Non-precipitating cumulus convection and its parameterization

Abstract

SUMMARYThis paper discusses the thermodynamic transports of heat, liquid water and (briefly) water vapour by non-precipitating cumulus convection. It is shown that because of the irreversible mixing between cloud and environment, there is a downward transport of enthalpy in the cumulus layer. A lapse-rate adjustment model relates stratification to the life-cycle of a model cloud parcel. A sub-cloud layer model specifies the lower boundary of the lapse-rate model, and the convective transports through cloud-base. Budget equations together with the lapse-rate model, and its time dependent boundary conditions, predict the time development of the cumulus layer, and show the dependence on large-scale mean vertical motion, cloud-base variations, and the surface sensible heat flux.LIST OF SYMBOLS temperature potential temperature equivalent potential temperature saturation equivalent potential temperature liquid water potential temperature (defined in Section 2) flux of p c p 0 3 8p2 3 8/32 for wet adiabat entropy change total moist air pressure partial pressure of dry air height co-ordinate time air density total water mixing ratio saturation vapour mixing ratio liquid water mixing ratio = rs/l + 7 = 7~/ 1

Effects of explicit convection on global land‐atmosphere coupling in the superparameterized CAM

“…That is, high evaporation is associated with shallow PBL and high moist static energy (MSE). It is more efficient to lower the LCL than the PBL top, and leads to cumulus mass flux generation [Betts, 1973;Gentine et al, 2013a,b]. Superparameterization alters the rainfall frequency and intensity [Kooperman et al, 2016], and impacts the coupling strength defined by TFS and AFS by altering quantifications of afternoon rainfall and morning EF (through changing the soil moisture state and the coupling strength in the terrestrial segment).…”

Unified treatment of dry convective and stratocumulus‐topped boundary layers in the ECMWF model

“…This is done with an entraining/detraining bulk plume model for the variables φ = {s l , q t } (e.g. Betts, 1973) and updraught kinetic energy w u2 /2 (Simpson and Wiggert, 1969):…”

The onset of precipitation in warm cumulus clouds: An observational case‐study

“…The mean environmental values of θ l and θ v (black dots) are averaged over a distance of about 1 to 2 km on both sides of the cloud. The liquid water potential temperature θ l , like the total water content q t , is conserved during adiabatic ascent of a non-precipitating convective cell and it mixes linearly when environmental air is entrained into the cloud (Betts, 1973). A trend of the cloud values towards the environmental ones therefore reflects cloud mixing with its environment, as long as the cloud water does not precipitate.…”