a simple parameterization for detrainment in shallow cumulus hirlam results for rico
DESCRIPTION
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: - PowerPoint PPT PresentationTRANSCRIPT
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A simple parameterization for detrainment in shallow cumulus
Hirlam results for RICO
Wim de Rooy & Pier SiebesmaRoyal Netherlands Meteorological Institute (KNMI)
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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
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Mass flux concept
MM M
•Fixed and :No dependence on environmental
humidity conditions
•Buoyancy sorting conceptComplex, fundamental problems
Fraction of environmental air
z
MM
c
c
1Courtesy: Stephan de Roode
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Conventional fixed =z-1 and =0.00275 m-1 okay for BOMEX but for RICO?
What’s going on?
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
4 6 8 10 12 14 16
RICO (LES and SCM, No Rain)
qt [gr/kg]
z [m
] LES no rain (24:00 UTC) fixed and (24:00 UTC) inital profile (0:00 UTC)
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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
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(e.g. BOMEX)
Cloud layer depth=1000m
Mass flux profiles with =z-1 and =0.00275
Cloud layer depth=200m
Cloud layer depth=2000me.g. RICO
Cloud ensembles
z
M
M
M
z
zbot
ztop
ztop
ztop
zbot
zbot
Cloud Layer Height dependence
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LES Non-dimensionalized mass flux profiles
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0ARM LES
(z
-zbo
t)/(z
top-
z bot)
M/Mb
17:30 UTC 18:30 UTC 19:30 UTC 20:30 UTC 21:30 UTC 22:30 UTC 23:30 UTC 24:30 UTCz*
ARM case LES
Eliminate cloud height dependence by looking at a non-dimensionalized mass flux profile
Dependence on environmental conditions
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Suppose we would know the non-dimensionless mass flux m* halfway the cloud layer at height z*
Mz
Mcz
mM
M(z :zz atbot
**
)(
)
1
*
)(
)ln(
*
*
*
bot
bot
zzmz
z
Z*
Zbot
Ztop
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0.00 0.03 0.06 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30 0.330.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
m*
mean c
m* RICO m* Bomex m* ARM
From LES, the non-dimensionalized mass flux half way the cloud layer as a function of c
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0
250
500
750
1000
1250
1500
1750
2000
2250
2500
4 6 8 10 12 14 16
RICO (LES and SCM, No Rain)
qt [gr/kg]
z [m
]
LES (24:00 UTC) fixed and (24:00 UTC) new (24:00 UTC) initial profile (0:00 UTC)
Good results with the new parameterization for ARM, BOMEX and:
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0
250
500
750
1000
1250
1500
1750
2000
2250
2500
2 4 6 8 10 12 14 16 18
RICO (LES with and without rain, SCM with Rain)
qt [gr/kg]
z [m
]
LES with Rain (24:00 UTC) new (24:00 UTC) fixed and (24:00 UTC) LES no rain (24:00 UTC)
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ConclusionsThe proposed detrainment parameterization is simple but includes two important dependencies:
•Cloud layer height dependenceCurrent mass flux schemes ignore this dependence which evidently can lead to large discrepancies with observed mass flux profiles.
•Environmental conditionsWith the c dependence the new scheme can be seen as an alternative for more complex buoyancy sorting schemes (without some of the disadvantages)
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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)
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45 50 55 60 65 70 75 80 850.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
m*
Relative humidity [%]
m* RICO m* Bomex m* ARM
LES: The non-dimensionalized mass flux half way the cloud layer as a function of RH
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LES Non-dimensionalized
mass flux profilesNon-dimensionalized mass
flux profiles with fixed and
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0ARM LES
(z-z
bot)/
(zto
p-z
bot)
M/Mb
17:30 UTC 18:30 UTC 19:30 UTC 20:30 UTC 21:30 UTC 22:30 UTC 23:30 UTC 24:30 UTC
ARM case
Eliminate cloud height dependence by looking at a non-dimensionalized mass flux profile
Dependence on environmental conditions