Studies on hurricanes: Intensity change and early genesis

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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. *****