Modeling Studies of Transitions from Slow to Fast Tropical Cyclone Intensification

这项研究项目是一项更广泛努力的一部分，目的是促进目前对欠发达热带气旋如何增强为潜在破坏性飓风的理解。将进行计算机模拟研究，以解决在存在与中层和低层气旋环流(TILT)严重错位有关的明显不对称对流时运行的强化过程的性质和有效性方面的知识不足。快速强化机制取代慢速机制所需的不对称状态的变化，以及在各种环境条件下发生这种变化的时间尺度将被阐明。从该项目获得的知识将有助于作出补充努力，提高业务强化预报的准确性，以确定适当减轻热带气旋预测路径所造成的沿海或岛屿社区损害所需的准备工作。除了提供与预报相关的新见解外，该项目还将支持学生实习，这将有助于下一代大气科学家的发展。研究战略将包括简化和全物理建模研究相结合。简化的模式研究将在干燥原始方程中添加参数化非绝热强迫，主要表示与对流层低涡中心的对流集中下倾有关的加热。预计在非绝热强迫、涡旋状态和环境垂直风切变的扩展的多维参数空间上存在各种增强机制。可能性的范围从非常慢的非对称自旋模式到与核心改造相关的快速模式。每种不同的强化机制的适用范围将通过广泛的数值实验来确定。我们将寻求超曲面的理论公式，这些超曲面将参数空间中不同强化机制运行的区域分开。全物理模拟将用于阐明驱动每种强化机制的对流的湿热流体动力学，并阐明导致热带气旋从慢速旋转到快速旋转的过程。海洋表面温度和垂直风切变将发生变化，以揭示各种过渡类型及其发生的环境。许多转变预计将通过收缩或相对切变的倾斜向量重新定向，这是热带气旋错位的特征。因此，为了更好地了解是什么控制了向快速自旋转变的时机，该项目的相当大一部分将涉及分析非绝热过程如何调节模拟热带气旋倾斜的衰减率和进动率。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This research project is part of a broader effort to advance current understanding of how underdeveloped tropical cyclones intensify into potentially devastating hurricanes. Computer modeling studies will be conducted to address deficiencies in our knowledge of the nature and effectiveness of the intensification process that operates when there exists markedly asymmetric convection linked to substantial misalignment of the mid-level and low-level cyclonic circulations (tilt). Changes to the asymmetric state that are required for a fast intensification mechanism to supersede a slow mechanism, and the time scale for such changes to occur under a variety of environmental conditions will be elucidated. Knowledge gained from this project will assist complementary efforts to improve the accuracy of operational intensification forecasts that determine the preparations needed to adequately mitigate damage to coastal or island communities that lie in the predicted path of a tropical cyclone. In addition to offering new insights relevant to forecasting, this project will support student internships that will contribute to the development of the next generation of atmospheric scientists.The research strategy will entail a combination of reduced and full-physics modeling studies. The reduced modeling studies will add parameterized diabatic forcing to the dry primitive equations primarily to represent the heating associated with convection concentrated downtilt of the lower tropospheric vortex center. A variety of intensification mechanisms are expected to exist over the expansive multidimensional parameter space of the diabatic forcing, the state of the vortex, and the environmental vertical wind shear. The spectrum of possibilities ranges from very slow asymmetric modes of spinup to a fast mode associated with core reformation. The domain of applicability for each distinct intensification mechanism will be determined through extensive numerical experiments. Theoretical formulas will be sought for the hypersurfaces that separate regions of parameter space in which different intensification mechanisms operate. The full-physics simulations will be used to elucidate the moist thermo-fluid dynamics governing the convection that drives each intensification mechanism, and to elucidate the processes that lead a tropical cyclone to transition from slow to fast spinup. The sea surface temperature and vertical wind shear will be varied to uncover an assortment of transition-types and the environments in which they occur. Many of the transitions are expected to transpire through contraction or shear-relative reorientation of the tilt vector that characterizes the misalignment of the tropical cyclone. Thus, to better understand what controls the timing of a transition to fast spinup, a sizeable part of this project will involve analyzing how diabatic processes regulate the decay and precession rates of the tilts of the simulated tropical cyclones.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.