This study presents a climatology of simulated low-latitude cloud regimes derived from MERRA and MERRA-2 data using an International Satellite Cloud Climatology Project (ISCCP) simulator. Physically meaningful cloud types are predicted from 25 years of reanalysis data using a clustering algorithm on joint histograms of simulated cloud-top pressure (pc) and optical thickness (τ). The ability of reanalysis to predict the full range of observed tropical and subtropical clouds or “weather states” is evaluated in addition to documenting the effects of including MERRA precipitation fluxes on the simulator results. Trends in the simulated cloud properties and cloud fraction as related to potential long-term changes in the tropical circulation are also discussed.
The simulated MERRA clouds qualitatively matched the observed distributions of pc and τ, though the tallest (pc < 310 hPa) and thickest (τ > 23) clouds were often missing from the reanalysis. The presence of tall, thin clouds is also unaccounted for in the simulated regimes, though this result was partially improved when using a random vertical cloud overlap parameterization. Convectively suppressed regimes are simulated well in MERRA data, albeit the reanalysis significantly underpredicts the observed cloud fractions for all the regimes. Finally, composite profiles of MERRA vertical velocity, temperature, and moisture for each ISCCP regime largely matched expectations and observations from previous studies, suggesting that the dynamic and thermodynamic properties of the cloud regimes are well captured by the reanalysis even if the simulated properties do no fully align with ISCCP observations.