts were directed westwards in the
Northern Hemisphere and eastwards in the Southern Hemisphere; during the
By-positive interval their directions were reversed. These two
asymmetries between the different orientations of IMF By and between
the two hemispheres are key to our understanding of the magnetospheric
phenomenon responsible for generating the bursts. They provide further
evidence in support of the idea that the bursts are a result of reconnection
in an asymmetric tail under the prolonged influence of IMF By.
Concurrent data from ground magnetometers and geosynchronous satellites
confirm that the bursts have no associated substorm characteristics,
consistent with previous studies.
Keywords. Ionosphere (Plasma convection; Ionospheremagnetosphere
interactions) – Magnetospheric Physics
(Magnetotail)
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