Year: 1997
Type: article
Abstract: he spring meeting provided rich fare for the MIST community.To begin the session on aurora and the cusp, David Willis reported on a database of ancient auroral observations from China, Japan and Korea that is being used to investigate both seasonal and secular variations, as well as the evidence for long-term variations in the occurrence of major geomagnetic storms.Peter Collis then presented coordinated observations using the Kilpisjärvi imaging riometer, the Porojärvi allsky TV and the EISCAT UHF radar.Three auroral intensifications had been observed in the magnetic zenith, separated by about 40 minutes, showing that the pre-break-up auroral arcs were collocated with arc-like features in absorption.Next, Steve Milan described CUTLASS Iceland radar observations of auroral electrojet irregularities at E and F region altitudes.At the higher altitude, a broad spectrum of line-of-sight velocities was consistent with zonal flow.In the E region, these velocities saturated at the ion acoustic speed c s , the spectra being broad (v < c s ) or narrow (v ≈ c s ). Cusp observationsKarlheinz Trattner showed three dimensional plasma measurements from the toroidal imaging mass-angle spectrograph (TIMAS) on the Polar satellite.Observations of H + , O + , He + and He ++ in the energy range 16 eV -33 keV revealed a velocity filter effect at the cusp, with magnetosheath ions arriving first at the observing satellite, while slower ions were seen later at higher latitudes.This seemed a constant feature for all the cusp crossings.Simultaneous observations of the cusp by the Ny Ålesund meridian scanning photometer, the CUTLASS Finland HF radar and the DMSP F13 satellite were presented by Tim Yeoman.Very strong radar returns coincided with optical and particle signatures of the cusp.The source of the backscatter was F region irregularities produced by soft ion precipitation.Peter Cargill had carried out MHD numerical simulations of the cusps for east-west and northward interplanetary magnetic field (IMF).In the east-west case, the magnetopause moved inward, its position determined by balance between the magnetic pressure of the IMF and the compressed magnetosphere.For northward IMF, the simulations demonstrated the existence of lobe reconnection in the presence of a realistic cusp field geometry.To conclude the session, Carlos del Pozo presented two case studies of multi-instrument observations of the dynamics of auroral arcs.For a substorm event, the Kilpisjärvi imaging riometer tracked several patches of intense ionization drifting south-east until the appearance of a magnetic bay.Subsequently, an enhanced electrojet crossed Tromsø, associated with north-south moving arcs.A quiet time case showed evidence of a localized field-aligned current system producing a dim arc.
Source: Astronomy & Geophysics
Author: M. Laird
Institution: King's College London
Language: English
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W1990507117