The DECIPHER project

aims at disentangling the effects of the various physical and chemical factors on atmospheric processes in mountain sites at different time and space scales. Specifically, it focuses on the following specific objectives:

• Understanding and quantifying connections between topography, surface properties, ambient stability and upper atmospheric forcing (including clouds and precipitation) on the development of mechanisms controlling transport and mixing processes over mountainous terrain, and in particular the role of thermally driven winds on transport and exchange (turbulent mixing, along with slope advection, entrainment/detrainment, upper convection,…) at different scales: surface layer, slope layer, free atmosphere.

• Identifying turbulence dynamics and structures and their role in the mechanisms controlling surface-atmosphere exchanges and hence daytime upslope winds, nighttime downslope winds, and the transitions between them.

• Defining the main drivers of aerosol transport and gaseous pollutants in mountain sites using specific chemical markers combined with meteorological measurements and observations of precipitation structure. In view of identifying dynamically-based criteria for determining the footprint of observations of tracers recorded at high altitude observatories.

• Testing the effectiveness of the proposed instrumental setup to study surface-atmosphere transport processes in complex terrain, in particular, the most advanced and unconventional devices.

• Suggesting and testing improvements in numerical weather prediction models (in particular in their parameterizations of surface processes and turbulence) and in pollutant dispersion modelling (in particular the structure of the stochastic terms parameterising turbulent mixing), both for forward- and back-trajectory models, turbulence parameterization.