A simple parameterization for detrainment in shallow cumulus hirlam results for rico
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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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A simple parameterization for detrainment in shallow cumulus hirlam results for rico

A simple parameterization for detrainment in shallow cumulusHirlam results for RICO

Wim de Rooy & Pier Siebesma

Royal Netherlands Meteorological Institute (KNMI)


Hirlam 1d

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


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

  • 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


Conventional fixed z 1 and 0 00275 m 1 okay for bomex but for rico

Conventional fixed =z-1 and =0.00275 m-1 okay for BOMEX but for RICO?

What’s going on?


Les results for bomex arm and rico show

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


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

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


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

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*


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

Suppose we would know the non-dimensionless mass flux m* halfway the cloud layer at height z*

Ztop

Z*

Zbot


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

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


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

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


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

  • 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)


Conclusions

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)


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

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


A simple parameterization for detrainment in shallow cumulus hirlam results for rico

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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