Seasonal and regional variability of upper ocean diapycnal heat flux in the Atlantic cold tongue.

Hummels, Rebecca, Dengler, Marcus and Bourles, B. (2013) Seasonal and regional variability of upper ocean diapycnal heat flux in the Atlantic cold tongue. Progress in Oceanography, 111 . pp. 52-74. DOI 10.1016/j.pocean.2012.11.001.

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Supplementary data:

Abstract

SST variability within the Atlantic cold tongue (ACT) region is of climatic relevance for the surrounding continents. A multi cruise data set of microstructure observations is used to infer regional as well as seasonal variability of upper ocean mixing and diapycnal heat flux within the ACT region. The variability in mixing intensity is related to the variability in large scale background conditions, which were additionally observed during the cruises. The observations indicate fundamental differences in background conditions in terms of shear and stratification below the mixed layer (ML) for the western and eastern equatorial ACT region causing critical Froude numbers (Fr) to be more frequently observed in the western equatorial ACT. The distribution of critical Fr occurrence below the ML reflects the regional and seasonal variability of mixing intensity. Turbulent dissipation rates (ε) at the equator (2°N-2°S) are strongly increased in the upper thermocline compared to off-equatorial locations. In addition, ε is elevated in the western equatorial ACT compared to the east from May to November, whereas boreal summer appears as the season of highest mixing intensities throughout the equatorial ACT region, coinciding with ACT development. Diapycnal heat fluxes at the base of the ML in the western equatorial ACT region inferred from ε and stratification range from a maximum of 90 Wm-2 in boreal summer to 55 Wm-2 in September and 40 Wm-2 in November. In the eastern equatorial ACT region maximum values of about 25 Wm-2 were estimated during boreal summer reducing to about 5 Wm-2 towards the end of the year. Outside the equatorial region, inferred diapycnal heat fluxes are comparably low rarely exceeding 10 Wm-2. Integrating the obtained heat flux estimates in the ML heat budget at 10°W on the equator accentuates the diapycnal heat flux as the largest ML cooling term during boreal summer and early autumn. In the western equatorial ACT elevated meridional velocity shear in the upper thermocline contributes to the enhanced diapycnal heat flux within this region during boreal summer and autumn. The elevated meridional velocity shear appears to be associated with intra-seasonal wave activity.

Document Type: Article
Additional Information: WOS:000318203700004
Keywords: equatorial Atlantic Ocean; TROPICAL INSTABILITY WAVES; EASTERN EQUATORIAL PACIFIC; SEA-SURFACE TEMPERATURE; MIXED-LAYER; INTERNAL WAVES; NORTH-ATLANTIC; EASTWARD CURRENTS; AFRICAN MONSOON; DIURNAL CYCLE; SHEAR-FLOW
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.pocean.2012.11.001
ISSN: 0079-6611
Projects: SOPRAN, BMBF Nordatlantik, Future Ocean
Expeditions/Models/Experiments:
Date Deposited: 06 Dec 2012 14:19
Last Modified: 04 Oct 2016 12:51
URI: http://oceanrep.geomar.de/id/eprint/19602

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