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Lutz Hasse and Stuart D. Smith

Abstract

Parameterization of turbulent wind stress and sensible and latent heat fluxes is reviewed in the context of climate studies and model calculations, and specific formulas based on local measurements are recommended. Wind speed is of key importance, and in applying experimental results, the differences between local and modeled winds must be considered in terms of their method of observation or calculation. Climatological wind data based on Beaufort wind force reports require correction for historical trends. Integrated long-term net turbulent and radiative heat fluxes at the sea surface, calculated from archived data, are consistent with meridional heat transport through oceanographic sections; this lends support to the methods used.

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Hans-Jörg Isemer and Lutz Hasse

Abstract

The Beaufort equivalent scale of the World Meteorological Organization (WMO), used for decades to transform marine Beaufort estimates to surface wind speeds over the oceans, contains systematic errors that depend nonlinearly on the wind speed. Applying a revised scientific equivalent scale instead of the WMO scale produces significant changes in statistics of surface wind speed U over the ocean and, consequently, in all air-sea fluxes that are related to U.

For the North Atlantic Ocean these biases are quantified as follows. The WMO scale underestimates climatological monthly means of U significantly: up to 1.6 m s−1in tropical latitudes throughout the year. In subpolar regions, differences are significant from spring through autumn and reach 1.3 m s−1. These regionally and seasonally different monthly biases are equivalent to an overestimate of the annual variation of U, which reaches 1.5 m s−1 in the westerlies. Local standard deviations may be overestimated up to 1.2 m s−1. The WMO scale underestimates climatological monthly estimates of latent heat flux up to 50 W m−2. (up to 25%). The bias of the mean annual North Atlantic evaporation rate is 0.3 m yr−1. The bias in annual net air-sea heat flux amounts to 27 W m−2, equivalent to an underestimate of the transequatorial oceanic heat transport by 1.15 PW (1 PW = 1015 W). Climatological monthly wind stress at the ocean surface is underestimated by more than 4.5 × 10−2 N m−2 (up to 50%) in the trade-wind region.

Most existing regional and global air-sea flux compilations (including COADS) have been derived using the WMO scale. Hence, large biases are included in these compilations, although they can be partially hidden by an artificial increase of parameterization coefficients. The wind statistics revised according to a more accurate scale allow the application of bulk coefficients in accordance with newer experimental results from the open ocean. Therefore means and statistics of wind speed and climatological estimates of air-sea fluxes over the World Ocean need revision.

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Hans-Jörg Isemer, Jürgen Willebrand, and Lutz Hasse

Abstract

An inverse technique is used to adjust uncertain coefficients and parameters in the bulk formulae of climatological air-sea energy fluxes in order to obtain an agreement of indirect estimates of meridional heat transport with direct estimates in the North Atlantic Ocean. Three oceanographic estimates of ocean heat transport at the equator, at 25°N, and 32°N are compatible with meteorological evidence provided that the uncertainties of both direct and indirect estimates are taken into account. The transport coefficient CE for estimation of the latent heat flux is the major contributor to the overall uncertainty in estimates of ocean heat transport. The constraint of 1 PW northward transport across 25°N leads to a set of parameterizations for which the parameter adjustments are only less than half as large as the estimated uncertainties. Based on this set of constrained parameterizations monthly climatological fields of the individual fluxes in the North Atlantic Ocean are computed which are consistent with direct transport estimates.

With a larger set of heat transport observations this method will provide a possibility to discriminate between various bulk formulations, and to obtain more accurate estimates of the air-sea energy flux.

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