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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: - PowerPoint PPT Presentation
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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)
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
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
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)
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
(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
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
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
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
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:
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)
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)
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)
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
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