Infrared absorption and liquid water content in stratocumulus clouds

Simultaneous measurements of narrow‐beam vertical infrared radiance (10–12μm), cloud dropsize distributions, temperature and humidity in some stratocumulus clouds are reported. Cloud volume absorption coefficients calculated from mean dropsize distributions are found to be well correlated with the cloud liquid water content. Values of cloud volume absorption coefficient are found to vary from 2 to 20 km −1 for a range in liquid water content from 0.02 to 0.27gm −3 . The equivalent variation in cloud mass absorption coefficient is from 700 to 1030g −1 cm 2 , with a mean value for all clouds of 765g −1 cm 2 . From the radiance measurements the clouds are found to become ‘black’ for depths ranging from about 100 to 450m. The variation of measured cloud emissivity with liquid water mass is found to be consistent, within the observed variabilities of the clouds, with the emissivities calculated from the above mean absorption coefficient. The results are compared with earlier flux measurements.