Dutch Atmospheric Large-Eddy Simulation Model (DALES v3.2) CGILS-S11 results

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1 Dutch Atmospheric Large-Eddy Simulation Model (DALES v3.2) CGILS-S11 results Stephan de Roode Delft University of Technology (TUD), Delft, Netherlands Mixed-layer model analysis: Melchior van Wessem (student, TUD) DALES development: Thijs Heus (MPI-Hamburg, Germany) Chiel van Heerwaarden (Un. Wageningen, Netherlands) Steef Boing (Delft University of Technology) McICA code: Robert Pincus (NOAA) Bjorn Stevens (MPI-Hamburg) Many thanks to the CGILS-LES group for helpful suggestions!

2 Dutch Atmospheric Large-Eddy Simulation Model (DALES v3.2) Open source code (GIT) KNMI, University of Wageningen, Delft Technical University of Technology (Thijs Heus: MPI-Hamburg) Benefits to users: Additions of new physics routines McICA Radiation: Pincus and Stevens 29, implemented by Thijs Heus CGILS-radiation scheme close to be fully operational in DALES v3.2 Coupled Surface Energy Balance model: van Heerwaarden, Wageningen University However, it requires a lot of dedication to keep up with the modifications increase in the number of switches

3 CGILS Simulation details Simulation time 1 days adaptive time step, dtmax = 1 secs radiation time step = 6 secs Domain size 4.8 x 4.8 x 4 km 3, 96 x 96 x 128 grid points (Δz = 25 m in lower part) Total CPU hours on 32 processors 27 hours

4 CGILS Inversion height z inv t = w e + w subs ( z = z inv )

5 CGILS Cloud liquid water path (LWP)

6 CGILS Cloud cover

7 more evaporation Turbulent Surface Fluxes

8 Top Of Atmosphere Net Radiative Fluxes

9 CGILS Hourly-averaged vertical mean profiles during the last 5 hours

10 CGILS Hourly-averaged turbulent fluxes during the last 5 hours

11 Steady state solutions Example: longwave radiative cooling at cloud top w e Δθ L ΔF /( ρc p ) Steady state θ L t = z/z i Requires constant flux wθ L z = <wθ l > (mk/s)

12 Steady state solutions Example: no precipitation w e Δq T Steady state q T t = z/z i Requires constant flux wq T z = <wq t > (m/s)

13 z/z i w e Δθ L ΔF /( ρc p ) Steady state solutions: <w θ v > <wθ > (mk/s) l 1.2 z/z i wθ L +11 wq T 1.8 w e Δq T.4.2 wθ L +18 wq T z/z i <wq > (m/s) t <wθ v > (mk/s) no decoupling

14 Steady state solutions Example: longwave radiative cooling large-scale horizontal advection 1.2 w e Δθ L 1 z/z i ΔF /( ρc p ) turbulent flux divergence balances advective cooling wθ L z = U θ L z large scale <wθ l > (mk/s)

15 w e Δθ L ΔF /( ρc p ) Steady state solutions: <w θ v > z/z i.6 z/z i <wθ > (mk/s) l w e Δq T z/z i <wθ v > (mk/s).5 wθ L +11 wq T wθ L +18 wq T <wq t > (m/s)

16 Steady state solutions & decoupling No decoupling (#) if wθ V > at cloud base height z base So wθ L z base > B d A d wq T zbase Flux divergence: wθ L z = wθ L wθ z L base < z base B d A d wq T z base + wθ L z base (#) This is a weak criterion. In fact, the flux can be slightly negative without the BL getting decoupled

17 Steady state solutions & decoupling Steady state if wθ L z = B d A d wq T z base + wθ L z base = U θ L x large scale

18 Steady state solutions & decoupling Steady state if wθ L z = B d A d wq T z base + wθ L z base = U θ L x large scale 15 height where <wθ v >= 1 5 CGILS Large-scale advection (K/h)

19 Steady state solutions & decoupling Decoupling due to large-scale advection alone not very likely However, two other processes cause steeper <w θ v > gradients In the subcloud layer: evaporation of drizzle longwave radiative cooling

20 CGILS: Inversion jumps (after 1 days) 2 ASTEX -2 Δq t [g/kg] -4-6 buoyancy reversal criterion ** S11 CTL P2K EUROCS -8 DYCOMS II Δ θ l [K]

21 Mixed-layer model BL mean ψ ML t entrainment flux ( ) = w e ψ FA ψ ML surface flux c D U ML ψ ψ ML + ΔS ψ z i ( ) source/sink θ L,FA q T,FA z/z inv.6 z/z inv.6 q T,ML.4 θ L,ML q T, θ L, liq. wat. pot. temp. θ L (K) total water content q T (g/kg)

22 Mixed-layer model BL mean ψ ML t entrainment flux ( ) = w e ψ FA ψ ML surface flux c D U ML ψ ψ ML + ΔS ψ z i ( ) source/sink z inv t = w e + w subs = w e Dz i

23 Mixed-layer model BL mean ψ ML t entrainment flux ( ) = w e ψ FA ψ ML surface flux c D U ML ψ ψ ML + ΔS ψ z i ( ) source/sink z inv t = w e + w subs = w e Dz i Closure (#) : w e = A ΔF rad θ L,FA θ L,ML (#) This closure is inspired by Moeng (2). Other closures need humidity jumps, cloud base height etc.

24 Mixed-layer model BL mean ψ ML t entrainment flux ( ) = w e ψ FA ψ ML surface flux c D U ML ψ ψ ML + ΔS ψ z i ( ) source/sink z inv t = w e + w subs = w e Dz i Closure: w e = A ΔF rad θ L,FA θ L,ML Upper BC: θ L,FA ( z) = θ L, + Γ θ z q T,FA = q T, + Δq T

25 Mixed-layer model solutions z inv t = w e + w subs = w e Dz i Closure: w e = A ΔF rad θ L,FA θ L,ML Approximation: (surface jump much smaller than inversion jump) θ L, θ L,ML << Γ θ z i Equilibrium height for the boundary layer z i = AΔF rad DΓ θ

26 CGILS Conclusions S11 goes to an equilibrium state Longwave radiative cooling, entrainment warming and large-scale advection Evaporation, entrainment drying, and large-scale advection Radiation in a future climate Hardly any change in radiation at top of the atmosphere if SST + 2K Outlook Do shallow cumulus and stratus runs Check influence advection scheme