T. Hirooka, T. Ichimaru (DEPS, Kyushu Univ.), H. Mukougawa (DPRI, Kyoto Univ.)

1. Chapman Conference Santorini, 24-28 Sep 2007 Predictability of stratospheric sudden warming events and associated stratosphere-troposphere coupling system T. Hirooka, T. Ichimaru (DEPS, Kyushu Univ.), H. Mukougawa (DPRI, Kyoto Univ.)

2. Motivation Observational errors and imperfection of numerical prediction models Predictable limit Few studies on the predictabilityin the stratosphere where different dynamics are dominant A practical predictable period for weather forecasts : 7 days To examine predictability of Stratospheric Sudden Warming (SSW) events by using the Japan Meteorological Agency (JMA) ensemble one-month forecast model

3. Contents • Comparison of the Observational Features of 3 Major SSWs in Dec 2001, Jan 2004 and Jan 2006 • Comparison of the Predictability of 3 Major SSWs • Statistics of the Predictability of Recent 12 Warmings During 2001/02 and 2005/06 Winters • Summary

4. Model and Data • 1-month forecast data of JMA ensemble prediction system • JMA operational Stratospheric assimilated data (Resolution) 1.25ºx 1.25º Lon-Lat grid spacing Vertical: 23 Pressure levels (1000hPa - 0.4hPa ) Resolution T106L40 hybrid coordinate Top Boundary 0.4 hPa Integration Period 34 days Number of Ensemble 13 members Perturbation Method BGM (Breeding of Growing Mode) Initialization Date Every Wednesday and Thursday Interval of Stored Data Daily (2.5 ºx 2.5 º) *Multiple forecasts from perturbed initial values to give the prediction reliability

5. Observational features of 3 Major SSWs (Dec 2001, Jan 2004, Jan 2006)

6. SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006 Easterlies (red) Westerlies (blue) Observation Latitude-timesections of zonal-mean Temperature and zonal wind at 10hPa Temperature Temperature Temperature 90N EQ Zonal wind Zonal wind Zonal wind 90N EQ Dec 2001 Jan 2002 Dec 2003 Jan 2004 Jan 2006 Major Minor Major Minor Major

7. Fz Fy deceleration (red) acceleration (blue) Observation Height-time sections of the averaged E-P flux and wave driving over 50-70N SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006 wave number 1 WN1 WN1 3hPa 200hPa wave number 2+3 WN2+3 WN2+3 3hPa 200hPa Major Major Minor Minor Major disturbed, wave number-1,2,3 contributing SSWs undisturbed, wave number-1 type SSW

8. Comparison of the Predictability of 3 Major SSWs

9. disturbed, Wave-1,2,3 contributing SHORT predictable period Weather forecast 7 days > Forecasts Time evolution of zonal mean temp. of ensemble forecasts at 10hPa, 80N undisturbed, Wave-1 type LONG predictable period SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006 16,15days before 23,22days before 18,17days before Minor Major Major Minor Major 16,15days before 9,8days before 11,10days before Dec 2001 Jan 2002 Dec 2003 Jan 2004 Jan 2006

10. Fz Fy deceleration (red) acceleration (blue) Observation Height-time sections of the averaged E-P flux and wave driving over 50-70N SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006 wave number 1 WN1 WN1 3hPa 200hPa wave number 2+3 WN2+3 WN2+3 3hPa 200hPa Major Major Minor Minor Major disturbed, wave number-1,2,3 contributing SSWs undisturbed, wave number-1 type SSW

11. －Predictability of wave number 1 component　－ SSW aftertheundisturbedsituation (Dec 2001) SSW after thedisturbedsituation (Jan 2004, Jan 2006) > Forecasts Time evolutionofnormalized Root Mean Square Errors(RMSE) estimated over 20N-90N at 10hPa SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006 16days before 8days before 10days before 2 2 2 WN1 WN1 WN1 1 1 1 0 0 0 Dec 2001 Jan 2004 Jan 2006 Forecasts Initialized 12 Dec Warming peak 28 Dec 1 Jan 9 Jan 12 Jan 22 Jan Forecasts height of Wave number 1 (WN1) Observational height of WN 1 standard deviation Observational amplitude of WN 1

12. SSW in Dec 2001 3-day averaged geopotential height at 500hPa Observation

13. SSW in Dec 2001 3-day averaged geopotential height at 500hPa Ensemble mean ( starting from 16,15 days before the warming peak )

14. Forecasts Time evolution ofNormalized RMSE (comparison of WN1 with WN2+3) SSW in Jan 2006 SSW in Jan 2004 8 days before 10days before 2 2 WN1 WN1 standard deviation 1 1 forecasts height of WN2,3 Observational height of WN2,3 0 0 Jan 2004 Jan 2006 Observational integrated amplitude of WN2,3 2 2 WN2+3 WN2+3 1 1 Predictability of each wave number component 0 0 WN 1 > WN 2+3 Jan 2004 Jan 2006 Forecasts Initialized 1 Jan Warming peak 9 Jan 12 Jan 22 Jan

15. Statistics of the Predictability of Recent 12 Warmings During 2001/02 and 2005/06 Winters

16. Here, • Extract major and (prominent) minor warmings during 2001/02 and 2005/06 NH winters 12 SSWs • Classify them into SSWs initiated from disturbed and undisturbed situation • Estimate their predictable periods

17. Predictable Period Diagram 15days (10days < 15days) t 10days Failed Case 20days Successful forecasts of SSW peaks 5days Predictable period 15days t Failed forecasts Successful Case (15days > 5days) 0 20days before 0 (warming peak) Days before the warming peak

18. Results at 10hPa(color) and 100hPa(black)

19. 12SSWsMajor & Minor • For initials near warming • peaks, predictable periods • become short. • SSWs initiated under undisturbed situation show better predictability. 16days 11days Undisturbed initials Disturbed initials 3days 2.5days

20. Summary • Predictable periods of SSWs differin a fairly wide range from one to three weeks in terms of RMSE as well as zonal mean temperature. • Predictability of SSWs initiated under undisturbed situation is better than that under disturbed situation. • Predictability is relatively low in case of SSWs with contributions from smaller-scale planetary waves.

22. 4 days Observation 10hPa geopotential height *undisturbed,Wave-1 type SSWin Dec 2001*disturbed, Wave-1,2,3 contributing SSWs in Jan 2004 and Jan 2006 SSW in Jan 2004 SSW in Jan 2006 SSW in Dec 2001 L L L H H H H H 2 days