1. Dynamic Climatology Presentation Speaker ： Pei-Yu Chueh Date ： 2011/01/10

2. Extratropical control of recent tropical Pacific decadal climate variability: a relay teleconnection Lixin Wu, Zhengyu Liu, Chun Li and Yan Sun (2006) Data: – ATM: NCEP reanalysis data – OCEAN: HadISST – MODEL: FOAM

3. Observational evidence Recent tropical Pacific decadal climate change may be associated with the surface wind changes over the extratropical North Pacific. – Fast coupled ocean-atmosphere surface bridge – Slow oceanic tunnel Nearly consistent equatorward drift. EP 160W-120W

4. Anomalous cyclonic wind → Warm SST with southwest trades → reduce the evaporative heat loss Generate warming in the tropics in the following season Bjerknes’s feedback Wind-evaporative-SST (WES) feedback WK HL anomalous westerlies

5. Warm SST mostly stay in the north of 10N Southwesterly and positive (downward) heat flux extend Southwesterly reduce evaporative heat loss, leading to a development of warm SST anomalies in late spring and summer Warm SST initiated around May, with reduction of turbulent heat loss and weakening of equatorial easterlies. WP,CP

6. Subtropical-Tropical Cell (STC) A weaker STC pumps less extratropical thermocline cold water into tropics, leading to warming in the tropics Attribute to weakening of northeast trades Reach equatorial region Warm anomalies in subtropics appear to penetrate to lower latitudes EP 170W-120W

7. The weakening of the northeast trades persists from mid-1970s to early 1990s. Origin of the weakening isn’t well understood. Observational analysis suggests that → WES feedback → anomalous westerlies → potentially slow down the STC → enhance tropical warming WP,CP

8. modelobservation

9. modelobservation WP,CP

10. modelobservation EP

11. Change of meridional overturning circulation Weakening of the STC → surface anomalous westerlies (by WES) Reduction of mass transport Broad meridional extension Unit: Sv (10 6 m 3 /s)

12. Conclusions Persistent strengthening of the Aleutian Low

13. ~End~