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

Few studies on the predictability in 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 Motivation Observational errors and imperfection of numerical prediction models Predictable limit

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

1-month forecast data of JMA ensemble prediction system JMA operational Stratospheric assimilated data (Resolution) 1.25º x 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 º x 2.5 º) Model and Data *Multiple forecasts from perturbed initial values to give the prediction reliability

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

Observation Latitude-time sections of zonal-mean Temperature and zonal wind at 10hPa MajorMinorMajorMinorMajor SSW in Dec 2001SSW in Jan 2004SSW in Jan 2006 Temperature 90N EQ 90N EQ Zonal wind Temperature Zonal wind Temperature Zonal wind Westerlies (blue) Easterlies (red) Dec 2001 Jan 2002 Dec 2003 Jan 2004 Jan 2006

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

Comparison of the Predictability of 3 Major SSWs

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

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

SSW in Dec 2001SSW in Jan 2004SSW in Jan 2006 Forecasts Time evolution of normalized Root Mean Square Errors (RMSE) estimated over 20N-90N at 10hPa Warming peak 28 Dec 9 Jan22 Jan Forecasts Initialized 12 Dec 1 Jan12 Jan standard deviation Forecasts height of Wave number 1 (WN1) Observational height of WN 1 Observational amplitude of WN days before 8days before 10days before WN1 Dec 2001Jan 2004Jan 2006 － Predictability of wave number 1 component － SSW after the undisturbed situation (Dec 2001) SSW after the disturbed situation (Jan 2004, Jan 2006) >

SSW in Dec day averaged geopotential height at 500hPa Observation

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

WN1 standard deviation forecasts height of WN2,3 Observational height of WN2,3 Observational integrated amplitude of WN2,3 SSW in Jan 2004 SSW in Jan 2006 WN2+3 WN1 Forecasts Predictability of each wave number component WN 1 > WN 2+3 Time evolution of Normalized RMSE (comparison of WN1 with WN2+3) 8 days before10days before WN2+3 Jan 2004Jan 2006 Warming peak 9 Jan Forecasts Initialized 1 Jan 22 Jan 12 Jan Jan 2004

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

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

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

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

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

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

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