1. The role of the mean relative humidity on the dynamics of shallow cumuli - LES Sensitivity experiments Stephan de Roode (KNMI/IMAU) Simon Axelsen (IMAU) Pier Siebesma (KNMI)

2. Large-eddy simulation - The BOMEX shallow cumulus case BOMEXExp 1,2,3,4 Km/s0.008 (g/kg)m/s0.052

3. LES sensitivity experiments - Set-up analogous to Derbyshire's EUROCS deep convection case  q  g/kg  BOMEX Exp 10.04-0.2 Exp 20.07-0.4 Exp 3-0.070.4 Exp 4-0.130.7

4. Results for cloud core : mass flux All averages taken over the 3rd hour

5. Results for cloud core : vertical velocity and core fraction

6. Mixed parcel diagram - Buoyancy reversal

7. Buoyancy reversal - Dependency on mean vertical gradients  0.0 1.0

8.  and fractional entrainment rate. Diagnosis from LES results.

9. Kain & Fritsch parameterization- Assume flat PDF for   =  0   2 (Bretherton et al. 2004)

10. Bowen ratio, convective velocity scale w * and mass-flux w'  ' 0 x 1000 [Km/s] w'q' v0  x 10 -5 [m/s] BOMEX8.05.2 Exp 19.94.2 Exp 213.62.1 Exp 36.16.2 Exp 44.27.3

11. Bowen ratio, convective velocity scale w * and mass-flux

12. Conclusions Set I - Change relative humidity, but keep mean buoyance the same Cloud fraction changes => Mass flux changes Set II - Change Bowen ratio, but keep surface buoyancy flux the same Cloud fraction changes => Mass flux changes (also at cloud base)

13. Results for cloud core : fractional entrainment and detrainment

14.  * from LES