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Can We Predict the Late Summer Turnaround in Zonal Wind over Vanscoy?

Can We Predict the Late Summer Turnaround in Zonal Wind over Vanscoy?. D. Wunch, M. Tingley, G. W. K. Moore, T. G. Shepherd, D. Sankey, K. Strong, James R. Drummond University of Toronto. Outline. Introduction Motivation Methodology data sets Looking for Memory in the System

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Can We Predict the Late Summer Turnaround in Zonal Wind over Vanscoy?

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

  2. Outline • Introduction • Motivation • Methodology • data sets • Looking for Memory in the System • autocorrelations • Summary

  3. What is Zonal Wind Turnaround? • Occurs when extra-tropical stratospheric zonal winds change direction • Driven by solar radiation • To first order is described by thermal wind equation • Occurs twice per year: in March/April and August • The focus: to investigate the turnaround event in the Northern Hemisphere late summer, where the stratospheric winds change from easterly to westerly

  4. NCEP Reanalysis Data

  5. 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

  6. When the Launch Misses Turnaround: The Flight of the MANTRA 1998 Balloon The two weeks following launch The day following launch

  7. Data Sets and Model Considered in the Study • NCEP/NCAR Reanalysis • 53-year data set • assimilated data • pressure lid at 10 mb • daily averages of zonal wind • UKMO Reanalysis • a 10-year data set • assimilated data • pressure lid at 0.32 mb • daily averages of zonal wind • CMAM Model Output • 24-year model output • pressure lid at 0.001 mb • 18-hourly data

  8. Looking for Memory in the System • Narrowed down predicted date of turnaround, based on historical trends. • Looking for measurable predictors to give information about when late summer turnaround will occur in a given year. • Recent evidence of persistence in stratospheric wind anomalies in wintertime (Baldwin & Dunkerton, 2001). • Sought correlations to predict the zonal winds over Vanscoy at 10mb. • Autocorrelations of zonal winds at Vanscoy. • Autocorrelations of mean zonal wind at 52°N.

  9. Significant Insignificant

  10. Correlations of Zonal Winds over Vanscoy

  11. Significant Insignificant

  12. Significant Insignificant

  13. Summary - Can We Predict the Late Summer Turnaround in Zonal Wind over Vanscoy? • Not yet. • There is little memory in the system that extends to the late summer turnaround time. • There is an interesting “cliff-like” structure in the correlations around the time of turnaround (a “predictability horizon”) • This phenomenon will be investigated further in the near future.

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