Precipitation efficiency in the tropical deep convective regime: A 2-D cloud resolving modeling study

Precipitation efficiency in the tropical deep convective regime is analyzed based on the hourly data from a 2-D cloud resolving simulation. The cloud resolving model is forced by the large-scale vertical velocity, zonal wind and large-scale horizontal advections derived from TOGA COARE for a 20-day period. Large-scale precipitation efficiency (LSPE) is defined as a ratio of surface rain rate to the sum of surface evaporation and moisture convergence, and cloud-microphysics precipitation efficiency (CMPE) is defined as a ratio of surface rain rate to the sum of condensation and deposition rates of supersaturated vapor. Moisture budget shows that the local atmospheric moisture gains (loses) when the LSPE is less (more) than 100%. The LSPE could be larger than 100% for strong convection. This suggests that in order to avoid moisture bias, the cumulus parameterization schemes used in general circulation models should allow the precipitation rate to be larger than the sum of surface evaporation and moisture convergence in strong convective region. Statistical analysis shows that the LSPE is about 80% of the CMPE when it is less than 60%, and the CMPE is a constant of about 70% when the LSPE is more than 60%. The CMPE increases with increasing mass-weighted mean temperature and increasing surface rain rate. This suggests that precipitation is more efficient for warm environment and strong convection.