Download Aquamod Atmospheric

Atmospheric Modeling
Vanda Grubišić
Desert Research Institute
Division of Atmospheric Sciences
18 July 2005
Interdisciplinary Modeling for
Acquatic Ecosystems
1
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”
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Interdisciplinary Modeling for
Acquatic Ecosystems
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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
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Interdisciplinary Modeling for
Acquatic Ecosystems
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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!)
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Important Scales
• Atmospheric processes encompass a wide range of
•
scales
Spatial and Temporal Scales Example Process
– Molecular (<< 2 mm, >min)
– Microscale (2 mm - 2 km, hours)
– Mesoscale (2 - 2000 km,
hours to days)
– Synoptic (500 - 10,000 km
days to weeks)
Diffusion
In cloud processes
Tornadoes to
Thunderstorms
Weather Systems:
Anticyclones,
Cyclones, Fronts
– Planetary (> 10,000 km, > weeks) Global Circulation
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Interdisciplinary Modeling for
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What Type of Atmospheric
Numerical Model to Choose?
• Scales
–
–
–
–
Model
Molecular (<< 2 mm, >min)
Microscale
Mesoscale
Synoptic
– Planetary
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Diffusion Equation
Microphysical and Cloud
Mesoscale (limited area)
Weather Prediction/
Regional Climate
(regional to hemispheric)
Global Circulation Model
Interdisciplinary Modeling for
Acquatic Ecosystems
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What about Vertical Scale?
• Air is a continuously
•
18 July 2005
stratified fluid (density
function of height)
All interesting
meteorological
phenomena occur in
the troposphere
Interdisciplinary Modeling for
Acquatic Ecosystems
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Mesoscale
The most interesting phenomenology
The most challenging forecasting
The most demanding computationally
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Synoptic
Mesoscale
Severe
Weather
Weather
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Mesoscale
Non-Hydrostatic Effects Important
Hydrostatic Equilibrium
vs.
Lack of It
Buoyancy and Topographic Effects Dominate
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Interdisciplinary Modeling for
Acquatic Ecosystems
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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)
v
1
1
2
 (v  v )   fzˆ  v    pa   a v  (  a K m)v
t
a
a
 v
1
v
dQn
 (v   v )  (  a K h ) v 

t
a
c p T n1 dt
N eh
q
1
 (v  q)  (  a K h )q   Rn
t
a
n1
N em
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Momentum Equation
Lagrangian
Derivative
}
Dv
Dt
v  (u,v,w)
v  v (x, y,z,t)
Gravity
Air motion vector (wind vector)
Function of space and time
Diffusion


v
1
1
2
ˆ
 (v  v )   fz  v    pa   a v  (  a K m)v
t
a
a

Coriolis Force Pressure Gradient
Force
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Interdisciplinary Modeling for
Acquatic Ecosystems
Eddy Diffusion
“Turbulence”
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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)
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Interdisciplinary Modeling for
Acquatic Ecosystems
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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)
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Interdisciplinary Modeling for
Acquatic Ecosystems
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How Mesoscale Models Work?
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Limited Area Models
Need initial and boundary conditions
from a larger-scale model!
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Grid-Point Models
Resolution
Horizontal and Vertical
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Vertical Coordinate
and Resolution
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Mesoscale Models
Effects of Increased Resolution
Price to be Paid
Several-fold increase in computational time and cost!
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Interdisciplinary Modeling for
Acquatic Ecosystems
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How to Increase Resolution
without Making Computation
Prohibitively Expansive?
• Answer: Domain Nesting
Horizontal resolution increased
by the factor of 3 for each
successive nested domain (twoway nesting)
Nested domains can be spawned
at any time
Vertical resolution (commonly)
the same in all domains
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Importance of BC Updates and
Assimilation of Observations
• Keep Models from Veering Off into Virtual
Reality
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Interdisciplinary Modeling for
Acquatic Ecosystems
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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
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Parameterizations
Near Surface Processes
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Convective Mixing
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Acquatic Ecosystems
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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,…)
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Interdisciplinary Modeling for
Acquatic Ecosystems
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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
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Interdisciplinary Modeling for
Acquatic Ecosystems
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Resources
• Beyond Meteorology 101
University Corporation for Atmospheric Research
(UCAR) MetEd (Meteorology Education & Training)
COMET Program pages
http://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
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Interdisciplinary Modeling for
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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
2) COAMPS - Naval Research Laboratory's Coupled
Ocean/Atmosphere Prediction System
http://www.nrlmry.navy.mil/coamps-web/web/home
3) WRF - Weather Research & Forecasting Model
1)
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
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Interdisciplinary Modeling for
Acquatic Ecosystems
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