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Climate Dynamics

, Volume 47, Issue 3–4, pp 1111–1125 | Cite as

Charging El Niño with off-equatorial westerly wind events

  • Shayne McGregorEmail author
  • Axel Timmermann
  • Fei-Fei Jin
  • William S. Kessler
Article

Abstract

The buildup of the warm water in the equatorial Pacific prior to an El Niño event is considered a necessary precondition for event development, while the event initiation is thought to be triggered by bursts of westerly wind. However, in contrast to the view that warm water slowly builds up years before an El Niño event, the volume of warm water in the equatorial Pacific doubled in the first few months of 2014 reaching values that were consistent with the warm water buildup prior to the extreme 1997/1998 El Niño. It is notable that this dramatic warm water buildup coincided with a series of westerly wind bursts in the western tropical Pacific. This study uses linear wave theory to determine the effect of equatorial and off-equatorial westerly wind events on the Warm Water Volume (WWV) of the Pacific. It is found that westerly wind events have a significant impact on equatorial WWV with all events initially acting to increase WWV, which highlights why WWEs are so effective at exciting ENSO. In fact, our results suggest that the single westerly wind burst, which peaked in the first few days of March in 2014, was largely responsible for the coincident dramatic observed increase in WWV. How long the equatorial region remains charged, however, depends on the latitude of the westerly wind event. For instance, a single equatorially symmetric westerly wind event ultimately acts to discharge WWV via the reflection of upwelling Rossby waves, which makes it difficult to more gradually build WWV given multiple WWEs. In contrast, when the wind events occur off the equator, the subsequent discharge is significantly damped and in some cases the equatorial region can hold the heat charge for the duration of the simulations (~6 months). As such, off-equatorial WWEs can not only charge equatorial region WWV in the short term, but are also a mechanism to more gradually build equatorial region WWV in the longer term. Given that these off-equatorial WWEs have a relatively small projection onto the equatorial Kelvin wave, we argue these events can be considered as a mechanism to modulate the background state in which ENSO operates.

Keywords

El Nino ENSO Warm water volume Westerly wind event Equatorially trapped wave theory 

Notes

Acknowledgments

SM would like to thank Mike McPhaden, Niklas Schneider, Leela Frankhome and Matthew. H. England for helpful discussions. We would also like to acknowledge the use of data from TAO Project Office of NOAA/PMEL.

