How and why does the tropical trade-wind convective boundary layer vary?

Abstract:

Many processes related to clouds, convection, and circulations are rooted in the trade-wind convective boundary layer, and the response of these shallow cumulus clouds to warming remains uncertain, hindering quantitative constraints on climate prediction. Our study takes advantage of extensive soundings (219 radiosondes and 978 dropsondes) performed as part of the EUREC4A campaign. The soundings were all released in a ca. 2°x2° area in the downstream trades of the North Atlantic, between 20 January and 20 February, 2020. Here, we ask two simple questions to characterize the trade-wind convective boundary layer. First, how does the thermodynamic structure of the convective boundary layer vary, and what is the most concise way to represent this variability? Second, why do these boundary layer thermodynamic structures vary, and what are the dominant large-scale environmental influences on boundary layer variability on different scales? We perform a variance decomposition of the boundary layer thermodynamic budget at different spatiotemporal scales based upon environmental controlling factors, including vertical velocity and radiative cooling from soundings. We then explore the ability of a conceptual model to reproduce the dependence of the boundary layer thermodynamic budget on the large-scale environment and cast this conceptual model into a Bayesian framework to obtain joint posterior distributions of boundary layer thermodynamic properties.