Modelling of the rapid response of tree canopy to its ambient microenvironment from a coupled LES-SVAT model

Forests play an important role in biosphere-atmosphere exchanges of momentum, energy, water vapor, and carbon dioxide. Quantifying such exchanges is important in many environmental applications as well as in weather and climate forecasting. In order to better understand these exchanges at very fine spatial and temporal scales, a Large-eddy Simulation (LES) airflow model is coupled with a SVAT (Soil-Vegetation-Atmosphere Transfer) model.

The LES model is the Advanced Regional Prediction System (ARPS) that has been previously modified in order to simulate turbulent flow within and above heterogeneous vegetation canopies. LES allows one to have access to instantaneous (1Hz) dynamical and thermodynamics fields. The SVAT model is a multilayer, multileaf process-based biosphere-atmosphere gas exchange model, called MuSICA (Multi-layer simulator of the interactions between a vegetation stand and the atmosphere). This model determines the vertical distribution of the leaf energy balance (radiative, sensible, and latent heat fluxes) and photosynthesis within the canopy by distinguishing several leaf age classes.

This new LES-SVAT model is applied for moderate unstable conditions over a continuously homogeneous pine forest, characterized by a dense crown layer and a sparse and large trunk space. Microenvironmental variables (wind speed, air temperature and humidity) simulated by the model will be first compared with in situ measurements. Then, the rapid response of the tree canopy to its ambient microenvironment will be discussed.