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Atmospheric Modeling

Atmospheric Modeling. Vanda Grubiši ć Desert Research Institute Division of Atmospheric Sciences. Atmospheric Model. A component of complex ecosystem models

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Atmospheric Modeling

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  1. Atmospheric Modeling Vanda Grubišić Desert Research Institute Division of Atmospheric Sciences Interdisciplinary Modeling for Acquatic Ecosystems

  2. Atmospheric Model • A component of complex ecosystem models • Provides external “forcing” (e.g., precipitation, temperature, winds, relative humidity, radiation, etc.) for a variety of other constituent models • In jargon of many environmental modeling disciplines often referred to as “meteorology” Interdisciplinary Modeling for Acquatic Ecosystems

  3. Model vs. Computer Model • Model: A mathematical representation of a process (analytical model, parameterized model - insight is a key, empirical models - regression fit) • Computer (Numerical) Model: Discretized model equations numerically solved with use of computers Interdisciplinary Modeling for Acquatic Ecosystems

  4. How sophisticated atmospheric model one needs? • Dictated by the importance of atmospheric forcing to the problem at hand (e.g. Lake Tahoe clarity vs. algae growth) • Always be aware of uncertainties and errors (especially if atmospheric forcing is a key input into your model!) Interdisciplinary Modeling for Acquatic Ecosystems

  5. Important Scales • Atmospheric processes encompass a wide range of scales • Spatial and Temporal ScalesExampleProcess • Molecular (<< 2 mm, >min) Diffusion • Microscale (2 mm - 2 km, hours) In cloud processes • Mesoscale (2 - 2000 km, Tornadoes to hours to days) Thunderstorms • Synoptic (500 - 10,000 km Weather Systems: days to weeks) Anticyclones, Cyclones, Fronts • Planetary (> 10,000 km, > weeks) Global Circulation Interdisciplinary Modeling for Acquatic Ecosystems

  6. What Type of Atmospheric Numerical Model to Choose? • ScalesModel • Molecular (<< 2 mm, >min) Diffusion Equation • Microscale Microphysical and Cloud • Mesoscale Mesoscale (limited area) • Synoptic Weather Prediction/ Regional Climate (regional to hemispheric) • Planetary Global Circulation Model Interdisciplinary Modeling for Acquatic Ecosystems

  7. What about Vertical Scale? • Air is a continuously stratified fluid (density function of height) • All interesting meteorological phenomena occur in the troposphere Interdisciplinary Modeling for Acquatic Ecosystems

  8. Mesoscale The most interesting phenomenology The most challenging forecasting The most demanding computationally Interdisciplinary Modeling for Acquatic Ecosystems

  9. Synoptic Mesoscale Severe Weather Weather Interdisciplinary Modeling for Acquatic Ecosystems

  10. MesoscaleNon-Hydrostatic Effects Important Hydrostatic Equilibrium vs. Lack of It Buoyancy and Topographic Effects Dominate Interdisciplinary Modeling for Acquatic Ecosystems

  11. Equations and Approximations • Set of coupled partial differential equations describing the motion (conservation of momentum), thermodynamic state of the atmosphere (1st law of thermodynamics), and continuity equations for air (+particles+chemical spiecies) (conservation of mass) Interdisciplinary Modeling for Acquatic Ecosystems

  12. Momentum Equation Lagrangian Derivative Air motion vector (wind vector) Function of space and time } Gravity Diffusion Coriolis Force Pressure Gradient Force Eddy Diffusion “Turbulence” Interdisciplinary Modeling for Acquatic Ecosystems

  13. First Attempts at Atmospheric Numerical Modeling • Lewis Fry Richardson, 1913-1919 experiment (Richardson 1922) Numerical solutions to a simplified set of equations obtained by human “computers” • John von Neumman 1946 Numerical solutions to a (different) simplified set obtained by an electronic computer (ENIAC) Interdisciplinary Modeling for Acquatic Ecosystems

