Toward improvement of GCM’s
cloud feedback through the
comparative analysis with
global cloud resolving model
NICAM
Yoko Tsushima1, Shin-ichi Iga1, Hirofumi Tomita1
and Masaki Satoh1,2
1 JAMSTEC/Frontier Research Center for Global
Change
2 Center for Climate System Research
Models and their settings for perpetual July and +2K simulations
NICAM
•
Dynamics
– Finite Volume Method
– Grid Horizontal: Icosahedral,
Vertical: Lorenz
– Topography Terrain following
coordinate
– Non-hydrostatic elastic system
with deep atmosphere
• Physics
– Turbulence & surface process
Mellor&Yamada 2 / Louis(1979)
– Radiation MSTRNX ( Sekiguchi,
2005 )
– Microphysics Grabowski(1998)
• Cloud liquid, rain, cloud ice,
snow
– Land-surface Buckets
Settings
• Spatial resolution: g-level9 (14km)Z40
• Integration 200 days. Last 30 days for
the analysis.
MIROC (CCSR/NIES/FRCGC GCM)
• Dynamics
– Spectral dynamics
– σ vertical coordinate
– Grid advection for tracers (FFSL)
3.8K
Climate sensitivity
•
– Prognostic Arakawa-Schubert cumulus
+ Prognostic cloud water for layer cloud
Physics
– Turbulence & surface process:
Mellor&Yamada 2
– Radiation MSTRN8 (Nakajima et
al.2000)
– Microphysics Direct and indirect
radiative effects of aerosols (for cloud
riquid) (dust / sea salt / sulfate / carbon)
Takamura et al.(2001)
• Cloud liquid, cloud ice
– Land-surface MATSIRO (vegetation
canopy + 3-layer snow + 5-layer soil)
Settings
• Spatial resolution: T42l20
• Integration: 240days. Last 120 days for the
analysis.
Changes in ISCCP-simulator
clouds
ISCCP cloud classification
50
CIRRUS
CIRROSTRATUS
DEEP
CONVECTION
440
560
680
clouds
310
ALTOCUMULUS
ALTOSTRATUS
NIMBOSTRATUS
CUMULUS
STRATOCUMULUS
STRATUS
800
LOW
1000
0
HIGH
MIDDLE
Invisible
CLOUD TOP PRESSURE (MB)
180
0.3
1.3
3.6
9.4
23
CLOUD OPTICAL THICKNESS
60
379
Changes in ISCCP-simulator cloud cover
NICAM
MIROC
High
High
Mid
Mid
Low
Low
Changes in condensates
NICAM
Liquid
Cloud liquid + rain
solid
Cloud ice + snow
MIROC
Cloud liquid
Cloud ice
Changes in high clouds
NICAM
High-Thin
High-Medium
High-Thick
High-Medium
High-Thick
MIROC
High-Thin
Changes in deep convective clouds
NICAM
MIROC
“High-invisible” clouds and high clouds
NICAM
High-invisible
MIROC
High-invisible
High
High
The changes in global mean ISCCP clouds
NICAM
CIRRUS
CIRRO
STRATUS
DEEP
CONVECTIO
N
ALTO
CUMULUS
ALTOSTRAT
US
NIMB
STRATUS
CUMULUS
STRATO
CUMULUS
STRATUS
CFMIP comparison
Perpetual July +2K & 2xCO2 experiments
Ringer et al.,2006
MIROC
CIRRUS
CIRRO
STRATUS
DEEP
CONVECTIO
N
ALTO
CUMULUS
ALTOSTRAT
US
NIMB
STRATUS
CUMULUS
STRATO
CUMULUS
STRATUS
Changes in radiative fluxes
PDFs of OLR in the control and
+2K simulations
+2K
CTL
Fig.4 cloud radiative forcing (+2K-ctl)
SW cloud forcing change
LW cloud forcing change
NICAM
MIROC
90S 60S 30S EQ 30N 60N 90N
90N 60N 30N EQ 30S 60S 90S
Hypotheses of radiative feedback
by high clouds
• Lindzen, 1990. Drier air over the subtropics by
deeper convection in the tropics.
• Ramanathan and Collins,1987. Anvils get thicker
with temperature increase.(Thermostat effect:
negative feedback)
• Lindzen et al.,2001. Detrainment of cirrus from
deep convetion decreases with the temperature
increase. (Adaptive Iris: negative feedback)
Hypotheses of radiative feedback
by high clouds
• Lindzen, 1990. Drier air over the subtropics by
deeper convection in the tropics.
• Ramanathan and Collins,1987. Anvils get thicker
with temperature increase.(Thermostat effect:
negative feedback)
• Lindzen et al.,2001. Detrainment of cirrus from
deep convetion decreases with the temperature
increase. (Adaptive Iris: negative feedback)
• This study: High thin cirrus cover the whole
tropics and the subtropics (like blanket: positive
feedback)
Are these results good news or bad
news?
• The dominant cloud feedback in climate sensitivity
study using the current version of NICAM is the
strong positive feedback in LW, which is quite
different from the results from CFMIP GCMs.
• These results indicates the uncertainty in the
response of high level clouds which is recognized
but not shown by the current GCMs. (Convection,
cloud microphysics are different.)
• New satellite data is promising.
– Information for “ISCCP Invisible” clouds also may be useful.
We hope our results contribute to understand,
hopefully reduce the uncertainty in cloud feedbacks
in climate change simulations.