Evaluation of Trade Wind Mesoscale Morphology Evolution and Transitions

Mesoscale cloud morphology patterns in the trade-winds can be grouped by their distinct appearance, size, and radiative properties into four categories: Sugar, Gravel, Flowers, and Fish (Stevens et al. 2019, Bony et al. 2020, Schulz 2022). We utilize a synergistic, multi-platform observational dataset developed during the 2020 EUREC4A-ATOMIC joint campaign to investigate the evolution of sub-cloud dynamics on Eulerian and Lagrangian scales as a function of shallow convective organizational structures in the winter-time trade-winds. We focus on two multi-day periods when observational platforms were longitudinally distributed across the ocean in parallel with Barbados. These periods were dominated, respectively, by Sugar (Jan. 31- Feb. 3) and Gravel (Jan. 9 - 15) clouds at the RV Ronald H. Brown, which either persisted as or transitioned to larger cloud structures (i.e., Gravel, Flowers) by the time they reached Barbados. Understanding what contributes to Gravel occurrence in cases of persistence vs. under transitions from smaller clouds has utility in predicting occurrence of larger cloud structures in this region under climate change.

Forward and backward 30-hr boundary layer Lagrangian trajectories are initialized every 3-hr at the RV Ronald H. Brown and used to connect observations from upwind (e.g., the Northwest Tropical Atlantic Station buoy) and downwind (e.g., the Barbados Cloud Observatory) platforms. Satellite observations and reanalysis provide additional context. Motion-stabilized Doppler-lidar observations at the RV Ronald H. Brown and the Barbados Cloud Observatory allow us to examine cloud updraft, fraction, size, height, base mass fluxes, and, in combination with large-scale vertical velocity measurements, entrainment characteristics across morphologies and over their Lagrangian evolution. The impact of environmental conditions expected to influence cloud organization and development (e.g., surface wind speeds, energy and moisture fluxes, stability, and both large- and meso-scale subsidence) as well as the relative importance of updraft characteristics and cloud-base fraction on Lagrangian transitions are evaluated.