The influences of air heat storage, plant photosynthesis and soil water movement on surface energy balance over the loess plateau

Abstract

The surface energy imbalance problem has become a challenge in the study of surface land process since it was found in the late 1980s. By using data provided by the program the Loess Plateau Land-surface Process Experiment (LOPEX) and introducing the vertical sensible heat flux into the surface energy balance equation, in the paper, we estimate the heat storage associated with change of air temperature and humidity as well as the energy stored in plants due to the photosynthesis, determine the water vertical flux in the shadow soil layer both by water conservation principle and two-level soil temperature, and investigate the influences of air and plant photosynthesis energy storages and heat transferred by the soil water movement on the surface energy budget. It is found that the diurnal variation peaks of averaged energy storages of air and plant photosynthesis reach 1.5 and 2.0 Wm-2 respectively. Additionally, the diurnal variation peak of mean heat transferred by vertical water movement is close to 8.0 Wm-2. The closure of energy balance is improved from 88.1% to 89.6% by adding the three additional energy terms to the energy balance equation. As a whole, the energy storage related to air and the plant photosynthesis, and the heat transferred by the soil water movement both promote the surface energy balance to some extent. Furthermore, the semi-arid climate and the vegetation condition of Loess Plateau essentially lead to significant differences of energy storage be tween this area and other climatic districts.