Limitations of Absolute Current Densities Derived from the Semel & Skumanich Method

TL;DR

This paper evaluates the limitations of the Semel & Skumanich method for deriving absolute electric current densities from magnetic field data, revealing that it can underestimate current densities by factors of 1.2 to 2.0 under certain conditions.

Contribution

The study identifies specific conditions where the Semel & Skumanich method produces significant errors in current density calculations using a numerical MHD model.

Findings

Errors occur when magnetic azimuth changes with near-zero horizontal field.

The method underestimates |Jz| by factors of 1.2 to 2.0 in certain scenarios.

Limitations are linked to the combination of azimuth changes and weak horizontal fields.

Abstract

Semel and Skumanich proposed a method to obtain the absolute electric current density, |Jz|, without disambiguation of 180 degree 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 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 |Jz| too small by factors typically 1.2 ~ 2.0.