Vertical cloud properties in the tropical western Pacific Ocean: Validation of the CCSR/NIES/FRCGC GCM by shipborne radar and lidar

Abstract

This study examined the vertical cloud structure over the tropical western Pacific Ocean using 95‐GHz radar and lidar data observed from September to December 2001 during the MR01‐K05 cruise of the research vessel Mirai. The cloud vertical structure was homogeneous between 6 and 10 km, and the maximum cloud occurrence was 20% and located at 12 km. The mean precipitation occurrence was 11.5% at 1 km. The cloud fraction, radar reflectivity factor, and lidar backscattering coefficient were simulated along the Mirai cruise track using the output from the Center for Climate System Research, University of Tokyo; National Institute for Environmental Studies; and Frontier Research Center for Global Change (CCSR/NIES/FRCGC) general circulation model (GCM). The original output showed the maximum cloud fraction at 15 km; however, after considering attenuation and the minimum sensitivity of the radar, the maximum shifted to 12 km. The model overestimated the cloud fraction above 8 km, with the simulated fraction more than twice as large as the observed fraction. The model overpredicted the frequency of deep convection reaching the upper atmosphere above 12 km. Further, it overestimated precipitation frequency. Simulated radar reflectivity was underestimated throughout the entire altitude range, whereas simulated and observed lidar backscattering were in good agreement above 12 km with subgrid‐scale treatment. The ice effective radius of 40 μm and ice water content were reasonable in thin clouds, but the radius was underestimated in other regions. The simulated liquid water content was overestimated.