1 dynamical polar warming amplification and a new climate feedback analysis framework ming cai...
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Dynamical Polar Warming Amplification and a New Climate
Feedback Analysis Framework
Ming Cai Florida State UniversityTallahassee, FL 32306
Cai (2005, GRL); Cai (2006, Climate Dynamics)Cai and Lu (2007, Climate Dynamics)Lu and Cai, and Cai and Lu (2008, Climate Dynamics)
2Obs
erve
d gl
obal
war
min
g pa
tter
n (N
CE
P R
2)
0.22 K/decade
1st EOF(30% var.)
Latitude
∆T(K)
Meridional Profile of global warming inIPCC AR4 Climate Simulations
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Questions
• Science: What are the roles of atmospheric motions (turbulences, convections, large-scale motions) for the spatial (vertical and horizontal) variations of the warming pattern? Specifically, can a change in the atmospheric circulation alone explain a larger warming in high latitudes?
• Technique: How do we incorporate atmospheric/oceanic dynamics in the climate feedback analysis?
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Coupled Atmosphere-Surface Climate Feedback-Response Analysis Method
(CFRAM) for CGCM feedback analysis
(Sv−R
uv)
net rad. cooling/heating1 2 3 +
Quvconv
+Quvturb
−Duvv
−Duvh
+Wuvu fric
non−radiative dyn. heating/cooling1 24 4 4 4 4 34 4 4 4 4 =0
ΔF ext + Δ(Sv
− Ruv
)
change in net rad. cooling/heating1 24 34 +
ΔQuvconv
+ ΔQuvturb
− ΔDuvv
− ΔDuvh
+ ΔWuvu fric
change in non−radiative dyn. heating/cooling1 24 4 4 4 4 44 34 4 4 4 4 4 4 = 0
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Mathematical formulation of CFRAM
∂Ruv
∂Tuv
⎛
⎝⎜⎞
⎠⎟ΔT
uvtot= {ΔF
uvext+ Δ(α )S
v+ Δ(c)(S
v− R
uv) + Δ(w)(S
v− R
uv)
radiative1 24 4 4 4 44 34 4 4 4 4 4
+ ΔQuvconv
+ ΔQuvturb
− ΔDuvv
− ΔDuvh
+ ΔWuvu fric
non−radiative1 24 4 4 4 4 44 34 4 4 4 4 4 4 }
The radiation flux change only due to a change in theatmosphere-surface column temperature
+=
Radiative energy input due to the external forcing
Energy flux perturbations that are not due to the radiation change associated with temperature changes
∂Ruv
∂Tuv
⎛
⎝⎜⎞
⎠⎟Planck feedback
matrix
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Planck Feedback Matrix
Positive along diagonal
Off-diagonals are negative and numerically are much smaller than diagonal
Not degenerated!!
Positive along diagonal
Off-diagonals are negative and numerically are much smaller than diagonal
Not degenerated!!
∂Ruv
∂Tuv
⎛
⎝⎜⎞
⎠⎟
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Mathematical formulation of CFRAM
ΔTuvtot
=∂R
uv
∂Tuv
⎛
⎝⎜⎞
⎠⎟
−1
{ΔFuvext
+ Δ(α )Sv
+ Δ(c)(Sv
− Ruv
) + Δ(w)(Sv
− Ruv
)
+ΔQuvconv
+ ΔQuvturb
− ΔDuvv
− ΔDuvh
+ ΔWuvu fric
}
ΔT
uv(n)=
∂Ruv
∂Tuv
⎛
⎝⎜⎞
⎠⎟
−1
ΔFuv(n)
ΔT
uvtot=
n∑ ΔT
uv(n)
RHS: external forcing plus energy flux perturbations due toeach of (thermodynamic, local, and non-local dyn. feedbacks
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Feedback Gain Matrices in CFRAM
ΔT
uvtot= GΔF
uvext= G0 (I + g(n)
n>0∑ )ΔFuvext
G0 =∂Ruv
∂Tuv
⎛
⎝⎜⎞
⎠⎟
−1
=r1,1 K r1,M+1
M O M
rM+1,1 L rM+1,M+1
⎛
⎝
⎜⎜⎜
⎞
⎠
⎟⎟⎟
g(n) =
g1,1(n) 0 L 0
0 g2,2(n) 0 M
M 0 O 0
0 L 0 gM+1,M+1(n)
⎛
⎝
⎜⎜⎜⎜⎜⎜
⎞
⎠
⎟⎟⎟⎟⎟⎟
gi,i(n) =
ri,mΔFm(n)
m=1
M+1∑
ri,mΔFmext
m=1
M+1∑
Feedback gain matrix
Initial gain matrix= inverseof the Planck feedback matrix
Both feedbacks and their effects are additive!
