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Equatorial Annual Cycle

Equatorial Annual Cycle. Shang-Ping Xie IPRC/Met, University of Hawaii 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 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. Mitchum, G. T., and Lukas, R. 1990: Westward propagation of annual sea level and wind signals in the western Pacific Ocean. J. Climate, 3, 1102-1110. Xie, S.-P., 1994: On the genesis of the equatorial annual cycle. J. Climate, 7, 2008-2013. Xie, S.-P., 2003: The shape of continents, air-sea interaction, and the rising branch of the Hadley circulation. In The Hadley Circulation: Past, Present and Future, H. F. Diaz and R. S. Bradley (eds.), Cambridge University Press. Available in pdf at http://iprc.soest.hawaii.edu/~xie

  2. 90W, Eq SST 165W, 20N

  3. SST Wind Cloud SST: Mean & Annual Harmonic Xie (2004, in Hadley Circulation …)

  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)

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

  7. OLR SST Sea surface height (cm) August-May Difference Mitchell and Wallace (1992)

  8. Buoy Measurements at 110W, Eq. Xie (1994)

  9. Simple Theory of Equatorial Annual Cycle 1D Ocean Linearization (coupling)

  10. Evaporation: E= Upwelling: Xie 1998, J. Climate, Eq. (2.5), p. 191. -1< <0 • 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)

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

  12. Model Results Xie 1994, J. Climate

  13. Response to cross-equatorial winds

  14. Dynamic Adjustment Mitchum and Lukas (1990)

  15. SSH Annual Harmonic (Upper) Amplitude of the annual harmonic of sea level height (SSH; shade > 5 cm) measured by T/P satellite. (Lower-right) Longitude-time section along 5N and (lower-left) latitude-time section at 165W of SSH.

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

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

  18. 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)

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

  20. 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.

  21. Atlantic equatorial cold tongue African monsoon + --

  22. Wind Stirring Ocean Storms Experiments (47.5N, 139.25W) tx ty Sept. 1, 1987 Large and Crawford (1995, JPO, p.2831)

  23. 80 60 40 20 Kessler

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