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Mechanisms controlling warm water volume interannual variations in the Equatorial Pacific: Diabatic versus adiabatic processes

Mechanisms controlling warm water volume interannual variations in the Equatorial Pacific: Diabatic versus adiabatic processes
Mechanisms controlling warm water volume interannual variations in the Equatorial Pacific: Diabatic versus adiabatic processes
Variations of the volume of warm water above the thermocline in the equatorial Pacific are a good predictor of ENSO (El Nin˜o/Southern Oscillation) and are thought to be critical for its preconditioning and development. In this study, the Warm Water Volume (WWV) interannual variability is analysed using forced general circulation model experiments and an original method for diagnosing processes responsible for WWV variations. The meridional recharge/discharge to higher latitudes drives 60% of the ENSO-related equatorial WWV variations, while diabatic processes in the eastern equatorial Pacific account for the remaining 40%. Interior meridional transport is partially compensated by western boundary transports, especially in the southern hemisphere. Diabatic equatorial WWV formation (depletions) during La Nina (El Nino) are explained by enhanced (reduced) diathermal transport through enhanced (reduced) vertical mixing and penetrating solar forcing at the 20?C isotherm depth. The respective contribution of diabatic and adiabatic processes during build-ups/depletions strongly varies from event-toevent.
The WWV build-up during neutral ENSO phases (e.g. 1980–1982) is almost entirely controlled by meridional recharge, providing a text-book example for the recharge/discharge oscillator’s theory. On the other hand, diabatic processes are particularly active during the strongest La Nina events (1984, 1988, 1999), contributing to more than 70% of the WWV build-up, with heating by penetrative solar fluxes explaining as much as 30% of the total build-up due to a very shallow thermocline in the eastern Pacific. This study does not invalidate the recharge/discharge oscillator theory but rather emphasizes the importance of equatorial diabatic processes and western boundary transports in controlling WWV changes.
El Nin˜o/Southern Oscillation ? Warm water volume ? Equatorial Pacific ? Western boundary currents ? Solar penetration ? Vertical mixing
0930-7575
1031-1046
Lengaigne, M.
64572929-e2cd-4234-83a5-0a6281c3ff97
Hausmann, U.
22b036fd-d098-4e23-b266-77bb07710d9f
Madec, G.
7e2ec04b-896a-4861-b2d0-b74f39d748c2
Menkes, C.E.
9839b7ef-4a80-4fab-9dd7-7d9a01ca9156
Vialard, J.
fb000633-202c-4606-b203-0fb9bac9db0e
Molines, J.M.
d3ef07f2-dd14-433f-9ef2-d16a9f1a0d60
Lengaigne, M.
64572929-e2cd-4234-83a5-0a6281c3ff97
Hausmann, U.
22b036fd-d098-4e23-b266-77bb07710d9f
Madec, G.
7e2ec04b-896a-4861-b2d0-b74f39d748c2
Menkes, C.E.
9839b7ef-4a80-4fab-9dd7-7d9a01ca9156
Vialard, J.
fb000633-202c-4606-b203-0fb9bac9db0e
Molines, J.M.
d3ef07f2-dd14-433f-9ef2-d16a9f1a0d60

Lengaigne, M., Hausmann, U., Madec, G., Menkes, C.E., Vialard, J. and Molines, J.M. (2012) Mechanisms controlling warm water volume interannual variations in the Equatorial Pacific: Diabatic versus adiabatic processes. Climate Dynamics, 38, 1031-1046. (doi:10.1007/s00382-011-1051-z).

Record type: Article

Abstract

Variations of the volume of warm water above the thermocline in the equatorial Pacific are a good predictor of ENSO (El Nin˜o/Southern Oscillation) and are thought to be critical for its preconditioning and development. In this study, the Warm Water Volume (WWV) interannual variability is analysed using forced general circulation model experiments and an original method for diagnosing processes responsible for WWV variations. The meridional recharge/discharge to higher latitudes drives 60% of the ENSO-related equatorial WWV variations, while diabatic processes in the eastern equatorial Pacific account for the remaining 40%. Interior meridional transport is partially compensated by western boundary transports, especially in the southern hemisphere. Diabatic equatorial WWV formation (depletions) during La Nina (El Nino) are explained by enhanced (reduced) diathermal transport through enhanced (reduced) vertical mixing and penetrating solar forcing at the 20?C isotherm depth. The respective contribution of diabatic and adiabatic processes during build-ups/depletions strongly varies from event-toevent.
The WWV build-up during neutral ENSO phases (e.g. 1980–1982) is almost entirely controlled by meridional recharge, providing a text-book example for the recharge/discharge oscillator’s theory. On the other hand, diabatic processes are particularly active during the strongest La Nina events (1984, 1988, 1999), contributing to more than 70% of the WWV build-up, with heating by penetrative solar fluxes explaining as much as 30% of the total build-up due to a very shallow thermocline in the eastern Pacific. This study does not invalidate the recharge/discharge oscillator theory but rather emphasizes the importance of equatorial diabatic processes and western boundary transports in controlling WWV changes.

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Published date: 2012
Keywords: El Nin˜o/Southern Oscillation ? Warm water volume ? Equatorial Pacific ? Western boundary currents ? Solar penetration ? Vertical mixing
Organisations: Marine Systems Modelling

Identifiers

Local EPrints ID: 174077
URI: https://eprints.soton.ac.uk/id/eprint/174077
ISSN: 0930-7575
PURE UUID: 29a66fd9-7adf-4cf8-90bc-289437c0bdbf

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Date deposited: 10 Feb 2011 11:51
Last modified: 18 Jul 2017 12:11

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Contributors

Author: M. Lengaigne
Author: U. Hausmann
Author: G. Madec
Author: C.E. Menkes
Author: J. Vialard
Author: J.M. Molines

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