Breakup of Temperature Inversions in Deep Mountain Valleys: Part II. Thermodynamic Model

Abstract

A thermodynamic model is developed to simulate the evolution of vertical temperature structure during the breakup of nocturnal temperature inversions in mountain valleys. The primary inputs to the model are the valley floor width, sidewall inclination angles, characteristics of the valley inversion at sunrise, and an estimate of sensible heat flux obtained from solar radiation calculations. The outputs, obtained by a numerical integration of the model equations, are the time-dependent height of a convective boundary layer that grows upward from the valley floor after sunrise, the height of the inversion top, and vertical potential temperature profiles of the valley atmosphere. The model can simulate the three patterns of temperature structure evolution observed in deep valleys of western Colorado. The well-known inversion breakup over flat terrain is a special case of the model, for which valley floor width becomes infinite. The characteristics of the model equations are investigated for several limiting conditions using the topography of a reference valley and typical inversion and solar radiation characteristics. The model is applied to simulate observations of inversion breakup taken in Colorado's Eagle and Yampa Valleys in different seasons. Simulations are obtained by fitting two constants in the model, relating to the surface energy budget and energy partitioning, to the data. The model accurately simulates the evolution of vertical potential temperature profiles and predicts the time of inversion destruction.