卫星遥测纬向剖面地形谱分析——青藏高原背风侧地区地形扰动与西风扰动的耦合模态  

A Spectral Analysis of Satellite Topographic Profile: A Coincident Pattern between Latitudinal Topographic and Westerly Perturbation on the Lee Side of Qinghai-Tibet Plateau

作　　者：王宛亭[1] 王元[1] 

机构地区：[1]南京大学大气科学系中尺度灾害性天气教育部重点实验室,南京210093

出　　处：《南京大学学报（自然科学版）》2004年第3期304-318,共15页Journal of Nanjing University（Natural Science）

基　　金：江苏省自然科学基金(BK99020);国家自然科学基金项目(40175025;40333025);"973-CHERES"项目(G1998040907)

摘　　要：　遥感地形资料具有空间离散分布特点,因此根据离散谱空间变换中谱能不变性约束下的谱分析方法,研究了遥感地形谱空间域分布基本特征和地形强迫对大气受迫运动的作用机制.并通过定义地形扰动和地形扰动特征尺度的概念,发现位于青藏高原背风侧的我国中东部地区纬向(东西向)剖面地形扰动特征尺度在454.5km,即该地区地形扰动可以定义为中α尺度扰动(比照大气尺度分类);地形扰动尺度与该地区主要致灾天气系统MαCS(Meso＿αConvectiveSystem,中α尺度对流系统)尺度上的一致性揭示了地形对于MαCS的触发作用.进一步通过对卫星遥感离散地形场测度进行分形学分析,计算出该区域纬向剖面分数维为1.26,说明该地区地形的基本分形元是Koch三角生成元,即青藏高原背风侧地区剖面地形强迫作用机制本质上是基本西风气流与三角形元组合型山脉剖面障碍物相互作用的结果.这种相互作用的物理图象表现为:在我国青藏高原背风侧地区,冬季和夏季700hPa纬向平均风速扰动谱最强峰与地形扰动谱最强峰存在着明显的地形 纬向风速偶合关系,地形 纬向风速共振模态是该地区冬季纬向环流扰动的典型触发机制;而夏季,地形 纬向风速偶合模态转变为向小尺度漂移的高阻尼模态.同时,地形和纬向风速的分形分析表明,关于地形强迫下的受迫扰动的偶?The paper proposes a spatial spectral analysis method under the restriction of conservation of spectrum power between the discrete and continuous space in order to deal with the discrete topographic data from remote sensing observation. So_called topographic perturbation and its characteristic scale are introduced to detect the mechanism of topographic forcing on atmosphere, as well as the main distribution characteristics of topographic spectra. On the Lee Side of Plateau, the research shows, that the characteristic scale of latitudinal topographic profile is 454.5 km, which is indeed the meso_scale perturbation. The scale coincidence between the characteristic scale of topography and MαCS implies that the topographic trigging effect might play an important role in the formulation of MαCS. By analyzing the remote sensing topographic data in the framework of fractal method, we find that the fractal dimension on the Lee Side of Qinghai_Tibet Plateau equals 1.26, which means the basic fractal unit of this region is the triangle unit. In fact, the fundamental mechanism of topographic forcing is the result of the interaction between basic flow and triangle blockings. Such interaction mechanism clearly is presented in the Lee Side of Tibet Plateau, where the coincident pattern for such interaction does exist between latitudinal wind spectra at 700 hPa layer and latitudinal profile of topographic spectra during summer and winter. In winter, the resonant coincident pattern is further found as a typical trigging mechanism for the latitudinal perturbation. In summer, however, the resonant coincident pattern changes into the strong damping mode so that the resonant pattern is no longer an issue; instead, it shifts to smaller scales because of the strong damping. The fractal analysis on topography and latitudinal wind shows that the conclusion about the topographic forcing mechanism and the coincident pattern of topographical forcing perturbation can be extended to the unobserved small scales testified by the cascad

关 键 词：青藏高原背风侧 地形扰动谱 地形-纬向风速偶合模态 分形 大气受迫运动 

分 类 号：P461.3[天文地球—大气科学及气象学] P432