藏东南地区草地下垫面湍流通量和辐射平衡各分量的变化特征

Variation Characteristics of the Surface Turbulent Flux and the Components of Radiation Balance over the Grassland in the Southeastern Tibetan Plateau

利用2013年5月20日至7月9日藏东南林芝地区草地下垫面的野外试验站点观测资料,分析了晴雨转换过程中林芝地区草地下垫面的近地层基本气象要素、湍流通量和辐射平衡各分量的变化特征,并着重分析了各个变量之间的相互关系,对比分析它们在典型晴天和阴天条件下的差异。结果表明:(1)草地观测站的各气象要素的变化趋势相互吻合,即相对湿度与降水有着一致的变化趋势,而气温、地面温度和风速均与降水的变化相反;观测期间草地站的潜热交换大于感热交换,在无降水时期,感热明显偏高,潜热偏低,降水时期则相反;感热与向下短波辐射的变化趋势一致,同时,向上短波辐射、向上长波辐射、净辐射、地表反照率和土壤热通量均与向下短波辐射保持同步的变化关系,而向下长波辐射则呈现出相反的变化。(2)典型晴天和阴天的分析结果表明,晴天条件下各变量的日变化均比阴天条件下剧烈,在白天,感热和潜热在典型晴天的值均大于典型阴天天气下的值,除向下长波辐射外,其他地表辐射分量在晴天条件下的值远大于阴天的值;在夜间,晴天的向上长波辐射、净辐射和土壤热通量小于阴天的值。(3)相对湿度最大值出现在早晨,最低值出现在午后;风速的最小值出现在早晨,最大值出现在中午,且基本上都是晴天天气下大于阴天天气下。因此,藏东南林芝地区草地下垫面的感热、潜热、土壤热通量、辐射平衡各分量、基本气象要素均与晴、雨的转化有着非常密切的协同变化关系,这些变量之间相关系数高,吻合度好,表明了该边界层观测数据的可靠性,该观测试验数据可为数值模式在藏东南林芝地区地气交换过程的模拟提供重要的数据基础。

Based on field observations of the grassland over Nyingchi area in the southeastern Tibetan Plateau for the period from 20 May to 9 July 2013,the variation characteristics of the basic meteorological elements,the surface turbulent flux and the components of the radiation balance over the grassland in Nyingchi area under different weather changes were analyzed,and the relationships among these variables and their features under typical sunny day and cloudy day were analyzed emphatically in this paper. The results show that：（1） The change trends among each meteorological elements are match well with each other,the variation of the relative humidity is correlated with that of the precipitation,but that those of the air temperature,ground temperature and wind speed are anti-correlated with that of precipitation; During the observation period,more latent heat than sensible heat is exchanged,sensible heat flux is definitely higher during the days without rain,but latent heat flux is lower,things are the opposite in the precipitation period; The variation of the sensible heat flux is consistent with that of the total solar radiation（ DR）,and the variations of the reflective solar radiation（ UR）,the long wave radiation from the earth（ ULR）,the net radiation（ Rn）,the surface albedo and the soil heat flux are also correlated with the DR,but that of the long wave radiation from the atmosphere（ DLR） is anti-correlated with the DR.（2） The analysis results of the typical sunny day and the typical cloudy day show that the diurnal variation amplitude of sensible heat flux and latent heat flux in sunny condition is larger than that in cloudy condition,during the daytime,the sensible heat flux and the latent heat flux in the typical sunny day is significantly greater than that in the typical cloudy day,except the dow nw ard long wave radiation,the other components of the surface radiation balance in the sunny day are much larger than that in the cloudy day; At night,the upw ard long wave radiation,the net radiation and the soil heat flux in the sunny day are smaller than that in the cloudy day.（ 3） The maximum value of relative humidity appears in the morning,and the low est value occurs in the afternoon; The minimum value of wind speed appears in the morning and the maximum value appears at noon,and the values in the sunny day are mostly greater than that in the cloudy day. As a result,the sensible heat flux,latent heat flux,soil heat flux,each components of radiation balance and basic meteorological elements over the grassland at Nyingchi area in the southeastern Tibetan Plateau all have very close coordinated variation relationships with weather changes,the correlation coefficients betw een these variables are high,and these variables fit well with each other. It show s that this boundary layer observation data has high reliability,and this experiment observed data can provide important data basis for numerical model to simulate the surface-to-air exchange process over Nyingchi area in the southeastern Tibetan Plateau.