Abstract
Abstract. For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for large-amplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients 'geoeffective', which have the tendency to recur with the solar rotation period.Key words. Ionosphere (Aural ionosphere; Ionosphere- magnetosphere interactions) · Magnetospheric Physics (current system)
Highlights
The polar cusp/cleft region which maps the magnetopause and adjacent layers is rich in transient events in Correspondence to: H
In this study we present a statistical survey of largeamplitude travelling convection vortices (TCVs) events from the recordings of the IMAGE magnetometer network during the six months, October 1993 through March 1994
We have performed a statistical study of large-amplitude TCVs
Summary
The polar cusp/cleft region which maps the magnetopause and adjacent layers is rich in transient events in Correspondence to: H. Goertz et al, 1985; Lanzerotti et al, 1986, 1987) The motivation for these studies came from theoretical works predicting the ground signature of FTEs (Saunders et al, 1984; Southwood, 1987; Lee, 1986). By using an array of magnetometers they showed that the magnetic deections matched an interpretation of steady ionospheric current systems moving at a velocity of several km/s from east to west overhead the stations. This class of magnetic impulses was termed travelling convection vortices (TCV). The occurrence frequency versus local time, as reported by these authors, showed a clear peak at 08 MLT
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