Study On The Variation Of Soil Heat Flux And The Characteristics Of Surface Energy Balance In Shanghai

To analyze the variation of the soil heat flux and the influence of ground source heat pump system on the surface heat transfer conditions in Shanghai,one-year long observation on the soil heat flux and related meteorological parameters in Shanghai was conducted.The characteristics of surface energy balance in Shanghai were summarized.The influence of ground source heat pump system on surface heat transfer was analyzed by establishing a model.Firstly,the selection criteria of typical day are put forward according to the weather standard.The characteristics of soil heat flux variation at different depths in summer and winter are analyzed.The shallow soil heat flux is affected by the weather condition.The variation of soil heat flux on different weather conditions is obviously different.The variation range of soil heat flux at 5 mm depth on clear day in summer is from-23.62 W·m^-2to 111.81 W·m^-2,which in winter is from-21.46 W·m^-2 to 69.30 W·m^-2.With weather conditions ranging from clear days to cloudy days to rainy days,the change of soil heat flux decreases in turn.Solar radiation plays a leading role in variation of shallow soil heat flux.The increase of soil water content results in the decrease of the variation of soil heat flux.The variation of deep soil heat flux is mainly affected by soil temperature gradient,which is usually stable.The shading of surrounding buildings has great influence on the daily variation characteristics of shallow soil heat flux.Secondly,the components of surface energy balance equation is calculated by combining the empirical model.In this paper,the reliability of soil heat flux measurement at 5 mm depth is verified by Thermal Diffusion Equation-Correction?TDEC?method,which is used to replace surface heat flux.The net radiation is consistent with the variation trend of direct solar radiation.It reaches the peak around 12:00,which is 626.40 W·m^-2 on clear day in summer and 326.64 W·m^-2 in winter.The variation of atmospheric counter radiation is stable,the mean value of which is 381.71 W·m^-2 in summer and down to 255.31 W·m^-2 in winter.The sensible heat flux and net radiation in summer have the same tendency of variation.On cloudy and rainy days,the sensible heat flux decreases and the latent heat flux increases.The variation tendency of sensible heat flux is opposite to that of net radiation in winter.The variation of sensible heat flux and latent heat flux is stable on cloudy and rainy days in winter.Then,the variation of surface energy balance is characterized by Ordinary Linear Regression?OLR?and Bowen Ratio Energy Balance?BREB?method.The energy balance closure of bare soil surface can reach over 70%.The increase of precipitation and soil water content will decrease the surface energy balance closure.The bowen rate of clear days is above 1,which means sensible heat flux is dominant compared with latent heat flux.On cloudy and rainy days,the bowen rate is close to 0.The simulation software is used to establish a model to simulate and analyze the influence of the ground source heat pump system on the surface heat transfer under different operating strategies.The simulated values and measured values have the same variation trend,magnitude and phase.The simulation analysis shows that the operation of the ground source heat pump system will increase the surface heat absorption in summer and decrease the surface heat loss in winter,which will improve the underground soil temperature.To sum up,the soil heat flux in Shanghai has obvious variation characteristics.The operation of ground source heat pump system will affect the variation of surface heat flux.The results of this study contribute to the observation of soil heat flux in urban areas in the future and provide a new direction for the study of the interaction between ground source heat pump system and local microclimate.