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How do we predict weather and climate?

How do we predict weather and climate?. Review of last lecture. Tropical climate: Mean state: The two basic regions of SST? Which region has stronger rainfall? What is the Walker circulation? El Nino and La Nina: Which region has warm SST anomaly during El Nino? 4-year period.

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How do we predict weather and climate?

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  1. How do we predict weather and climate?

  2. Review of last lecture Tropical climate: • Mean state: The two basic regions of SST? Which region has stronger rainfall? What is the Walker circulation? • El Nino and La Nina: Which region has warm SST anomaly during El Nino? 4-year period. • Land-sea contrasts: seasonal monsoon, diurnal sea and land breeze Extratropical climate: • Mean state: westerly winds, polar vortex • What is the primary way El Nino affect extratropics? (PNA) • The oscillations associated with strengthening/weakening of polar vortex: AO, AAO

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

  4. Video: Constructing a climate model http://www.nas-sites.org/climatemodeling/page_3_1.php

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

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

  7. General Circulation Model: Basics • General circulation models are systems of differential equations based on the basic laws of physics, fluid motion, and chemistry. • Scientists divide the planet into a 3-dimensional grid (100-500 Km wide), apply the basic equations within each grid and evaluate interactions with neighboring points.

  8. General Circulation Model: Basic equations (Conservation of monmentum) • 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 H2O, CO2 and other chemical species. (Conservation of mass) (Conservation of energy)

  9. Before 1955: Numerical models and the prehistory of AGCMs • 1922 - 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. • 1954, 1955 - Routine forecast: The Swedish Institute of Meteorology, the US JNWP. Barotropic model.

  10. 1955-1965: Establishment of general circulation modeling • 1955: Norman Philips developed the first AGCM • NOAA Geophysical Fluid Dynamics Lab: Joseph Smagorinsky and Syukuro Manabe • UCLA: Yale Mintz and Akio Arakawa • Lawrence Livermore National Lab: Cecil E. "Chuck" Leith • National Center for Atmospheric Research: Akira Kasahara and Warren Washington • UK Met Office:

  11. 1965-1975: The spread of GCMs

  12. World’s Major Global Climate Models

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

  14. Framework of Climate System Model Atmosphere Coupler . Land Sea Ice Ocean

  15. Example: Land Model (From Bonan 2002)

  16. Supercomputer power (FLOPS) • 1960: 2x105 • 1970: 3x107 • 1980: 4x108 • 1990: 2x1010 • 2000: 7x1012 • 2007: 4x1014

  17. Video: Climate Modeling With Supercomputers • http://www.youtube.com/watch?v=izCoiTcsOd8

  18. Success and biases of current climate system models: (1) Tropical mean state Obs Double-ITCZ Contours: precipitation Shading: SST

  19. Success and biases of current climate system models: (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

  20. Success and biases of current climate system models: (2) The subseasonal variability

  21. About 1/3 of the models can produce the subseasonal variability, but the amplitudes are generally too weak and speeds are too fast Obs

  22. Mesoscale model • Mesoscale: 1 Km- 1000 Km, 1 min - 1 day • Grid size: 1 Km - 10 km • Three characteristics: Non-hydrostatic processes Nested grid Topography effects

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

  24. Mesoscale model: Nested grid • Finer grids in regions of interest

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

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

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