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N. M. Zoumakis
and
G. A. Efstathiou

Abstract

The factors that affect the atmospheric energy budget approach used in the thermodynamic valley inversion destruction model of Whiteman and McKee are investigated theoretically. The height at which the sinking inversion top meets the rising convective boundary layer to destroy valley inversions can be uniquely determined by the topographic characteristics of the valley and an adjustable model parameter, relating to the fraction of sensible heat flux going to convective boundary layer growth, through a simple parabolic relationship. The time required to break a temperature inversion can be expressed with very good approximation as a simple power-law function of the topographic parameters and the fraction of extraterrestrial solar flux that is partitioned to sensible heat flux in the valley atmosphere. The theoretical estimates compare very favorably to predictions from the bulk thermodynamic model of Whiteman and McKee. A new approach to handle time-dependent sensible heat fluxes is outlined. The paper ends with recommendations for future research.

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N. M. Zoumakis
and
G. A. Efstathiou

Abstract

A simple thermodynamic parameterization based on a modified version of the Whiteman and McKee inversion destruction model is presented to simulate the evolution of vertical temperature structure during the inversion breakup period in idealized valleys under clear, undisturbed weather conditions. The proposed method adopts simplified semiempirical parameterizations of radiation and surface energy budgets at the valley floor and sidewalls and an empirical scheme for the partitioning of energy in the valley atmosphere, eliminating the need for selecting arbitrary values for the adjustable model parameters. The model accurately simulates the changes with time of the height of the inversion top and the depth of the convective boundary layer during the breakup of nocturnal temperature inversions in a wide range of valley topography. The theoretical estimates were validated and compared with dynamical model predictions and actual measurements. Because of its simplicity and its fair agreement with observations, the proposed method may be useful in applications in boundary layer, air pollution, and complex terrain meteorology. It is recognized that more work is necessary before the validity of the suggested procedure can be fully established.

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