1. Can We Predict the Fall Turnaround in Zonal Wind over Vanscoy? D. Wunch, M. Tingley, G. W. K. Moore, T. G. Shepherd, D. Sankey, K. Strong, J. R. Drummond University of Toronto

2. 10th GCC Workshop, Toronto, December 16th and 17th 20022 Outline Definition of Turnaround Motivation for this Work Methodology Simple Historical Statistical Prediction Methods scoring fitting summer winds Looking for Memory in the System autocorrelations cross-correlations Summary

3. 10th GCC Workshop, Toronto, December 16th and 17th 20023 What is Zonal Wind Turnaround? Turnaround occurs when the zonal winds change direction: that is, when the vertical shear in zonal wind is zero. Turnaround is driven by temperature and is largely described by the thermal wind equation. Turnaround occurs twice per year: in March/April and August. The focus of this work has been to investigate the turnaround event in the Northern Hemisphere Fall, where the stratospheric winds change from easterly to westerly.

4. 10th GCC Workshop, Toronto, December 16th and 17th 20024 Motivation for this Work The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) Campaign consists of high-altitude balloon flights during which a suite of instruments are lifted to 40-km and atmospheric gas measurements are taken. The stratospheric winds during a high-altitude balloon campaign need to be very low for three reasons: 1. Launch 2. Telemetry 3. Recovery

5. 10th GCC Workshop, Toronto, December 16th and 17th 20025 Motivation Continued We would like to know when turnaround will occur over our launch site, Vanscoy, Saskatchewan (52°N, 107°W), within a couple of days, at least 30 days in advance. This will allow us to prepare our field campaign determine arrival dates at the field site allow the appropriate amount of time to prepare our instruments and the payload give us the opportunity to launch a sufficient number of sondes for flight validation

6. 10th GCC Workshop, Toronto, December 16th and 17th 20026 What Happens when the Launch Misses Turnaround: The Flight of the MANTRA 1998 Balloon The day following launch The two weeks following launch

7. 10th GCC Workshop, Toronto, December 16th and 17th 20027 Methodology We used NCEP Reanalysis and CMAM data to search for predictors for Fall turnaround over Vanscoy. First, simple historical trending was used to determine the most likely date for turnaround to occur. Second, we attempted to find measurable predictors that have a high correlation with turnaround at Vanscoy.

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9. 9 NCEP Reanalysis Data

10. 10th GCC Workshop, Toronto, December 16th and 17th 200210 Two Simple Predictions of Turnaround Date This work uses the NCEP reanalysis data. 1.For each year, the days corresponding to acceptably low stratospheric zonal wind speed were recorded, and a score was generated for each day of the year. The results give a predicted turnaround day of Julian day 240 (August 28th) with a standard deviation of almost 6 days. 2.A polynomial was fit to the region of low variability in the NH summertime, and the maximum easterly value of the zonal winds was correlated with the minimum wind value. No correlation was found.

11. 10th GCC Workshop, Toronto, December 16th and 17th 200211 NCEP Reanalysis Data

12. 10th GCC Workshop, Toronto, December 16th and 17th 200212 NCEP Reanalysis Data

13. 10th GCC Workshop, Toronto, December 16th and 17th 200213 NCEP Reanalysis Data

14. 10th GCC Workshop, Toronto, December 16th and 17th 200214 Looking for Memory in the System We have narrowed down the predicted date of turnaround, based on the previous historical trends. However, we have not found an acceptably accurate prediction of when turnaround will occur in a given year. We are looking for measurable predictors that will give information about when Fall turnaround will occur. We sought correlations to predict the zonal winds over Vanscoy at 10mb. Autocorrelations of the zonal winds at Vanscoy. Autocorrelations of the mean zonal wind at 52°N. Cross-correlations of the mean zonal wind to the zonal wind over Vanscoy. Cross-correlations of the NAM (Northern Hemisphere Annular Mode) Index to the zonal winds over Vanscoy. Cross-correlations of the mean zonal winds at 62.5°N to the zonal winds over Vanscoy.

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23. 10th GCC Workshop, Toronto, December 16th and 17th 200223 NCEP Reanalysis Data

24. 10th GCC Workshop, Toronto, December 16th and 17th 200224 NCEP Reanalysis Data

25. 10th GCC Workshop, Toronto, December 16th and 17th 200225 Summary - Can We Predict the Fall Turnaround in Zonal Wind over Vanscoy? Not yet. We can narrow down the turnaround date to day 241 (August 29 th ), with a standard deviation of just more than 3 days. There seems (so far) to be little memory in the system that extends to the fall turnaround time. We will continue to look for other possible correlations.