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Abstract

The millimeter and sub-millimeter continuum of the solar spectrum is expected to serve as a “linear thermometer” of the solar chromosphere. Using the Atacama Large Millimeter/Submillimeter Array (ALMA), the Sun can be observed with arcsecond resolution or better at these crucial wavelengths, providing novel insight into the structure of the chromosphere and helping to constrain magneto-hydrodynamic models of the solar atmosphere. In this work, we present high-resolution (~ 0.5”), wide-field mosaics of two regions observed in ALMA Band 7 (0.85 mm): (1) a region of concentrated unipolar magnetic field; and (2) an active region containing several sunspots. We characterize these regions by examining the distribution and evolution of the sub-mm brightness temperature (Tb) in these regions and comparing them to simultaneous observations in the ultraviolet obtained from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory (SDO/AIA) as well as the Interface Region Imaging Spectrometer (IRIS). We also present statistical comparisons with observations of similar regions observed in ALMA Bands 3 (3 mm) and 6 (1.3 mm), which sample slightly higher regions of the chromosphere, and in the infrared vibrational spectrum of carbon monoxide, which is sensitive to cooler regions (plasma) at the top of the solar photosphere.