A 20 Year Assessment of the Frequency and Intensity of McMurdo Area High Wind Events

1. A 20 Year Assessment of the Frequency and Intensity of McMurdo Area High Wind Events 1Antarctic Meteorological Research Center 2 Department of Atmospheric and Oceanic Science University of Wisconsin-Madison, Madison, Wisconsin David M. Rasmussen Jr.1,*, Linda M. Keller1,2, and Matthew A. Lazzara1 The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.

2. 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.

3. 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.

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

5. 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.

6. 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.

7. Beaufort Wind Force Scale Review The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.

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

9. 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.

10. 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.

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

12. 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.

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

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. Acknowledgements • This material is based upon work supported by the National Science Foundation under Grant Numbers: ANT-0537827, ANT-0636873, and ANT 0838834 The 5th Antarctic Meteorological Observations, Modeling, and Forecasting Workshop. Columbus, Ohio July 12-14, 2010.