Climate Modeling MEA 719 Lecture Set6 Climate models AGCMs, OGCMs, AOGCMs

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Climate Modeling MEA 719 Lecture
Set-6Climate models (AGCMs, OGCMs, AOGCMs)
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AGCM EQUATIONS
Guiding question State the equations used to
construct AGCMs. Give the physical significance
of each term and identify the main differences
from the ones used for OGCMs
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AGCM EQUATIONS

• Zonal momentum
• Meridional momentum
• First law of thermodynamics
• Conservation of mass
• Hydrostatic equation
• Conservation of moisture
• Equation of state

QNet heating
Mcondensation
EEvaporation
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• This is a system of seven (7) equations and seven
  unknowns ( ). Therefore it
  can be solved if we know Q(diabatic heating) and
  F(Frictional forces)
• Solution is obtained after transforming equations
  into numerical form defined on a discretized grid
  Stability, accuracy, and efficiency are the
  criteria for determining the appropriateness of a
  scheme

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Model Horizontal Grid
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Model Vertical Grid
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Simple Numerical Transformationsat a general
point-
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Solution at new time stepfor each of the seven
variables
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Governing equations for Ocean General Circulation
Models (OGCMsWashington Parkinson)Guiding
question State the equations used to construct
OGCMs. Give the physical significance of each
term and identify the main differences from the
ones used for AGCMs

• Much of the basis for Ocean modeling is similar
  to the governing equations used for Atmospheric
  GCMs (AGCMs)
• However there are significant differences
• (i) Time and space scales are different. Dominant
  time scales in the Ocean are longer than those in
  the atmosphere because of the greater thermal
  inertia

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• (ii) Horizontal length scales of motion in the
  ocean are about one tenth of those in the
  atmosphere

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Mass Conservation Equation
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Equations of Motion

• Zonal momentum
• Meridional momentum

DDissipation due to eddy viscosity
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Advective-Flux-Lagrangian Forms
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Advective-Flux-Lagrangian Forms (for momentum
equation)
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Equation of State
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Salinity Equation
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Role of Salinity

• In the atmosphere latitudinal and longitudinal
  differences in heating can cause density
  differences which largely drive the large-scale
  circulation cells
• In the Oceans salinity differences cause density
  differences and can result in deep THERMOHALINE
  circulation.
• Thermo temperature influence
• Haline salinity influence

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First Law of Thermodynamic
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OGCM EQUATIONS

• Zonal momentum
• Meridional momentum
• First law of thermodynamics
• Conservation of mass
• Hydrostatic equation
• Salinity equation
• Equation of state

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OGCM EQUATIONS
AGCM EQUATIONS
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• This is a system of seven (7) equations and seven
  unknowns ( ). Therefore it
  can be solved.
• Solution is obtained after transforming equations
  into numerical form defined on a discretized grid
  Stability, accuracy, and efficiency are the
  criteria for determining the appropriateness of a
  scheme

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Coupling of the Ocean General Circulation Models
(OGCMs) Atmospheric General Circulation Models
(AGCMs)Guiding question Identify the processes
through which the evolution of the atmosphere and
the ocean are coupled

• Interfacial fluxes
• Longwave radiation flux
• Solar radiation flux
• Sensible heat flux
• Momentum flux (wind stress C-stress)
• Latent heat flux
• Salinity flux (function of P-E)
• PgtE imply seawater becomes less saline
• PltE imply seawater becomes more saline