Evaluation of Cloud Fraction Parameterizations Using Long-term ARM Observations

Zhenduo Zhu Florida International University
Ping Zhu Florida International University

Category: Cloud Properties

Working Group: Cloud Life Cycle

Relative humidity (RH) is often used as a predictor for parameterizing sub-grid cloud fraction in general circulation models, such as CAM3. In this study, the cloud fraction parameterization based on RH is evaluated using 12-year ARM observations over Southern Great Plains (SGP) and Tropical Western Pacific (TWP). The atmospheric profiling is obtained from the ARM sounding. The diagnosed cloud fraction is then compared with the cloud fraction obtained from ARM Climate Modeling Best Estimate (CMBE). The diurnal, seasonal, and annual variations of the RH-based cloud fraction parameterization are examined. It is shown that the parameterization produced reasonable low and middle cloud fraction compared with the CMBE data. However, the parameterization significantly underestimates the cloud fraction of high clouds. We also explored how to use the long-term ARM data to evaluate other types of cloud fraction parameterizations.

This poster will be displayed at ASR Science Team Meeting.