Continuous treatment of convection: from dry thermals to deep precipitating convection J.F. Guérémy CNRM/GMGEC

The association of turbulence and convection schemes have to represent sub-grid convective processes with and without condensation, the turbulence scheme (K-diffusion) dealing with horizontally quasi-homogeneous processes (having a rather weak vertical extension), and the convection scheme (mass-flux) dealing with horizontally heterogeneous processes (having a larger vertical extension).  Aim: to go beyond version 4 of ARPEGE-Climat, trying to achieve a better association of the two schemes, and improving them at the same time.

Process representation: The turbulence scheme - represents turbulence with and without condensation until shallow convection, taking into account an overestimated PBL mixing length. The convection scheme - represents convection with condensation and precipitations (all condensed water), while cancelling the sub-grid transport produced by the turbulence scheme. The turbulence scheme - represents turbulence with and without condensation until very shallow convection (cumulus humilissimus, 1 layer). The convection scheme - represents convection with and without condensation (PBL dry thermals), precipitating or not. The time tendencies of both schemes are added. Version 4:Version 4+:

- Version 4: - Turbulence: Ricard-Royer 1993, TKE (production= dissipation, Mellor-Yamada 1982), turbulent sub-grid scale cloud scheme (Deardorff, Mellor 1977), without prognostic condensate; precipitations (Smith 1990). - Convection: Bougeault 1985, mass flux. - Version 4 +: - Turbulence: Ricard-Royer 1993 modified by Guérémy- Grenier 2005 (mixing length and top PBL entrainment), TKE (production= dissipation, Mellor-Yamada 1982), turbulent sub-grid scale cloud scheme (Deardorff, Mellor 1977), with prognostic condensate; precipitations (Smith 1990). - Convection: Guérémy 2005, mass flux; precipitations (Smith 1990). Schemes:

- Version 5: Process representation: Idem version 4+ Schemes: - Turbulence: Cuxart-Bougeault-Redelsperger 2000, pronostic TKE, turbulent sub-grid scale cloud sheme (Deardorff, Mellor 1977), with prognostic condensate; precipitations (Lopez 2002). - Convection: Guérémy 2005, mass flux; precipitations (Smith 1990).

Convection scheme Key elements for a continuous treatment of convection: compensating subsidence term and detrainment term, M mass flux - Cloud Profile: Dry adiabat until the lifting condensation level, then moist adiabat, including entrainment process. - Mass flux formulation: Product of the grid fraction affected by convective ascents (equal to the bottom quantity  -to be determined by the closure condition- times a height decreasing function  -computed from the convective cloud mass budget-) by the convective vertical velocity - prognostic equation-.

- Entrainment and detrainment : Organised entrainment and detrainment: Internal computation from the convective cloud mass budget, including a statistical model based upon the concept of buoyancy sorting. Turbulent entrainment and detrainment: Analytical profile depending on the convective vertical velocity (large entrainment for a weak ascent and vice versa). - Closure condition: CAPE relaxation to zero, according to a characteristic time proportional to the ratio of the convective depth to the mean convective vertical velocity. - Convective precipitation: Precipitation is computed with Smith’s scheme (such as the stratiform precipitation)

Results Validation strategy: Validation starts with 1D simulations of different types of convective situations corresponding to well documented cases (observations and explicit simulations), in order to represent processes at best possible. [EUROCS strategy] The tuned schemes are then assessed in 3D (annual cycles), giving possibly rise to a new set of tuned parameters; this new version is finally tested in 1D to close the cycle.

Bomex Case: Non precipitating shallow convection V4 V4+

V4V4+

Cloudiness 7h-16hMass flux 7h-16h

Q1 7h-16hQ2 7h-16h

Theta 16h Humidity 16h

Entrainment-detrainment 7h-16h

Idealised ARM case: diurnal cycle of continental convection: from dry PBL to deep precipitating convection

Q1 and Q2 averaged above the PBL (between 800 and 100 hPa)

Prospects RICO 1D case, notably with ARPEGE-Climat Version5 physics Validation in 3D LAM (ALADIN-Climat) on documented cases (observations and CRM simulations), as an intermediate step between traditional 1D and 3D assessments. Intensifying 3D global validation (transects, coupled simulation, seasonal forecasts, …)