am2 cloud sensitivity to details of convection and cloud paramerization – the gpci case

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


Outline

• AM2 cloud and convection parameterization

• Experiments

• Results

• Summary


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


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


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).


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


Results


Liquid water path


SW absorption at TOA


Cloud fraction


Cloud liquid (g/kg)


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


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


Large-scale/stratiform precipitation


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


Relative humidity


Convective mass flux (kg/m2/s)


radturbp

c

cond

l

t

T

t

T

c

gM

t

q

NOGMC case


CNTRL vs. NOGMC


CNTRL vs NOGMC


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.


End


Total precipitation


Cloud fraction tendencies from convection (1/day)


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


Cloud fraction tendencies from turbulent erosion (1/day)


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


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


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


Vertical pressure velocity (hPa/day)


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.


Sub-cloud layer TKE and cloud detrainment

Sub-cloud TKE 0''

TKE

wbt

TKEs

s360

p

qgMqqgD

t

q lululs

shcu

l

,

2

0

20

1

1

suunsat

cu

unsats

MD

MD

DDD

Cloud detrainment luul

shcu

l qPt

q

t

q

,

sc0 1

uv,

v

0

fraction of environmental air

virt

ual p

oten

tial t

empe

ratu

re

saturated be tomixturesfor air

tenvironmen offraction maximum :

entrained be tomixturesfor air

t environmen offraction maximum :

flux massupdraft cloud :

ratet entrainmen : 0

s

c

uM


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

l

lcll Kq

qqDt

q

)( ,

a

aa Kq

qDt

q

)1(

vsa

l

qqq

q

cl

vs

cll

DqqqK

qq

,

,

)(1

steady state solution

-1-6 s x105K

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

cl

vsa

DqqqK

q

,

)(1

1

am2 cloud sensitivity to details of convection and cloud paramerization – the gpci case

Documents