may, 2002numerical weather prediction 1 robert r. gotwals, jr. (bob2) computational science educator...
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May, 2002 Numerical Weather Prediction
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Numerical Weather Prediction
Robert R. Gotwals, Jr. (“Bob2”)
Computational Science Educator
The Shodor Education Foundation, Inc.
http://www.shodor.org
http://www.shodor.org/talks/nwp
May, 2002 Numerical Weather Prediction
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Session Goals
• Describe application, algorithm, and architecture
• Describe and demonstrate the various NWP programs and codes
• Describe appropriate and authentic classroom activities using online NWP tools
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Application - First Principles
• Definition:• The use of computer
models to predict the future state of the atmosphere given observations and equations that describe relevant physical processes
• Some givens:• Weather prediction is
really hard• Synoptic scale
calculations, but local influences
• Equations are nonlinear
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Application - Results
• Example plots• Temperature• Dewpoint• Mean sea level
pressures (MSLP)• Winds, surface and aloft• Cloud cover • Precipitation and types• Severe weather indices
• CAPE• Helicity
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Algorithm - NWP Desks
• Desk seat 1: calculates east-west component of the wind
• Desk seat 2: calculates north-south component of the wind
• Desk seat 3: keeps track of the air entering or leaving the box. If more is coming in than going out, decides how much air rises or sinks
• Desk seat 4: calculates the effects of adding or taking away heat
• Desk seat 5: keeps track of water in all forms and how much is changing to or from vapor, liquid, or ice
• Desk seat 6: calculates the air temperature, pressure, and density
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Architecture - Platforms
• NWP requires significant computing power• True supercomputing required
– Gigaflops - billions of calculations (floating point operations) per second
– Teraflop - trillions of calculations per second
• Data storage– NCAR - late 2000, 200 terabytes of
data stored• NCAR machine
– 11th most powerful supercomputing in the world
– IBM SP Power 3– 1260 CPUs (processors)– Peak capabilities: 1890 Gigaflops
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Architecture - Codes
• General categories– By resolution– By scale
• Global (northern hemisphere)• National• relocatable
– By outlook (time-based)• Well-known codes
– Nested Grid Model (NGM)– ETA– Aviation Model (AVN)– Rapid Update Cycle (RUC)– Medium Range Forecast (MRF)– Mesoscale Model 5 (MM5)
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Nested Grid Model (NGM)
• National model• Short-range model (+48
hours), every 6 hour forecasts
• Forecast output– Temperature– Precipitation– Upper and lower
trough positioning– Surface highs and lows
• Grid size: 80 km• Operational status: being
phased out http://weather.uwyo.edu/models/fcst/index.html?MODEL=ngm
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ETA
• Name comes from eta coordinate system
• Short-range model• Four runs daily: 0000Z, 0600Z, 1200Z,
1800Z• 32 km horizontal domain, with 45
vertical layers• Significantly outperforms other models
in precipitation predictions
http://weather.uwyo.edu/models/fcst/index.html?MODEL=eta
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Rapid Update Cycle
• Regional model
• Short-term forecasts
– Up to 12 hours
• Focuses on mesoscale weather features
• 25 vertical layers, 40 km horizontal resolution
• New experimental version: MAPS
• RUC/MAPS generate significant amount of data
http://weather.unisys.com/ruc/index.html
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Medium Range Forecast (MRF) Model
• Global model
• Medium to long-range predictions: 60 to 240 hours
• Resolution: 150 km
• Other global models
– UKMET
– ECMWF
– Global Ocean Model
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Aviation Model
• Generates aviation-focused data
• 42 vertical layers, 100 km horizontal resolution
• Advantage: medium-range forecasting (up to 72 hours)
• One of the oldest operational models
• Data results available mostly in MOS (model output statistics) format
http://weather.unisys.com/aviation/index.html
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MM5
• Fifth generation mesoscale NWP
• Study types – hurricanes – cyclones – monsoons – fronts (formation,
interactions) – land-sea breeze
meteorology – urban heat islands – mountain-valley
circulations http://rain.mmm.ucar.edu/mm5/
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Sample Prediction• Question: assuming
precipitation, what will it be?• Tools:
– Atmospheric sounding (weather balloon data)
• Shows temperature and dewpoint temperature from surface to upper atmosphere
– Flowchart: precipitation type decision tree
• Analysis/solution shown on next slide
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Sample Prediction - Solution
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Classroom Integration - Forecasting Rules of thumb
• Will it be cloudy or clear?– On the 700-mb forecast chart,
the 70% relative humidity line usual encloses areas that are likely to have clouds
• Will it rain?– On the 700-mb forecast chart,
the 90% relative humidities line often encloses areas where precipitation is likely.
• Will it rain or snow?– On the 850-mb forecast chart,
snow is likely north of the -5 C (23 F) isotherm, rain to the south
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Classroom Integration - Weather observations
• Correlating low-tech weather observations– Use “instant weather
prediction chart”– Shows various
weather 24 hours out based on easily observable meteorological phenomenon
– Can correlate this with model data http://www.shodor.org/bob2/wx/weather predict.html
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Classroom Integration
• Good starting place: meteograms– Relatively easy to
interpret– Contain a lot of data– Typically project out
24 to 72 hours– Relatively good
resolution (normally 22 km)
– Available from a variety of models http://www.emc.ncep.noaa.gov/mmb/meteograms/
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Classroom Integration• Harder: atmospheric
soundings graphs• Substantial amounts of
information• Graphical and text-based
information– Graphical:
temperature, dewpoint temperatures, wind speeds and directions
– Text: key meteorological indices
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Questions?
• Chat Sessions
– Monday, May 13 3:30-4:30 PM and 6:00-7:00 PM
– Wednesday, May 15 3:30-4:30 PM
– Monday, May 20 6:00-7:00 PM
– Thursday, May 23 3:30-4:30 PM and 6:00-7:00 PM