Studies on hurricanes: Intensity change and early genesis

飓风是大气中的剧烈漩涡。对于飓风预测，仍然存在两个主要问题。一是预测风暴的快速加强（RI），二是预测风暴何时形成。 眼壁中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主要的能量来源。它的空间分布影响 RI，特别是当对流爆发发生在最大风半径范围内时。其次，眼壁中的潜热加热会产生一个中空的位涡 (PV) 塔，该塔支持传播的涡旋罗斯贝波 (VRW)，该涡旋罗斯贝波 (VRW) 可能会变得不稳定，从而将眼壁 PV 混合到眼睛中，从而影响强度变化。此外，飓风涡旋中的 VRW 会辐射重力波，导致另一种不稳定性，称为辐射泵浦。然而，这种不稳定性可以在涡核外部的临界半径处减弱，其中波的角速度与流体旋转速率相匹配。了解这些不稳定性对于改进飓风预报非常重要。 大西洋飓风通常是由非洲以外的东风波扰动引发的，但只有一小部分发展成为热带风暴。最近的一项理论规定，热带气旋发生在类似于母波临界层内的猫眼再循环区域的袋中是有利的。然而，目前还没有关于造口袋如何形成的全面研究。 拟议研究计划的目标是通过理论分析、高分辨率建模和诊断研究，增进我们对飓风强度变化和早期热带气旋形成的理解。需要回答的相关科学问题是： a) 微物理过程如何调节可能对飓风强度产生强烈影响的潜热和水负荷的分布？ b) 不稳定性和临界半径如何影响飓风强度变化？ c) 在飓风的早期发生阶段，造口袋是如何形成的？ 将利用理论分析、高分辨率计算机建模和诊断研究来回答上述问题。 该研究计划将增进我们对飓风强度变化及其成因机制的理解。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.