Atomospheric energy and water cycle of Tibetan Plateau

在大气湍流测量的基础上，采用涡动相关法直接测量了大气与地表界面的感热和潜热交换。在IOP期间建立了安多、MS3478、BJ（那曲）和MS3637四个通量站点并进行了测量。同时测量了这些站点的辐射收支、土壤表面温度、土壤温度剖面、土壤水分剖面和土壤热通量。这些测量结果可作为研究地表-大气相互作用的一致数据库。结果表明，安多地区的感热通量和潜热通量的日变化和季节变化都很明显，并获得了最长和连续的数据。在季风之前，地面非常干燥，地表温度的日变化高达50摄氏度。潜热通量很小，感热通量占主导地位，随着季风开始后地表变湿，潜热通量增大，感热通量减小。这种变化与地表温度的下降是一致的。在季风前、季风中期和季风后期也获得了典型的日变化通量（Ishikawa et al ., 1999）。Tsukamoto等（2001）比较了四个站点的通量观测。它们还表明，感热通量控制着混合层深度的发展。在这些通量点，Tanaka等人（2001a, 2001c）、Miyazaki等人（2001）、Wang（2001）和Kim等人（2001）报道了“通量平衡”。他们认为造成这种不平衡的原因有很多。他们还强调了气团平均垂直运动的重要性，这种运动可能是由小规模有组织扰动引起的。Tanaka et al. （2001c）对土壤热通量的测量进行了讨论。他们利用土壤湿度和温度数据，粗略估计了4月至6月融化永久冻土和加热土层所需的地表土壤热通量。所需的地表热通量平均约为30W/m^2，大于土壤热板测量的地表热通量。Tanaka等人（2001b）用数值方法研究了热板的性能，并建议对土壤热通量进行一些修正。表面不平衡问题还没有解决。这严重限制了观测到的通量数据的有用性。西藏西部是气象站分布非常稀疏的地区。在改则和石川河建立了2个自动化气象站，对地表边界层和部分土壤变量进行了连续测量。Haginoya（2001）报告了这些地点的地面气象和用博文比法估计的通量。Xu和Haginoya（2001）利用常规地面观测资料估算了西藏14个站点的月平均地表通量。安多站点的PBL塔观测在IOP之后继续进行。Tanaka et al. （2001d）通过比较塔台数据和IOP期间的湍流通量，计算了现场感热通量的总体传递系数。该系数作为体积理查德森数的函数得到。利用该系数和持续的塔观测数据，他们计算了2000年7月之前的感热通量。年际变化明显，在感热通量最大的春季，即使塔观测也失败。少

The exchange of sensible and latent heat at the interface of atmosphere and the land surface was directly measured by eddy correlation method based on the measurement of atmospheric turbulence. Four flux sites, Amdo, MS3478, BJ(Naqu) and MS3637, were set up and the measurements were conducted during the IOP. In these sites the radiation budget, soil surface temperature, soil temperature profile, soil moisture profile and soil heat flux were also measured. These measured results serve as a consistent database to study land surface-atmosphere interaction.With this results both diurnal and seasonal changes of the sensible and latent heat flux were clearly detected at Amdo where the longest and continuous data was obtained. Before the monsoon the ground surface was very dry and the diurnal change of the surface temperature was as large as 50 degree Celsius. The latent heat flux was very small and the sensible heat flux was dominant As the ground surface became wet after the onset of monsoo … More n, the latent heat flux increased and the sensible heat flux decreased. This change was in harmony with the decease of the ground surface temperature. Typical diurnal change of fluxes was also obtained for pre-monsoon, mid-monsoon and late-monsoon periods (Ishikawa et al, 1999). Tsukamoto et al(2001) compared the flux observation at four sites. They also show that the sensible heat flux controls the development of the depth of mixing layer.At these flux sites, Tanaka et al. (2001a, 2001c), Miyazaki et al. (2001), Wang (2001) and Kim et al. (2001) reported fluximbalance'. They suggest that many factors are responsible for the imbalance. They also stress the importance of mean vertical motion of air mass which may be induced by small scale organized disturbances. Tanaka et al. (2001c) give a discussion on the measurement of soil heat flux. They roughly estimated the surface soil heat flux needed to melt the permafrost and to heat the soil layer from April to June using the soil moisture and temperature data. The required surface heat flux was about 30W/m^2 on average, which was greater than that measured by soil heat plate. Tanaka et al. (2001b) examined the performance of a heat plate numerically and suggested that some correction is necessary to the soil heat flux. The surface imbalance problem has not yet been resolved. This severely limits the usefulness of the observed flux data.The western Tibet is a region where the distribution of meteorological station is very sparse. Two automated meteorological stations were set up at Gaize and Shichuanhe and the continuous measurement of surface boundary layer and some soil variables has been conducted. Haginoya(2001) reported the surface meteorology and fluxes estimated by the Bowen ratio method at these sites. Xu and Haginoya(2001) estimated the monthly averaged surface fluxes at fourteen Tibetan sites using conventional surface observation data. At Amdo site PBL tower observation has been continued after the IOP. Tanaka et al. (2001d) compute the bulk transfer coefficient for the sensible heat flux at the site by comparing the tower data with turbulent flux during IOP. The coefficient is obtained as a function of the bulk Richardson number. With this coefficient and the continued tower observation data they computed the sensible heat flux until July 2000. The data suggests the strong inter annual variation, even the tower observation failed in Spring, when the sensible heat flux is largest in the year. Less