References

  1. An S-I, Kang I-S (2001) Tropical Pacific basin-wide adjustment and oceanic waves. Geophys Res Lett 28:3975–3978. doi: 10.1029/2001GL013363 CrossRefGoogle Scholar
  2. Battisti DS (1988) The dynamics and thermodynamics of a warming event in a coupled tropical atmosphere/ocean model. J Atmos Sci 45:2889–2919CrossRefGoogle Scholar
  3. Bjerknes J (1969) Atmospheric teleconnections from the equatorial Pacific. Mon Wea Rev 97:163–172. doi: 10.1175/1520-0493(1969)097<0163:ATFTEP>2.3.CO;2 CrossRefGoogle Scholar
  4. Bosc C, Delcroix T (2008) Observed equatorial Rossby waves and ENSO-related warm water volume changes in the equatorial Pacific Ocean. J Geophys Res 113:C06003. doi: 10.1029/2007JC004613 CrossRefGoogle Scholar
  5. Cane MA, Sarachik ES (1977) Forced Baroclinic ocean motions. Part II: the linear bounded case. J Mar Res 35:395–432Google Scholar
  6. Cane MA, Zebiak SE (1985) A theory for El Niño and the southern oscillation. Science 228(4703):1085–1087. doi: 10.1126/science.228.4703.1085 CrossRefGoogle Scholar
  7. Chang P, Yamagata T, Schopf P, Behera SK, Carton J, Kessler WS, Meyers G, Qu T, Schott F, Shetye S, Xie S-P (2006) Climate fluctuations of tropical coupled systems—the role of ocean dynamics. J Clim 19:5122–5174CrossRefGoogle Scholar
  8. Chelton DB, Wentz FJ, Gentemann CL, de Szoeke RA, Schlax MG (1998) Satellite microwave SST observations of transequatorial tropical instability waves. Geophys Res Lett 27(1239–1242):2000Google Scholar
  9. Chiodi AM, Harrison DE (2015) Equatorial Pacific easterly wind surges and the onset of La Nina events. J Clim 28:776–792. doi: 10.1175/JCLI-D-14-00227.1 CrossRefGoogle Scholar
  10. Clarke AJ (2007) An introduction to the dynamics of El Niño & the Southern Oscillation, Academic Press, New York, 308 pp, ISBN: 978-0-12-088548-0Google Scholar
  11. Eisenman I, Yu L, Tziperman E (2005) Westerly wind bursts: ENSO’s tail rather than the dog? J Clim 18:5224–5238CrossRefGoogle Scholar
  12. Fedorov AV, Hu S, Lengaigne M, Guilyardi E (2014) The impact of westerly wind bursts and ocean initial state on the development, and diversity of El Niño events. Clim Dyn 44(5):1381–1401. doi: 10.1007/s00382-014-2126-4 Google Scholar
  13. Geise BS, Harrison DE (1990) Aspects of the Kelvin wave response to episodic wind forcing. J Geophys Res 95:7289–7312CrossRefGoogle Scholar
  14. Geise BS, Harrison DE (1991) Eastern equatorial Pacific response to three composite westerly wind types. J Geophys Res 96:3239–3248CrossRefGoogle Scholar
  15. Harrison DE, Vecchi GA (1997) Surface westerly wind events in the tropical Pacific 1986–1995. J Climate 10:3131–3156CrossRefGoogle Scholar
  16. Hasegawa T, Hanawa K (2003) Decadal-scale variability of upper ocean heat content in the tropical Pacific. Geophys Res Lett 30. doi: 10.1029/2002GL016843
  17. Jin F-F (1997) An equatorial ocean recharge paradigm for ENSO. Part I: conceptual model. J Atmos Sci 54:811–829CrossRefGoogle Scholar
  18. Kessler WS (1991) Can reflected extra-equatorial Rossby waves drive ENSO? J Phys Oceanogr 21(3):444–452CrossRefGoogle Scholar
  19. Kessler WS (2001) EOF representations of the Madden–Julian Oscillation and its connection with ENSO. J Clim 14:3055–3061CrossRefGoogle Scholar
  20. Kessler WS (2002) Is ENSO a cycle or a series of events? Geophys Res Lett 29(23):2125. doi: 10.1029/2002GL015924 CrossRefGoogle Scholar
  21. Kessler WS, Kleeman R (2000) Rectification of the Madden–Julian oscillation into the ENSO cycle. J Clim 13:3560–3575CrossRefGoogle Scholar
  22. Kessler WS, McPhaden MJ, Weickmann KM (1995) Forcing of intraseasonal Kelvin waves in the equatorial Pacific. J Geophys Res 100:10613–10631CrossRefGoogle Scholar
