天山北麓绿洲-荒漠过渡带芨芨草地地表能量通量研究

Characteristics of land surface energy over: Achnatherum splendens grassland in the oasis-desert ecotone of Northern Piedmont of Tianshan Mountains

利用天山北麓绿洲-荒漠过渡带芨芨草地的小气候实测资料,分析了该地区不同天气条件下地表能量及其能量分配日变化特征,并进一步探讨了潜热与其它地表能量的关系。结果表明:晴天各地表能量分量曲线呈"单峰型",阴天表现为峰谷频繁交替的"多峰型",雨天则显示为"偏峰型"。由于该区以晴天为主,阴雨天气发生频率少,平均情况下的各能量曲线变化与晴天基本一致。任何天气条件下能量传输均以潜热(LE)为主,其次为感热(H)和土壤热通量(G)。观测期内LE/Rn平均值介于沙漠和绿洲之间,很好地在能量分配上体现出自身的过渡性。各种天气条件下能量分配的日动态变化趋势基本一致,白天均以潜热为主,夜间则有所不同。LE/Rn、H/Rn、G/Rn曲线白天变化平稳,夜间持续波动,日出和日落前后波动最为剧烈。其中,日出时刻以LE/Rn和G/Rn曲线波动最为强烈,且两者峰谷互补。因辐射强度和日照时数的不同,不同天气条件下曲线早、晚剧烈变化开始时间也有所差别。晴天、平均、阴天(8:00—18:00)波文比依次减小,且均小于1,表明它们在白天能量分配均以潜热为主。而雨天波文比则表现出较大的波动性,整体呈上升趋势。LE与Rn、H、G相关性程度均表现为:晴天与平均相当,阴天次之,雨天最小。

Oasis-desert ecotone that lies between oasis and desert is bridgehead of the advance and retreat of Oasis（ desert）,which is ecological fragile zone taking on the trend of degradation. Its special characteristics of the surface energy exchange has a profound impact on the formation and development of the regional ecological environment. Therefore,better studying the law of surface energy transmission of oasis-desert ecotone can provide the scientific foundation of establishing the micro-climate model of the ecotone,achieving the optimal allocation of natural resources and promoting sustainable development of oasis. Based on the observed data of the experiment carried out in the oasis-desert ecotone of northern piedmont of Tianshan Mountains from July to September in 2010,the characteristics of the daily variations of the surfaceenergy balance,energy distribution and the relationship between latent heat and other surface energy were analysed. The results show that there are many differences in the daily variations of the surface energy under different weather conditions.Each energy component curve appears as‘single peak＇type on clear day,whose circadian variation is significant. Affect by the variation of cloudiness,the curve of overcast day displays as ‘multiple peak ＇type with peak and valley frequently alternating. Influenced by the precipitation change,the curve of rainy day manifests ‘partial peak ＇type. Owing to the precipitation,the curve of average is basically consistent with the clear day. Unlike the most previous experimental results of the arid areas,the latent heat（ LE） is the main energy transmission of the oasis-desert zone under any weather conditions,followed by sensible heat（ H） and soil heat flux（ G）. The LE / Rn of sunny day reaches 72.4%.Due to the complement of the soil heat flux（ G）,LE / Rn of overcast day is up to 131%. As the transitional hydrothermal property and the dry-heat air transported by advection from desert,the average value of LE / Rn（ 58. 8%） was much larger than Hexi Corridor desert,Dunhuang gobi for the same period in the arid zone,while smaller than the irrigated wheat area of oasis. That the average LE / Rn is between desert and oasis well reflects the transitional character of energy distribution. The daily changing trends of energy distribution under any weather condition are basically in accordance： energy of daytime is latent heat mainly and night is different. The curve of G / Rn、H / Rn and LE / Rn in daytime is smooth,that fluctuate continually in night,however,the most violent in sunrise and sunset. The LE / Rn and G / Rn curve of sunrise fluctuations strongest,which display the peakvalley complementarity. The Bowen ratio（ 8： 00—18： 00） of the clear,average and overcast day decreases in turn. They are less than 1,indicating that energy distribution are mainly the latent heat in the daytime. However,the rainy day shows greater volatility with the upward trend as a whole. The correlation coefficients between LE and other energy including Rn,H,G are different due to weather condition. They are all highly correlated in clear days,followed by cloudy days and rainy days,while in clear days they show similar to the average condition.