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Estimates of vertical mixings during a Lagrangian experiment off the Galician coast

Lamy, F. and Sherwin, T. and Soetaert, K.E.R. and Herman, P.M.J. and Torres, R. (2001) Estimates of vertical mixings during a Lagrangian experiment off the Galician coast. Journal of Marine Systems, 30, 165-179. ISSN 0924-7963.

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An adjoint 1-D model was used to determine vertical diffusivity coefficients from temperature profiles collected within a filament escaping from the Galician coast following an upwelling event. The optimisation scheme ended with relatively high diffusivity values within the thermocline (9 x 10(-1) m(2) s(-1)). Such high values are relevant for biogeochemical exchanges between surface and deep waters in stratified areas. The optimised values were several orders of magnitude higher than the bulk of diffusivity measurements recorded with a free- falling device; however, the optimisation solution was consistent with the arithmetic mean of the measurements in the thermocline (7.7 x 10(-5) m(2) s(-1)), giving more weight to the few largest values. Below the thermocline, the data assimilation method failed because of the three-dimensional nature of the advective field of the upwelling system. Ignoring this advective forcing in the model led to estimates that were two orders of magnitude too high. The results suggest that turbulent mixing is a random process where a few intense events determine the average mixing that drives the long-term evolution of the water column structure. This statistical property is very important when one wants to use instantaneous diffusivity measurements for modelling purposes. [KEYWORDS: 1-D numerical modelling; NE Atlantic; ocean margin; data assimilation; vertical mixing Turbulent dissipation; upper ocean; shelf seas; decay]

Item Type:Article
Institutes:Nederlands Instituut voor Ecologie (NIOO)
ID Code:11030
Deposited On:24 Nov 2011 01:00
Last Modified:31 Mar 2014 10:57

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