Wind spatial structure triggers ENSO’s oceanic warm water volume changes.

Neske, Sonja , McGregor, Shayne , Zeller, Matthias and Dommenget, Dietmar (2021) Wind spatial structure triggers ENSO’s oceanic warm water volume changes. Open Access Journal of Climate, 34 . pp. 1985-1999. DOI 10.1175/JCLI-D-20-0040.1.

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Abstract

This study demonstrates that the generalization that strong anomalous equatorial Pacific westerly (easterly) winds during El Niño (La Niña) events displays strong adjusted warm water volume (WWV) discharges (recharges) is often incorrect. Using ocean model simulations, we categorize the oceanic adjusted responses to strong anomalous equatorial winds into two categories: (i) transitioning (consistent with the above generalization); and (ii) neutral adjusted responses (with negligible WWV re- and discharge) During the 1980-2016 period only 47% of strong anomalous equatorial winds are followed by transitioning adjusted responses, while the remaining are followed by neutral adjusted responses. Moreover, 55% (only 30%) of the strongest winds lead to transitioning adjusted responses during the pre-2000 (post-2000) period in agreement with the previously reported post-2000 decline of WWV lead time to El Niño-Southern Oscillation (ENSO) events. The prominent neutral adjusted WWV response is shown to be largely excited by anomalous wind stress forcing with a weaker curl (on average consistent with a higher ratio of off-equatorial to equatorial wind events) and weaker Rossby wave projection than the transitioning adjusted response. We also identify a prominent ENSO phase asymmetry where strong anomalous equatorial westerly winds (i.e., El Niño events) are roughly 1.6 times more likely to strongly discharge WWV than strong anomalous equatorial easterly winds (i.e., La Niña events) are to strongly recharge WWV. This ENSO phase asymmetry may be added to the list of mechanisms proposed to explain why El Niño events have a stronger tendency to be followed by La Niña events than vice versa.

Document Type: Article
Keywords: El Niño Southern-Oscillation (ENSO); warm water volume precursor; Rossby waves; wind stress curl; ENSO dynamics; ENSO asymmetry; Ocen Dynamics
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-OD Ocean Dynamics
Main POF Topic: PT2: Ocean and Cryosphere
Refereed: Yes
Open Access Journal?: No
Publisher: AMS (American Meteorological Society)
Date Deposited: 16 Dec 2020 12:15
Last Modified: 07 Feb 2024 15:52
URI: https://oceanrep.geomar.de/id/eprint/51316

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