Roles of Regional Ocean-Atmosphere Coupling and Remote Forcing in Northwest Pacific Monsoon Variability

夏季是东亚的雨季。从青藏高原东侧向东北延伸，经过朝鲜和日本的梅雨-白乌雨带是该地区最重要的气候现象。今年夏季雨带在7月下旬的终止与菲律宾以东西北太平洋热带对流的突然爆发有关，通过夏季降雨变率的纬向偶极子模式。西北太平洋对流的突然爆发仍然没有解决，当地海表温度（SST）早在6月就上升到28摄氏度以上。本项目的工作将调查这样一种假设，即通过浅层对流逐渐增湿对流层低层导致热带西北太平洋上空突然对流开始的阈值行为。在1979年开始的卫星时代，热带西北太平洋对流的年际变化与厄尔尼诺/南方涛动（ENSO）有很好的相关性。具体而言，一个异常的反气旋环流（AAC）的形式和降水减少热带西北太平洋后厄尔尼诺的夏天。通过早期的研究，在夏季西南季风盛行时，由于AAC和印度-西北太平洋SST之间的相互作用，已经确定了一个正反馈。我们将探讨这种区域耦合模式的机制和可预测性。AAC和ENSO之间的相关性在20世纪20年代和70年代的世纪的一半时间里被打破。弱ENSO振幅被认为是造成低相关性的原因。这方面以及随机噪声的作用，由于大气内部的变化将进行严格的探讨。在当地，西北太平洋对流影响美国附属的北方马里亚纳群岛和关岛。在遥远的地方，它影响到南亚和东亚季风区，那里有30亿人。这项研究将有助于改善该地区的季节预报和气候变化预测，从而为几个正在进行的国际研究项目做出贡献。该项目通过将研究生和博士后纳入研究团队并让他们参与国际合作来培养下一代气候科学家。

Summer is the rainy season for East Asia. The Meiyu-Baiu rain band, extending from the eastern flank of the Tibetan Plateau northeastward through Korea and Japan, is the single most important climate phenomenon of the region. The termination of this summer rain band in late July has been tied to the abrupt onset of tropical convection over the Northwest Pacific east of the Philippines, through a meridional dipole pattern of summer rainfall variability. The abrupt onset of Northwest Pacific convection remains unsolved with local sea surface temperature (SST) rising above 28 degrees C as early as in June. Effort under this project will investigate the hypothesis that the gradual moistening of the lower troposphere via shallow convection leads to a threshold behavior of abrupt convective onset over the tropical Northwest Pacific. During the satellite era starting 1979, interannual variability in tropical Northwest Pacific convection is well correlated with El Nino/Southern Oscillation (ENSO). Specifically, an anomalous anticyclonic circulation (AAC) forms and rainfall decreases over the tropical Northwest Pacific in post-El Nino summers. Through earlier studies a positive feedback has been identified due to interactions between the AAC and Indo-Northwest Pacific SST during summer when the southwest monsoonal winds prevail. We will investigate the mechanisms and predictability of this regional coupled mode. The correlation between the AAC and ENSO breaks down during half of the 20th century from the 1920s and 1970s. Weak ENSO amplitudes are considered to have caused the low correlation. This aspect as well as the role of random noise due to atmospheric internal variability will be explored critically. Locally, Northwest Pacific convection affects the U.S. affiliated Northern Mariana Islands and Guam. Remotely, it affects the South and East Asian monsoon regions, home to three billion people. This research will help improve seasonal forecast and climate change projection in the regions, thereby contributing to several ongoing international research programs. The project trains the next generation of climate scientists by including graduate students and postdocs in the research team, and by exposing them to international collaborations.