【作者】 蒋兴文；

【导师】 李跃清； 马振锋；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2007， 硕士

【摘要】 利用青藏高原东部及其邻近地区1981年—2002年22年探空资料、地面观测资料、ECMWF再分析资料,使用多种诊断方法,首先分析了青藏高原东部及其邻近地区夏季水汽输送的基本特征,然后研究了水汽输送异常的年际变化特征及相应的大气环流异常特征,最后讨论了水汽输送异常与长江流域降水异常之间的关系,并深入分析了青藏高原东部水汽变化对长江流域降水的影响。研究结果表明:(1)青藏高原东部及其邻近地区水汽输送在空间垂直方向上表现出很大的差异,空间各层的水汽输送形式及水汽主要来源各不相同,水汽输送量由下向上逐渐减小。整层积分的水汽输送能综合反映各等压面上水汽输送的基本特征。青藏高原向东的纬向水汽输送对长江流域的纬向水汽输送具有重要的贡献。水汽输送的主要辐合区位于长江流域、高原东南角、高原西北部和四川盆地,最大的辐合中心在四川盆地西部,水汽辐合区都是夏季的多雨中心及大江大河的所在地。(2)瞬变扰动水汽输送表现出不同于定常水汽输送的特征,有较强的经向性。最大的瞬变扰动输送在长江中下游。瞬变扰动水汽主要表现为由长江流域向北输送,长江以北地区向北的水汽输送几乎全部由瞬变扰动输送来完成。大气水汽含量整体呈纬向分布,各等压面的分布形式有较大的差别,青藏高原对地表面的抬升作用对大气湿度的水平分布有重要的影响。瞬变扰动水汽输送方向由大气湿度梯度方向唯一决定,其方向与湿度梯度方向一致,大小由湿度梯度大小及天气尺度扰动强弱共同决定。瞬变扰动水汽输送有很强的年际变化。(3)复数EOF分析表明,大气水汽输送异常主要由低层水汽输送异常变化引起。中高层水汽输送异常对整层积分水汽输送异常的贡献主要表现在青藏高原。水汽输送异常特征向量所解释的方差越大,其在空间所表现出的异常结构就越均一,其异常的总体强度也就越大,反映在年际变化上的空间异常形态相同或相反就越多。在青藏高原东部地区的三条水汽输送带主要存在同步异常的特征。长江流域水汽输送的异常辐合与辐散是最为显著的水汽输送异常模态,水汽输送在长江流域的异常辐合对应降水的增多,而异常水汽输送辐散对应降水的减小。当西太平洋副热带高压偏强偏南偏西、印度季风低压偏弱、乌拉尔山及鄂霍次克海为高压脊、贝加尔湖地区为低压槽时,形成长江流域地区异常的水汽辐合;当西太平洋副热带高压偏弱偏北偏东、印度季风低压偏强、贝加尔湖至中西伯利亚为高压脊、日本海为弱脊时,在长江流域没有明显的水汽输送辐合特征,造成异常的水汽辐散。(4)青藏高原东部地区水汽输送对长江中上游的降水有重要的影响。青藏高原东部水汽输送对长江流域降水的影响不但与自身强度有关,同时也与西太平洋副热带高压的位置有关。RegCM3能很好的模拟1998年和1983年夏季降水的主要位置、强度及季节内变化。青藏高原东部水汽向东流出高原之后,沿着副高西北外侧呈西南风向长江流域输送,随着副高位置的不同,高原向东水汽输送影响长江流域的位置不同,进而影响长江流域降水的位置也不同。当降水减少后,凝结潜热减弱,加上水汽变化对辐射的影响,改变热力结构,在西太平洋副热带高压左侧激发反气旋式流场,改变左侧水汽输送,引起周边地区降水的变化。更多还原

【Abstract】 Using the sounding and ground-based observational data in the east and nearby area of Tibetan Plateau and ECMWF reanalysis data from 1981 to 2002 in summer, with many diagnostic methods, first, we analyzed the water vapor transportation characteristics in summer in the east and nearby area of Tibetan Plateau. Second, we studied the interannual characteristics of water vapor transportation anomaly and its corresponding general circulation. Finally, we discussed the relationship between water vapor transportation and precipitation in Yangtze River, and deeply analyzed the influence of water vapor change in the eastern Tibetan Plateau on precipitation in Yangtze River. The results showed as follows:(1) The water vapor transportation characteristics vary in the vertical direction that transporting forms and water vapor source are different in each layer and water vapor flow capacity gradually decreases with the height increasing. The vertically integrated values of water vapor transportation can reflect the main characteristics of different isotonic levels. The eastward water vapor transportation has significant contributions to the latitudinal water vapor transportation over Yangtze River. The main areas of water vapor convergence are Yangtze River, southeastern corner and northwestern part of Tibetan Plateau, and Sichuan Basin. The largest amount of water vapor convergence is Sichuan Basin. The areas of water vapor convergence are generally the rainy centers and rivers.(2) It is different between water vapor transported by transient eddies and stationary disturbance that the former is mainly the longitudinal transportation. The largest transient eddies transportation occurs in Yangtze River, and water vapor is transported northward from Yangtze River. Almost all water vapor northward in the north of Yangtze River is transported by transient eddies. The atmospheric water vapor distribution is basically zonal, and the isotonic levels are distinct from each other, for which the orographic lifting of Tibetan Plateau is very important to the horizontal distribution of atmospheric humidity. The direction of water vapor transported by transient eddies is same as the humidity gradient direction, and is determined only by the latter, while the numerical value depends on the humidity gradient and synoptic-scale disturbance. Furthermore, this kind of transportation has obvious interannual variation.(3) Complex EOF analysis indicates that water vapor transportation anomalies are mainly due to the anomalies of lower-layer water vapor transportation, and middle-high layer anomalies of water vapor transportation are mostly exhibited in the Tibetan Plateau. The more the eigenvector accounts for the total variance, the more consistent of the spatial distribution and intensities of anomalies. The three belts of water vapor transportation in the southeast part of Tibetan Plateau vary at the same phrase. Divergence (corresponding to precipitation decreasing) or convergence (corresponding to precipitation increasing) anomaly of water vapor in Yangtze River is the most remarkable mode. When the West Pacific Subtropical High Pressure (WPSHP) is strong and shifts southward and westward, Indian Monsoon Low Pressure (IMLP) is weak, Ural and Okhotsk are occupied by High Pressure Ridge, and Baikal is Low Pressure trough, it is easy to lead to anomalous water vapor convergence in Yangtze River. When WPSHP is weak and shifts northward and eastward, IMLP is strong, from Baikal to Middle Siberian there exist High Pressure Ridges, and Japan Sea is little High Pressure Ridge, it is unfavorable for water vapor convergence and could lead to anomalous water divergence in Yangtze River.(4) The water vapor transportation over east part of Tibetan Plateau has an important effect on precipitation in the middle and upper course of Yangtze River, and the effect is not only related to the intensity of itself, but also to the position of West Pacific Subtropical High Pressure(WPSHP). RegCM3 is efficient to simulate the main position, intensity and intra-seasonal variability of summer precipitation in 1993 and 1983. When water vapor over Tibetan Plateau flows eastward, it extends to Yangtze River along with the periphery of WPSHP. It is obvious that the precipitation region depends on the position of WPSHP. When the precipitation reduces, the latent heat flux also decreases, in addition to the influence on radiation caused by water vapor decreasing, the thermal field will be changed and could generate a cyclonic circulation on the left of WPSHP which will alter the water vapor transportation and lead to anomalous precipitation.更多还原