is the system constrained?*+
TRANSCRIPT
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Is the Earth’s climate system constrained?*+
Graeme Stephens, Denis O’Brien, Peter Webster,Peter Pilewskie,Seiji
Kato,Juilin Li *Stephens et al., 2014;The albedo of Earth, Rev Geophys,+ Stephens and L’Ecuyer, 2014;The Earth's Energy Balance ¬ progress, surprises and challenges, J. Atmos Res., (in prep)
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I will address the following :• The energy balance of Earth is highly constrained and mostly by clouds
• That the symmetric energy balance is a fundamental expression of hemispheric thermodynamic steady state under the condition that X=0
• That models energy balance is not similarly constrained.
• Raise man questions including the so what?
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Data sources:CERES EBAF2.6rLoeb et al., 2009
CERES EBAFsurface fluxes,Kato et al., 2009
CloudSat/CALIPSO Geoprof
Stephens et al., 2102
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NH‐SH flux differences
Although the hemispheres are structurally different, the reflected flux is identical (~0.1Wm‐2) – VonderHaar and Suomi, 1969; Voigt et al., 2012; Stephens et al 2014
Mostly from greater aerosol amounts of NH
SH is cloudier
VonderHaar &Suomi, 1969
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Much of the clear‐sky differences (warmer NH) offset by higher (colder) NH cloud tops
NH‐SH
We see very clear evidence of cloud regulation of the hemispheric energy balances towards symmetry both in reflected sunlight and OLR
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2003-2010 Hemisphere Average
400 600 800 1000 1200 1400 1600Wavelength (nm)
0.0
0.1
0.2
0.3
0.4
Ref
lect
ance
NHSH
Is this accidental (Voigt et al., 2012)?
SCHIAMARCHY DATA
A little ore more anecdotal evidence
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Stephens & L’Ecuyer, 2014
Feb
August
Annualmean
39S 37N ?????
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In a balanced, steady stateN1+N2=0 (1)
where N1=S1‐L1 =Xand N2=S2‐L2=‐X In the special case of X=0 then L1=L2 otherwise a thermodynamic force is exerted to X≠ 0 and
N1=N2=0 (2)S1=S2 (3)
Current Earth conditions:NH, N1=‐0.04±0.06PW (ie X~0)SH N2=0.44±0.1PWSo one hemisphere is balanced, the other not and N1+N2 ≠ 0 (0.4PW or ~0.8Wm‐2)
XX
N1=S1‐L1 N2=S2‐L2
T2T1Eq NPSP
A symmetric balance is the balance of a steady unforced climate system with X=0.
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Earth system models?
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CMIP5 analysis
1) There is a general lack of hemispheric symmetry in models
2) The reasons for this vary – in some models the SH clouds are too bright, for others clouds aren’t bright enough & yet in others the surface is too bright
NH‐SH
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Key areas affected by monsoonal precipitation
Haywood et al., personal communication
mm/day
Precip biasHadGEM2‐ESminus GPCP
Precip change when hemispheric abedosare equilibrated
Bias ratioAlso Haywood et al., 2013Frierson & Huang, 2012Voigt et al., 2013
Wet season Precip
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Interannual variability of the global‐mean reflected flux ~0.2 Wm‐2
Local (1X1 degree) mean std deviation (deasonalized ~ 9 Wm‐2)
Variability is mostly from clouds and is highly regulated with connected regions of increase and decrease
(also Smith et al. 1990)
X
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CERES Variability Between 2000‐2010
Paltridge, 1978MEP hypothesis& Convection hypothesis
e.g. OBrien &Stephens,1993
(both in QJRMS),
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
CMIP5 Model Interannual variability
STD Wm
‐2In the mean, model interannualvariability is ~ 4 times the observed.
Does this matter??
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Summary:• Is the Earth’s Climate system constrained?
– The reflected energy from Earth is highly regulated & this regulation by clouds. The most dramatic example of this appears in hemispheric symmetry of reflected solar radiation
– Hemispheric OLR also appears regulated by clouds– The symmetry is not accidental?? but is a condition
required for a steady state with X=0 • If some overriding symmetric steady state
constraint exist, what is its significance?– synchronized planetary response to asynchronized
hemispheric or more local forcings (e.g solar, aerosol..).– Insight on global feedbacks (e.g clouds) ‐
fundamentally negative?• Are models similarly constrained?
– Models don’t have the same behavior as the observed Earth – they lack the same degree of regulation and symmetry. Does this really matter? It seems so.
Many unresolved questions remain
• Timescale?• CERES data
precision?• Is there a
fundamental theory for why X=0?
• How might we further test of steady state?
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Supporting material
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Each ‘box’ has five unknowns(i) Surface Temperature T(ii) Meridional flux by atmosphere and oceans, X=XO+XA(iii) Cloud cover θ(iv) Latent and sensible heat flux LE+HThe Paltridge system has no dynamics (OBrien & Stephens, 1993, QJRMS,)It is closed and solved using • Surface and TOA energy balance (T, θ, LE+H, surface albedo, cloud albedo ……)and introducing two hypotheses• The introduction of a Maximum Entropy Production (MEP) hypothesis • The introduction of a Convection Hypothesis (OBrien and Stephens, 1993)
The Paltridge Model
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• MEP – a constraint on X – X is chosen to maximize
MEP=
• Convection Hypothesis – for a given ratio XA & X0, the cloud cover is such as to maximize LE+H –constrains ratio XA/X0 and expresses LE+H in terms of T and cloud cover θ
• His solutionsA ‘remarkable’ result & even today (35 yrslater) MEP still has followers and conjures interest. But …..
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Constrained by linear and angular momentum
MEP constraint
Goody’s main point ‐ not all parts of the system come under the MEP constraint and thus MEP cant be a powerful global system constraint.
Perhaps the clearest analysis of the relevance of MEP to climate is that of Goody, 2004
Eddies
Mean (steady) meridional transport
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Suppose a steady state exists N1+N2=0; N1=X, N2=‐X
On some time scale, steady state requires
XX
N1=S1‐L1 N2=S2‐L2
T2T1
Eq NPSP
Suppose T1≠T2 then a thermodynamic force is produced driving a circulation between hemispheres
T
Fluxes of momentum and angular momentum across the equator must be zero implying the net mass flux is zero across the equator and the flux of heat too is zero (as observed). Thus
X=0 N1=N2=0 L1=L2 (T1=T2) S1=S2
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Unresolved questionsCMIP5 500 year controlUnchanged forcings, ….
CMIP5 historical ‐ time varying forcings
We can’t use present models to test ideas because they are neither balanced nor in steady state (eg as in control). The hemispheric differences of models (historical) exceed that observed.
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The (near) symmetry
1) The NH is balanced , the SH gains heat – ie the ocean uptake occurs in southern oceans
2) This slight imbalance occurs through a slight OLR asymmetry
3) Less obvious is the also near symmetry in meridionalheat transport
These are 11 year averages of the EBAF data
80-4004080et Flux (Wm
-2)
OLR
Abs solar
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Stephens & L’Ecuyer, 2014
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Interannual variability of the global‐mean reflected flux ~0.2 Wm‐2
Local (1X1 degree) mean std deviation (deasonalized ~ 9 Wm‐2)
Variability is mostly from clouds and is highly regulated