Increased dynamic efficiency in mesoscale organized trade wind cumulus clouds

Abstract

Abstract. Mesoscale organization of boundary layer clouds modulates their radiative properties and contributes to the tropical hydrologic cycle. Trade wind cumuli (Cu) have varying organization and are a source of uncertainty in global climate models (GCMs). The linkage between Cu development and dynamics is difficult to capture, impacting low cloud feedback estimates. We investigate the relationship between mesoscale organization and Cu updraft dynamics in their early development stages using wintertime shipborne observations. We contrast two periods with similar cloud sizes but more (MO) and less (LO) organized states. MO clouds are dynamically more efficient than LO clouds: for a given core size, MO clouds have stronger sub-cloud and cloud-base updrafts, implying greater vertical moisture transport. Despite similar background plume behaviors, cloud-topped plumes are wider and more frequently successful for MO than LO. Updraft strength is persistent despite diurnal environmental variations. MO turbulence is enhanced by early-morning surface flux maximization and LO updrafts may be assisted by daytime environmental conditions. MO cloud amount persists, while LO clouds suffer daytime depredations. We hypothesize that, once established, MO clouds are maintained through the assistance of cloud-layer-driven mesoscale circulations that increase dynamic efficiency through reinforcing plumes and their updrafts. Dynamic efficiency is likely a key contributor to the moisture–convection feedback critical to mesoscale organization. Organizational modulation of cloud dynamics through enhancing updrafts is another unresolved factor in GCM parameterizations. Understanding this efficiency, and the potential environmental resilience of MO clouds, will be informative for simulating Cu behaviors under current and future climates.