  14. Common Theme That Continues to Today… • It is impossible to explicitly numerically resolve all scales and processes  simplifications, approximations, and parameterizations necessary even as model resolution increases (grid spacing decreases) • Lack of data for verification: Density of observational networks continues to lag increases in model resolutions (due to computing technology advances) Interdisciplinary Modeling for Acquatic Ecosystems

  15. How Mesoscale Models Work? Interdisciplinary Modeling for Acquatic Ecosystems

  16. Limited Area Models Need initial and boundary conditions from a larger-scale model! Interdisciplinary Modeling for Acquatic Ecosystems

  17. Grid-Point ModelsResolutionHorizontal and Vertical Interdisciplinary Modeling for Acquatic Ecosystems

  18. Vertical Coordinateand Resolution Interdisciplinary Modeling for Acquatic Ecosystems

  19. Mesoscale Models Effects of Increased Resolution Price to be Paid Several-fold increase in computational time and cost! Interdisciplinary Modeling for Acquatic Ecosystems

  20. How to Increase Resolution without Making ComputationProhibitively Expansive? • Answer: Domain Nesting Horizontal resolution increased by the factor of 3 for each successive nested domain (two-way nesting) Nested domains can be spawned at any time Vertical resolution (commonly) the same in all domains Interdisciplinary Modeling for Acquatic Ecosystems

  21. Importance of BC Updates and Assimilation of Observations • Keep Models from Veering Off into Virtual Reality Interdisciplinary Modeling for Acquatic Ecosystems

  22. Parameterizations of Subgrid-Scale Processes • Parameterizations: Modeling the effect of a process (emulation) rather than modeling the process itself (simulation) • Why do we need parameterizations? • Processes either too small or too complex to be resolved and directly simulated • Processes not understood enough • Yet, important for obtaining accurate simulation and/or forecast Interdisciplinary Modeling for Acquatic Ecosystems

  23. Parameterizations Near Surface Processes Convective Mixing Interdisciplinary Modeling for Acquatic Ecosystems

  24. How are Mesoscale Models Used? • Real-Time Weather Forecasting (NWS-USA, Universities-regional forecasting efforts) • Research Tool • Real-data simulations (“Case and Sensitivity Studies”) • Idealized simulations (uniform wind and/or stability profiles, simplified topography, simple initial and BC, 2D,…) Interdisciplinary Modeling for Acquatic Ecosystems

  25. Open Questions • Continuous need for high-resolution observations for model verification [mesoscale field campaigns, e.g. Terrain-induced Rotor Experiment (T-REX) 2006 in Sierra Nevada, CA] • Increase in horizontal resolution does not always lead to better results [e.g., Quantitative Precipitation Forecasting, model skill worse at 4.5 and 1.5 km than at 13.5 km, Grubišić et al. (2005), Colle et al. (2002) • Range of validity of parameterizations Interdisciplinary Modeling for Acquatic Ecosystems

  26. Resources • Beyond Meteorology 101 University Corporation for Atmospheric Research (UCAR) MetEd (Meteorology Education & Training) COMET Program pageshttp://meted.ucar.edu Some of My Favorites: • Rain Gauges: Are They Really Ground Truth? • How Models Produce Precipitation & Clouds • Intelligent Use of Model-Derived Products Interdisciplinary Modeling for Acquatic Ecosystems

  27. Resources Mesoscale Models - Large Community Models, Open Source • MM5 - Pennsylvania State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model v5 http://www.mmm.ucar.edu/mm5 • COAMPS - Naval Research Laboratory's Coupled Ocean/Atmosphere Prediction System http://www.nrlmry.navy.mil/coamps-web/web/home • WRF - Weather Research & Forecasting Model National Center for Atmospheric Research (NCAR), National Oceanic and Atmospheric Administration (NOAA) Forecast System Laboratory (FSL) and the National Centers for Environmental Prediction (NCEP), Air Force Weather Agency (AFWA), Naval Research Laboratory (NRL), University of Oklahoma, Federal Aviation Administration (FAA) http://www.wrf-model.org Interdisciplinary Modeling for Acquatic Ecosystems

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