  23. Lengaigne M, Guilyardi E, Boulanger JP, Menkes C, Delecluse P, Inness P, Cole J, Slingo J (2004) Triggering of El Nino by westerly wind events in a coupled general circulation model. Clim Dyn 23:601–620CrossRefGoogle Scholar
  24. Lian T, Chen D, Tang Y, Wu Q (2014) Effects of westerly wind bursts on El Niño: a new perspective. Geophys Res Lett 41:3522–3527. doi: 10.1002/2014GL059989 CrossRefGoogle Scholar
  25. Matsuno T (1966) Quasi-geostrophic motions in the equatorial area. J Meteor Soc Jpn 44:25–43Google Scholar
  26. McGregor S, Timmermann A, Schneider N, Stuecker MF, England MH (2012) The effect of the South Pacific Convergence Zone on the termination of El Niño events and the meridional asymmetry of ENSO. J Clim 25:5566–5586. doi: 10.1175/JCLI-D-11-00332.1 CrossRefGoogle Scholar
  27. McGregor S, Ramesh N, Spence P, England MH, McPhaden MJ, Santoso A (2013) Meridional movement of wind anomalies during ENSO events and their role in event termination. Geophys Res Lett 40. doi: 10.1002/grl.50136
  28. McGregor S, Spence P, Schwarzkopf FU, England MH, Santoso A, Kessler WS, Timmermann A, Böning CW (2014) ENSO driven interhemispheric Pacific mass transports. J Geophys Res Oceans 119. doi: 10.1002/2014JC010286
  29. McPhaden MJ (1999) Genesis and evolution of the 1997–98 El Niño. Science 283:950–954CrossRefGoogle Scholar
  30. McPhaden MJ (2012) A 21st century shift in the relationship between ENSO SST and Warm Water Volume Anomalies. Geophys Res Lett 39:L09706. doi: 10.1029/2012GL051826 CrossRefGoogle Scholar
  31. McPhaden MJ, Yu X (1999) Equatorial waves and the 1997–98 El Niño. Geophys Res Lett 26:2961–2964CrossRefGoogle Scholar
  32. McPhaden MJ, Zebiak SE, Glantz MH (2006) ENSO as an integrating concept in earth science. Science 314:1740. doi: 10.1126/science.1132588 CrossRefGoogle Scholar
  33. Meinen CS, McPhaden MJ (2000) Observations of Warm Water Volume changes in the equatorial Pacific and their relationship to El Niño and La Niña. J Clim 13:3551–3559CrossRefGoogle Scholar
  34. Menkes CE, Lengaigne M, Vialard J, Puy M, Marchesiello P, Cravatte S, Cambon G (2014) About the role of Westerly Wind Events in the possible development of an El Niño in 2014. Geophys Res Lett 41:6476–6483. doi: 10.1002/2014GL061186 CrossRefGoogle Scholar
  35. Moore DW, Philander SGH (1977) Modeling of the tropical oceanic circulation. The Sea, vol 6Google Scholar
  36. Tollefson J (2014) El Niño tests forecasters. Nature 508(7494):20–21. doi: 10.1038/508020a CrossRefGoogle Scholar
  37. Vialard J, Menkes C, Boulanger J-P, Deleclus EP, Guilyardi E, McPhaden MJ, Madec G (2001) A model study of oceanic mechanisms affecting Equatorial Pacific sea surface temperature during the 1997–98 El Niño. J Phys Oceanogr 31(7):1649–1675CrossRefGoogle Scholar
  38. Wyrtki K (1985) Water displacements in the Pacific and the genesis of El Niño cycles. J Geophys Res Oceans 90:7129–7132CrossRefGoogle Scholar
  39. Zavala-Garay J, Moore AM, Perez CL (2003) The response of a coupled model of ENSO to observed estimates of stochastic forcing. J Clim 16:2827–2842CrossRefGoogle Scholar
  40. Zebiak (1989) Oceanic heat content variability and El Niño Cycles. J Phys Oceanogr 19:475–486CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Shayne McGregor
    • 1
    • 2
    Email author
  • Axel Timmermann
    • 3
    • 4
  • Fei-Fei Jin
    • 5
  • William S. Kessler
    • 6
  1. 1.School of Earth, Atmosphere and EnvironmentMonash UniversityClaytonAustralia
  2. 2.ARC Centre of Excellence for Climate System ScienceUniversity of New South WalesSydneyAustralia
  3. 3.International Pacific Research Center, SOESTUniversity of HawaiiHonoluluUSA
  4. 4.Department of Oceanography, SOESTUniversity of HawaiiHonoluluUSA
  5. 5.Department of Meteorology, SOESTUniversity of HawaiiHonoluluUSA
  6. 6.Pacific Marine Environmental LaboratoryNOAASeattleUSA

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