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Henry Stommel

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Henry Stommel
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Henry Stommel

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ENTRAINMENT OF AIR INTO A CUMULUS CLOUD

(Paper presented 27 December 1946 at the Annual Meeting, A.M.S., Cambridge, Massachusetts)

Henry Stommel

Abstract

A theory of convective clouds is presented, the fundamental hypothesis being that the ascending current in a cloud entrains air from its surroundings. A method is developed for computing the amount of entrainment from a knowledge of the temperature and specific humidity inside and outside the cloud. The concentration of water in the form of drops is also determined. Finally the theory is applied to some observations of trade cumulus made near San Juan, Puerto Rico.

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Ants Leetmaa and Henry Stommel

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Vertical profiles of current, temperature and salinity were taken in the upper ocean from 3°S to 2°N along 55°30′E in the Indian Ocean during February–June in 1975 and 1976. During both years a strong O(80 cm s−1) equatorial undercurrent was present throughout the measurement period in the vicinity of the equator. A second region of eastward flow above the thermocline was observed at 3°S. During May and June the undercurrent moved southward and merged with the southern region of eastward flow. The meridional flow field was dominated by transients that during strong events were antisymmetric about the equator and had a vertical wavelength of ∼180 m. The transient events strongly affected the zonal flow field; during strong events the undercurrent was almost eliminated. This is in contrast to the GATE observations where the undercurrent was advected back and forth across the equator.

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Henry Stommel and George Veronis

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Michele Fieux and Henry Stommel

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The time and type of onset of the southwest monsoon over the Arabian Sea is studied using ship reports of surface wind tabulated by 1° squares daily along two densely occupied shipping lanes. It is found that several types of onset occur, and that the mean time of onset, suitably defined, changes very little from year to year.

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Laurence Armi and Henry Stommel

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Data from four cruises to the “β-triangle” centered at 27°N, 32°30′W were smoothed by fitting second-degree polynomials at each of about 30 different density surfaces. The density intervals were Δσp=0.3‰, corresponding to about 50 db intervals in pressure. From the polynomials, determination was made of central values, horizontal derivatives and Laplacians of the fields of pressure, salt, oxygen and dynamic height. In addition, maps of the fits and deviations of each nation from the smoothed fits were produced.

From the steady advective diffusive equation and the smoothed fits to the age oxygen and dynamic height fields, the lateral isopycnal diffusivity as estimated to be K H ∼ 0.5 × 103 m2 s−1. Although the salt field was reasonably stable from cruise to cruise, the variability of the baroclinic velocity shear was found to be as large as the baroclinic shear itself. The maps suggest a wobble of the gyre. The standard deviation of the fluctuations at each nation from the smoothed fits, when normalized by the gradient l′ = s′/|∇S′| gives the mixing length of the horizontal turbulence. This was found to be ∼80 km, presumably due to mesoscale turbulence. These fluctuations were all Found, with one exception, to be normally distributed, suggesting the suitability in the subtropical gyre of a Fickian gradient transport diffusion. The one notable exception to the normal distribution was the discovery at one out of 143 stations of relatively undiluted Mediterranean water. The anomaly of salinity was as large as 0.65‰ or 20 standard deviations. A crude estimate suggests that the flux divergence due to the anomaly is approximately an order of magnitude less than either the advective or diffusive flux divergence.

There is a range of densities over which horizontal gradients of potential vorticity are small or nearly indeterminate. This range of densities intersects the ocean surface where the wind stress curl produces downwelling at the base of the Ekman layer. Deep density surface that intersect farther north at upwelling latitudes have strong potential vorticity gradients.

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James Luyten and Henry Stommel

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The combined effects of buoyancy forcing and wind in a gyre-scale steady ocean circulation are modeled using discrete layers with an interfacial flux, not necessarily vertical. The equations for vorticity conservation of the geostrophic flow in this system are fully nonlinear, involving a Jacobian for the layer thicknesses. These equations are written in a form which can be solved by the method of characteristics. The form of these equations invites the interpretation that the geostrophic baroclinic flow is driven by buoyancy and steered by the wind. Two examples are solved and discussed, a subtropical gyre with heating, and a subpolar gyre with cooling. In each case, there are distinct regimes of flow, depending upon whether the characteristics originate at the eastern or western boundaries of the model. A simple geometrical argument illustrates that the difference between these two regimes, the direct and indirect cells, depends upon the sign of the true vertical velocity relative to the interfacial flux.

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Joseph Pedlosky and Henry Stommel

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The authors describe a self-sustaining baroclinic inertial oscillation whose energy source rests in a uniform horizontal temperature gradient. This energy is released through the agency of a stratification-dependent mixing law that is meant to crudely model the occurrence of enhanced mixing when the stratification weakens. The mixing is chosen to be negligible over most of the cycle and large only when the stratification is small.

Sustained inertial oscillations are shown to be the natural end state of the instability of possible steady solutions when the decrease of the mixing rate with temperature exceeds a critical value. If the variation of the mixing rate with temperature is abrupt, a finite-amplitude oscillation is sustained, although a possible steady solution is linearly stable.

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