Alan Robock Department of Environmental Sciences Rutgers University, New Brunswick, New Jersey USA

Alan RobockDepartment of Environmental Sciences

Rutgers University, New Brunswick, New Jersey USA

[email protected]

http://envsci.rutgers.edu/~robock

Climate Dynamics11:670:461

Lecture 15, 10/28/13



Alan RobockDepartment of Environmental

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Evolution of processes included in state-of-the-art climate models

FAR: First IPCC Assessment ReportSAR: Second ReportTAR: Third ReportAR4: Fourth Report

IPCC AR4, Chapter 1


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IPCC AR4, Chapter 1


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General Circulation Models (GCMs) 1

Basic Physical Laws:

Conservation of energy (First law of thermodynamics)Conservation of momentum (Newton’s second law of

motion)Conservation of mass (Continuity equation)Conservation of moistureHydrostatic equilibriumGas law


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General Circulation Models (GCMs) 2Physical Processes That Must or Can Be Included:

Wind Sea iceRadiation SnowPrecipitation GlaciersSoil moisture VegetationGround water Ocean biotaAerosolsClouds, convective and large-scaleAir-sea exchanges of moisture, energy, and momentumAir-land exchanges of moisture, energy, and momentumChemistry, particularly O3 and CO2

Ocean temperature, salinity, and currents


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Real World vs. Model World


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H o w to C o ns tru c t a C lim a te M o d el

P ro g ram a tico b je ctives M a na ge m e nt

d irec t ives

P re v io uskn o w le d ge

In te rp re ta tiono f o b serva tio ns

C o m p ute r co ded e ve lop m e nt

R e aso na b lea ssum ptio ns

F u rth eru n de rsta nd ing

F u rthe r re fin em en t o fim p orta n t d e ta ils

P u b lica tion

A g re e m e n tb e tw e en the o ry

a n d o bs e rva tio ns

C o m p u ter m od e l resu lts

S o p h is tica tedco m p u ter m o d e l

T h e o re t ic a lu n de rsta nd ing

R e gu la r a ndfreq ue nt

o b serv a tio ns

Theory of Climate Model Development How to Construct a Climate Model

Programmaticobjectives

Management directives

Preconceivednotions

Incorrect interpretationof observations

Codeerrors

Unrealisticassumptions

Furthermisunderstanding

Further refinement ofunimportant details

Publication

Coincidental agreementbetween theory

and observations

Confusion

Sophisticatedcomputer model

Theoreticalmisunderstanding

Sparse andinfrequent

observations

Actual Climate Model Development


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Typical grid spacing of a GCM is now 1° x 1° latitude-longitude by 1 km in the vertical.Each time the horizontal resolution is increased by a factor of 2, the time needed to run the model goes up by a factor of 8.When the vertical resolution is doubled the time required doubles in general, but can go up by more, if winds become faster.


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To include all the processes in a climate model which are of a scale smaller than is resolved by the model, they must be “parameterized.”One of the most important and difficult climate elements to parameterize is cloudiness. Clouds have a much smaller spatial and temporal scale than a typical GCM grid box.Usually, we consider separately 2 types of clouds, layer clouds and convective clouds. There is no fundamental prognostic equation for clouds (no conservation of clouds principle); rather they form when condensation takes place and dissipate due to precipitation and evaporation.


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Rows and flows of angel hairAnd ice cream castles in the airAnd feather canyons everywhere;I’ve looked at clouds that way.

But now they only block the sun.They rain and they snow on everyone.So many things I would have doneBut clouds got in my way.

I’ve looked at clouds from both sides now.From up and down, and still somehowIt’s cloud illusions I recall.I really don't know clouds at all.

— Joni Mitchell Both Sides Now, 1967


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Documents

Alan Robock Department of Environmental Sciences Rutgers University, New Brunswick, New Jersey USA