Raman lidar measurements of water vapor and cirrus clouds during the passage of Hurricane Bonnie

The NASA GSFC Scanning Raman Lidar (SRL) was stationed on Andros Island in the Bahamas during August-September 1998 as a part of the third Convection and Moisture Experiment (CAMEX 3) which focused on hurricane development an d tracking. During the period August 21-24, Hurricane Bonnie passed near An dros Island and influenced the water vapor and cirrus cloud measurements ac quired by the SRL. Two drying signatures related to the hurricane were reco rded by the SRL and other sensors. Cirrus cloud optical depths (at 351 nm) were also measured during this period. Optical depth values ranged from les s than 0.01 to 1.5, The influence of multiple scattering on these optical d epth measurements was studied. A correction technique is presented which mi nimizes the influences of multiple scattering and derives information about cirrus cloud optical and physical properties. The UV/IR cirrus cloud optic al depth ratio was estimated on the basis of a comparison of lidar and GOES 8 measurements. Simple radiative transfer model calculations compared with GOES satellite brightness temperatures indicate that satellite radiances a re significantly affected by the presence of cirrus clouds if IR optical de pths are similar to0.005 or greater. Using the International Satellite Clou d Climatology Project (ISCCP) detection threshold for cirrus clouds on the GOES data presented here, a high bias of up to 40% was found in the GOES pr ecipitable water retrieval.