Energetic and Hydrologic Balance in the Surface Layer During the Monsoon Season in Korea

ENERGETIC AND HYDROLOGIC BALANCE IN THE SURFACE LAYER DURING THE MONSOON SEASON IN KOREA INTRODUCTION The atmosphere is a dynamic system with a high number of liberty degrees and intrinsically chaotic. Its state, in a given instant, is described by the spatial distribution of wind, temperature, pressure, humidity, solar radiation and other important variables. As it is a fluid, its evolution is described in mathematic terms by analytic equations such as the conservation of mass, energy and linear mo- mentum. Doing experimental studies and carrying out measurements directly in the environment, particularly in the boundary layer, is very complex due to the variability of the system itself and to the dimensions of the phenomena to be analysed. A possible solution to these problems is repre- sented by numerical modelling, which, thanks to continuous developments of computational tools, attains high levels of reliability and allows to simulate the most various fluid dynamic situations. In the last years there’s been a significant development in the acknowledgement of the importance of the turbulent fluxes of sensible and latent heat and of soil humidity in the large scale evaluation of the climatic system and of the hydrologic cycle. The latent heat flux is an important term which governs the energy balance in the presence of water, thus connecting energy to the hydrologic cy- cle. It is the result of evapotranspiration (vegetation or bare soil) and condensation at the surface; evapotranspiration takes place from water surfaces, humid soil and vegetated surfaces, whenever the overtopping air is drier than the air closest to the ground. The latent heat flux plays a decisive part in climate: it allows the energy flux also at planetary scale, though this doesn’t imply the exis- tence of strong temperature gradients. From a microclimatic point of view, the latent heat flux al- lows to balance the radiative flux without causing a large daily temperature range. The processes of evapotranspiration and of precipitation are one of the most important mechanisms of energy redis- tribution within the planet. Soil humidity, which rules the energy repartition in terms of sensible and latent heat fluxes, is very important too. A wrong estimate can lead to wrong simulations of the surface bound evolution, and the forecasts of precipitation and of cloud cover are consequently affected. This holds true for the large and small scale simulations, particularly where local convection is well developed. Moreover, the soil humidity content directly affects both the radiative and the convection and conduction terms. Actually a different humidity content affects the values of soil albedo (lower for wetter soils), of thermic conductibility (growing along with humidity) and, most of all, the terms of latent heat flux and of evapotranspiration. A study carried out by Cassardo et al. (2007) in the summer of 7