GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

AM2 cloud sensitivity to details of convection and cloud paramerization – the GPCI case

Ming ZhaoGFDL / Princeton University

September 18-21, 2006Joint GCSS-GPCI / BLCL - RICO Workshop

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Outline

• AM2 cloud and convection parameterization

• Experiments

• Results

• Summary

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Tiedtke prognostic cloud scheme

radturbp

c

cond

l

t

T

t

T

c

gM

t

q

p

qgMqqgD

t

q lclcl

conv

l

,

microerosevapcondconv

t

q

t

q

t

q

t

q

t

q

dt

dq llllll

AM2 cloud and convection parameterization

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Relaxed Arakawa-Schubert (RAS) convection scheme

Cloud model: Ensemble entraining plumes with each entrainment rate calculated

so that it reaches a model level with neutral buoyancy

Non-entraining plumes

Tokioka entrainment rate limiter

Applying Tokioka limiter only to deep plumes above 500 hPa

Local modification of critical cloud work function

Closure: Relax plume cloud work function to specified critical values with

specified time-scale.

025.0,0 LCLz

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

UW shallow cumulus scheme (Bretherton et. al 2004)

Cloud model: Bulk entrainment-detrainment plume Buoyancy-sorting determination of entrainment/detrainment rate Explicit vertical momentum equation Cumulus cloud-top penetrative mixing

Closure: Cloud-base mass flux is determined by boundary layer TKE and

convective inhibition (CIN).

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Experiments (GPCI 1998)• CNTRL : AM2 default with FV dynamic core

• NOSHA: Same as CNTRL except disallowing RAS plumes below 500hPa

• NONON: Same as CNTRL except applying Tokioka to all RAS plumes (eliminating non-entraining plume)

• UWSCU: Same as NONON except applying UW-ShCu before RAS, and disallowing RAS plumes below UW-ShCu calculated convective depth H

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Results

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Liquid water path

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

SW absorption at TOA

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud fraction

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud liquid (g/kg)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud liquid water tendencies from convection (g/kg/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud liquid water tendencies from large-scale condensation (g/kg/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Large-scale/stratiform precipitation

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Specific humidity tendencies from convection (g/kg/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Relative humidity

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Convective mass flux (kg/m2/s)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

radturbp

c

cond

l

t

T

t

T

c

gM

t

q

NOGMC case

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

CNTRL vs. NOGMC

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

CNTRL vs NOGMC

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

SummaryTropical low cloud fraction and condensate are susceptible

to the detailed treatment of shallow convection. Weaker shallow convection leads to large increase of low clouds.

Budget analysis show that the increase of low clouds is due to increased large-scale condensation instead of convective detrainment.

Sensitivity study show that wetter lower troposphere and reduced compensating subsidence resulting from weaker shallow convection are two primary causes.

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

End

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Total precipitation

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud fraction tendencies from convection (1/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud fraction tendencies from large-scale formation (1/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud fraction tendencies from turbulent erosion (1/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud liquid tendencies from large-scale evaporation (g/kg/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud liquid tendencies from turbulent erosion (g/kg/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Cloud liquid tendencies from microphysics (g/kg/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Vertical pressure velocity (hPa/day)

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

SummaryTropical low cloud fraction and condensate are susceptible

to the detailed treatment of shallow convection. Weaker shallow convection leads to large increase of low clouds.

Budget analysis show that the increase of low clouds is due to large-scale condensation instead of convective detrainment.

Budget analysis and sensitivity study show that wetter lower troposphere and reduced compensating subsidence resulting from weaker shallow convection are two primary causes.

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

Sub-cloud layer TKE and cloud detrainment

Sub-cloud TKE 0''

TKE

wbt

TKEs

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q lululs

shcu

l

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2

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20

1

1

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unsats

MD

MD

DDD

Cloud detrainment luul

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uv,

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fraction of environmental air

virt

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saturated be tomixturesfor air

tenvironmen offraction maximum :

entrained be tomixturesfor air

t environmen offraction maximum :

flux massupdraft cloud :

ratet entrainmen : 0

s

c

uM

GFDL Geophysical Fluid Dynamics GFDL Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey

m500/sgm 2

gkg 8

s x105

1-2

1

-1-6

D

qq

K

vs

Steady state solution for the dominant balance

depend on entrainment rate

cloud liquid

cloud fraction

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steady state solution

-1-6 s x105K

depend on both entrainment rate and cloud-base mass flux / cloud work function

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