Propagation Diversity of 20–40-Day Oscillation of Summer Precipitation in the Middle and Lower Reaches of the Yangtze River

IF 3.8 2区 地球科学 Q2 METEOROLOGY & ATMOSPHERIC SCIENCES
Yanfei Shi, Suxiang Yao
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Abstract

The summer precipitation in the middle and lower reaches of the Yangtze River (MLYR) is characterized by obvious intra-seasonal oscillations. This study investigates the propagation diversity of the 20–40-day summer precipitation oscillation in MLYR and its underlying mechanism. The 20–40-day oscillation events manifest as three types: northward propagation, southward propagation, and local oscillation. For northward and southward events, the propagation of precipitation is accompanied by the movement of 20–40-day low-frequency cyclonic vortices in the lower troposphere. Further investigation into the mechanism of anomalous vorticity propagation accompanying low-frequency vortices reveals that positive relative vorticity advection in the north of the vortex facilitates its northward propagation. Moreover, the positive advection is primarily reliant on the background southerly winds to transport the low-frequency vorticity. Diabatic heating dominates the southward propagation of low-frequency precipitation. The center of the latent heating is located in the south of the low-frequency vortex, which steers its southward migration. Furthermore, the uneven spatial distribution of latent heating across the vortex may be attributed to the non-uniform distribution of mean humidity. Based on the above results, sensitivity experiments are conducted using a regional climate model (RegCM4.6). The results demonstrate that when the southerly winds are increased (decreased) or the specific humidity gradient is decreased (increased), the southward (northward) events weaken and disappear, or transitioned into local oscillations or northward (southward) events. This further validates the physical processes through which the basic flow and humidity inhomogeneities affect the meridional propagation of the 20–40-day oscillations of precipitation.

长江中下游夏季降水 20-40 天振荡的传播多样性
长江中下游夏季降水具有明显的季节内振荡特征。本研究探讨了长江中下游地区夏季降水 20-40 天振荡的传播多样性及其内在机制。20-40 天振荡事件表现为三种类型:向北传播、向南传播和局地振荡。在北传和南传事件中,降水的传播伴随着对流层低层 20-40 天低频气旋涡的移动。对伴随低频涡旋的异常涡度传播机制的进一步研究表明,涡旋北部的正相对涡度平流促进了涡旋的向北传播。此外,正平流主要依靠背景偏南风来输送低频涡度。静态加热主导了低频降水的向南传播。潜热中心位于低频涡旋的南部,引导低频涡旋向南移动。此外,潜热在整个涡旋中的空间分布不均匀可能是由于平均湿度分布不均匀造成的。根据上述结果,利用区域气候模式(RegCM4.6)进行了敏感性实验。结果表明,当南风增强(减弱)或湿度梯度减小(增大)时,南向(北向)事件会减弱和消失,或过渡为局地振荡或北向(南向)事件。这进一步验证了基本气流和湿度不均匀性影响降水 20-40 天振荡经向传播的物理过程。
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来源期刊
Journal of Geophysical Research: Atmospheres
Journal of Geophysical Research: Atmospheres Earth and Planetary Sciences-Geophysics
CiteScore
7.30
自引率
11.40%
发文量
684
期刊介绍: JGR: Atmospheres publishes articles that advance and improve understanding of atmospheric properties and processes, including the interaction of the atmosphere with other components of the Earth system.
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