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Equatorial Annual Cycle

Equatorial Annual Cycle. Shang-Ping Xie IPRC/Met, University of Hawaii Ocean University of China PowerPoint file available at http://iprc.soest.hawaii.edu/~xie/ppt/annual.ppt. References

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Equatorial Annual Cycle

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  1. Equatorial Annual Cycle Shang-Ping Xie IPRC/Met, University of Hawaii Ocean University of China PowerPoint file available at http://iprc.soest.hawaii.edu/~xie/ppt/annual.ppt References Mitchell, T.P. and J.M. Wallace, 1992: The annual cycle in equatorial convection and sea surface temperature. J. Climate, 5, 1140-1156. Xie, S.-P., 1994: On the genesis of the equatorial annual cycle. J. Climate, 7, 2008-2013.

  2. 90W, Eq SST 165W, 20N Galapagos SST and Precipitation

  3. ENSO’s Seasonal Phase Locking Nino3 std dev Calendar Month

  4. Equatorial Annual Cycle T u v • Why annual? • Why Strong in the east? • Why propagate westward?

  5. i[ wt - f(x) ] t = A(x)e ty ty tx tx A(x) f(x) Lukas and Firing (1985, J. Phys. Oceanogr.) cf. Horel (1982, Mon. Wea. Rev.)

  6. SST, Precipitation and Surface Winds Mar-Apr Aug-Sept

  7. Sept-Mar SST & Wind Diff (COADS) August-May Difference Sea surface height (cm) cf. Mitchell and Wallace (1992)

  8. Buoy Measurements at 110W, Eq. From Xie (1994, JC) Why is the annual cycle in h small in the Eq Pacific?

  9. Linearization (coupling) Simple Theory of Equatorial Annual Cycle 1D Ocean  How to make this coupled equation unstable? Hint: atmospheric model.

  10. Evaporation: E= Upwelling: Xie 1998, J. Climate, Eq. (2.5), p. 191. -1< <0 cf: Giese & Carton (1994, JC); Chang (1996, JC) • Northward displaced ITCZ ( >0)  Annual frequency (V’); • Tilt of the thermocline H(x)  Stronger annual cycle in the east; • Prevailing easterlies ( <0)  Westward phase propagation. (Xie 1994, J. Climate, p.2008) cf: Liu & Xie (1994, JAS)

  11. |V|  Annual |V|  Annual 0 Annual V’ in both cases

  12. Temperature along equator SST’ & u’ at Eq - + Veq

  13. Model Results Xie 1994, J. Climate

  14. Response to cross-equatorial winds Philander & Pacanowski (1981, Tellus)

  15. SST Wind Cloud SST: Mean & Annual Harmonic

  16. Sensitivity to the length of year 1 yr = 12 mon 1 yr = 18 mon SST tx ty Giese and Carton (1994, JC)

  17. Control Flux corrected Li and Hogan (1999, JC)

  18. Improved the mean state (asymmetrical about the equator)  Annual cycle on the equator Control Annual-mean correction Obs Seasonal correction Li and Hogan (1999, JC)

  19. Prescribed observed cloudiness in a CGCM • Improved the mean state (asymmetrical about the equator) • Seasonal forcing by cloud Gordon et al. (2000, JC) Yu and Mechoso (1999, JC)

  20. Pacific 110oW, Eq Atlantic 0o, Eq

  21. Equatorial Annual Cycle in the Atlantic Ocean dynamics play a more important role Depth (m) Houghton (1983, JPO, p. 2070)

  22. Annual-mean March-April July-August

  23. I year I year Annual cycle in the equatorial oceans Mitchell and Wallace (1992) Role of Air-sea interaction

  24. CTL-APR CTL run APR run June April Longitude Seasonal cycle of equatorial zonal wind:(1) Local air-sea interaction Ueq (m/s)

  25. ITCZ Eq. Monsoon Effect June-April diff in APR run with cold tongue removed Surface wind & precip Equatorward momentum advection Mean

  26. Monsoon  Cold tongue Cold tongue effect CTL-APR anomalies in June Surface wind (m/s) and precipitation (mm/day) Monsoon effect June-April diff in APR run with cold tongue removed Okumura and Xie (2004, J. Climate)

  27. Summary • Northward displaced ITCZ  Annual frequency (V’) • Tilt of the thermocline  Stronger annual cycle in the east • Prevailing easterlies  Westward phase propagation • While secondary in the eastern Pacific, ocean dynamics are important for equatorial annual cycle in the Atlantic. • Atlantic equatorial cycle is strongly influenced by continents and African monsoon in particular.

  28. Eq IO seasonal cycle: uncoupledin the central basin tx SST uo SST  cloud: 1 yr Zonal wind & current: 0.5 yr Wyrtki jets

  29. T = 0.5 year (period) L = 5,6327 km (basin width) K R K wind wind Basin-mode resonance at the semi-annual period Jensen (1993, JGR,22 533-); Han et al. (1999, JPO, 2191-) Cn=163 cm/s, m = 1, Cn = 82 cm/s, m =2, Cane and Sarachik (1981, JMR); Cane and Moore (1981, JPO)

  30. AVHRR SST (C, 5-day, 85-99) COADS Zonal Wind (m/s) Nov Nov TOPEX/Poseidon SSH (cm) COADS SST (C) Nov easterly acceleration and SST response

  31. Nov Jun Thermocline depth control of SST variability Rms SST (1982-2003) T/P SSH (cm) 20W 0 40W Yuko Okumura, U of Hawaii

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