the late 1980s climate regime shift during boreal winter

The late 1980s climate regime shift during boreal winter

Speaker : Tzu-Ting Lo

Department of Atmospheric Sciences

National Taiwan University

What is regime shift?

10-15 years

10-15 years

1976/77 regime shift

1976

Mantua (1997)

MotivationFrom IPCC AR4

variable region

Hare (2000)100 biological and physical index

North Eastern Pacific

Watanabe (1999) temperature East Asia

Comiso (2003) temperature polar region

Paper reviews:1980s regime shift

Data

Season winter (JFM) Time 1941-2002MethodSequential t-test analysis of regime shifts (STARS)Rodionov (2004), Lo and Hsu (2007)

CRU 2.0 x 2.0 1901-2002

Hadslp2 5.0 x 5.0 1871-2007

Hadisst 2.0 x 2.0 1870-2007

ERA40 2.5 x 2.5 1958-2001

BADC-H500 5.0 x 5.0 1945-2006

JEDAC 5.0 x 2.0 1955-2003

When RSI (regime shift index) > 0, change point year is identified. A larger RSI yields more confidence on the identification.

Pdo-index

Method-STARS

1,.....,1,0,*

,

lml

xRSI

mj

ji l

iji length=10

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Change points in Northern Hemisphere in late 1980s Shaded: RSI > 0

Europe: (0-50E, 40-70N)East Asia: (90-140E, 30-60N)

Kuroshio region: (140-180E, 30-45E)Southeastern N. America: (80-110W, 15-40N)

Eastern Canada: (80-110W, 15-40N)

Change year: 1987

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Black--Europe: (0-50E, 40-70N) Green--East Asia:(90-140E, 30-60N)Blue--Kuroshio region:(140-180E, 30-45E) Red--Eastern Canada:(50-90W, 50-70N)Orange--Southeastern N. America: (80-110W, 15-40N)

19879-year-running mean

AO index Westerly wind stronger

Eurasia warmer

Cause – AO

Jeong and Ho (2005)

Gong (2001) There is significant out-of-phase relationship between AO and East Asian winter monsoon.

Relation between AO and EAM

Besides Arctic oscillation, was there any other factor which strengthen the warming in the East Asia?

Temp

SLP 500mb geopotential height

Precipitationu200

Contour: climatologyShaded: 1988-1997 subtract 1978-1987

East Asia

HHHH

LL LL

200mb wind

200mb vorticity

Wave activity flux

Warming ?

Atlantic:30-60W average

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RSIShaded > 0

JEDAC Surface SST(1988-1997) minus (1978-1987)

90-140E averageshaded: temperature contour: u-wind vector: v-w

HH

HHLL

LL

200mb wind

climatology(1988-1997) ― (1978-1987)

warm

illustration

The abrupt warming in East Asia is strong.

Major characteristics include:

weaker-than-normal Aleutian low and Siberian high

low-level northeasterly along the East Asian coast weakened

AO index changed from negative to positive--

strengthening polar vortex and less southward penetration of polar cold air

descending motion in East Asia (wave + hill)

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ConclusionsUsing change-point analysis, five temperature shift regions, i.e., Europe, East Asia, Kuroshio, Southeastern N. America and Eastern Canada, are defined.

After 1987, not only temperature but also sea level pressure, wind and precipitation change simultaneously.

When the AO index changed from negative to positive, some place including Europe and Asia became warmer, because of the strengthening polar vortex and less southward penetration of polar cold air.

Strong wave activity was forced by the warmer Atlantic SST after 1987, indicating wave energy propagation from the Atlantic to East Asia. This may be a factor that strengthened the descending motion in East Asia.

Thank you for your attention!

OutlineMethod and data

Define regime shift region

Change in circulation

Look for possible causes, especially in East Asia

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IntroductionComiso(2003)

After 1987/88, temperature was warming in the midlatitude and cooling in the polar region.

Walsh et al.(1996) After the late 1980s, sea level pressure increased in the

midlatitude and decreased in the polar region.

Watanabe et al.(1999). Temperature in East Asia increased and the snow content

decreased after the late 1980s.

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t = 2.101(99%)

b

ca

l=10 R1=a

P=0.01Critical value b.c

RSI

Smooth length find regime 1

lt l22diff=

step1 step2

a+diff, a-diff are critical value

change point is found, RSI reflect the confidence of regime shift

1960>b1960<c

1960< b1960> c New regime 1

RSI>0

RSI< 0Back find new regime

1,.....,1,0,*

,

lml

xRSI

mj

ji l

iji

new

Change-point year RSI

L=8 1987 0.54

L=10 1987 0.63

L=12 1971 & 1987 0.07 & 0.67

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t = 2.101(99%)

Regime Length=?

L=8

L=10

L=12

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Ex: NCEP temperature (90-140E,30-60N) Length=10 t=2.101

1966 19871966 1987

Length=15 t=2.101

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A. Europe

B. East Asia

C. Kuroshio region

D. Eastern Canada

E. Eastern America

five regions

count number of change points with positive RSI

in the five region

(use STARS method)

standardized time series

identify the year of regime shift (greater than 1 standard deviation and max)

Lo and Hsu (2007)

1987

TSLP

TSLP

TSLP

TSLP

: Zooplankton

: vertical velocity

:kuroshio velocity

:fish

Summary

Temp

SLP 500mb geopotential height

Precipitationu200

Contour:climatologyShaded: 1988-1997 minus 1978-1987

Atlantic

Europe (0-50E average) vertical profile

Shaded: w- downward w+ upward

u-w

u-w

v-w

Europe (0-50E average) vertical profile

shaded: temperature contour: u-wind vector: v-w

climatology (1988-1997)minus(1978-1987)

Westerlies strong

East part of North America (270-300E average) vertical profile

u-w

u-w

v-w

Shaded: w- downward w+ upward

East part of North America (270-300E average) vertical profile

shaded: temperature contour: u-wind vector: v-w

climatology (1988-1997)minus(1978-1987)

baroclinic wave

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Hurrel(1995)

Divergent wind (1988-1997)-(1978-1987)

East Asia (90-140E average) vertical profile

shaded: temperature contour: u-wind vector: v-w

climatology (1988-1997) ― (1978-1987)

Downward motionWhy?Why?

Watanabe(2004)

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CRU+Hadisst temperature 1941-2002(JFM)

15%

12%

8%

1976

1987

?

EOF

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AO-index

EOF1temperature

EOF1TemperatureCut(1987-2002)

EOF1TemperatureCut(1968-1987)

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Black--Europe: (0-60E,60-80N)Green--East Asia:(95-155E,55-80N)Blue--Atlantic: (25-85W,60-80N)Red--South America: (45-105W,30-50N)Orange--Tropical Atlantic:(25-65W,0-30N)

1987

Black: EuropeGreen:East asiaYellow:atlanticRed:South America

1987

North europe:0-70E,55-70N

South europe:0-45E,35-50N

East Asia: 80-120E,20-40N

North America:55-80W,50-70N

South America: 80-100W,30-45N

Black(North europe:0-70E,55-70N)

Green(South europe:0-45E,35-50N)

Yellow(East Asia: 80-120E,20-40N)

Red(North America:55-80W,50-70N)

Pink(South America: 80-100W,30-45N)

1987