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Ann. Geophys., 25, 1141-1156, 2007
www.ann-geophys.net/25/1141/2007/
© European Geosciences Union 2007
A new method to estimate ionospheric electric fields and currents using data from a local ground magnetometer network
H. Vanhamäki and O. Amm
Finnish Meteorological Institute, Space Research Unit, P.O. Box 503, 00101 Helsinki, Finland
Abstract. In this study we present a new method to estimate ionospheric electric fields
and currents using ground magnetic recordings and measured or modeled
ionospheric electric conductivity as the input data. This problem has been
studied extensively in the past, and the standard analysis technique for such
a set of input parameters is known as the KRM method (Kamide et al., 1981). The new
method presented in this study makes use of the same input data as the
traditional KRM method, but differs significantly from it in the mathematical
approach that is used. In the KRM method one tries to find such a potential
electric field, that the resulting current system has the same curl as the
ionospheric equivalent currents. In the new method we take a different
approach, so that we determine such a curl-free current system that, together
with the equivalent currents, it is consistent with a potential electric
field. This approach results in a slightly different equation, that makes
better use of the information contained in the equivalent currents. In this
paper we concentrate on regional studies, where the (unknown) boundary
conditions at the borders of the analysis area play a significant role in the
KRM solution. In order to overcome this complication, we formulate a novel
numerical algorithm to be used with our new calculation method. This
algorithm is based on the Cartesian elementary current systems (CECS). With
CECS the boundary conditions are implemented in a natural way, making
regional studies less prone to errors. We compare the traditional KRM method
and our new CECS-based formulation using several realistic models of typical
meso-scale phenomena in the auroral ionosphere, including a uniform
electrojet, the Ω-bands and the westward traveling surge. It is found
that the error in the CECS results is typically about 20%–40%, whereas
the errors in the KRM results are significantly larger.
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