RADAR OBSERVATIONS OF AURORAL-ZONE FLOWS DURING A MULTIPLE-ONSET SUBSTORM

J P Morelli, R J Bunting, S W H Cowley, C J Farrugia, M P Freeman, E Friischristensen, G O L Jones, M Lester, R V Lewis, H Lubr, D Orr, M Pinnock, G D Reeves, P J S Williams, T K Yeoman

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Abstract

We present an analysis of ground magnetic field, ionospheric flow, geosynchronous particle, and interplanetary data during a multiple-onset substorm on 12 April 1988. Our principal results concern the modulations of the ionospheric flow which occur during the impulsive electrojet activations associated with each onset. During the first hour of the disturbance these take place every similar to 12.5 min and involve the formation of a new intense westward current filament in the premidnight sector, just poleward of the preexisting extended current system driven by the large-scale flow. These filaments are similar to 1 h MLT wide (similar to 600 km), and initially expand poleward to a width of similar to 300 km before contracting equatorward and coalescing with the preexisting current, generally leaving the latter enhanced in magnitude and/or expanded in latitude. Within the impulsive electrojets the flow is found to be suppressed to values 50-100 m s(-1) or less during the first few minutes, before surging equatorward at 0.5-1.0 km s (-1) during the phase of rapid coalescence. The implication is that the precipitation-induced Hall conductivity within the impulsive electrojet initially rises to exceed similar to 100 mho, before decaying over a few minutes. This value compares with Hall conductivities of similar to 20 mho in the quasi-steady current regions, and a few mho or less in the regions poleward of the electrojets and in the preonset ionosphere. Preliminary evidence has also been found that the flow surges propagate from midnight to the morning sector where they are associated with arrested equatorward motion or poleward contractions of the current system. These observations are discussed in terms of present theoretical paradigms of the global behaviour of fields and flows which occur during substorms.

Original languageEnglish
Pages (from-to)1144-1163
Number of pages20
JournalAnnales geophysicae-Atmospheres hydrospheres and space sciences
Volume13
Issue number11
Publication statusPublished - Nov 1995

Keywords

  • WESTWARD TRAVELING SURGE
  • TWO-DIMENSIONAL OBSERVATIONS
  • GROUND-BASED OBSERVATIONS
  • HIGH-LATITUDE IONOSPHERE
  • SOLAR-WIND CONTROL
  • ELECTRIC-FIELDS
  • MAGNETOSPHERIC SUBSTORMS
  • MAGNETIC OBSERVATIONS
  • GEOMAGNETIC-ACTIVITY
  • CURRENT SYSTEMS

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