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Ann. Geophys., 23, 325-342, 2005
www.ann-geophys.net/23/325/2005/
© European Geosciences Union 2005
Mesoscale ionospheric electrodynamics of omega bands determined from ground-based electromagnetic and satellite optical observations
O. Amm1, A. Aksnes2, J. Stadsnes2, N. Østgaard2,3, R.R. Vondrak4, G.A. Germany5, G. Lu6, and A. Viljanen1
1Finnish Meteorological Institute, Geophysical Research, P.O. Box 503, FIN-00101 Helsinki, Finland
2Department of Physics and Technology, University of Bergen, Bergen, Norway
3University of California, Berkeley, CA 94720-7450, USA
4NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
5University of Alabama in Huntsville, AL 35899, USA
6HAO/NCAR, P.O. Box 3000, Boulder, CO 80301-3000, USA
Abstract. We present ground-based electromagnetic data from the MIRACLE and BEAR
networks and satellite optical observations from the UVI and PIXIE
instruments on the Polar satellite of an omega band event over Northern
Scandinavia on 26 June 1998, which occured close to the morning side edge of
a substorm auroral bulge. Our analysis of the data concentrates on one omega
band period from 03:18-03:27 UT, for which we use the method of
characteristics combined with an analysis of the UVI and PIXIE data to
derive a time series of instantaneous, solely data-based distributions of
the mesoscale ionospheric electrodynamic parameters with a 1-min time
resolution. In addition, the AMIE method is used to derive global Hall
conductance patterns. Our results show that zonally alternating regions of
enhanced ionospheric conductances ("tongues") up to ~60S and low
conductance regions are associated with the omega bands. The tongues have a
poleward extension of ~400km from their base and a zonal extension
of ~380km. While they are moving coherently eastward with a velocity
of ~770ms-1, the structures are not strictly stationary. The
current system of the omega band can be described as a superposition of two
parts: one consists of anticlockwise rotating Hall currents around the
tongues, along with Pedersen currents, with a negative divergence in their centers.
The sign of this system is reversing in the low conductance areas. It causes
the characteristic ground magnetic signature. The second part consists of
zonally aligned current wedges of westward flowing Hall currents and is
mostly magnetically invisible below the ionosphere. This system dominates
the field-aligned current (FAC) pattern and causes alternating upward and
downward FAC at the flanks of the tongues with maximum upward FAC of
~25µA m-2. The total FAC of ~2MA are comparable to the
ones diverted inside a westward traveling surge. Throughout the event, the
overwhelming part of the FAC are associated with gradients of the
ionospheric conductances, and 66-84% of the FAC are connected with
ionospheric Hall currents.
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