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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. 1976. What is regime shift?. 10-15 years. Mantua (1997). 10-15 years. 1976/77 regime shift. Motivation. From IPCC AR4.

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The late 1980s climate regime shift during boreal winter

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  1. The late 1980s climate regime shift during boreal winter Speaker : Tzu-Ting Lo Department of Atmospheric Sciences National Taiwan University

  2. 1976 What is regime shift? 10-15 years Mantua (1997) 10-15 years 1976/77 regime shift

  3. Motivation From IPCC AR4 Paper reviews:1980s regime shift

  4. Data Seasonwinter (JFM) Time1941-2002 Method Sequential t-test analysis of regime shifts (STARS) Rodionov (2004), Lo and Hsu (2007)

  5. Method-STARS Pdo-index length=10 When RSI (regime shift index) > 0, change point year is identified. A largerRSI yields more confidence on the identification.

  6. Change points in Northern Hemisphere in late 1980s Shaded: RSI > 0 East Asia: (90-140E, 30-60N) Europe: (0-50E, 40-70N) Eastern Canada: (80-110W, 15-40N) Kuroshio region: (140-180E, 30-45E) Southeastern N. America: (80-110W, 15-40N) Change year: 1987 2014/10/10 6

  7. 1987 9-year-running mean 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) 2014/10/10 7

  8. Cause – AO Westerly wind stronger AO index Eurasia warmer

  9. Jeong and Ho (2005) Relation between AO and EAM Gong (2001) There is significant out-of-phase relationship between AO and East Asian winter monsoon.

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

  11. Temp East Asia Contour: climatology Shaded: 1988-1997 subtract 1978-1987 SLP 500mb geopotential height u200 Precipitation

  12. 200mb wind H L H L 200mb vorticity

  13. Warming ? Wave activity flux Atlantic:30-60W average

  14. RSI Shaded > 0 JEDAC Surface SST (1988-1997) minus (1978-1987) 2014/10/10 14

  15. 200mb wind H L H 90-140E average shaded: temperature contour: u-wind vector: v-w L climatology (1988-1997) ― (1978-1987)

  16. illustration H L H warm L

  17. 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) 2014/10/10 17

  18. Conclusions • Using 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.

  19. Thank you for your attention!

  20. Outline Method and data Define regime shift region Change in circulation Look for possible causes, especially in East Asia 2014/10/10 22

  21. Introduction Comiso(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.

  22. new b a c t = 2.101(99%) 1960< b 1960> c Newregime 1 step1 step2 RSI< 0 l=10 R1=a P=0.01 Critical value b.c Back find new regime RSI change point is found, RSI reflect the confidence of regime shift RSI>0 1960>b 1960<c Smooth length find regime 1 diff= a+diff, a-diff are critical value 2014/10/10 24

  23. Regime Length=? t = 2.101(99%) L=8 L=10 L=12 2014/10/10 25

  24. 1966 1987 1966 1987 Ex: NCEP temperature (90-140E,30-60N) Length=10 t=2.101 Length=15 t=2.101 2014/10/10 26

  25. A. Europe 1987 B. East Asia C. Kuroshio region D. Eastern Canada E. Eastern America Lo and Hsu (2007) 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) 2014/10/10 27

  26. Summary : vertical velocity :kuroshio velocity : Zooplankton :fish SLP T SLP T SLP T T SLP

  27. Atlantic Temp Contour:climatology Shaded: 1988-1997 minus 1978-1987 SLP 500mb geopotential height u200 Precipitation

  28. Europe (0-50E average) vertical profile Shaded: w- downward w+ upward u-w u-w v-w

  29. Europe (0-50E average) vertical profile shaded: temperature contour: u-wind vector: v-w (1988-1997)minus(1978-1987) climatology Westerlies strong

  30. Shaded: w- downward w+ upward East part of North America (270-300E average) vertical profile u-w u-w v-w

  31. East part of North America (270-300E average) vertical profile shaded: temperature contour: u-wind vector: v-w (1988-1997)minus(1978-1987) climatology baroclinic wave

  32. Hurrel(1995) 2014/10/10 34

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

  34. East Asia (90-140E average) vertical profile shaded: temperature contour: u-wind vector: v-w climatology (1988-1997) ― (1978-1987) Why? Downward motion

  35. Watanabe(2004)

  36. EOF CRU+Hadisst temperature 1941-2002(JFM) 15% 1987 12% 1976 8% ? 2014/10/10 39

  37. AO-index EOF1 temperature EOF1 Temperature Cut(1987-2002) EOF1 Temperature Cut(1968-1987) 2014/10/10 40

  38. 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 2014/10/10 41

  39. Black: Europe Green:East asia Yellow:atlantic Red:South America 1987

  40. North europe:0-70E,55-70N North America:55-80W,50-70N South europe:0-45E,35-50N South America: 80-100W,30-45N East Asia: 80-120E,20-40N

  41. 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

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