Studies on hurricanes: Intensity change and early genesis

飓风是大气中的猛烈漩涡。对于飓风预测，仍然存在两个主要问题。一种是预报风暴的快速加强(RI)，另一种是预报风暴何时形成。*眼壁的对流可以通过两种方式影响RI。首先，云过程中释放的潜热是能量的主要来源。当对流爆发发生在最大风径范围内时，其空间分布对RI的影响尤为明显。其次，眼壁的潜热产生了一个中空的位涡(PV)塔，支持传播的涡旋Rossby波(VRW)，它可能会变得不稳定，将眼壁PV混合到眼睛中，从而影响强度变化。此外，飓风涡旋中的VRW可以辐射重力波，导致另一种称为辐射泵浦的不稳定。然而，这种不稳定性可以在涡核外的一个临界半径处被衰减，在那里波的角速度与流体的旋转速度相匹配。对这些不稳定因素的了解对于改进飓风预报非常重要。*大西洋飓风通常是由来自非洲的东风波扰动引发的，但只有一小部分会发展成热带风暴。最近的一种理论认为，热带气旋发生在与猫眼在母波临界层内的再循环区相似的气囊中。然而，关于眼袋是如何形成的，还没有全面的研究。*拟议的研究计划的目标是通过理论分析、高分辨率模拟和诊断研究来促进我们对飓风强度变化和早期热带气旋生成的理解。要回答的相关科学问题是：*a)微物理过程如何调节潜热和水负荷的分布，这可能对飓风强度有很大影响？*b)不稳定性和临界半径如何影响飓风强度变化？*c)在飓风形成的早期阶段如何形成气囊？*将通过理论分析、高分辨率计算机模拟和诊断研究来给出上述问题的答案。*该研究计划将提高我们对飓风强度变化和成因机制的理解。它将有助于预测这些暴力系统。*****

Hurricanes are violent vortices in the atmosphere. For hurricane prediction, two major problems remain. One is to forecast the rapid intensification (RI) of the storm and the other is to forecast when a storm will form.***Convection in the eyewall can affect RI in two ways. First, latent heating released in cloud processes is a main source of energy. Its spatial distribution affects RI especially when bursts of convection occur inside the radius of maximum wind. Second, latent heating in the eyewall produces a hollow tower of potential vorticity (PV) that supports propagating vortex Rossby waves (VRW) which may become unstable to mix eyewall PV into the eye to effect intensity change. Additionally, VRWs in a hurricane vortex can radiate gravity waves leading to another instability known as radiative pumping. However, this instability can be damped at a critical radius outside the vortex core where the angular velocity of the waves matches the fluid rotation rate. The understanding of these instabilities is important to improve hurricane forecasting. ***Atlantic hurricanes are often initiated from easterly wave disturbances out of Africa, but only a small fraction ever develop into a tropical storm. A recent theory stipulates that tropical cyclogenesis is favored in a pouch which is similar to the cat's eye recirculation region within the critical layer of the parent wave. However, there are no comprehensive studies on how a pouch forms. ***The objective of the proposed research program is to advance our understanding of hurricane intensity change and early tropical cyclogenesis through theoretical analysis, high resolution modeling, and diagnostic studies. The relevant scientific questions to answer are:***a) How microphysical processes regulate the distributions of latent heating and water loading which may bear strongly on hurricane intensity? ***b) How do instabilities and the critical radius affect hurricane intensity change?***c) How does a pouch form during the early genesis stage of a hurricane?***Theoretical analysis, high resolution computer modeling, and diagnostic studies will be brought to bear to yield answers to the above questions. ***The research program will improve our understanding of hurricane intensity change and the mechanism for genesis. It will help in the forecasting of these violent systems. *****