The magnetogram inversion technique (MIT) is a computational method for calculating the global pattern of ionospheric current using ground magnetic disturbance data as input. By assuming the ionospheric electric conductivity distribution, the technique makes it further possible to estimate the distribution patterns of such electrodynamic quantities as electric field, electric potential, field-aligned current and Joule heating rate. Although the MIT is an indirect method, it provides instantaneous electrodynamical pictures of the entire polar ionosphere with a high time resolution while more direct measurements by radar, rocket and satellite are vital to understand the ionospheric phenomena but they provide informations only over a limited area. Since the output of the MIT are very sensitive to the choice of the ionospheric conductivity distribution, a companion paper will be devoted to the topic. Various electrodynamic quantities over the polar ionosphere, which are now available through the magnetogram inversion technique, will be also discussed in another companion paper.

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