Cloud Optical Depth of Shallow Cumulus Clouds

Description

Cloud optical depth of low altitude cumulus clouds are historically not measured well, but 15% of global cover is small clouds [Wood and Field 2011] and 50% of low clouds are optically thin [Leahy et al. 2012]. Although the fraction of world’s albedo contributed is still an open question, Hartmann et al. 1992 estimated the global albedo of low clouds to be equal to 5.6% for the DJF (December January February) Season, which makes up 38% of global cloud albedo. Thin low-altitude cumulus clouds are common in subtropical Miami during quiescent time periods and prevailing Atlantic trade-winds. We present two techniques, one from lidar and another from zenith radiance, for calculating cloud optical depth [Delgadillo 2015] that will be applied to the upcoming LASIC (Layered Atlantic Smoke Interactions with Clouds) study. Lidar has been underutilized to measure cloud optical of low thin clouds. We present a technique developed for micro-pulse lidar (MPL) similar to MPL that will be used in LASIC. The technique is applied to the 2014 DJF season in Miami. Alternatively, zenith radiance measurements will also be used to measure cloud optical depth, which will be compared to the MPL results. LASIC will also include a zenith radiometer. Consequently, the Miami zenith radiance measurements may provide insights on what we may expect to see during LASIC given that the predominant cloud type at Ascension Island is also shallow cumulus.