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Ann. Geophys., 23, 343-358, 2005
www.ann-geophys.net/23/343/2005/
© European Geosciences Union 2005
Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison
A. Aksnes1, O. Amm2, J. Stadsnes1, N. Østgaard1,3, G. A. Germany4, R. R. Vondrak5, and I. Sillanpää2
1Department of Physics and Technology, University of Bergen, Bergen, Norway
2Finnish Meteorological Institute, Geophysical Research Division, P.O. Box 503, FIN–00101 Helsinki, Finland
3University of California, Berkeley, CA 94720-7450, USA
4University of Alabama in Huntsville, AL 35899, USA
5NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
Abstract. Global instantaneous conductance maps can be derived from remote
sensing of UV and X-ray emissions by the UVI and PIXIE cameras
on board the Polar satellite. Another technique called the 1-D method of
characteristics provides mesoscale instantaneous conductance
profiles from the MIRACLE ground-based network in Northern
Scandinavia, using electric field measurements from the STARE
coherent scatter radar and ground magnetometer data from the IMAGE
network. The method based on UVI and PIXIE data gives conductance
maps with a resolution of ~800km in space and ~4.5min
in time, while the 1-D method of characteristics
establishes conductances every 20s and with a spatial
resolution of ~50km. In this study, we examine three periods
with substorm activity in 1998 to investigate whether the two
techniques converge when the results from the 1-D method of
characteristics are averaged over the spatial and temporal
resolution of the UVI/PIXIE data.
In general, we find that the calculated conductance sets do not
correlate. However, a fairly good agreement may be reached when
the ionosphere is in a state that does not exhibit strong local
turbulence. By defining a certain tolerance level of turbulence,
we show that 14 of the 15 calculated conductance pairs during
relatively uniform ionospheric conditions differ less than ±30%.
The same is true for only 4 of the 9 data points derived
when the ionosphere is in a highly turbulent state. A correlation
coefficient between the two conductance sets of 0.27 is derived
when all the measurements are included. By removing the data
points from time periods when too much ionospheric turbulence
occurs, the correlation coefficient raises to 0.57. Considering
the two very different techniques used in this study to derive the
conductances, with different assumptions, limitations and scale
sizes, our results indicate that simple averaging of mesoscale
results allows a continuous transition to large-scale results.
Therefore, it is possible to use a combined approach to study
ionospheric events with satellite optical and ground-based
electrodynamic data of different spatial and temporal resolutions.
We must be careful, though, when using these two techniques during
disturbed conditions. The two methods will only give results that
systematically converge when relatively uniform conditions exist.
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