Abstract
Abstract. We investigate 1-D models of the westward substorm electrojet using magnetic field observations along a meridian chain of stations. We review two respective linear models from Kotikov et al. (1987) and Popov et al. (2001) with a large number of elementary currents at fixed positions. These models can be applied to a magnetometer chain with many magnetic stations. A new nonlinear method with one current element is designed for cases with a small number of stations. We illustrate the performance of these methods using data from the IMAGE (International Monitor for Auroral Geomagnetic Effects) and Yamal Peninsula stations. Several corrective measures are proposed to account for unphysical solutions or local extrema from the optimized functions. We also advertise a generic maximum likelihood approach to a problem that is feasible for any empiric model.
Highlights
A ground-based magnetometer is the oldest instrument for space weather research
One can study evolution of the main geomagnetic field, as well as geomagnetic variations. Most of the latter are driven by the magnetospheric and ionospheric currents, which depend on solar activity
We use the following approximation of the 1-D westward auroral electrojet (Fig. 3): (1) the electrojet flows at a fixed altitude of 110 km above the flat land; (2) the electrojet is infinitely thin vertically; (3) the electrojet flows along in the latitudinal direction; and (4) the electrojet does not vary with longitude
Summary
A ground-based magnetometer is the oldest instrument for space weather research. Data from hundreds of permanent and temporary magnetic stations all over the world are available. One can study evolution of the main geomagnetic field, as well as geomagnetic variations Most of the latter are driven by the magnetospheric and ionospheric currents, which depend on solar activity. The main substorm characteristic is the amplitude of magnetic variations in the northern auroral zone, which is summarized using the AE, AU, and AL geomagnetic indices. These variations are driven primarily by the westward auroral electrojet, which is an electric current that shortcuts the magnetotail cross-tail current (Ganushkina et al, 2018). More global models exist that recover electric currents from a distributed set of stations (e.g., Mishin, 1990) Most of these methods, which use instantaneous measurements, require a large number of stations to discover the electrojet spatial structure.
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