THE IONOSPHERIC SIGNATtMES OF}•lO ( TRANSFfR EVENTS AND SOLAR WIND DYNAMIC PRESSURE CHANG•
Abstract. The generation of flow and current vortices in the dayside auroral ionosphere has been predicted for two processes ocurring at the dayside magnetopause. The first of, these mechanisms is time-dependent •mgnetic reconnection, in "flux transfer events " (]•Es); the second is the ac...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.695.448 http://www.eiscat.rl.ac.uk/Members/mike/publications/pdfs/1990/72_Lockwoodetal_1990.pdf |
| Summary: | Abstract. The generation of flow and current vortices in the dayside auroral ionosphere has been predicted for two processes ocurring at the dayside magnetopause. The first of, these mechanisms is time-dependent •mgnetic reconnection, in "flux transfer events " (]•Es); the second is the action of solar wind dynamic pressure changes. The ionospheric flow signature of an I•E should be a twin vortex, with the mean flow velocity in the central region of the pattern equal to the velocity of the pattern as a whole. On * the other hand, a pulse of enhanced or reduced dynamic pressure is also expected to produce a twin vortex, but with the central plasma flow being generally different in speed from, and almost orthogonal to, the motion of the whole pattern. In this paper, we make use of this distinction to discuss recent observations of vortical flow patterns in the dayside auroral ionosphere in terms of one or other of the proposed mechanisms. We conclude that some of the observations reported are consistent only with the predicted signature of FTEs. We then evaluate the dimensions of the open flux tubes required to explain some recent simultaneous radar and auroral observations and infer that they are typically 300 km in north-south extent but up to 2000 km in longitudinal extent (i.e., roughly 5 hours of MLT). Hence these observations suggest that recent theories of l•Es which invoke.time--varying reconnection at an elongated neutral line may be correct. We also present some simultaneous observations of the interplanetary magnetic field (IMF) and solar wind dynamic pressure (observed using the IMP8 satellite) and the ionospheric flow (observed using the EISCAT radar) which are also only consistent with the [TE model. We estimate that for continuously southward IMF ( • 5 nT) these l•Es contribute about 30 kV to the mean total transpolar voltage (•30•). |
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