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  • Author or Editor: STEFAN L. HASTENRATH x
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Stefan L. Hastenrath

Abstract

Various models of the mean meridional circulations are examined in terms of the vorticity equation. These include: 1) the traditional model of two Hadley cells joining in a region of ascending motion near the equator; 2) a model with two “equatorial cells” enclosed between the traditional Hadley cells, implying subsidence over the equator; and 3) a model with a single “equatorial cell” enclosed between the two Hadley cells, with ascending motion on one side, and subsidence on the other side of the equator. All three models are considered compatible with the vorticity equation, under specific conditions of latitudinal and vertical distributions of absolute vorticity, frictional force, and vertical and zonal wind components. The existence of twin equatorial cells requires the eastward directed frictional force in the lower layers to decrease from the kinematical equator poleward, within the subsiding portion of either of the two equatorial cells. It is suggested that this may be related to the existence of (eastward directed) equatorial undercurrents in the Pacific and Atlantic Oceans. The requirements for twin equatorial cells do not seem to be met over the interior of the tropical continents.

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Stefan L. Hastenrath

Abstract

The field of large-scale vertical motion and the atmospheric-oceanic energy budget in the areas of the Caribbean Sea and the Gulf of Mexico are studied with emphasis on seasonal and regional variations, using the available radiosonde data of the entire year 1960. The atmosphere over the Caribbean Sea exports latent heat during the winter half of the year, changing to import during summer, while divergence of the latent heat flux prevails over the Gulf of Mexico during most of the year with the exception of midsummer. The troposphere as a whole imports geopotential energy and sensible heat during winter in the Caribbean, and during most of the year in the Gulf area, this being effected by the upper-tropospheric westerly current originating over the equatorial regions of the eastern Pacific. During the summer half of the year, an export of geopotential energy and sensible heat takes place over the Caribbean Sea, being concentrated in the upper-tropospheric easterlies, this pattern also including the area of the Gulf of Mexico in midsummer. Regarding the total energy budget, the troposphere over the Caribbean Sea acts as an exporter of energy to other parts of the globe throughout the year, while import is indicated for the Gulf of Mexico during some winter months. Ocean currents export heat from the Caribbean Sea during the summer half of the year, while conspicuous import is indicated for the Gulf of Mexico throughout the year, with the exception of midsummer. The tropospheric energetics are discussed with respect to their role in the general circulation.

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