Simultaneous optical and radar signatures of poleward-moving auroral forms

Thorolfsson, A.; Cerisier, J. C.; Lockwood, Mike; Sandholt, P. E.; Senior, C.; Lester, M.

doi:10.1007/s00585-000-1054-2

Cited by 36 publications

(20 citation statements)

References 37 publications

(28 reference statements)

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“…The Southwood [1987] FTE model is lacking a current sheet to put a latitudinal constraint on the return flow. Instead, the return flows are supposed to broaden very quickly due to incompressibility [ Thorolfsson et al , 2000]. In section 4.3 we proposed two alternative explanations for the RFE phenomenon:…”

Section: Summary and Concluding Remarksmentioning

confidence: 99%

“… Pinnock et al [1993] noticed a reduction in the background flow. Thorolfsson et al [2000] carried out a detailed study of distorted flow around poleward moving auroral forms (PMAFs) combined with SuperDARN and optical data. They found clear evidence for return flow near the eastward and westward edges of east–west elongated PMAFs, consistent with their own simulation of Southwood FTEs, but no continuous return flow channels were to be expected.…”

Section: Introductionmentioning

confidence: 99%

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On the relationship between thin Birkeland current arcs and reversed flow channels in the winter cusp/cleft ionosphere

et al. 2008

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[1] In this paper we study reversed flow events (RFEs) that seem regulated by Birkeland current arcs in the winter cusp ionosphere above Svalbard. An RFE is a longitudinally elongated, 100-200 km wide channel, in which the flow direction is opposite to the background convection, persisting for 10-20 min. The RFE onset occurs with the brightening of a discrete arc near the open-closed boundary. The auroral arc is situated exactly at a sharp clockwise flow reversal, consistent with a converging electric field and an upward field-aligned current. One category of RFEs propagates into the polar cap in tandem with poleward moving auroral forms, while another category of RFEs moves with the cusp/cleft boundary. The RFE phenomenon is addressed to a region void of electron precipitation, and in lack of direct sunlight the E-region conductivity will be very low. We propose two possible explanations: (1) the RFE channel may be a region where two MI current loops, forced by independent voltage generators, couple through a poorly conducting ionosphere and (2) the reversed flow channel may be the ionospheric footprint of an inverted V-type coupling region. Electron beams of <1 keV will not give rise to significant conductivity gradients, and the form of a discontinuity in the magnetospheric electric field will be conserved when mapped down to the ionosphere, although reduced in amplitude. These two explanations may be related in the sense that the boundary discontinuity in the magnetospheric electric field in (1) may be the driver for the inverted V in (2).

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Section: Summary and Concluding Remarksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On the relationship between thin Birkeland current arcs and reversed flow channels in the winter cusp/cleft ionosphere

et al. 2008

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“…The MHD simulation by Fedder et al (2002) indicates that the FTE gives a possible mechanism to resolve flux stagnation in the concentration zone. As a result, dayside reconnection under the nonzero IMF B y condition can be the cause of transient phenomena around the cusp ionosphere (such as magnetopause FTE, the FTE related auroral patch, the dayside auroral transient, and the poleward-moving auroral forms) (Newell and Sibeck 1993;Fasel 1995;Thorolfsson et al 2000). These progressing ionospheric disturbance events occur during intervals of southward IMF being related to variations of IMF B y component (Stauning et al 1995).…”

Section: Obliquely Southward Imfmentioning

confidence: 99%

Magnetosphere–Ionosphere Convection as a Compound System

Tanaka

2007

Space Sci Rev

119

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Convection is the most fundamental process in understanding the structure of geospace and disturbances observed in the magnetosphere-ionosphere (M-I) system. In this paper, a self-consistent configuration of the global convection system is considered under the real topology as a compound system. Investigations are made based on the M-I coupling scheme by analyzing numerical results obtained from magnetohydrodynamic (MHD) simulations which guarantee the self-consistency in the whole system under the Bv (magnetic field and velocity) paradigm. It is emphasized in the M-I coupling scheme that convection and field-aligned current (FAC) are different aspects of same physical process characterizing the open magnetosphere. Special attention is given in this paper to the energy supplying (dynamo) process that drives the FAC system. In the convection system, the dynamo must be constructed from shear motion together with plasma population regimes to steadily drive the convection. Convection patterns observed in the ionosphere are also the manifestation of achievement in global self-consistency. A primary approach to apply these concepts to the study of geospace is to consider how the M-I system adjusts the relative motion between the compressible magnetosphere and the incompressible ionosphere when responding to given solar-wind conditions. The above principle is also applicable for the study of disturbance phenomena such as the substorm as well as for the study of apparently unique processes such as the flux transfer event (FTE), the sudden commencement (SC), and the theta aurora. Finally, an attempt is made to understand the substorm as the extension of enhanced convection under the southward interplanetary magnetic field (IMF) condition.

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“…Results of detailed case studies of corresponding ionospheric and magnetopause features (Elphic et al, 1990;Neudegg et al, 1999Neudegg et al, , 2000 have been complemented by statistical studies of the location, occurrence, and relation to IMF B y of ionospheric flow bursts (e.g., McWilliams et al, 2000). Provan et al (1998, and Thorolfsson et al (2000) have used radars and optical observations to determine the size, shape, velocity and recurrence rate of the ionospheric signatures of FTEs. All these observations are consistent with intermittent and/or patchy magnetic reconnection in the form of an FTE driving an ionospheric signature consisting of a localised and sporadic flow burst.…”

Section: Flux Transfer Eventsmentioning

confidence: 99%