【作者】 尹志聪；

【导师】 王亚非；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2010， 硕士

【摘要】 本文首先分析了1954-2005年江淮梅雨期降水的低频振荡特征,并针对其中的准双周振荡进行了详细的讨论。通过定义梅雨准双周振荡强度指数QAI和对10-25天滤波的降水序列进行位相划分,讨论了梅雨准双周振荡强度的年际变化及其所对应的大气环流特征。其次验证了区域气候模式RegCM3.0对梅雨周期特征的模拟能力,并进行了基于侧边界信号的数值实验。在外强迫的研究方面,通过诊断分析和数值模拟研究了前期春季黑潮区海温异常对梅雨准双周振荡的影响,力求增加梅雨短期气候预测的预报因子。在文章的最后,通过分析大气环流准双周振荡的传播特征,在一定程度上解释了梅雨期降水经向非均匀性产生的原因。全文主要结论包括：(1)梅雨的10-25天振荡是一个能够反映梅雨降水多寡的较强信号,原始降水序列在10-25天振荡的第3位相(正位相)的降水显著多于第7位相(负位相)：(2)低层环流中一条从南海延伸至西北太平洋的低频Rossby波列非常显著,波列通过子系统向西南移动来完成位相的转换。波列西段的反气旋(气旋)自日本东部向南海传播,调控西太平洋副热带高压进入(退出)南海,它和后方的气旋(反气旋)共同作用在江淮上空形成气流的辐合(辐散),有利(不利)于江淮流域降水。同时高层环流、垂直环流和水汽通量也表现和低层相一致的特征；(3)梅雨准双周振荡强度存在显著的年际变化。QBWO活跃年,大气中存在从热带向中纬度呈西南—东北向延伸的准双周振荡活跃带。梅雨降水偏多的第3位相和降水偏少的第7位相在QBWO活跃年和不活跃年的偏差场,表明在活跃年第3位相的环流表现为增加该位相的准双周降水正距平的形势,而第7位相则会产生更大的降水负距平。各个位相降水距平的变化的最终增大了准双周降水的振幅,也即增强了梅雨的准双周振荡强度。(4)数值实验的结果表明相对于内因—梅雨锋而言,周围大气环流这个外因在梅雨降水准双周振荡的形成起到更重要的作用。当侧边界有10-25天大气环流信号加入后,一般只有本周期的低频降水受到影响。(5)诊断分析和数值模拟的结果表明,前期3月至同期的黑潮及其延伸区SST异常通过海气相互作用影响,可以影响梅雨的准双周振荡强度。当黑潮及其延伸区的海温持续偏高时,西太平洋副热带高压较为频繁的进入和退出南海,导致梅雨降水准双周振荡强烈。(6)在江淮流域降水经向非均匀的异常年里,不仅江淮梅雨期降水量存在经向不均匀,降水的准双周振荡特征也同样存在经向不均匀分布的特征。与降水的分布相对应,准双周水汽通量及其散度,西太副高和垂直环流的传播都会存在南北偏移。更多还原

【Abstract】 The low-frequency oscillation of Meiyu over Yangtze-huaihe basin is examined, of which the qusi-biweekly oscillation (QBWO) is discussed in detail. By defining an index QAI to measure the intensity of QBWO, we discussed the annual variability of QBWO, and corresponding circulation characteristics. Then the ability of a regional climate model to simulate the periodic characteristic is verified, and several series of numerical experiments based on the signal of lateral boundary layer are carried out. With respect to the external forcing, the impact of the pre-spring sea surface temperature anomaly on the qusi-biweekly oscillation of Meiyu is studied through diagnostic analysis and numerical simulation, which is conducive to improve the possibility of short-term climate prediction. Also, the longitudinal heterogeneity of Meiyu can be explained to some extent by the propagation of the qusi-biweekly oscillation of Meiyu.The main conclusions are as follows:(1) The 10-25 day oscillation of rainfall is a strong signal which can reflect the temporal heterogeneity of the original rainfall very well. (2) In the lower troposphere, a downstream Rossby wave train extending from the South China Sea to the Western North Pacific is significant, and the phases are transformed when the systems of the wave train keep moving southwestward. The double anti-cyclone and cyclone in the western part modulate the Western Pacific subtropical high to shift southwestward into South China Sea. Coacted with the divergent circulation in the upper troposphere, the convective activity is intensified, thus supports favorable updraft for the rainfall. A mass of water vapor is transported from South China Sea to Yangtze-Huaihe river basin, which forms a convergent belt of water vapor extending zonally. (3) The interannual variability of the intensity of QBWO is significant, and there is an active zone of QBWO from southwest to northeast in atmospherer. The circulation in active years caused more positive rainfall anomaly in phase 3, and a larger negative anomaly in phase7. So the circulation could enlarge the amplitude to intensify the QBWO. (4) The results of the numerical simulation showed that the circulation played more important role in forming the rainfall QBWO than the inner factor, Meiyu front. (5) Through diagnostic analysis and numerical simulation, we find the pre-spring sea surface temperature anomaly has an efffect on the qusi-biweekly oscillation of Meiyu by air-sea interaction. The lasting positive offshore SST anomaly strengthens Meiyu quasi-biweekly oscillation by regulating the Western Pacific Subtropical High to enter and quit South China Sea. (6) During the rainfall longitudinal heterogeneous anomaly years, not only the precQAItation but also the periodic characteristic shows the obvious longitudinal heterogeneous characteristic. Corresponding to the distribution, the 10-25-day filtered water vapor flux, divergence the flux, subtropical high and the vertical circulation all take on the feature of south-north deviation.更多还原