Coupled Climate ModelsCoupled Climate Models

OCEAN-ATMOSPHEREOCEAN-ATMOSPHERE

INTERACTIONSINTERACTIONS

What is climate?What is climate?

Different meaningsDifferent meanings– an external, forcing agentan external, forcing agent– influence on society and socio-influence on society and socio-

economicseconomics– a background norm on which weather a background norm on which weather

is imposedis imposed– temperature, rain, and humiditytemperature, rain, and humidity

Climatic SystemClimatic System

5 Major Components5 Major Components HydrosphereHydrosphere AtmosphereAtmosphere CryosphereCryosphere LithosphereLithosphere BiosphereBiosphere

Why does climate vary?Why does climate vary?

VARIATIONS IN CLIMATE VARIATIONS IN CLIMATE COMPONENTSCOMPONENTS

Climate Forcings: the basis for Climate Forcings: the basis for changechange

Forcing: a change on the planetary Forcing: a change on the planetary energy balance system (flux)energy balance system (flux)

2 separate categories:2 separate categories:– External ForcingsExternal Forcings– Internal ForcingsInternal Forcings

HumanHuman NaturalNatural

Climate Forcings: ExternalClimate Forcings: External

Milankovitch CyclesMilankovitch Cycles– EccentricityEccentricity– ObliquityObliquity– PrecessionPrecession

Solar ActivitySolar Activity Comet/meteorite impactsComet/meteorite impacts

Climate Forcings: InternalClimate Forcings: InternalHuman inducedHuman induced

Greenhouse Greenhouse GasesGases

Tropospheric Tropospheric AerosolsAerosols

Ozone DepletionOzone Depletion Land Surface Land Surface

ChangesChanges

KNOWN FORCINGSKNOWN FORCINGS

Climate Forcings: InternalClimate Forcings: InternalNaturalNatural

Ocean circulation changesOcean circulation changes Volcanic eruptionsVolcanic eruptions Heat Transfer from interiorHeat Transfer from interior

Measurements that Drive the Measurements that Drive the ModelsModels

Sea surface temperatureSea surface temperature Air temperature and humidityAir temperature and humidity Wind velocityWind velocity Net radiation flux at ocean and Net radiation flux at ocean and

underlying surfaces and upper underlying surfaces and upper atmospheric boundaryatmospheric boundary

Fluxes of momentum, heat and moisture Fluxes of momentum, heat and moisture at the ocean-atmosphere boundaryat the ocean-atmosphere boundary

Coupled Climate ModelCoupled Climate Model

Combine oceanic Combine oceanic and atmospheric and atmospheric modelsmodels

General Circulation Model: General Circulation Model: GCMGCM

3-dimensional 3-dimensional modelmodel– scaling issuesscaling issues

General Circulation Model: General Circulation Model: GCMGCM

Solve for the Solve for the main main features of features of the the atmosphere atmosphere and ocean and ocean through a through a series of series of equationsequations

Atmospheric GCMAtmospheric GCM

AGCM variablesAGCM variables

Surface PressureSurface Pressure 2 horizontal wind 2 horizontal wind

componentscomponents TemperatureTemperature MoistureMoisture Geopotential Geopotential

heightheight

AGCM: Physical ProcessesAGCM: Physical Processes

Radiative TransferRadiative Transfer– daily and annular daily and annular

cyclescycles– short- and long-wave short- and long-wave – cloudsclouds

Boundary LayerBoundary Layer– frictionfriction– diurnal temperature diurnal temperature

and humidity and humidity variationsvariations

AGCM: Physical ProcessesAGCM: Physical Processes

Large-scale rainfallLarge-scale rainfall

ConvectionConvection

AGCM: Physical ProcessesAGCM: Physical Processes

Land Surface ParameterizationLand Surface Parameterization– gravity wave draggravity wave drag

Oceanic GCMOceanic GCM

DriversDrivers– WindsWinds– Salinity and densitySalinity and density

Detailed schemesDetailed schemes– Stronger currents on western sides of Stronger currents on western sides of

basinbasin

OGCMsOGCMs

Swamp ModelSwamp Model Slab ModelSlab Model Detailed Detailed

Mixed Layer Mixed Layer ModelModel

Dynamic Dynamic Ocean ModelOcean Model

OGCM: GridOGCM: Grid

Other Other SchemesSchemes

CyrosphereCyrosphere– hydrologic cyclehydrologic cycle– albedosalbedos

wind and heatwind and heat VegetationVegetation

– different scalesdifferent scales– lack of validation lack of validation

datadata

Coupled Model: AOGCMCoupled Model: AOGCM

AOGCM ProblemsAOGCM Problems

Time ScalesTime Scales Grid ScalesGrid Scales CostsCosts

AOGCM SolutionsAOGCM Solutions

Asynchronous CouplingAsynchronous Coupling

ConclusionConclusion

There is a long way to go before we have RELIABLEModels with which to predict CLIMATE and CLIMATE CHANGE …