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

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

4. uvT Equatorial Annual Cycle  Why annual?  Why Strong in the east?  Why propagate westward?

5. Lukas and Firing (1985, J. Phys. Oceanogr.) xx xx yy yy  = A(x) e i[  t -  (x) ] A(x)  (x) cf. Horel (1982, Mon. Wea. Rev.)

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

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

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

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

10.  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) Evaporation: E= Upwelling: Xie 1998, J. Climate, Eq. (2.5), p. 191. -1< <0 cf: Giese & Carton (1994, JC); Chang (1996, JC)

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

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

13. Xie 1994, J. Climate Model Results

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 SST xx yy 1 yr = 12 mon1 yr = 18 mon Giese and Carton (1994, JC)

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

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

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

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

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

22. Annual-mean March-April July-August

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

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

25. Surface wind & precip Monsoon Effect June-April diff in APR run with cold tongue removed ITCZ Eq. 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.  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. Summary

28. Eq IO seasonal cycle: uncoupled in the central basin SST xx uouo Wyrtki jets SST  cloud: 1 yr Zonal wind & current: 0.5 yr

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

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

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