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

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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

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Outline

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

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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

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NCEP Reanalysis Data
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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

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

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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 52N.

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Significant
Insignificant
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Correlations of Zonal Winds over Vanscoy
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Significant
Insignificant
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Significant
Insignificant
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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.