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 and tracking. During the period August 21-24, Hurricane Bonnie passed near Andros Island and influenced the water vapor and cirrus cloud measurements acquired by the SRL. Two drying signatures related to the hurricane were recorded by the SRL and other sensors. Cirrus cloud optical depths (at 351 nm) were also measured during this period. Optical depth values ranged from less than 0.01 to 1.5, The influence of multiple scattering on these optical depth measurements was studied. A correction technique is presented which minimizes the influences of multiple scattering and derives information about cirrus cloud optical and physical properties. The UV/IR cirrus cloud optical 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 are significantly affected by the presence of cirrus clouds if IR optical depths are similar to0.005 or greater. Using the International Satellite Cloud 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 precipitable water retrieval.