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Impact of resolving the diurnal cycle in an ocean–atmosphere GCM. Part 1: a diurnally forced OGCM

Impact of resolving the diurnal cycle in an ocean–atmosphere GCM. Part 1: a diurnally forced OGCM
Impact of resolving the diurnal cycle in an ocean–atmosphere GCM. Part 1: a diurnally forced OGCM
The diurnal cycle is a fundamental time scale in the climate system, at which the upper ocean and atmosphere are routinely observed to vary. Current climate models, however, are not configured to resolve the diurnal cycle in the upper ocean or the interaction of the ocean and atmosphere on these time scales. This study examines the diurnal cycle of the tropical upper ocean and its climate impacts. In the present paper, the first of two, a high vertical resolution ocean general circulation model (OGCM), with modified physics, is developed which is able to resolve the diurnal cycle of sea surface temperature (SST) and current variability in the upper ocean. It is then validated against a satellite derived parameterization of diurnal SST variability and in-situ current observations. The model is then used to assess rectification of the intraseasonal SST response to the Madden–Julian oscillation (MJO) by the diurnal cycle of SST. Across the equatorial Indo-Pacific it is found that the diurnal cycle increases the intraseasonal SST response to the MJO by around 20%. In the Pacific, the diurnal cycle also modifies the exchange of momentum between equatorially divergent Ekman currents and the meridionally convergent geostrophic currents beneath, resulting in a 10% increase in the strength of the Ekman cells and equatorial upwelling. How the thermodynamic and dynamical impacts of the diurnal cycle effect the mean state, and variability, of the climate system cannot be fully investigated in the constrained design of ocean-only experiments presented here. The second part of this study, published separately, addresses the climate impacts of the diurnal cycle in the coupled system by coupling the OGCM developed here to an atmosphere general circulation model.
0930-7575
575-590
Bernie, D.J.
48ce2ca0-8eb5-480d-9eb4-0c8b3506178a
Guilyardi, E.
d8e3cd51-7353-401c-994a-7bee46dc4b6b
Madec, G.
7e2ec04b-896a-4861-b2d0-b74f39d748c2
Slingo, J.M.
2e390b0a-d76e-4896-8234-3b24aeac0512
Woolnough, S.J.
80ef891d-d64b-4048-808a-1b2152f2c36d
Bernie, D.J.
48ce2ca0-8eb5-480d-9eb4-0c8b3506178a
Guilyardi, E.
d8e3cd51-7353-401c-994a-7bee46dc4b6b
Madec, G.
7e2ec04b-896a-4861-b2d0-b74f39d748c2
Slingo, J.M.
2e390b0a-d76e-4896-8234-3b24aeac0512
Woolnough, S.J.
80ef891d-d64b-4048-808a-1b2152f2c36d

Bernie, D.J., Guilyardi, E., Madec, G., Slingo, J.M. and Woolnough, S.J. (2007) Impact of resolving the diurnal cycle in an ocean–atmosphere GCM. Part 1: a diurnally forced OGCM. Climate Dynamics, 29 (6), 575-590. (doi:10.1007/s00382-007-0249-6).

Record type: Article

Abstract

The diurnal cycle is a fundamental time scale in the climate system, at which the upper ocean and atmosphere are routinely observed to vary. Current climate models, however, are not configured to resolve the diurnal cycle in the upper ocean or the interaction of the ocean and atmosphere on these time scales. This study examines the diurnal cycle of the tropical upper ocean and its climate impacts. In the present paper, the first of two, a high vertical resolution ocean general circulation model (OGCM), with modified physics, is developed which is able to resolve the diurnal cycle of sea surface temperature (SST) and current variability in the upper ocean. It is then validated against a satellite derived parameterization of diurnal SST variability and in-situ current observations. The model is then used to assess rectification of the intraseasonal SST response to the Madden–Julian oscillation (MJO) by the diurnal cycle of SST. Across the equatorial Indo-Pacific it is found that the diurnal cycle increases the intraseasonal SST response to the MJO by around 20%. In the Pacific, the diurnal cycle also modifies the exchange of momentum between equatorially divergent Ekman currents and the meridionally convergent geostrophic currents beneath, resulting in a 10% increase in the strength of the Ekman cells and equatorial upwelling. How the thermodynamic and dynamical impacts of the diurnal cycle effect the mean state, and variability, of the climate system cannot be fully investigated in the constrained design of ocean-only experiments presented here. The second part of this study, published separately, addresses the climate impacts of the diurnal cycle in the coupled system by coupling the OGCM developed here to an atmosphere general circulation model.

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Published date: 28 November 2007

Identifiers

Local EPrints ID: 64329
URI: https://eprints.soton.ac.uk/id/eprint/64329
ISSN: 0930-7575
PURE UUID: f77b6cf8-4365-4cec-be92-b49b87e10e3a

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Date deposited: 10 Dec 2008
Last modified: 13 Mar 2019 20:22

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Contributors

Author: D.J. Bernie
Author: E. Guilyardi
Author: G. Madec
Author: J.M. Slingo
Author: S.J. Woolnough

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