How do we predict weather and climate?

Review of last lecture Extratropical climate: Mean state: westerly winds, polar vortex Mean state: westerly winds, polar vortex The natural oscillations associated with strengthening/weakening of polar vortex: AO, NAO, AAO The natural oscillations associated with strengthening/weakening of polar vortex: AO, NAO, AAO Effect of global warming on polar vortex Effect of global warming on polar vortex What is the primary way El Nino affect extratropics? (PNA) What is the primary way El Nino affect extratropics? (PNA)

Outline General circulation models (prediction of global climate & weather) 1.History 2.Nuts and bolts 3.Current challenges Mesoscale models (prediction of regional climate & weather) 1.History 2.Nuts and bolts 3.Current challenges

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

Video: Climate Modeling With Supercomputers

General Circulation Model: Usages Global climate projections Global weather predictions Global climate predictions

General Circulation Model: Basics General circulation models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry. General circulation models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry.differential equationsphysicsfluid motionchemistrydifferential equationsphysicsfluid motionchemistry Scientists divide the planet into a 3-dimensional grid ( Km wide), apply the basic equations within each grid and evaluate interactions with neighboring points. Scientists divide the planet into a 3-dimensional grid ( Km wide), apply the basic equations within each grid and evaluate interactions with neighboring points.

General Circulation Model: Basic equations This set of equations is called the Navier-Stokes equations for fluid flow, which are at the heart of the GCMs. This set of equations is called the Navier-Stokes equations for fluid flow, which are at the heart of the GCMs. There are other equations dealing with the conservation of H 2 O, CO 2 and other chemical species. There are other equations dealing with the conservation of H 2 O, CO 2 and other chemical species. (Conservation of monmentum) (Conservation of mass) (Conservation of energy)

Before 1955: Numerical models and the prehistory of AGCMs Lewis Richardson’s “forecast factory”: filled a vast stadium with 64,000 people, each armed with a mechanical calculator. Failed! Lewis Richardson’s “forecast factory”: filled a vast stadium with 64,000 people, each armed with a mechanical calculator. Failed! 1940s - von Neumann assembled a group of theoretical meteorologists at Princeton to run the first computerized weather forecast on the ENIAC. The results were encouraging. 1940s - von Neumann assembled a group of theoretical meteorologists at Princeton to run the first computerized weather forecast on the ENIAC. The results were encouraging. 1954, Routine forecast: The Swedish Institute of Meteorology, the US JNWP. Barotropic model. 1954, Routine forecast: The Swedish Institute of Meteorology, the US JNWP. Barotropic model.

: Establishment of general circulation modeling 1955: Norman Philips developed the first AGCM 1955: Norman Philips developed the first AGCM NOAA Geophysical Fluid Dynamics Lab: Joseph Smagorinsky and Syukuro Manabe NOAA Geophysical Fluid Dynamics Lab: Joseph Smagorinsky and Syukuro Manabe UCLA: Yale Mintz and Akio Arakawa UCLA: Yale Mintz and Akio Arakawa Lawrence Livermore National Lab: Cecil E. "Chuck" Leith Lawrence Livermore National Lab: Cecil E. "Chuck" Leith National Center for Atmospheric Research: Akira Kasahara and Warren Washington National Center for Atmospheric Research: Akira Kasahara and Warren Washington UK Met Office: UK Met Office:

: The spread of GCMs

World’s Major Global Climate Models

Required model complexity Global weather prediction (up to 1 month) - Atmospheric GCM (AGCM) Global weather prediction (up to 1 month) - Atmospheric GCM (AGCM) Global climate prediction (beyond 1 season) - Coupled ocean-atmosphere GCM (CGCM) Global climate prediction (beyond 1 season) - Coupled ocean-atmosphere GCM (CGCM) Global climate projections (beyond 10 years) - Climate system model (CSM) Global climate projections (beyond 10 years) - Climate system model (CSM)

Coupler. LandSea Ice Atmosphere Ocean Framework of Climate System Model

Example: Land Model (From Bonan 2002)

Supercomputer power (FLOPS)

Video: Computer Modeling of Hurricanes

Mesoscale model Mesoscale: 1 Km Km, 1 min - 1 day Mesoscale: 1 Km Km, 1 min - 1 day Grid size: 1 Km - 10 km Grid size: 1 Km - 10 km Three characteristics: Three characteristics: Non-hydrostatic processes Non-hydrostatic processes Nested grid Nested grid Topography effects Topography effects

Mesoscale model: Non-hydrostic processes Non-hydrostatic processes need to be considered Non-hydrostatic processes need to be considered

Mesoscale model: Nested grid Finer grids in regions of interest Finer grids in regions of interest

Mesoscale model: Topography Topography strongly influences mesoscale processes (e.g. land breeze, mountain breeze) Topography strongly influences mesoscale processes (e.g. land breeze, mountain breeze)

Summary General circulation models: Grid size. 3 usages. Name of the basic set of equations. General circulation models: Grid size. 3 usages. Name of the basic set of equations. 4 components of the climate system model. 4 components of the climate system model. Mesoscale models: grid size. 3 characteristics. Mesoscale models: grid size. 3 characteristics.