Dongqian Wang

Bing Zhou Chenghu Sun

The features of EAWM 2012/13 and possible influencing factors

Beijing Climate Center04-09-2013

1) The climate in DJF 2012/13

2) Features of 2012/13 EAWM

3) Possible influencing factors of EAWM

4) Summary

Outline

冷！cold

暖！warm

Temperature Anomalies (DJF 2012/13)

colder than normal in most places of the world.

1-4 below normal in central-℃northeastern Asia, with temperatures more than 4 below normal in ℃northern East Asian and parts of southern Russia.

Monthly Temperature Anomalies Dec 2012 Jan 2013

Feb 2013

strong intra-seasonal variations

8-12 below normal in central and ℃western Siberia in December, and in late winter, the colder regions shifted eastward.

DJF Temperature index of China

In DJF 2012/13, the seasonal mean temperatures over China was -3.7°C, with 0.3°C below normal (-3.4 ). ℃

Stronger Siberian High and EAWM

Smallest Arctic Sea Ice extent in Sep. since 1979.

Slighter stronger Indian Ocean(IOBW).

CGCM1.0/BCC

Slight weaker Arctic Oscillation

cold

warm

cold

Slight stronger Tibetan Plateau Height

Prediction of Winter Temperature Anomaly over China

Precipitation Anomalies (DJF 2012/13)

少！

多！

dry

wet

50-100% more than normal in most West Asia, Central Asia, central South Asia, most Northeast China

at least 50% less than normal in central-northern Russia, most Southwest China.

1) The climate in DJF 2012/13

2) Features of 2012/13 EAWM

3) Possible influencing factors of EAWM

4) Summary

Time series of EAWM index

Strong

Weak

EAWM =U500(80-120E;25-35N)-U500(80-120E,50-60N)

as proposed by Y.F Zhu(2008)

East Asian winter monsoon (EAWM) was in the stronger than normal period of inter-decadal variation, was stronger than normal for 6th consecutive year

Time series of SH index

The Siberian High (SH) was also in the stronger than normal period of inter-decadal variation, but in last winter, SH was weaker than normal

)6040;12080( NESLPSH

EAWM

The first threecomponents of EOF of winter temperature fields

Temperature anomalies in winter 2012/13

EAWMAtmospheric circulation anomalies correspond to EAPC-1

Atmospheric circulation anomalies in winter 2012/13

EAWM

850hPa wind anomalies correspond to EAPC-1

850hPa wind anomalies in winter 2012/13

southerly wind anomalies

easterly wind anomalies

Daily Siberian High index

exhibited strong intra-seasonal variations , stronger than normal in the early winter, weaker than normal in the middle winter and changed from strong to weak in the late winter

Daily EAWM index

Strong

Weak

strong intra-seasonal variations

1) The climate in DJF 2012/13

2) Features of 2012/13 EAWM

3) Possible influencing factors of EAWM

4) Summary

a) AO

Arctic Oscillation kept negative phase

Correlation between AO

and Surface air temperature

Correlation between AO

and 200hPa zonal wind

b) pre-autumn Artic sea ice

Distribute of pre-autumn Artic sea ice

Arctic sea ice extent was significantly lower than normal since summer 2012. The Arctic Sea Ice Extent and concentration in Sep.2012 are the smallest since 1979

Studies show that ASI anomaly in Sep. has significantly negative correlation with Siberian High.

c) Propagation of positive stratospheric anomalies

weak polar vortex in the stratosphere

stratospheric sudden warming

Downward propagation of positive stratospheric anomalies

150hPa outgoing heat flux

20hPa zonal wind

an anomalous strengthen of outgoing heat flux

the convergence of heat flux at stratosphere lead to the deceleration of polar night jet

suppressed the outgoing of heat flux, lead to a sudden warming happened in the stratosphere.

The atmospheric circulation adjust to the radiation balance in the non-adiabatic process, resulting in strengthen of polar night jet.

In this process, polar night jet was weaker than normal, which was conducive to the changing of AO from positive to negative, or the persistence of negative AO

The 1000hPa GPH anomalies composited with respect to positive anomaly downward propagation events

(Chen, 2009)

01.11-02.28 mean SLP anomalies

1) The climate in DJF 2012/13

2) Features of 2012/13 EAWM

3) Possible influencing factors of EAWM

4) Summary

Summary

　 In DJF 2012/2013, temperatures were extremely below normal over East Asian, with key circulations as following:

-The EAWM intensity exhibited strong intra-seasonal variations

-Arctic Oscillation kept negative phase

-Low pre-autumn Arctic Sea ice might be the influencing factors on EAWM

-The downward propagation of stratospheric anomalies was the possible causes of intra-seasonal climatic variation over East Asian.