Vector Magnetic Fields and Electric Currents from the Imaging Vector Magnetograph

TL;DR

This paper presents a detailed methodology for producing high-quality vector magnetograms using the Imaging Vector Magnetograph, and applies it to analyze electric currents in active solar regions, achieving precise measurements and insights into magnetic field structures.

Contribution

The paper introduces a comprehensive procedure for high-resolution vector magnetogram production and a novel calculation method for vertical electric current density without disambiguation.

Findings

Uncertainties in magnetic field measurements are minimized to 10 G for longitudinal and 40 G for transverse fields.

Vertical current density increases with magnetic field strength, more so in complex active regions.

The method achieves an uncertainty of about 7.0 mA/m^2 in current density calculations.

Abstract

First, we describe a general procedure to produce high quality vector magnetograms using the Imaging Vector Magnetograph (IVM) at Mees Solar Observatory. At the spatial resolution 2"x2", the Stokes Q,U,V uncertainty reaches 0.001-0.0005 in time-averaged data over 1-hour in the quiet Sun. When vector magnetic fields are inferred from the time-averaged Stokes spectral images of FeI 6302.5A, the resulting uncertainties are on the order of 10 G for the longitudinal fields, 40 G for the transverse field strength and 9 degree for the magnetic azimuth. The magnetic field inversion used in this work is the "Triplet" code, which was developed and implemented in the IVM software package by the late Barry J. LaBonte. The inversion code is described in detail in the Appendix. Second, we solve for the absolute value of the vertical electric current density, |Jz|, accounting for the above IVM problems, for two different active regions. One is a single sunspot region (NOAA 10001 observed on 20 June 2002) while the other is a more complex, quadrupolar region (NOAA10030 observed on 15 July 2002). We use a calculation that does not require disambiguation of 180 degree in the transverse field directions. The |Jz| uncertainty is on the order of 7.0 mA m^-2. The vertical current density increases with increasing vertical magnetic field. The rate of increase is about 1 -2 times as large in the quadrupolar NOAA 10030 region as in the simple NOAA 10001, and it is more spatially variable over NOAA 10030 than over NOAA 10001.