Do Observations Support Ideas Behind Common Mass Flux Closures?

The cloud-base mass flux closure is a critical component of convective parameterizations and usually consists of scalings for the cloud(-core) area fraction and vertical velocity. Here we evaluate if observations from the EUREC⁴A campaign support ideas behind two common closures. All closure parameters are diagnosed at the mesoscale from dropsonde data and turbulence measurements. The closure models are compared to the observed mass flux estimated as a residual of the sub-cloud layer mass budget from the same dropsonde arrays. Both closures capture the magnitude of the reference mass flux. However, the closure based on the surface-based convective velocity scale strongly underestimates mass flux variability, whereas the closure using a convective inhibition based area fraction and turbulence kinetic energy (TKE) based vertical velocity scale strongly overestimates it. TKE alone explains nearly 80% of mass flux variability, suggesting that TKE aggregates information of area fraction and vertical velocity of cloud-base updrafts.