The Origin and Structure of the Monsoon Onset Vortex

阿拉伯海上空的两个事件是印度夏季风的明显先驱者：海表温度升高（SSTs）的“迷你暖池”的形成，以及索马里低空喷气机从东非海岸延伸到印度西海岸。该急流将水汽从温暖的阿拉伯海温蒸发到印度沿海，引发季风，在许多年里，季风的爆发伴随着一个被称为季风爆发涡（MOV）的气旋性涡旋。MOV之所以引起人们的兴趣，不仅是因为它与季风的发生有关，还因为它可以演变成台风，并在登陆时造成广泛的破坏。本合同项下的工作旨在了解MOV的形成，同时考虑到小型暖池的影响和索马里喷气机的影响。前者鼓励深层对流，从而促进对流层中层涡旋的形成，而后者可以通过急流所在的对流层低层正压不稳定产生涡旋。这项工作的目标是了解这两种机制如何结合起来创建MOV。这项工作包括分析来自卫星任务的数据和再分析数据集，以及用简单的理想模式和天气研究与预报（WRF）模式生成的模拟。该项目还包括考虑到其纬向切变和时间变化的索马里急流的稳定性分析。考虑到MOV与季风的发生及其产生强大登陆台风的趋势之间的联系，这项工作具有社会和科学意义。该项目还为两名研究生和两名本科生提供支持和培训。此外，PI还担任高中学生的导师，并为北卡罗来纳大学科学与数学学院的夏季研究项目做出贡献。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Two events over the Arabian Sea are clear precursors to the Indian summer monsoon: the formation of a "mini warm pool" of heightened sea surface temperatures (SSTs), and the extension of the low-level Somali jet across the Sea from the East African coast to the west coast of India. The jet brings moisture evaporated from the warm Arabian SSTs to coastal India triggering the monsoon, and in many years monsoon onset is accompanied by a cyclonic vortex known as the Monsoon Onset Vortex (MOV). The MOV is of interest not only for its association with monsoon onset but also because it can evolve into a typhoon and cause extensive damage on landfall.Work under this award seeks to understand the formation of the MOV, taking into account the influence of the mini warm pool and the influence of the Somali jet. The former encourages deep convection which in turn can promote vortex formation at mid-tropospheric levels, while the latter can generate a vortex through barotropic instability at the lower-tropospheric level where the jet is found. The goal of the work is to understand how these two mechanisms combine to create an MOV. The work involves analysis of data from satellite missions and reanalysis datasets along with simulations generated with both simple idealized models and the Weather Research and Forecasting (WRF) model. The project also includes a stability analysis of the Somali jet, taking into account both its latitudinal shear and its time variation.The work is of societal as well as scientific interest given the connection of the MOV with monsoon onset and its tendency to generate powerful landfalling typhoons. The project also provides support and training to two graduate students and two undergraduates. In addition, the PI serves as a mentor to high school students and contributes to the summer research program of the NC School of Science and Math.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.