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A simple parameterization for detrainment in shallow cumulus Hirlam results for RICO

A simple parameterization for detrainment in shallow cumulus Hirlam results for RICO. Wim de Rooy & Pier Siebesma Royal Netherlands Meteorological Institute (KNMI). Hirlam 1D. Hirlam but with: Statistical cloud scheme Tiedtke mass flux convection scheme with updates:

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A simple parameterization for detrainment in shallow cumulus Hirlam results for RICO

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  1. A simple parameterization for detrainment in shallow cumulusHirlam results for RICO Wim de Rooy & Pier Siebesma Royal Netherlands Meteorological Institute (KNMI)

  2. Hirlam 1D Hirlam but with: • Statistical cloud scheme • Tiedtke mass flux convection scheme with updates: • Mass flux closure at cloud base (Neggers et al. 2002) • Triggering (Jacob & Siebesma 2003) • versions with a conventional or a new lateral mixing concept

  3. Fixed  and : • No dependence on environmental • humidity conditions Mass flux concept • Buoyancy sorting concept • Complex, fundamental problems M M M Courtesy: Stephan de Roode Fraction of environmental air

  4. Conventional fixed =z-1 and =0.00275 m-1 okay for BOMEX but for RICO? What’s going on?

  5. LES results for BOMEX, ARM and RICO show: • Not much variation in . For a correct simulation of the Mass flux profile, =z-1 is good enough. • Much more variation in . The value of  mainly depends on: - Cloud Layer Height - Environmental conditions

  6. Cloud Layer Height dependence Cloud ensembles Mass flux profiles with =z-1 and =0.00275 ztop Cloud layer depth=1000m z (e.g. BOMEX) zbot M ztop Cloud layer depth=200m zbot M ztop Cloud layer depth=2000m e.g. RICO z zbot M

  7. Dependence on environmental conditions Eliminate cloud height dependence by looking at a non-dimensionalized mass flux profile LES Non-dimensionalized mass flux profiles ARM case LES z*

  8. Suppose we would know the non-dimensionless mass flux m* halfway the cloud layer at height z* Ztop Z* Zbot

  9. From LES, the non-dimensionalized mass flux half way the cloud layer as a function of c

  10. Good results with the new parameterization for ARM, BOMEX and:

  11. Conclusions • The proposed detrainment parameterization is simple but includes two important dependencies: • Cloud layer height dependence • Current mass flux schemes ignore this dependence which evidently can lead to large discrepancies with observed mass flux profiles. • Environmental conditions • With the c dependence the new scheme can be seen as an alternative for more complex buoyancy sorting schemes (without some of the disadvantages)

  12. Conclusions • Good results for a wide range of shallow convection cases (BOMEX, ARM, RICO) • Easy to incorporate in existing mass flux schemes (and will be incorporated in an EDMF dual mass flux environment)

  13. LES: The non-dimensionalized mass flux half way the cloud layer as a function of RH

  14. Dependence on environmental conditions Eliminate cloud height dependence by looking at a non-dimensionalized mass flux profile LES Non-dimensionalized mass flux profiles ARM case Non-dimensionalized mass flux profiles with fixed  and 

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