Observations of a Rain-Formed Mixed Layer

James F. Price Graduate School of Oceanography, University of Rhode Island, Kingston, 02881

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Abstract

The structure and dynamics of a rain-formed mixed layer (ML) are studied using hourly STD and profiling current meter casts. Because the fluid beneath the rain-formed ML was vertically homogeneous, the ML buoyancy g′ and horizontal velocity difference δV were easily observable as the ML depth h increased by entrainment from 7 to 18 m in a period of 8 h. The overall Richardson number of the mixed layer g′(h + d/2)/δV2 ≈ 0.7 during that period, where d is the thickness of the transition layer at the base of the ML. The entrainment rate was consistent with that of a laboratory surface half-jet (Ellison and Turner, 1959).

The transition layer thickness was an appreciable fraction of the ML thickness, roughly dh/3. The density profile through the transition layer was linear and symmetric, and the overall Richardson number of the transition layer gdV2 ≈ 1/4.

Abstract

The structure and dynamics of a rain-formed mixed layer (ML) are studied using hourly STD and profiling current meter casts. Because the fluid beneath the rain-formed ML was vertically homogeneous, the ML buoyancy g′ and horizontal velocity difference δV were easily observable as the ML depth h increased by entrainment from 7 to 18 m in a period of 8 h. The overall Richardson number of the mixed layer g′(h + d/2)/δV2 ≈ 0.7 during that period, where d is the thickness of the transition layer at the base of the ML. The entrainment rate was consistent with that of a laboratory surface half-jet (Ellison and Turner, 1959).

The transition layer thickness was an appreciable fraction of the ML thickness, roughly dh/3. The density profile through the transition layer was linear and symmetric, and the overall Richardson number of the transition layer gdV2 ≈ 1/4.

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