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Douglas H. K. Lee
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H. N. Lee

Abstract

Simple and efficient formulas for calculating surface fluxes are presented for the nondimensional profile functional forms of wind and temperature in the atmospheric surface layer. Four formulations representing nondimensional profile functional forms are examined. New approximate solutions for the relationship between z/L and the bulk Richardson number are proposed. These new solutions are an improvement over the existing approximate solutions and give much better agreement with the numerical solutions obtained by iteration. The approach can be extended to other similar nondimensional profile functional forms.

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CHARLES H. LEE

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Rev. CHARLES H. LEE

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David H. Lee

Abstract

Methods were devised using information from an objective analysis to determine the assimilation level of cloud motion vectors. Rawinsonde data and SMS 2 satellite-derived cloud motion vectors were assimilated using the NCAR Limited Area Multivariate Statistical Objective Analysis, with persistence as the first guess. The geographical area included the northwestern Pacific Ocean, Central America and most of North America; a 6 h time interval between analyses and a three-day period were used. The four experiments varied the method of cloud-wind vertical placement, and included wind insertion 1) at the level nearest the cloud-top temperature; 2) at all levels within the cloud layer as defined by the cloud-top temperature and a physical thickness; 3) at the level nearest the cloud base; and 4) at the wind-fit level, at which the insertion wind most agrees with the first guess wind.

Insertion at the wind-fit level had characleristics and produced results which were unreasonable. Other level determination methods generated meaningful analysis results. In rawinsonde data-sparse regions, wind insertion at cloud-base level gave results which were in better agreement with satellite imagery. The sensitivity of the analysis to variation in the vertical distribution of the inserted winds revealed the importance of assimilating cloud motion vectors at the proper level.

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Douglas H. K. Lee
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H. N. Lee

Abstract

Advective transport using the flexible and stable semi-Lagrangian scheme coupled with the highly accurate spectral interpolation in a limited domain is demonstrated. The spectral method for solving nonperiodic boundary problems is based on a technique of decomposing a solution into a polynomial and a periodic Fourier residual. The fast Fourier transform is applied only to a periodic residual. A fifth-order polynomial is used and a method to obtain it is described. The numerical tests of the advective transport of a mass in a nonuniform deformational and a uniform rotational flow, as well as the plume transport from a continuous source, are also presented. As will be shown in the paper, the technique proved to be efficient and accurate, providing excellent results.

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CHARLES H. LEE

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H. N. Lee

Abstract

A semi-Lagrangian model was developed based on the atmospheric transport-diffusion equation, employing the semi-Lagrangian technique incorporated with the spectral method. The numerical algorithms of the semi-Lagrangian technique and the spectral method for solving the transport-diffusion equation, subjected to boundary conditions, are described. The model simulated the transport and diffusion of pollutants from an elevated point source. The accuracy of the algorithms was revealed by numerical tests compared with analytical solutions in cases of simple profiles of the mean wind and the eddy diffusivity. To demonstrate the feasibility of the algorithms for studying air pollution in the atmospheric boundary layer, the model, using realistic profiles of the mean wind and the eddy diffusivity, simulated the distributions of pollutant concentrations under various atmospheric stabilities. As will be shown, the algorithms are capable of producing excellent results, making them attractive and promising for regional studies of pollutant transport and diffusion in the atmosphere.

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H. Lee Dantzler Jr.

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Expendable bathythermograph records are combined with stability information to provide estimates of the potential energy associated with vertical displacements in the tropical and subtropical North Atlantic thermocline. The geographic distribution of potential energy magnitudes provides a means by which the dynamics implications of thermocline displacements in areas of differing vertical density structures can quantitatively be compared. A broad zonal minimum in potential energy exists along 24–°N in the eastern and western North Atlantic basins. From this minimum potential energy levels increase significantly in magnitude to the north and to a lesser extent to the south with highest values indicated for the boundary-circulation-associated regions of the subtropical gyre. More geographically restricted maxima are found along the flanks of the Mid-Atlantic Ridge and near the Antilles Islands Arc, indicating that topographic influences may be important in addition to what appears predominantly to be a current-related potential energy field. Comparisons of these estimates with observations suggest that the areas of potential energy maxima are associated with significant eddy activity and that the conditions observed during MODE are statistically characteristic of the more quiescent central zone.

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