| The land-atmosphere interaction in arid area has an important influence on regional climate and even global climate and atmospheric circulation changes, and energy balance problem is a problem that can not be ignored when investigate in land-atmosphere interaction. The scope of the arid region is very large,reaches about 1/3 of global land area, the difference of surface energy balance on different surface underlying is very obvious, and the surface energy balance of the same surface underlying changes sharply with the seasons, weather and the dry and wet change of soil. In order to further understand the characteristics of surface energy balance,the land surface observation data under the uniform bare soil in the arid area and cropland non-uniform underlying in northwest China is selected,and the characteristics of the surface energy balance changes in different seasons are analyzed,at the same time,the influence of weather conditions on the energy balance is analysised and the characteristics and mechanism of surface energy balance on different underlying surfaces in arid area are discussed.The main research results are as followings:(1) According to the analysis of precipitation process influence to the characteristics of the surface energy balance,before the precipitation in arid areas, soil moisture is quite low on desert underlying surface, sensible heat flux is significantly greater than the latent heat flux, the surface available energy mainly releases in the form of sensible heat;while the surface water is enough after the rain,latent heat flux is greater than sensible heat flux, the surface available energy mainly releases in the form of latent heat.Comparing the energy closure conditions before and after precipitation, analysis showes that soil moisture has a significant effect on energy closure, closure of energy increase with the increase of soil moisture significantly; influence of torrential rain process on the energy balance can last about three days.(2) According to the analysis of energy balance using EBR method,the influence of surface heat flux calculated by PlateCal and TDEC method has certain difference on energy closure, the energy closure got by PlateCal methord is superior to that by TDEC method;OLS method analysis shows that closure by TDEC methord is superior to PlateCal method. According to the analysis of seasonal change characteristics of energy balance, choose EBR method, the integral superiority of closure is: autumn > summer > spring > winter when choosing EBR method; while the closure have common features by PlateCal and TDEC method, superiority of the closure is: summer > spring > autumn > winte when choosing OLS method.(3) The surface energy imbalance on desert underlying is mainly influenced by air heat storage and vertical air advection transport effects,the maximum average daily variation of air heat storage can reach 4.7W?m-2, the maximum average daily variation of vertical advection transport can reach 36.3 W?m-2. After compensating the air heat storage and vertical advection transport,the maximum of average daily unclosure residual variation dropped from 84.1W?m-2 to 60.6W?m-2,the surface energy balance closure degree increased from 82% to 98%.(4) Surface energy imbalance on the farmland inhomogeneous underlying surface is influenced by air heat storage, photosynthesis, biomass storage heat and the vertical advection transport. The maximum average daily variation of air heat storage can reach 10.6W?m-2, maximum average daily variation of photosynthesis can reach 9.9W?m-2,and the maximum average daily variation of biomass thermal storage comes to 32.4W?m-2,the the maximum average daily variation of vertical advection transport can reach 22.9 W?m-2.After compensating the air heat storage, photosynthesis, biomass storage heat and the vertical advection transport,the maximum of average daily unclosure residual variation dropped from105.9 W?m-2 to79.3W?m-2,the surface energy balance closure increases from 79% to 90%.In addition,temperature inversed in farmland underlying surface is influenced by vegetation canopy,causing the calculated surface heat flux bigger,leading to over closed phenomenon, and it is more accurate using the directly measured 5 cm deep soil temperature to calculate the soil thermal storage.(5) The closure in uniform bare soil in the arid area is higher than that in cropland non-uniform underlying surface, in the desert underlying surface, which is uniform, the effect mechanism is simple, and the condition is closer to the ideal underlying surface; while there are many factors effect the surface closed in cropland non-uniform underlying surface, where surface energy balance unclosure is more apparent. |
PDF Full Text Request