The aim of my PhD work is to characterize pooling and draining processes in deep alpine valleys under decoupled stable conditions and quantify their effects on pollutant dispersion.
Cold-air pools form in landscape depressions and can lead to particularly poor air quality. Such cold-air pools are characterized by very stable stratification and can trap air for many hours or even days, resulting in peak pollution episodes in and around urbanized areas, especially when they are intense, shallow, and long lasting. In these conditions, thermally driven slope and valley winds are key to maintaining some degree of ventilation.
The first part of this work focus on the characterization of the interactions between slope and valley winds, and a developing cold-air pool in idealized valleys of different geometries. The numerical model WRF is used for this purpose.
As a first step, the influence of thermally driven down-valley winds on a developing cold-air pool in an idealized alpine valley which opens on a plain is studied. Results from numerical model simulations in a three-dimensional (3D) valley, which allows for the formation of a down-valley wind, and in a two-dimensional (2D) valley, where the formation of a down-valley wind is inhibited, are analyzed and compared.
The forthcoming work consists in an idealized study of the Passy valley, situated in the French Alps. The sensitivity of the down-valley wind to the particular geometry of the valley will be investigated, analyzing the impact on the cold-air pool evolution.