Comparison of Estimated and Measured Marine Surface Wind Speed

A large portion of marine surface wind data is based on Beaufort estimates made subjectively from the visual appearance of the sea surface. At the time being, beaufort number from several decades are converted to wind speed by one equivalent scale. Application of a revised scientific equivalent scale (Kaufeld, 1981) to wind estimates of the period after World War II eliminates

Meridional temperature fluxes in the subtropical eastern North Atlantic

In a regional study of the eastern North Atlantic Ocean east of 35°W between 41°N and 8°N the mean meridional ocean temperature flux was computed from oceanographic and meteorological measurements using the direct method. In the area of the permanent subtropical gyre between 36°N and 22°N, a southward geostrophic temperature flux dominates. The Ekman temperature flux is weak and changes from a southward flux north of 32°N to a northward flux south of 32°N. In the area of the North Equatorial Current and in the tropics the Ekman temperature flux is comparable in magnitude to the geostrophic temperature flux. Therefore, the total temperature flux changes to a northward direction at 20°N, where the geostrophic transport is still to the south, and becomes large in the tropics, where both components show northward temperature fluxes. The heat flux divergence for the area investigated leads to an ocean heat gain of 0.19 PW. A comparison of annual mean temperature fluxes with temperature fluxes of east-west CTD sections from the winter half-year shows a small seasonal signal in the geostrophic temperature flux in the subtropical gyre but large differences in the tropics. The seasonal changes for the Ekman temperature fluxes are weak

Seasonal variability of meridional temperature fluxes in the eastern North Atlantic Ocean

Seasonal meridional ocean temperature fluxes were computed in a regional study of the eastern North Atlantic Ocean east of 30°30′W between 12°30′N and 39°30′N for the upper 1500 m of the ocean. Historical oceanographic and meteorological measurements are the data base for the direct method of computing temperature fluxes. Seasonal changes in temperature fluxes caused by the seasonality of Ekman transport and geostrophic transport are strongly dependent on latitude. Between 19N and 25N the meridional temperature flux shows low seasonality. In this area the permanent subtropical gyre and the stable trade-winds result in low seasonal changes. North of 25N the Ekman transport shows large seasonal variations. The latitude of the transition of southward Ekman temperature flux to northward Ekman temperature flux is located at 28N in winter. In summer it is found at 38N. The seasonal variability of the meridional temperature fluxes in the subtropics north of 25N is influenced by this annual cycle in Ekman transport, as well as by the southward displacement in summer and the northward movement of the Azores Current in winter. The tropical eastern Atlantic Ocean shows seasonal changes both in the geostrophic and Ekman transports. South of 17N the total temperature flux is always to the north. The largest meridional temperature fluxes, with more than 0.7 PW, are found in fall at 12°30′N directed northward, and in winter at 33°30′N to the south. In general the subtropical eastern North Atlantic Ocean transports heat to the south all the year round, while in the tropics heat is transported to the north. The seasonality in the eastern Atlantic Ocean is found to be different from seasonal variations in global investigations. The seasonal heat budget computations show a heat gain in the ocean in the area investigated from April to September and a heat loss from October to March. Over the whole year the eastern North Atlantic gains about 0.09 PW from the atmosphere

On the Origin of the Azores Current

The Azores Current, south of the Azores Archipelago, is part of the subtropical North Atlantic gyre. Using an international hydrographic data set, we analyze mean and seasonal geostrophic transport fields in the upper 800 m of the ocean in order to determine the origin of the Azores Current in the western basin and seasonal changes in the related flow. Geostrophic currents are obtained by using the method applied by Stramma (1984) in the eastern basin. The Azores Current is found to originate in the area of the Southwest Newfoundland Rise (Figure 10). In winter an almost uniform current connects this region of origin with the Azores Current, while a branching into two current bands is observed in summer, with the southern band forming a marked cyclonic loop. Within the upper 800 m, all of the transport in the northern band and about 70% of the transport in the southern band recirculates in the eastern basin. Additionally, expendable bathythermograph data from the Azores Current region indicate an increase of eddy potential energy from winter to summer

Some observations of the Azores Current and the North Equatorial Current

The regions containing the two zonal currents of the subtropical gyre in the eastern North Atlantic, the Azores Current and the North Equatorial Current (NEC), have quite different physical characteristics. Associated with the Azores Current are strong horizontal thermohaline gradients that can be located easily both at the surface and at depth with temperature data alone, thus making satellite IR imagery and expendable bathythermograph profiles suitable for observing it. During winter, the surface expression of the Azores Current is often found to the north of the strongest subsurface gradients. In contrast to the Azores Current and to the central water mass boundary just to the south, the NEC has relatively weak horizontal temperature and salinity gradients, requiring density information in order to identify it. There is no clear surface manifestation found with the NEC. Common to both currents, though, is that each transports O(8 Sv) in the upper 800 m of the ocean near 27°W, with the largest velocities being in the upper 400 m