Diagnostics of auroral oval boundaries on the basis of the magnetogram inversion technique

Abstract

It is shown that the convection reversal boundary is a fundamental parameter of the magnetosphere-ionosphere coupling, which determines a strong analogy between the electrostatic potential of the ionosphere and the equivalent current function in the dipole geomagnetic field approximation and the uniform ionospheric conductance. We have developed a new ground-based method for automatically diagnosing boundaries of the auroral oval using output data obtained with the magnetogram inversion technique (MIT). Using maps of the current function and field-aligned currents, calculated at the first stage of MIT with uniform ionospheric conductance, we determine the convection reversal boundary, polar cap boundary, equatorial boundary of the auroral oval, and line of maximum density of auroral electrojets. These parameters have previously been determined by a visual-manual method: analyzing maps of field-aligned and equivalent currents on the monitor screen and carrying out predetermined boundaries with the mouse — this took a very long time (weeks and months). The comparison between manually and automatically obtained boundaries has shown that the correlation coefficient between the two boundaries is, on average, 0.85, and the root-mean-square deviation does not exceed 2° in latitude. By providing an adequate accuracy for the boundary determination, the automatic method reduces the time for map processing by a factor of 2–3 (to minutes and hours), releasing a researcher from laborious visual work. The new method is implemented as one of the important modules in the updated MIT software.

Keywords

• ionospheric convection
• equivalent current function
• auroral oval
• polar cap
• field-aligned currents
• convection reversal boundary