1. 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. Keller 1,2, and Matthew A. Lazzara 1 1 Antarctic Meteorological Research Center 2 Department of Atmospheric and Oceanic Science University of Wisconsin-Madison, Madison, Wisconsin

2. 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

3. 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

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

5. 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

6. 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

7. The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010. Beaufort Wind Force Scale Review ForceWind Speed Description 713.9-17.1 m/sTrees in motion, effort needed to walk against the wind. *Pegasus North and Herbie Alley AWS 8 (Gale) 17.2-20.7 m/sSome twigs broken from trees. Cars veer on road. Progress on foot is seriously impeded. *Cape Bird AWS

8. The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010. Beaufort Scale cont. ForceWind Speed Description 920.8-24.4 m/sSome 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/sTrees are broken off or uprooted, saplings bent and deformed. Poorly attached asphalt shingles and shingles in poor condition peel off roofs. *Black Island AWS

9. 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

10. 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

11. The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010. Difficulties cont. Instrument changes at AWS sites Missing data by seasons

12. 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

13. 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

14. 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

15. 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)

16. 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

17. 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’

18. 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

19. 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