Modeling Studies of Transitions from Slow to Fast Tropical Cyclone Intensification

这个研究项目是一项更广泛的努力的一部分，目的是促进目前对不发达的热带气旋如何增强为潜在的破坏性飓风的理解。将进行计算机模拟研究，以解决我们对强化过程的性质和有效性的认识不足，当存在与中层和低层气旋环流严重失调（倾斜）有关的明显不对称对流时，强化过程就会发生。快速强化机制取代缓慢强化机制所需的非对称状态变化，以及在各种环境条件下发生这种变化的时间尺度将得到阐明。从该项目中获得的知识将有助于提高业务强化预报的准确性，以确定为充分减轻热带气旋预测路径内沿海或岛屿社区的损害所需要的准备工作。除了提供与预测相关的新见解外，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。研究策略将需要简化和全物理建模研究的结合。简化的模型研究将在干燥原始方程中加入参数化的绝热强迫，主要用于表示与对流层低层涡旋中心集中下降倾斜的对流相关的加热。在非绝热强迫、涡旋状态和环境垂直风切变的广阔多维参数空间中，存在多种强化机制。可能性的范围从非常缓慢的非对称自旋模式到与核心重组相关的快速模式。每种不同强化机制的适用范围将通过广泛的数值实验确定。将寻求理论公式的超曲面分离区域的参数空间，其中不同的强化机制运作。全物理模拟将用于阐明控制对流的湿热流体动力学，这种对流驱动每一种增强机制，并阐明导致热带气旋从缓慢旋转到快速旋转的过程。海面温度和垂直风切变的变化将揭示各种过渡类型及其发生的环境。许多转变预计将通过以热带气旋不对准为特征的倾斜矢量的收缩或切变相对重新定向而发生。因此，为了更好地理解是什么控制了向快速旋转转变的时间，这个项目的很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和进动率。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。

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.