Increased Dynamic Efficiency in Mesoscale Organized Trade Wind Cumulus Clouds

Abstract. Mesoscale organization of boundary layer clouds modulates low cloud radiative properties and contributes to the tropical hydrologic cycle. Trade-wind cumuli have varying organization and are a notable source of uncertainty in global climate models (GCMs). The linkage between cumulus development and dynamics is difficult to capture, impacting low cloud feedback estimates. We investigate the relationship between mesoscale organization and updraft dynamics in the wintertime trades using ship-borne observations, including a motion-stabilized Doppler-wind lidar. We contrast two periods with similar cloud structure sizes but different clustering: more (MO) and less (LO) organized clouds. MO are dynamically more efficient than LO clouds: for a given core size, MO have stronger sub-cloud and cloud base updrafts, leading to greater vertical moisture transport. Despite similar background environmental plume distributions, cloud-topped plumes are wider for MO than LO. MO updraft strength is less responsive to diurnal variations in environmental factors than LO although both are enhanced during early morning surface flux maximization. Once established, MO clouds may be maintained through the assistance of cloud-layer circulations that facilitate increased dynamic efficiency through reinforcing plumes. Dynamic efficiency is likely a key contributor to the mesoscale moisture-convection feedback critical to these regimes. The influence of mesoscale organization on cloud dynamics through increased velocity variability is another unresolved factor in GCM parametrizations. Understanding this efficiency, and the potential environmental resilience of MO clouds, will be informative for simulating cumulus behaviors under current and future climates.