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Stephan de Roode (KNMI/IMAU) Simon Axelsen (IMAU) Pier Siebesma (KNMI)

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). Large-eddy simulation - The BOMEX shallow cumulus case.

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Stephan de Roode (KNMI/IMAU) Simon Axelsen (IMAU) Pier Siebesma (KNMI)

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  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

  3. LES sensitivity experiments - Set-up analogous to Derbyshire's EUROCS deep convection case

  4. Results for cloud core : mass fluxAll 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 G 1.0 0.0

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

  9. Kain & Fritsch parameterization- Assume flat PDF for ce = e02 (Bretherton et al. 2004)

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

  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. c* from LES

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