Abstract. We present SuperDARN radar observations of the ionospheric flow during a well-observed high-latitude substorm which occurred during steady northward IMF conditions on 2 December 1999. These data clearly demonstrate the excitation of large-scale flow associated with the substorm expansion phase, with enhanced equatorward flows being observed in the pre-midnight local time sector of the expansion phase auroral bulge and westward electrojet, and enhanced return sunward flows being present at local times on either side, extending into the dayside sector. The flow pattern excited was thus of twin-vortex form, with foci located at either end of the substorm auroral bulge, as imaged by the Polar VIS UV imager. Estimated total transpolar voltages were ∼40 kV prior to expansion phase onset, grew to ∼80 kV over a ∼15 min interval during the expansion phase, and then decayed to ∼35 kV over ∼10 min during recovery. The excitation of the large-scale flow pattern resulted in the development of magnetic disturbances which extended well outside of the region directly disturbed by the substorm, depending upon the change in the flow and the local ionospheric conductivity. It is estimated that the nightside reconnection rate averaged over the 24-min interval of the substorm was ∼65-

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[1] We analyze Geotail observations of magnetic field and flow oscillations in the dayside magnetosphere that occurred in direct association with an event of traveling convection vortices observed in the northern high-latitude ionosphere. Geotail was positioned on a magnetic flux tube that mapped very close to the centers of the driving field-aligned currents in the ionosphere. These are the first in situ observations from the source region of such events. The flow signature is seen clearly in the cold, dense plasma population, which the satellite encounters during the event, in addition to a hot magnetospheric (plasma sheet -like) population. This report will present the observations and briefly discuss their implications for our understanding of the traveling convection vortex (TCV) signature. We interpret the event in terms of a boundary wave at the magnetopause. Our analysis suggests that strong gradients in the magnetic field strength or plasma density in the inner magnetosphere should play an important role in this process.

Abstract. Standing Alfvén waves of 1.1 mHz (∼15 min in period) were observed by the Cluster satellites in the mid-tail during 06:00-07:00 UT on 8 August 2003. Pulsations with the same frequency were also observed at several ground stations near Cluster's footpoint. The standing wave properties were determined from the electric and magnetic field measurements of Cluster. Data from the ground magnetometers indicated a latitudinal amplitude and phase structure consistent with the driven field line resonance (FLR) at 1.1 mHz. Simultaneously, quasi-periodic oscillations at different frequencies were observed in the post-midnight/early morning sector by GOES 12 (l 0 ≈8.7), Polar (l 0 ≈11-14) and Geotail (l 0 ≈9.8). The 8 August 2003 event yields rare and interesting datasets. It provides, for the first time, coordinated in situ and ground-based observations of a very low frequency FLR in the mid-tail on stretched field lines.

In recent years, quantitative analysis of the magnetosphere-ionosphere coupling and electrodynamics of the polar ionosphere received much attention. Though remarkable progress has been made in this field by using a variety of magnetogram inversion techniques in order to infer the global ionospheric current distribution, there is still a need for modeling ionospheric currents locally, over a certain region, for comparison with other geophysical ground-based and satellite observations. This paper presents a simple method for estimating equivalent ionospheric currents using magnetic field observations along a meridian chain of ground-based vector magnetometers. The method can be applied in an automatic fashion to any available magnetometer chain data, for example, from the DMI Greenland west coast chain. We first describe how we separate contributions to the observed geomagnetic variations from external (ionospheric) and internal (induced) sources. We then model the ionospheric electrojet by a sequence of narrow current strips and apply the Biot-Savart law to formulate an inversion problem. Using a regularization technique, we find a stable distribution of the equivalent ionospheric currents crossing the magnetometer chain in eastward and westward direction. Simulation tests and a case study (20 March 1999) are discussed in order to illustrate properties of the solution to the inverse problem and to present a practical tool, which is accessible through the DMI World Wide Web site.