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We present results from the Austral Winter 2003 observing campaign of SPARO,a 450 micron polarimeter used with a two-meter telescope at South Pole. Wemapped large-scale magnetic fields in four Giant Molecular Clouds (GMCs) in theGalactic disk: NGC 6334, the Carina Nebula, G333.6-0.2 and G331.5-0.1. We finda statistically significant correlation of the inferred field directions withthe orientation of the Galactic plane. Specifically, three of the four GMCs(NGC 6334 is the exception) have mean field directions that are within 15degrees of the plane. The simplest interpretation is that the field directiontends to be preserved during the process of GMC formation. We have also carriedout an analysis of published optical polarimetry data. For the closest of theSPARO GMCs, NGC 6334, we can compare the field direction in the cloud asmeasured by SPARO with the field direction in a larger region surrounding thecloud, as determined from optical polarimetry. For purposes of comparison, wealso use optical polarimetry to determine field directions for other regions ofsimilar size and distance. Overall, the results from this optical polarimetryanalysis are consistent with our suggestion that field direction tends to bepreserved during GMC formation. Finally, we compare the disorder in ourmagnetic field maps with the disorder seen in magnetic field maps derived fromMHD turbulence simulations. We conclude from these comparisons that themagnetic energy density in our clouds is comparable to the turbulent energydensity.Comment: Submitted to Astrophys. J. (one color figure

Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds