Abstract
Abstract. We investigate particle and fields data during a conjunction of the Polar and Cluster spacecraft. This conjunction occurs near the dayside cusp boundary layer when a dayside inverted-V was observed in the particle data of both satellites. Electron, ion, electric field, and magnetic field data from each satellite confirm that the dayside inverted-V (DSIV) structure is present at the location of both satellites and the electric fields persist from the altitude of the Polar (lower) spacecraft to the altitude of the Cluster spacecraft. We observe accelerated, precipitating electrons and upward ions along the magnetic field. In addition, large amplitude electric fields perpendicular to the ambient magnetic field seen by Polar and by Cluster suggest significant parallel electric fields associated with these events. For similar DSIV events observed by the Polar spacecraft, plasma waves (identified as possible Alfvén waves) have been observed to propagate in both directions along the magnetic field line. Future conjunctions will be necessary to confirm that DSIVs are associated with reconnection sites.
Highlights
Introduction and backgroundThe term “Inverted-V” is used to describe the signature of auroral electron precipitation as observed on energy-vs-time spectrograms seen on both the nightside and dayside of the Earth
Lin and Hoffman reported that dayside invertedV (DSIV) are shorter in spatial extent than those in the evening sector and DSIVs have a peak energy of only about 1 keV compared to about 5 keV for the evening hours from 19:00 to 01:00 MLT
In this paper we investigate a DSIV observed by the Polar spacecraft during a higher altitude conjunction with the Cluster spacecraft
Summary
The term “Inverted-V” is used to describe the signature of auroral electron precipitation as observed on energy-vs-time spectrograms seen on both the nightside and dayside of the Earth. Menietti and Smith (1993) presented several examples of dayside inverted-Vs in which ion convection and energy dispersion appeared to span the region of both open and closed field lines. The DSIV carries an upward current from the ionosphere (Burch et al, 1990) and may be a result of the reconnection process, but the plasma of the field lines still appears closed at the time and location of the observations by DE-1, because the high-energy trapped plasma had not enough time to escape along the open field lines. The region-1 currents carried by the upward electrons observed just poleward of the DSIV and equatorward of the cusp may be due to current closure through the ionosphere (cf Southwood, 1987; Saunders, 1989; Smith and Lockwood, 1990). These electrons will collapse in pitch angle with altitude and be seen as beams as observed in the DE-1, Polar, and Cluster data
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