Calculation of an Equivalent Current System in the Polar E Region

In order to interpret VHF aurora backscatter communications, it is necessary to get some information about the extent, the movement, and the strength of the polar electrojet. In this paper a method is given to calculate an equivalent current system in the polar E region by determining the unknown parameters (height, direction, width of the current, etcetera) from the measured disturbance vectors of the earth's magnetic field, ΔH, ΔD, and ΔZ. With a model of a simple current‐density distribution it is possible to solve the Biot‐Savart formula. The consideration of positive, negative, and induced currents leads to a system of nonlinear equations of eight unknown parameters in this special instance. With an iterative method given by Newton and Raphson this system of equations can be solved if approximate values of the solution are known. These approximate values are given by physical conditions or can be obtained by model calculation. In this paper, results are shown for a current system calculated with values of ΔH, ΔD, and ΔZ from the magnetograms of Leirvogur, Lerwick, Eskdalemuir, and Hartland during a period of about five hours on March 23–24, 1969.