First, we describe a general procedure to produce high-quality vector magnetograms using the Imaging Vector Magnetograph (IVM) at Mees Solar Observatory. Two IVM effects are newly discussed and taken into account: (1) the central wavelength of the Fabry-Pérot is found to drift with time as a result of undiagnosed thermal or mechanical instabilities in the instrument; (2) the Stokes V-sign convention built into the IVM is found to be opposite to the conventional definition used in the study of radiative transfer of polarized radiation. At the spatial resolution 2'' × 2'', the Stokes Q, U, V uncertainty reaches ~1 × 10–3 to 5 × 10–4 in time-averaged data over 1 hr in the quiet Sun. When vector magnetic fields are inferred from the time-averaged Stokes spectral images of FeI 6302.5 ?, the resulting uncertainties are on the order of 10 G for the longitudinal fields (B ∥), 40 G for the transverse field strength (B ⊥) and ~9° 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 B. 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 2002 June 20) while the other is a more complex, quadrupolar region (NOAA10030 observed on 2002 July 15). We use a calculation that does not require disambiguation of 180° 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.
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