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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

Atmospheric Modeling

Vanda Grubišić

Desert Research Institute

Division of Atmospheric Sciences

Interdisciplinary Modeling for Acquatic Ecosystems

atmospheric model
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

model vs computer model
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

how sophisticated atmospheric model one needs
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

important scales
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

what type of atmospheric numerical model to choose
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

what about vertical scale
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

mesoscale

Mesoscale

The most interesting phenomenology

The most challenging forecasting

The most demanding computationally

Interdisciplinary Modeling for Acquatic Ecosystems

synoptic mesoscale
Synoptic Mesoscale

Severe

Weather

Weather

Interdisciplinary Modeling for Acquatic Ecosystems

mesoscale non hydrostatic effects important
MesoscaleNon-Hydrostatic Effects Important

Hydrostatic Equilibrium vs. Lack of It

Buoyancy and Topographic Effects Dominate

Interdisciplinary Modeling for Acquatic Ecosystems

equations and approximations
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

momentum equation
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

first attempts at atmospheric numerical modeling
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

common theme that continues to today
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

how mesoscale models work
How Mesoscale Models Work?

Interdisciplinary Modeling for Acquatic Ecosystems

limited area models
Limited Area Models

Need initial and boundary conditions

from a larger-scale model!

Interdisciplinary Modeling for Acquatic Ecosystems

grid point models resolution horizontal and vertical
Grid-Point ModelsResolutionHorizontal and Vertical

Interdisciplinary Modeling for Acquatic Ecosystems

vertical coordinate and resolution
Vertical Coordinateand Resolution

Interdisciplinary Modeling for Acquatic Ecosystems

mesoscale models effects of increased resolution
Mesoscale Models Effects of Increased Resolution

Price to be Paid

Several-fold increase in computational time and cost!

Interdisciplinary Modeling for Acquatic Ecosystems

how to increase resolution without making computation prohibitively expansive
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

importance of bc updates and assimilation of observations
Importance of BC Updates and Assimilation of Observations
  • Keep Models from Veering Off into Virtual Reality

Interdisciplinary Modeling for Acquatic Ecosystems

parameterizations of subgrid scale processes
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

parameterizations
Parameterizations

Near Surface Processes

Convective Mixing

Interdisciplinary Modeling for Acquatic Ecosystems

how are mesoscale models used
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

open questions
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

resources
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

resources27
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