Limitations of absolute current densities derived from the Semel & Skumanich method

Semel and Skumanich proposed a method to obtain the absolute electric current density, |J _z |, without disambiguation of 180° in the transverse field directions. The advantage of the method is that the uncertainty in the determination of the ambiguity in the magnetic azimuth is removed. Here, we investigate the limits of the calculation when applied to a numerical MHD model. We have found that the combination of changes in the magnetic azimuth with vanishing horizontal field component leads to errors, where electric current densities are often strong. Where errors occur, the calculation gives |J _z | too small by factors typically 1.2-2.0.