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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 ConferenceSantorini, 24-28 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
MotivationObservational 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 coordinateTop Boundary 0.4 hPaIntegration Period 34 daysNumber of Ensemble 13 membersPerturbation Method BGM (Breeding of Growing Mode)Initialization Date Every Wednesday and ThursdayInterval 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 2001 SSW in Jan 2004 SSW in Jan 2006Temperature
90N
EQ
90N
EQ
Zonal wind
Temperature
Zonal wind
Temperature
Zonal wind
Westerlies(blue)
Easterlies(red)
Dec2001
Jan2002
Dec2003
Jan2004
Jan2006
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 2004 SSW in Jan 2006
Fy
Fz
MajorMinorMinorMajor
wave number 1 WN1 WN1
wave number 2+3 WN2+3 WN2+3
3hPa
200hPa
undisturbed, wave number-1 type SSW
disturbed, wave number-1,2,3 contributing SSWs
3hPa
200hPa
Comparison of the Predictabilityof
3 Major SSWs
Forecasts Time evolution of zonal mean temp. of ensemble forecasts at 10hPa, 80N
SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006
Major
23,22days before
undisturbed, Wave-1 type LONG predictable period
disturbed, Wave-1,2,3 contributing SHORT predictable period
Weather forecast7 days>
16,15days before 18,17days before
16,15days before 9,8days before 11,10days before
MajorMinor MajorMinor
Dec2001
Jan2002
Dec2003
Jan2004
Jan2006
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 2004 SSW in Jan 2006
Fy
Fz
MajorMinorMinorMajor
wave number 1 WN1 WN1
wave number 2+3 WN2+3 WN2+3
3hPa
200hPa
undisturbed, wave number-1 type SSW
disturbed, wave number-1,2,3 contributing SSWs
3hPa
200hPa
SSW in Dec 2001 SSW in Jan 2004 SSW in Jan 2006
Forecasts Time evolution of normalized Root Mean Square Errors (RMSE) estimated over 20N-90N at 10hPa
Warming peak28 Dec 9 Jan 22 Jan
Forecasts Initialized 12 Dec 1 Jan 12 Jan
21
211
21
1
A
ZZNRMSE
N
iigif
standard deviation
1A
1fZ
1gZ
Forecasts height of Wave number 1 (WN1)
Observational heightof WN 1
Observational amplitude of WN 1
1
0
2
1
0
2
1
0
216days before 8days before 10days before
WN1 WN1 WN1
Dec 2001 Jan 2004 Jan 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 2001 3-day averaged geopotential height at 500hPa
Observation
SSW in Dec 2001 3-day averaged geopotential height at 500hPa
Ensemble mean ( starting from 16,15 days before the warming peak )
WN1
kk
N
iigif
A
ZZNRMSE
2
2
21
1
standard deviation
kA
fZ
gZ
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
1
0
2
1
0
2
1
0
2
1
0
2
Predictability of each wave number component
WN 1 > WN 2+3
Time evolution of Normalized RMSE(comparison of WN1 with WN2+3)
8 days before 10days before
WN2+3
Jan 2004 Jan 2006
Jan 2006Warmingpeak9 Jan
ForecastsInitialized
1 Jan22 Jan12 Jan
Jan 2004
Statistics of the Predictabilityof
Recent 12 WarmingsDuring 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
Predictableperiod
Days before the warming peak
0 (warming peak)20days before0
20daysSuccessful
forecasts of SSWpeaks
Failedforecasts
(15days > 5days)
(10days < 15days)10days
15days
15days
5days
Failed Case
SuccessfulCase
t
t
Predictable PeriodDiagram
Results at 10hPa(color) and 100hPa(black)
Undisturbed initials Disturbed initials
12SSWs Major & Minor •For initials near warmingpeaks, 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 2004 SSW in Jan 2006
H
LH
L
HH
L
H
*undisturbed, Wave-1 type SSW
in Dec 2001
*disturbed, Wave-1,2,3 contributing
SSWs in Jan 2004 and Jan 2006
4 days 2 days
Observation
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