VERTICAL MOTION, DIVERGENCE, AND VORTICITY IN THE TROPOSPHERE OVER THE CARIBBEAN, AUGUST 3–5, 1963

M. A. LATEEF National Hurricane Research Laboratory, IAS, ESSA, Miami, Fla.

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Abstract

Vertical motion, divergence, and vorticity have been computed at points over a grid covering the Caribbean and adjoining areas and at seven levels (1000 to 100 mb.) for the period August 3 to August 5, 1963. The synoptic situation during the period was marked by the westward passage of a low-level easterly wave underneath an extensive upper-level anticyclone and the presence of an upper-tropospheric cyclone over the western Caribbean.

Vertical velocities were evaluated from solutions to finite-difference approximations of the pressure-differentiated form of the continuity equation, with suitable boundary conditions. Computed values of divergence and vorticity associated with the easterly wave and the upper-level cyclone compare favorably with those reported in certain previous independent investigations. The computed vertical motion patterns appear realistic though the absolute magnitudes may be in error.

Estimates of the magnitudes of terms in the vorticity equation indicate that the local time-change term is the largest, followed in order of magnitude by the horizontal advection of vorticity and the convergence terms. Vertical transport of vorticity and twisting terms are relatively small. Computed values of the convergence terms (involving vertical derivatives of ω) are not accurate enough for verification on the basis of correlation coefficients between grid-point values of observed vorticity changes and expected vorticity changes. However, improvement of estimates of expected vorticity changes is noticed in many instances when terms in the vorticity equation are averaged over a sizeable area.

Abstract

Vertical motion, divergence, and vorticity have been computed at points over a grid covering the Caribbean and adjoining areas and at seven levels (1000 to 100 mb.) for the period August 3 to August 5, 1963. The synoptic situation during the period was marked by the westward passage of a low-level easterly wave underneath an extensive upper-level anticyclone and the presence of an upper-tropospheric cyclone over the western Caribbean.

Vertical velocities were evaluated from solutions to finite-difference approximations of the pressure-differentiated form of the continuity equation, with suitable boundary conditions. Computed values of divergence and vorticity associated with the easterly wave and the upper-level cyclone compare favorably with those reported in certain previous independent investigations. The computed vertical motion patterns appear realistic though the absolute magnitudes may be in error.

Estimates of the magnitudes of terms in the vorticity equation indicate that the local time-change term is the largest, followed in order of magnitude by the horizontal advection of vorticity and the convergence terms. Vertical transport of vorticity and twisting terms are relatively small. Computed values of the convergence terms (involving vertical derivatives of ω) are not accurate enough for verification on the basis of correlation coefficients between grid-point values of observed vorticity changes and expected vorticity changes. However, improvement of estimates of expected vorticity changes is noticed in many instances when terms in the vorticity equation are averaged over a sizeable area.

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