ATMOSPHERIC ABSORPTION DURING THE ATMOSPHERIC RADIATION MEASUREMENT (ARM) ENHANCED SHORTWAVE EXPERIMENT (ARESE)

The objectives of the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE) are to directly measure clear and cloudy sky shortwave atmospheric absorption and to quantify any absorption f ound in excess of model predictions. We undertake detailed model compa risons to near-infrared and total solar flux time series observed by s urface and airborne radiometric instruments during the ARESE campaign. Model clear-sky absorption biases generally fall within the range of uncertainty generated by sample size, and assumptions of aerosol prope rties and surface albedo. Direct measurements by stacked aircraft on t he overcast day of October 30, 1995, confirm the detection of enhanced cloud shortwave absorption during ARESE. The detection is substantiat ed by, and consistent with, three independent measures of cloudy sky a bsorption estimated in previous studies: cloud forcing ratio, insolati on forcing ratio, and albedo/transmission slope. A significant portion of the enhanced absorption occurs at visible wavelengths. Collocated measurements of liquid water path (LWP) suggest the magnitude of the e nhanced absorption increases with LWP.