Abstract
Abstract. The upper ocean heat budget (0–300 m) of the North Atlantic from 20°–60° N is investigated using data from Argo profiling floats for 1999–2005 and the NCEP/NCAR and NOC surface flux datasets. Estimates of the different terms in the budget (heat storage, advection, diffusion and surface exchange) are obtained using the methodology developed by Hadfield et al. (2007a, b). The method includes optimal interpolation of the individual profiles to produce gridded fields with error estimates at a 10°×10° grid box resolution. Closure of the heat budget is obtained within the error estimates for some regions – particularly the eastern subtropical Atlantic – but not for those boxes that include the Gulf Stream. Over the whole range considered, closure is obtained for 13 (9) out of 20 boxes with the NOC (NCEP/NCAR) surface fluxes. The seasonal heat budget at 20–30° N, 35–25° W is considered in detail. Here, the NCEP based budget has an annual mean residual of −55±35 Wm−2 compared with a NOC based value of −4±35 Wm−2. For this box, the net heat divergence of 36 Wm−2 (Ekman=−4 Wm−2, geostrophic=11 Wm−2, diffusion=29 Wm−2) offsets the net heating of 32 Wm−2 from the NOC surface heat fluxes. The results in this box are consistent with an earlier evaluation of the fluxes using measurements from research buoys in the subduction array which revealed biases in NCEP but good agreement of the buoy values with the NOC fields.
Highlights
Closure of the upper ocean heat budget has been a focus of many studies as it provides insights into the various processes controlling the temperature of the near surface layer and po-tentially places an important constraint on the air-sea heat exchange
There are a number of potential reasons for the differences between the NOC and NCEP/NCAR flux fields, the two main ones being: 1) variations in the parameterizations used to estimate the fluxes, with the NCEP fields known to have latent and sensible heat loss which is unrealistically strong at high latitudes (Renfrew et al, 2002); 2) sampling issues which have a direct impact on the purely observation based NOC fields and an indirect effect on the NCEP fields as these same observations are assimilated into the atmospheric model used for the reanalysis
An analysis of the heat budget of the upper ocean (0–300 m) for the North Atlantic from 20◦–60◦ N based on Argo profiling floats and surface flux fields from NCEP/NCAR and NOC has been presented
Summary
In this paper we use the Argo data together with estimates of surface heat exchange from the NCEP/NCAR reanalysis (referred to as NCEP hereafter, Kalnay et al, 1996) and the NOC1.1 surface flux dataset (NOC hereafter, Josey et al, 1999) to investigate the upper ocean heat budget in various regions of the North Atlantic. Using OCCAM sub-sampled at the Argo positions, it was found that the mixed layer monthly heat storage, in the subtropical North Atlantic but not including the Gulf Stream, has a sampling error of 10–20 Wm−2 when averaged over a 10◦×10◦ area. This sampling error is sufficiently small to provide useful estimates of the heat budget over a significant fraction of the basin.
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