The Effect of Forest in Dampening the Diurnal Cycle on Land-Atmosphere Interaction

Forests cover about one-third of the global land area and dominate substantial boundary conditions of land-atmospheric interaction in mountain regions. The critical role of forests in land-atmosphere interaction was investigated by satellite observation and model simulation. Compared to the open field in neighbor grids, the surface temperature of forests was significantly cooler in the daytime and warmer in the nighttime by satellite observation. The evapotranspiration caused the cooling effect during the day. At night, biomass heat storage (BHS) and larger roughness contributed to the warming effect. However, due to the limitation of the observation methodology, the modulation of forest could not be revealed in the dense forest, i.e., Amazon and Borneo rain forests, dominated by giant trees with large amounts of biomass. Therefore, in-situ paired observation within a reasonably close distance and idealized model simulation are scarce. From our observed results, the air temperature above the forest was cooler during the day and warmer at night by comparing the traditional weather station in an open field and above the forest. The damping effect of the forest regulates a diurnal temperature range of approximately 2 degrees. To further illustrate the impact of BHS on the hydro-climatological interaction, we used a land model to simulate how the diurnal cycle of surface heat flux changes. Considering the BHS in the model, the latent heat flux and sensible heat flux decrease during the daytime. At night, the heat stored in the biomass releases into the atmosphere and warms the air temperature above the canopy significantly. That is, the changes in the diurnal temperature range after deforestation might be larger than the previous simulated estimation. Thus, understanding the characteristics of hydro-climatological interaction in multiple land types from comprehensive local observation and regional model simulation is crucial for the diurnal atmospheric boundary layer development.