GFS SAS-based Mass-Flux Scheme for Shallow convection (sa-MF)

GFS saSAS Shallow Convection Module is an updated version of the previous mass-flux shallow convection scheme with scale and aerosol awareness and parameterizes the effect of shallow convection on the environment. GFS saSAS Shallow Convection Module is similar to GFS saSAS Deep Convection Module but with a few key differences. First, no quasi-equilibrium assumption is used for any grid size and the shallow cloud base mass flux is parameterized using a mean updraft velocity. Further, there are no convective downdrafts, the entrainment rate is greater than for deep convection, and the shallow convection is limited to not extend over the level where \(p=0.7p_{sfc}\). The paramerization of scale and aerosol awareness follows that of the SAMF deep convection scheme, although it can be interpreted as only having the "static" and "feedback" control portions, since the "dynamic" control is not necessary to find the cloud base mass flux.

The previous version of the shallow convection scheme (shalcnv.f) is described in Han and Pan (2011) [78] and differences between the shallow and deep convection schemes are presented in Han and Pan (2011) [78] and Han et al. (2017) [80] . Details of scale- and aerosol-aware parameterizations are described in Han et al. (2017) [80] .

In further update for FY19 GFS implementation, interaction with turbulent kinetic energy (TKE), which is a prognostic variable used in a scale-aware TKE-based moist EDMF vertical turbulent mixing scheme, is included. Entrainment rates in updrafts are proportional to sub-cloud mean TKE. TKE is transported by cumulus convection. TKE contribution from cumulus convection is deduced from cumulus mass flux. On the other hand, tracers such as ozone and aerosol are also transported by cumulus convection.

To reduce too much convective cooling at the cloud top, the convection schemes have been modified for the rain conversion rate, entrainment and detrainment rates, overshooting layers, and maximum allowable cloudbase mass flux (as of June 2018).