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Eric B. Kraus and Sydney Levitus

Abstract

The global poleward heat transport by the oceans tends to have a maximum in the vicinity of the Tropic circles. We have investigated the contribution of the Ekman flux to the heat transport in the Pacific and the Atlantic. Two different datasets were used for the Pacific computations. The results suggest that Ekman flows contribute about half of the grow transport in the Atlantic. In the much wider Pacific, they are the dominant influence. The meridional migration of the trade wind belt and the simultaneous seasonal changes in the mixed layer temperature tend to cause the Ekman part of the heat flux to be larger in summer than in winter. Semiannual harmonics in the zonally integrated Ekman heat-transport component can be associated with longitudinal variations of the specific heat flux, due to seasonal position shifts of the atmospheric centers of action.

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Eric B. Kraus and Lynn D. Leslie

Abstract

Subtropical status tends to form over relatively cold water, its presence then keeps the water cold. We have investigated the resultant downstream development in the framework of an interactive, two-dimensional, steady-state model of the oceanic and atmospheric mixed layers. Upstream boundary and interior conditions in both media, and irradiance and advection velocities are specified; mixed-layer temperature salinity, heat and moisture content are evolving dependent variables. The integration is continued downstream until convective instability develops or, failing that, for a distance of 2000 km.

Sensitivity tests show this development to be strongly affected by the upstream boundary conditions, implying an effect of coastal upwelling processes upon oceanic and atmospheric temperature profiles for a long distance downstream. The dependence on the advection velocity is very nonlinear. The amplitude of temperature changes is of the same order in both media, despite the greater oceanic heat capacity. This is due to the unequal advection rate, which causes a water column to remain in the affected area some fifty times longer than the air above.

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Eric B. Kraus and Howard P. Hanson

Abstract

The westward propagation of equatorial sea surface temperature anomalies exceeds the surface drift velocity and is probably associated with propagating changes in the depth of the surface mixed layer and upper thermocline. These can be caused by equatorial Rossby waves and/or by air-sea interactions. In the present paper, it is shown that changes in the stress and heat flux associated with the passage of air over an ocean surface of variable temperature can produce a westward propagation of the temperature pattern regardless of Coriolis effects.

The phenomenon is investigated in the framework of a two-layer channel model. A physical description of the mechanism is followed by the discussion of an approximate solution to the steady state and by a linear wave analysis which deals with the propagation and modification of an initially stipulated departure from the equilibrium.

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Francis P. Bretherton, Michael J. Mcphaden, and Eric B. Kraus

Abstract

Objective analysis of large-scale simulated anomalies is used to estimate statistically the effectiveness of different sampling arrays. The methodology, which includes a new use of Bayesian inference, is of fairly general applicability, but is illustrated by a specific requirement to measure five-year changes in the North Atlantic to an accuracy equivalent to ±10 W m−2. The numerical procedure require 1) specification of an overall measure of accuracy on an appropriate resolution, 2) a reference field approximating the long-term mean, 3) an assumed ensemble of large-scale anomalies, 4) the distribution of mesoscale eddy noise as derived from previous analyses of historical data and 5) a set of ship tracks and a sampling, in space and time along them. The numerical output is the expected accuracy and other diagnostic information.

The ship tracks and sampling are varied by trial and error until the expected accuracy is within requirements in an economical manner. The study indicates that the optimized sampling scheme is sensitive primarily to the specification of the overall accuracy requirements including both the resolution and the level of uncertainty. It is less sensitive to the distribution of mesoscale eddy noise and relatively insensitive to plausible changes in the reference field or in the assumptions about the ensemble of large-scale anomalies.

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