Characterization of ice cloud properties obtained by shipborne radar/lidar over the tropical western Pacific Ocean for evaluation of an atmospheric general circulation model

Abstract

This study analyzed 95-GHz radar/lidar data collected from the R/V Mirai over the tropical western Pacific to characterize the vertical distribution of ice cloud effective radius r eff, ice water content IWC, and in-cloud vertical velocity of the region in conjunction with weather regimes classified by International Satellite Cloud Climatology Project (ISCCP) cluster analysis. Ice clouds observed from the Mirai were roughly consistent with the ISCCP weather regimes; more convectively active regimes had larger amounts of high cloud consisting of deeper cloud with larger ice water path (IWP) and precipitating ice fraction. Ice cloud microphysics of the Center for Climate System Research, National Institute for Environmental Studies, Frontier Research Center for Global Change atmospheric general circulation model (AGCM) was then evaluated using the radar-lidar simulator and ISCCP weather regimes for comparison of the statistics at different scales. The model tended to produce a high cloud fraction that was two times larger in the cirrus regimes but 50% lower in the deepest convective regime. The simulated IWP could only weakly reproduce the observed variety and generally underestimated the observed values despite the weather regimes. Cutoff in the simulated grid mean IWC around 0.1 g -3 was too small, especially above 11 km. The AGCM successfully predicted the observed frequency distribution for r eff above 11 km, but produced large overestimation in the peak value below 11 km due to the excessively large fraction of r eff ∼100 m. Establishing a cutoff for cloud ice at r eff 120 m was found to be quite reasonable, although it would miss some of the larger particles that were observed. Copyright 2010 by the American Geophysical Union.