A new method to estimate ionospheric electric fields and currents using data from a local ground magnetometer network

摘要

In this study we present a new method to estimate ionospheric electric fieldsand currents using ground magnetic recordings and measured or modeledionospheric electric conductivity as the input data. This problem has beenstudied extensively in the past, and the standard analysis technique for sucha set of input parameters is known as the KRM method (Kamide et al., 1981). The newmethod presented in this study makes use of the same input data as thetraditional KRM method, but differs significantly from it in the mathematicalapproach that is used. In the KRM method one tries to find such a potentialelectric field, that the resulting current system has the same curl as theionospheric equivalent currents. In the new method we take a differentapproach, so that we determine such a curl-free current system that, togetherwith the equivalent currents, it is consistent with a potential electricfield. This approach results in a slightly different equation, that makesbetter use of the information contained in the equivalent currents. In thispaper we concentrate on regional studies, where the (unknown) boundaryconditions at the borders of the analysis area play a significant role in theKRM solution. In order to overcome this complication, we formulate a novelnumerical algorithm to be used with our new calculation method. Thisalgorithm is based on the Cartesian elementary current systems (CECS). WithCECS the boundary conditions are implemented in a natural way, makingregional studies less prone to errors. We compare the traditional KRM methodand our new CECS-based formulation using several realistic models of typicalmeso-scale phenomena in the auroral ionosphere, including a uniformelectrojet, the Ω-bands and the westward traveling surge. It is foundthat the error in the CECS results is typically about 20%–40%, whereasthe errors in the KRM results are significantly larger.