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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

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

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

The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.

Spatial Variation

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

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

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

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

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

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

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

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

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

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

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)

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

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’

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

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