Development of a simple model for temperature inversion breakup in a mountainous urban valley

The formation and destruction (breakup) of nocturnal temperature inversions in mountain basins is a topic of ongoing research. Temperature inversion exerts strong effects on the environmental conditions of deep valleys due to its influence on processes like the vertical transport of pollutants released to the low atmosphere from the surface. We study the temperature inversion breakup in the Aburrá Valley, which is a highly urbanized mountainous valley located in the tropical Andes of Colombia, in Northwest South America.

A simple model of temperature inversion breakup in deep valleys is developed. This model is an extension of the conceptual model of D. Whiteman (Whiteman, 1981). Its main features are as follows: (1) The topography is represented by a digital elevation model, thus leading to a spatially-distributed model. (2) A simplified, yet realistic, representation of the surface energy balance for each atmospheric column is explicitly introduced. (3) The spatial variation of solar radiation, as a result of the journey of the sun over the Valley, is included.

Two model experiments were performed. In the first one we model the inversion breakup in a single column, and compare the results with vertical atmospheric soundings obtained by using tethered and captive balloons. In the second experiment the model was applied to simulate the inversion breakup throughout the Valley. The sensitivity of the model results to several input parameters was tested aiming to discover physical sensitivities of interest.

Results from both experiments show the evolution of the convective boundary layer and the top of the inversion layer. Overall, model results are in good agreement with measurements. Qualitatively speaking, the model performance appears to be reasonably good, since it represents expected physical behaviors of the involved phenomena, and captures sentitivities to physical parameters.

Currently, our ongoing research work mainly deals with the following questions: How does land use influence the dynamics of the energy balance in the Aburrá Valley? and how does it affect the breakup of the temperature inversion? Both questions are asked in the face of global change, so large scale effects of global change will be considered in local scale evolution. Overall, our approach to answer these questions involve: (1) to model the energy balance in the Aburrá Valley in the face of global change factors, including local effects owing to land use changes, (2) to model the breakup of the temperature inversion in the valley involving the modeled energy balance, (3) to make some measurements and observations for contributing to the discussion, and (4) to advance in the understanding of the meteorological dynamics of the low atmosphere in the Aburrá Valley in particular, and in similar environments in general.