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Demonstration of the CFRAM in the context of a “dry” GCM without
hydrological cycle(manuscript in preparation)
The science question: Can the surface warming in response to anthropogenic greenhouse gases be still stronger in high latitudes than in low latitudes in the absence of ice-albedo and evaporation feedbacks in a dry GCM model?
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The key features of the coupled GCM model
Dynamical core: Suarez and Held (1992)Physics: • Fu et al. (1992)’s radiation model. • Dry convection adjustment so that maximum lapse
rate cannot exceed a preset meridional profile (6.5K/1km in tropics and 9.8K/1km outside).
• Atmospheric relative humidity is kept at a prescribed vertical and meridional profile.
• The surface energy balance model that exchanges sensible heat flux, emits long wave radiation out, and absorbs downward radiation at the surface.
• The annual mean solar forcing.• 1CO2 versus 2CO2 climate simulations
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Climatology of the dry GCM
E E
EW W
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2CO2 Climate forcing (w/m2) in the GCM
700 hPa
150 hPa (or “IPCC TOA”)
At the surface
At the model’s TOA
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(Total) Warming patternP
ress
ure
1.7 K
2.9 K 2.9 K2.1 K
0.9 K0.9 K
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2CO2 only
Partial ΔT due to 2CO2 & H2O
1.8 K
< 0 < 0
< 0
1.8 K
< 0 < 0
H2O change only
3.1 K
< 0 < 0
< 0
2CO2 + ΔH2O)
1.8 K
0.6 K0.6 K
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Partial ΔT due to dynamics
Vertical transport
2.8 K
0.9 K
Total dynamicalfeedback 1.0 K
2.0 K 2.0 KHorizontal transport
1.9 K 1.9 K
0.5 K 0.5 K
1.2 K
0 0
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Sum of partial ΔTs
2CO2 + ΔH2O)
Total dynamicalfeedback
1.0 K
2.0 K 2.0 K
3.1 K
< 0 < 0
< 0
Total change
1.7 K
2.9 K 2.9 K2.1 K
0.9 K0.9 K
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Summary• Radiative forcing of greenhouse gases (including water vapor) tend
to cause a stronger warming in low latitudes and weaker warming in high latitudes in atmos. and surf..
• Vertical convection reduces the surface warming in tropics • An enhanced poleward heat transport results in a “greenhouse-plus”
feedback (more back radiation from the air to the surface) => a large SURFACE warming in high latitudes than low-latitudes even without evaporation and ice-albedo feedbacks!
• The CFRAM allows us to explicitly isolate contributions to the global warming and its spatial pattern from external forcing alone and individual thermodynamic and dynamical feedback processes.
• Part of the total effects of individual thermodynamic and non-local dynamical feedbacks and the total effects of all local dynamical feedbacks are lumped into the lapse rate feedback in a TOA-based framework.
• CFRAM can be used identify the physical origins of climate projection uncertainties in IPCC AR4 models.
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In a realistic model with hydrological cycle:
• A much stronger reduction of the surface warming in tropics/subtropics due to the evaporation feedback (about 1-2 K warming reduction).
• Stronger moist convection in the deep tropics brings energy to further up => stronger poleward heat transport (including the latent heat transport) => a larger dynamical amplification of polar warming .
• Ice albedo feedback => further strengthens the polar warming amplification.
• Role of clouds? But the CFRAM can help to answer that question!
We expect: