a 20 year assessment of the frequency and intensity of mcmurdo area high wind events
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A 20 Year Assessment of the Frequency and Intensity of McMurdo Area High Wind Events. 1 Antarctic Meteorological Research Center 2 Department of Atmospheric and Oceanic Science University of Wisconsin-Madison, Madison, Wisconsin. - PowerPoint PPT PresentationTRANSCRIPT
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
A 20 Year Assessment of the Frequency and Intensity of McMurdo Area High Wind Events
David M. Rasmussen Jr.1,*, Linda M. Keller1,2, and Matthew A. Lazzara1
1Antarctic Meteorological Research Center2 Department of Atmospheric and Oceanic Science
University of Wisconsin-Madison, Madison, Wisconsin
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Outline
• Motivation
• Defining a ‘high wind event’
• Difficulties
• Results
• Conclusion
• Future Work
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Motivation
• Address hypothesis:– Recent structural damage in the McMurdo
region is do to an increase in the frequency, duration, and/ or intensity of ‘high wind events’
– Use wind speed data from AWS stations in McMurdo/ Ross Island Region
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Spatial Variation
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Wind Event Thresholds
• Thresholds ~2 standard deviations from mean wind speed
• Choose nearest Beaufort Wind Force Scale
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Wind Distributions
Pegasus North AWS Wind Speed Distribution 1990-2009
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Beaufort Wind Force Scale Review
Force Wind Speed
Description
7 13.9-17.1 m/s Trees in motion, effort needed to walk against the wind.
*Pegasus North and Herbie Alley AWS
8(Gale)
17.2-20.7 m/s Some twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded.
*Cape Bird AWS
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Beaufort Scale cont.
Force Wind Speed
Description
9 20.8-24.4 m/s Some branches break off trees, and some small trees blow over. Construction/temporary signs and barricades blow over.*Minna Bluff AWS
10(Storm)
24.5-28.4 m/s Trees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs.*Black Island AWS
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
High Wind Event Duration
• Meets 6, 12, and 24-hour duration requirements
• At least half of observations from each high wind event must:– not be missing– meet Beaufort Force thresholds assigned to each
AWS station
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Difficulties
• Too much missing wind data to make many clear assessments
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Difficulties cont.
Seasonal Missing AWS Data AWS Name DJF MAM JJA SON
Black Island 19% 24% 21% 14% Cape Bird 15% 0% 12% 18% Herbie Alley 9% 21% 55% 33% Minna Bluff 24% 15% 29% 33% Pegasus North 22% 15% 22% 18% Average 18% 15% 28% 23%
• Instrument changes at AWS sites
• Missing data by seasons
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Results
• Little or no change in frequency of 6, 12, and 24 hour wind events between 1990’s and 2000’s at 3 AWS sites
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Results cont.
• Maximum wind speeds
• Two-tailored Student’s t-test used to determine changes in annual maximum wind speeds between 1990’s and 2000’s
AWS t-test result Black Island Minor Significance Minna Bluff Not significant Pegasus North Not significant
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Results cont.Changes in the intensity of seasonal high wind events
Cape Bird AWS
Pegasus North AWS
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Results cont.
• AWS wind speed direction
Normalized Wind Direction (Scale 1-100)
Mean Wind Speed (m/s)
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Conclusion
• Slight increase in number of seasonal events at a few AWS sites seen between decades, but not significant
• Analysis heavily dependent upon quality of data, data availability– seasons and years with greater than 25% missing data
not included in analysis
• No significant change in high wind event frequency, duration and intensity seen across all sites between 1990’s and 2000’s, but analysis continuing
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Conclusion cont.
• No clear link between ENSO years and ‘high wind events’
• Re-verification that the fewest frequency of events occurs in the Austral Summer
• Disagreement exists between other seasons as to which has the greatest frequency of ‘high wind events’
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Future Work
• Continuing to improve wind observation consistency (esp. in austral winter months)
• Improvement in data distribution (missing years of Black Island AWS data)
• Meteorologists working more closely with Antarctic builders and/or architects
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The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.
Acknowledgements
• This material is based upon work supported by the National Science Foundation under Grant Numbers: ANT-0537827, ANT-0636873, and ANT 0838834