How do we predict weather and How do we predict weather and climate?climate?

Review of last lectureReview of last lecture

Tropical climate:Tropical climate: Mean state: The two basic regions of SST? Which region has Mean state: The two basic regions of SST? Which region has

stronger rainfall? What is the Walker circulation?stronger rainfall? What is the Walker circulation? El Nino and La Nina: Which region has warm SST anomaly El Nino and La Nina: Which region has warm SST anomaly

during El Nino? 4-year period.during El Nino? 4-year period. Land-sea contrasts: seasonal monsoon, diurnal sea and land Land-sea contrasts: seasonal monsoon, diurnal sea and land

breeze breeze

Extratropical climate:Extratropical climate: Mean state: westerly winds, polar vortexMean state: westerly winds, polar vortex What is the primary way El Nino affect extratropics? (PNA)What is the primary way El Nino affect extratropics? (PNA) The oscillations associated with strengthening/weakening of polar The oscillations associated with strengthening/weakening of polar

vortex: AO, AAOvortex: AO, AAO

OutlineOutline

General circulation models (prediction of global General circulation models (prediction of global climate & weather)climate & weather)

1.1. HistoryHistory2.2. Nuts and boltsNuts and bolts3.3. Current challengesCurrent challenges

Mesoscale models (prediction of regional climate Mesoscale models (prediction of regional climate & weather)& weather)

1.1. HistoryHistory2.2. Nuts and boltsNuts and bolts3.3. Current challengesCurrent challenges

Video: Constructing a climate modelVideo: Constructing a climate model

http://www.nas-sites.org/climatemodeling/page_3_1.php

The Global Climate System - Atmosphere, The Global Climate System - Atmosphere, ocean, biosphere, cryosphere, and geosphereocean, biosphere, cryosphere, and geosphere

General Circulation Model: UsagesGeneral Circulation Model: Usages

Global climate projections

Global weather predictions

Global climate predictions

General Circulation Model: BasicsGeneral Circulation Model: Basics

• General circulation models are systems of General circulation models are systems of differential equations based on the based on the basic laws of basic laws of physics, , fluid motion, and , and chemistry. .

• Scientists divide the planet into a 3-dimensional grid (Scientists divide the planet into a 3-dimensional grid (100-500 Km wide100-500 Km wide), apply the ), apply the basic equations within each grid and evaluate interactions with neighboring points. basic equations within each grid and evaluate interactions with neighboring points.

General Circulation Model: General Circulation Model: Basic equations Basic equations

This set of equations is This set of equations is called the called the Navier-Stokes Navier-Stokes equationsequations for fluid flow, for fluid flow, which are at the heart of which are at the heart of the GCMs.the GCMs.

There are other There are other equations dealing with equations dealing with the conservation of Hthe conservation of H22O, O,

COCO22 and other chemical and other chemical

species.species.

(Conservation of monmentum)

(Conservation of mass)

(Conservation of energy)

Before 1955: Numerical models and Before 1955: Numerical models and the prehistory of AGCMsthe prehistory of AGCMs

1922 - Lewis Richardson1922 - Lewis Richardson’’s s ““forecast factoryforecast factory””: filled a vast : filled a vast stadium with 64,000 people, stadium with 64,000 people, each armed with a mechanical each armed with a mechanical calculator. Failed!calculator. Failed!

1940s - von Neumann 1940s - von Neumann assembled a group of assembled a group of theoretical meteorologists at theoretical meteorologists at Princeton to run the first Princeton to run the first computerized weather forecast computerized weather forecast on the ENIAC. The results were on the ENIAC. The results were encouraging.encouraging.

1954, 1955 - Routine forecast: 1954, 1955 - Routine forecast: The Swedish Institute of The Swedish Institute of Meteorology, the US JNWP. Meteorology, the US JNWP. Barotropic model.Barotropic model.

