A model current system, in which magnetospheric and ionospheric sections are connected by currents flowing along the geomagnetic field lines, is proposed to represent the current system responsible for polar magnetic substorms. The magnetic perturbations from model current systems of this type are studied in terms of elementary loops, whose magnetic effects are evaluated numerically. The influence of currents induced in the ground is studied for a time‐independent case, but it is found that such effects do not change the gross character of the perturbation pattern. Using a north‐south chain of stations and an appropriate coordinate system, the model predictions are compared with the magnetic variations observed during some substorms. It is found that the model is capable of explaining the gross features of the magnetic perturbation pattern observed. However, at times there are minor deviations from the predictions, which suggest the presence of additional ionospheric and magnetospheric current syst