Modeling of equivalent ionospheric currents from meridian magnetometer chain data

In recent years, quantitative analysis of the magnetosphere-ionosphere coup ling and electrodynamics of the polar ionosphere received much attention. T hough remarkable progress has been made in this field by using a variety of magnetogram inversion techniques in order to infer the global ionospheric current distribution, there is still a need for modeling ionospheric curren ts locally, over a certain region, for comparison with other geophysical gr ound-based and satellite observations. This paper presents a simple method for estimating equivalent ionospheric currents using magnetic field observa tions along a meridian chain of ground-based vector magnetometers. The meth od can be applied in an automatic fashion to any available magnetometer cha in data, for example, from the DMI Greenland west coast chain. We first des cribe how we separate contributions to the observed geomagnetic variations from external (ionospheric) and internal (induced) sources. We then model t he ionospheric electrojet by a sequence of narrow current strips and apply the Biot-Savart law to formulate an inversion problem. Using a regularizati on technique, we find a stable distribution of the equivalent ionospheric c urrents crossing the magnetometer chain in eastward and westward direction. Simulation tests and a case study (20 March 1999) are discussed in order t o illustrate properties of the solution to the inverse problem and to prese nt a practical tool, which is accessible through the DMI World Wide Web sit e.