Close examination of Direct Normal Solar Irradiance (DNSI) and Downwelling Diffuse Irradiance (DDI) on cloud-free days at the ARM SGP site reveals anticorrelated short term (several minute) fluctuations, especially prominent in the hours around local solar noon; i.e., DDI increasing as DNSI decreases. These fluctuations are correlated or anticorrelated with other direct and derived radiometric quantities, including aerosol optical thickness (AOT) from MultiFilter Rotating Shadowband Radiometer (MFRSR) and Angstrom exponent, evaluated as - d ln (AOT)/ d ln wavelength. These fluctuations are attributed to increased relative humidity associated with intermittent rising air parcels. Examples of correlations will be given together with analysis of relative magnitudes of fluctuations in the several quantities establishing the consistency of this interpretation.
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