| The interactions of land-atmosphere in arid and semi-arid regions have significant influences of regional climate change, global climate change and general circulation of atmosphere. While the issue of energy unbalance cannot be ignored in the land-atmosphere interaction processes. Data used in this paper are taken from "Microclimate and Evaporation Experiment in Inner Mongolia"(MEEIM)(June22,2012-September20) and Semi-Arid Climate Observatory and Laboratoryof Lanzhou university (SACOL)(2007-2009, on22June-September20). Based on these data, we analyzed the abnormal phenomenon of instantaneous energy closure rate, then discussed the reason for abnormal energy closure rate, finally an evaluation methodology for energy balance was proposed. After that, we analyzed the characteristics of energy exchanges in surface layer in arid and semi-arid regions, then studied the energy closure rate of the two site by using three methods in determining the surface heat flux, especially focused on the impact on the energy balance rate caused by the atmosphere turbulence motions.After our research and analysis, the following conclusions could be drawn:(1)Abnormal value of single-point energy balance rate occurs with different methods determining soil heat flux. The theoretical energy balance is only an approximation of the actual observation in some degree, that is to say, the biggest frequency distribution of energy balance rate (EBR) value is around1. The proportion of abnormal EBR depends on the definition of abnormal one. Here we define if EBR value is not between0and2then we take it as abnormal EBR. Compared with different soil heat flux calculation methods, the biggest proportion of abnormal can be28.63%. The abnormal EBRs are mainly in the conditions of-100W/m2≤Rn-G≤100W/m2.(2) The negative abnormal EBR is the majority of the abnormal EBR, namely the energy transfer direction has a main effect on closure rate normal or abnormal. Both the negative abnormal EBR frequency distribution and the positive one reach their peak value in weak stable condition at sunrise or sunset. (3)The proportion of abnormal EBR is smallest in unstable conditions, neutrally conditions comes second, and the stable conditions is the biggest. Surface layer conforms to Monin-Obukhov similarity theory, turbulence and the uncertainty of soil heat flux can impact the distribution of EBR, but the motion structure of turbulence and the discrepancy of soil heat flux calculated by different methods are both not the significant reason that cause abnormal EBR.(4) It is reasonable that using a constant value to divide the available energy range, then evaluate energy balance state with OLSs or EBR method in different intervals. The constant value we choose is100W/m2,that is if the absolute value of available energy is among100W/m2then OLSs method can be used to calculate energy closure rate, and if it is bigger than100W/m2then EBR method can be used to evaluate the energy balance state.(5) Summer is the wet period of arid and semi-arid regions. In the daytime, the sensible heat flux accounts for52.54%of the available energy averagely, while the latent heat flux accounts for33.40%, which means that the sensible heat flux dominating the turbulent flux in arid zones; while in semiarid zones the sensible heat flux and latent flux accounted for separately37.74%and43.49%, Turbulence is given priority to with latent heat exchange.There were closed relationship between the turbulent exchange characteristic and surface water content in the arid and semiarid areas, which means the sensible heat flux is the primary one if the soil is relative dry and the latent heat flux will be the primary one is the soil moisture content is large enough. Since the evaporation power is large in arid and semi-arid surface, the exchange characteristics of latent heat flux dominating can only be last for a few days.(6) In the analysis of energy balance, the soil heat storage is important to the surface layer energy closure rate, the closure rates of different energy balance analysis methods have a certain difference. If no soil heat storage are considered, the closure rates of EBR method are the biggest, in particular, the corresponding closure rates for MEEIM and SACOL0.76and0.81separately, while the closure rates of the other two methods are all smaller than0.7. After considering soil heat storage, all closure rates are increased at various degrees, it is more obvious of the OLSs and the combined method than that of EBR method. For MEEIM, when EBR method were used to compute closure rate, the one which soil heat flux calculated by the PlateCal can improved more than the one used TDEC calculate soil heat flux, but for other stations and other closure rate calculate methods, TDEC performs better. The closure rates have an obvious diurnal variation, the value in the daytime are bigger than that at night. The combined methods solve the computational instability in the sunrise and sunset or at night, and it increased the energy closure rate of OLS method in the daytime. (7) There was a significant positive-correlated quadratic function relationship between the relative horizontal turbulence intensity and the vertical one, hence the relative vertical turbulence intensity alone can characterize the intensity of the atmosphere turbulent motions. By means of analyzing the relationship between the vertical turbulence and energy closure rate in two sites, we found that the observed surface layer energy closure rate depends on the intensity of the atmosphere turbulent motions. The energy closure rate increases with an increasing relative vertical turbulence intensity as a whole, but the increasing trend became gentle or even turned to an decreasing one when the relative vertical turbulence intensity reached a certain large value. Different soil heat flux calculation methods, different definitions of day and night and different energy balance analysis methods can all effect the energy balance rate, but they all cannot change the fact that the energy rate observed in surface layer is depending on the motion state of the atmosphere turbulence. |
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