the late 1980s climate regime shift during boreal winter
DESCRIPTION
The late 1980s climate regime shift during boreal winter. Speaker : Tzu-Ting Lo Department of Atmospheric Sciences National Taiwan University. 1976. What is regime shift?. 10-15 years. Mantua (1997). 10-15 years. 1976/77 regime shift. Motivation. From IPCC AR4. - PowerPoint PPT PresentationTRANSCRIPT
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