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Dynamic Climatology Presentation

Dynamic Climatology Presentation. Speaker ： Pei-Yu Chueh Date ： 2011/01/10. Extratropical control of recent tropical Pacific decadal climate variability: a relay teleconnection. Data: ATM: NCEP reanalysis data OCEAN: HadISST MODEL: FOAM. Lixin Wu, Zhengyu Liu, Chun Li and Yan Sun (2006).

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Dynamic Climatology Presentation

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  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 • Data: • ATM: NCEP reanalysis data • OCEAN: HadISST • MODEL: FOAM Lixin Wu, Zhengyu Liu, Chun Li and Yan Sun (2006)

  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. Wind-evaporative-SST (WES) feedback • 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 K W H L anomalous westerlies

  5. <winter, subtropics> • 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 <late spring, tropics> • 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 Warm anomalies in subtropics appear to penetrate to lower latitudes Reach equatorial region 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. model observation

  9. model observation WP,CP

  10. model observation 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 (106 m3/s)

  12. Conclusions • Persistent strengthening of the Aleutian Low

  13. ~End~

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