How do environmental mesoscale heterogeneities influence the trade-wind cloud organization?

Cumuli clouds in the trade winds are a great source of uncertainty for the future climate as their net radiative effect is hardly represented in global models. The spatial organization of these clouds, that drives their radiative effect, has been categorized into 4 major patterns: Sugar, Flower, Gravel and Fish (Bony et al. 2020). The processes governing their spatial organization and the relationships with the environmental properties remain however unclear. This study investigates the sensitivity of the Flower organization to the environmental mesoscale heterogeneities in water vapor and winds. A case of Flower organization, producing 100-km wide cloud clusters, is selected from the EUREC⁴A-ATOMIC campaign that took place east of Barbados in January-February 2020. A Large-Eddy Simulations using the Meso-NH model and a 100-m horizontal grid-spacing has been extensively validated by satellite and aircraft high-resolution observations (Dauhut et al., 2022) and serves as a reference. By removing alternatively the humidity or the wind heterogeneities, we show that mesoscale humidity anomalies play a critical role in driving cloud organisation into Flower. Further investigations indicate that humidity heterogeneities in the cloud layer influence the development of a shallow mesoscale circulation and have a larger impact than the heterogeneities in the sub-cloud layer. Different chains of processes are proposed to explain such a sensitivity.