Evaluation of mass flux closures using EUREC4A observations

Determining the shallow-convective mass flux at cloud base is the principle closure needed in convective parameterizations. Closure methods are usually developed and tested based on large-eddy simulations of a limited number of idealized cases. Here we evaluate how well common closures reproduce the magnitude and variability of the cloud-base mass flux observed during the recent EUREC⁴A field campaign upstream Barbados. The true observed mass flux is estimated as a residual of the sub-cloud layer mass budget from the circular dropsonde arrays at the 200km scale. To assess the closures, we diagnose all parameters of the chosen closures from the same dropsonde data or from coincident turbulence and cloud measurements of a second aircraft. Preliminary results suggest that (i) both variability in the area fraction and vertical velocity scales should be accounted for to reproduce the observed mass flux variability, (ii) methods using the turbulence kinetic energy to approximate the vertical velocity scale outperform methods based on the subcloud convective velocity scale, and (iii) the closure formulations should be general enough to remain useful when applied to other data and regimes.