1955-1965: Establishment of general 1955-1965: Establishment of general circulation modelingcirculation modeling

1955: Norman Philips developed the first AGCM1955: Norman Philips developed the first AGCM NOAA Geophysical Fluid Dynamics Lab: Joseph NOAA Geophysical Fluid Dynamics Lab: Joseph

Smagorinsky and Syukuro ManabeSmagorinsky and Syukuro Manabe UCLA: Yale Mintz and Akio ArakawaUCLA: Yale Mintz and Akio Arakawa Lawrence Livermore National Lab: Cecil E. "Chuck" LeithLawrence Livermore National Lab: Cecil E. "Chuck" Leith National Center for Atmospheric Research: Akira Kasahara National Center for Atmospheric Research: Akira Kasahara

and Warren Washingtonand Warren Washington UK Met Office: UK Met Office:

1965-1975: The spread of GCMs1965-1975: The spread of GCMs

WorldWorld’’s Major Global Climate Modelss Major Global Climate Models

Required model complexityRequired model complexity

Global weather prediction (up to 1 month) - Global weather prediction (up to 1 month) - Atmospheric GCM (AGCM)Atmospheric GCM (AGCM)

Global climate prediction (beyond 1 season) Global climate prediction (beyond 1 season) - Coupled ocean-atmosphere GCM (CGCM)- Coupled ocean-atmosphere GCM (CGCM)

Global climate projections (beyond 10 years) Global climate projections (beyond 10 years) - Climate system model (CSM)- Climate system model (CSM)

Coupler .

Land Sea Ice

Atmosphere

Ocean

Framework of Climate System ModelFramework of Climate System Model

Example: Land ModelExample: Land Model

(From Bonan 2002)

Supercomputer power (FLOPS)Supercomputer power (FLOPS)

1960: 2x101960: 2x1055

1970: 3x101970: 3x1077

1980: 4x101980: 4x1088

1990: 2x101990: 2x101010

2000: 7x102000: 7x101212

2007: 4x102007: 4x101414

Video: Climate Modeling With Video: Climate Modeling With SupercomputersSupercomputers

http://www.youtube.com/watch?v=izCoiTcsOd8

Success and biases of current climate system models: Success and biases of current climate system models:

(1) Tropical mean state(1) Tropical mean state

Contours: precipitation Shading: SST

Double-ITCZ

Obs

Success and biases of current climate system Success and biases of current climate system models: models:

(2) The ENSO(2) The ENSO

1/3 of the models: Too-short ENSO period (regular 2 or 3-year)

1/3 of the models: Too-long ENSO period (decadal variability)

1/3 of the models: Correct ENSO period

Success and biases of current climate system Success and biases of current climate system models: models:

(2) The subseasonal variability(2) The subseasonal variability

About 1/3 of the models can produce the subseasonal About 1/3 of the models can produce the subseasonal variability, but the amplitudes are generally too weak variability, but the amplitudes are generally too weak

and speeds are too fastand speeds are too fastObs

Mesoscale modelMesoscale model

Mesoscale: 1 Km- 1000 Km, 1 min - 1 dayMesoscale: 1 Km- 1000 Km, 1 min - 1 day Grid size: 1 Km - 10 kmGrid size: 1 Km - 10 km Three characteristics: Three characteristics:

Non-hydrostatic processesNon-hydrostatic processes

Nested gridNested grid

Topography effectsTopography effects

Mesoscale model: Non-hydrostic processesMesoscale model: Non-hydrostic processes

Non-hydrostatic processes need to be consideredNon-hydrostatic processes need to be considered

Mesoscale model: Nested gridMesoscale model: Nested grid

Finer grids in regions of interestFiner grids in regions of interest

Mesoscale model: TopographyMesoscale model: Topography Topography strongly influences mesoscale processes Topography strongly influences mesoscale processes

(e.g. land breeze, mountain breeze) (e.g. land breeze, mountain breeze)

SummarySummary

General circulation models: Grid size. 3 General circulation models: Grid size. 3 usages. Name of the basic set of equations. usages. Name of the basic set of equations.

4 components of the climate system model.4 components of the climate system model. Success and biases of current climate system Success and biases of current climate system

modelsmodels Mesoscale models: grid size. 3 characteristics.Mesoscale models: grid size. 3 characteristics.