87th AMS Annual Meeting

Wednesday, 17 January 2007: 12:00 AM
Diurnal variability of the tropical upper ocean and its climate impacts
214B (Henry B. Gonzalez Convention Center)
Dan Bernie, LOCEAN/IPSL, Paris, France; and E. Guilyardi, S. Woolnough, J. M. Slingo, G. Madec, and J. Cole
The climate system is naturally forced at three different time scales; orbital, seasonal and diurnal. The climate of the next century is affected by the latter two, but ocean-atmosphere coupling in the current design of general circulation models (GCM) deals only with seasonal variations. In this study some of the climate impacts of the diurnal cycle are examined with a coupled ocean-atmosphere GCM configuration which is able to accurately resolve the diurnal variability of the upper ocean and air-sea coupling.

Sensitivity to the diurnal cycle is first examined in a forced ocean GCM. The inclusion of a properly resolved diurnal cycle leads to an enhancement of the intraseasonal SST response to the Madden-Julian oscillation (MJO) and an increase in the strength of the Pacific Ekman cells.

Coupled sensitivity experiments are then used to demonstrate that the diurnal cycle leads to a more coherent MJO with improved propagation characteristics. Furthermore, the diurnal cycle's dynamical impact in the upper ocean leads to a positive feedback with the Walker circulation, resulting in an amplification of seasonality in the tropical Pacific.

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