U.S. Department of Commerce


Date of this Version



Published in Q. J. R. Meteorol. Soc. (2011) 137: 969–978; DOI:10.1002/qj.806


The precipitation efficiencies (RMPE, CMPE, and LSPE) can be defined as the ratio of rain rate to rainfall sources in the rain microphysical budget, the cloud microphysical budget, and the surface rainfall budget, respectively. The estimate of RMPE from grid-scale data serves as the true precipitation efficiency since the rain rate is a diagnostic term in the tropical rain microphysical budget. The accuracy of precipitation efficiency estimates with CMPE and LSPE is compared to that of RMPE by analyzing data from a 21-day two-dimensional cloud-resolving model simulation with imposed large-scale vertical velocity, zonal wind, and horizontal advection obtained from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment. The results show CMPE is generally smaller than RMPE. The root-mean-squared difference between RMPE and LSPE is larger than the standard deviation of RMPE. Thus, water vapour process data cannot be used to estimate precipitation efficiency.