气候平均场上西太平洋副热带高压双脊线过程可能成因的动力诊断分析

利用NCEP-DOE再分析数据集II，诊断分析了气候平均场上6次西太平洋副热带高压双脊线过程，借助一个两层半大气模式，从动力学上初步揭示了西太平洋热带大气准10天振荡（Quasi Ten-day Oscillation，简称QTO）向西北方向传播与季风槽东伸西撤之间的相互作用过程，探讨了气候平均场上西太副高双脊线可能的形成机制。分析表明季风槽准10天东西振荡是气候平均场上西太副高双脊线形成的主要原因，而季风槽东伸西撤与QTO传播密切相关。进一步分析发现，QTO向西北方向传播，东风切变作用于斜压辐散的经向梯度，在对流中心北侧生成正扰动涡度。QTO在季风槽东侧激发的气旋性扰动涡度，诱导季风槽东伸，侵入副高，造成副高外围变形，形成双脊线。因此，形成西太副高双脊线的主要原因之一可能是西太平洋热带大气QTO。尽管季风槽东伸直接引起副高双脊线发生，但是它只不过是受QTO影响的一种表现。本文仅为诊断结果，其结果还有待于模式敏感性试验的验证。

Dynamical Diagnosis on Possible Formation Cause of Climatological Western Pacific Subtropical High Double Ridges Process

NCEP-DOE reanalysis II datasets are used to explore the characteristics of the Western Pacific Subtropical High(WPSH) Double Ridges Process(DRP) from the viewpoint of climate mean,and then the possible mechanism for the WPSH DRP is derived on the basis of the interaction between northwestward propagating western Pacific tropical atmospheric QTO(Quasi-Ten-day Oscillation) and the 8-10-day zonal oscillation of the monsoon trough by use of a two-and-a-half layer model.Results show that the quasi-ten-day west-east oscillation of the monsoon trough over the South China Sea monsoon region is the main cause of the occurrence of climate-mean WPSH DRP.However,the zonal movement of the monsoon trough is closely related to the propagation of QTO.Further studies by virtue of a two-and-a-half layer model indicate that,accompanied with QTO northwestward propagating,a positive vorticity perturbation characterized by an equivalent barotropic structure is produced at a few latitude degrees north of the QTO-associated convection center,due to the easterly shear of the mean flow acting on the meridional gradient of the baroclinic divergence.The QTO-induced cyclonic vorticity perturbation leads to eastward extension of the monsoon trough and its consequent intrusion into the WPSH,and thus the formation of double ridges of WPSH.On this account,one of the main causes for the WPSH DRP is possibly QTO rather than the eastward extension of the monsoon trough because the latter is just the result of the former.Further numerical modeling is required to validate these observational study results.