WRF and GISS SCM simulations of convective updraft properties during TWP-ICE

The Weather Research and Forecasting (WRF) model, running at cloud-resolving model resolution (1.3 km and 0.6 km), is used to simulate cumulus updraft speeds associated with three distinct convective regimes sampled during the intensive observing period of the Tropical Warm Pool–International Cloud Experiment (TWP-ICE) near Darwin, Australia. The WRF model produces strong updrafts during a monsoon break period and weaker updrafts during an active monsoon period, consistent with observational proxies of convective strength. It also captures the observed feature of midlevel convection during a suppressed monsoon period. The ability of the WRF model to differentiate the updraft speeds among three subperiods is robust to changes in its microphysics and turbulence schemes, resolution, and forcing procedure. For comparison to the parameterized diagnostic updraft speeds in the Goddard Institute for Space Studies Single Column Model (GISS SCM), we define an equivalent mean updraft speed for deep convection in the WRF simulation as the ratio of the domain average upward flux of hydrometeors to the domain average hydrometeor water content. Parameterized convective updraft speeds diagnosed from the thermodynamic structure in the SCM can reproduce the WRF difference between the active and break period updraft strength and the shallower suppressed monsoon convection, but only if a free parameter that regulates entrainment strength is allowed to vary. SCM updraft speeds are consistently too strong in the upper troposphere compared with the WRF. Hydrometeor profiles in both the WRF and the SCM are sensitive to assumptions about the ice phase microphysics.