Interhemispheric observations of the ionospheric signature of tail reconnection during IMF-northward non-substorm intervals

摘要

This paper presents the first interhemispheric radar observationsinterpreted as the ionospheric response to tail reconnection duringIMF-northward non-substorm intervals. SuperDARN measurements of plasmaconvection in the nightside ionospheres of both hemispheres, taken on21–22 February and 26–27 April 2000, show bursts of flow in the midnight sectorwhich are understood to be characteristic of such phenomena. Upstreaminterplanetary magnetic field data confirm that the field orientation at thedayside magnetopause was northwards, but with a significant IMF B_ycomponent (negative during the first interval, positive during the second),for many hours prior to the bursts being observed. During theB_y-negative interval the bursts were directed westwards in theNorthern Hemisphere and eastwards in the Southern Hemisphere; during theB_y-positive interval their directions were reversed. These twoasymmetries between the different orientations of IMF B_y and betweenthe two hemispheres are key to our understanding of the magnetosphericphenomenon responsible for generating the bursts. They provide furtherevidence in support of the idea that the bursts are a result of reconnectionin an asymmetric tail under the prolonged influence of IMF B_y.Concurrent data from ground magnetometers and geosynchronous satellitesconfirm that the bursts have no associated substorm characteristics,consistent with previous studies.>Keywords. Ionosphere (Plasma convection; Ionospheremagnetosphereinteractions) – Magnetospheric Physics(Magnetotail)