Preprints
https://doi.org/10.5194/os-2021-5
https://doi.org/10.5194/os-2021-5

  05 Feb 2021

05 Feb 2021

Review status: this preprint is currently under review for the journal OS.

On the Role of Westerly Wind Anomalies in the Development of the 1982–1983 El Niño

David J. Webb David J. Webb
  • National Oceanography Centre, Southampton SO14 3ZH, U.K.

Abstract. A recent study of two strong El Niños highlighted the potential importance of a region of low sea level that developed in the western equatorial Pacific prior to the El Niños of 1982–1983 and 1997–1998. Here the cause of the low sea level in 1982 is investigated using a series of runs of a global ocean model with different wind fields and initial conditions.

The results indicate that the low sea level was due to the increased wind shear that developed just north of the Equator during 1982. This generated Ekman divergence at the latitudes of the North Equatorial Trough, raising the underlying density surfaces and increasing the depth of the trough. This also increased the strength of the North Equatorial Counter Current which lies on the southern slope of the trough.

The anomalous westerly winds associated with Madden Julian Oscillations are often held responsible for triggering El Niños through the generation of westerly wind bursts and the resulting equatorial Kelvin waves in the ocean. However if Webb (2018) is correct, the present results imply that a different physical process was involved in which Ekman divergence due to the same winds, increased the heat transported by the North Equatorial Counter Current early in the year and ultimately caused the strong 1982–1983 El Niño.

David J. Webb

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on os-2021-5', D. Wang, 11 Mar 2021
    • AC1: 'Reply to review by D. Wang', David Webb, 13 Mar 2021
  • RC1: 'Comment on os-2021-5', Anonymous Referee #1, 12 Mar 2021
    • AC2: 'Response to Referee #1', David Webb, 13 Mar 2021
  • RC2: 'Comment on os-2021-5', Anonymous Referee #2, 05 Apr 2021
    • AC3: 'Response to Reviewer #2', David Webb, 06 Apr 2021
  • RC3: 'Comment on os-2021-5', Anonymous Referee #3, 16 Apr 2021
    • AC4: 'Reply on RC3', David Webb, 16 Apr 2021

David J. Webb

David J. Webb

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Short summary
Research on strong El Niños has shown that they may be triggered by a stronger than normal North Equatorial Counter Current (NECC). A computer model used to study the increased NECC, prior to the 1982–1983 El Niño, showed that it was due to strong westerly winds close to the Equator. Previously such winds were thought to affect El Niños by reversing ocean currents close to the Equator. However this study shows that it is their effect on the NECC which is critical.