Central Vietnam is characterized by severe flooding associated with heavy rainfall events caused by interactions between multiscale atmospheric circulations and the complex local terrain. Previous studies believed rainfall in central Vietnam is closely related to the cold surge; however, it fails to explain the cause of the early rainfall occurrence in August in the subregion. For the first time, this study investigates the detailed atmospheric mechanisms associated with rainfall variations in central Vietnam using the empirical orthogonal function (EOF) applied to the recently developed high-resolution Vietnam gridded precipitation (VnGP) dataset. Reanalysis data NCEP/NCAR is used to associate the rainfall changes with respective atmospheric mechanisms. EOF analysis detected two dominant rainfall modes. The primary mode explains the rainfall variation from October to November over the central and is directly related to the interaction of cold surges and tropical disturbances. The second mode accounts for rainfall occurring in north central from September to mid-October, which is attributed to the westerly summer monsoon activities. Also, we revealed that, while the first mode exhibits a significant correlation with El Niño-southern oscillation, the second depends highly on the contrast of sea surface temperature in the northern and southern Hemispheres. This different oceanic forcing and the local topological effect of Truong Son mountain range reasonably explain the opposite rainfall pattern in central Vietnam in early fall.

中文翻译：

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地形效应与越南中部降雨的反趋势

越南中部的特点是多尺度大气环流与复杂的当地地形之间的相互作用导致严重的洪水与强降雨事件相关。此前的研究认为，越南中部的降雨与寒潮密切相关；但是，它无法解释该次区域 8 月出现提前降雨的原因。本研究首次使用应用于最近开发的高分辨率越南网格化降水 (VnGP) 数据集的经验正交函数 (EOF)，研究了与越南中部降雨变化相关的详细大气机制。再分析数据 NCEP/NCAR 用于将降雨变化与相应的大气机制联系起来。EOF 分析检测到两种主要的降雨模式。主要模态解释了 10 月至 11 月中部降雨量的变化，并与冷潮和热带扰动的相互作用直接相关。第二种模式解释了 9 月至 10 月中旬发生在中北部的降雨，这归因于夏季西风活动。此外，我们还发现，虽然第一种模式与厄尔尼诺-南方振荡具有显着相关性，但第二种模式在很大程度上取决于北半球和南半球海面温度的对比。这种不同的海洋强迫和长山山脉的局部拓扑效应合理地解释了早秋越南中部相反的降雨模式。