Chapter 10 - Clouds and Precipitation in Tropical Cyclones

Abstract

Abstract Tropical cyclones draw energy from warm ocean surfaces and use this energy to strengthen a cyclonic disturbance into an intense vortex, which is called a hurricane, typhoon, or cyclone, depending on where in the world it occurs. The tropical cyclone initiates from a collection of cumulonimbus clouds before the intense vortex dominates the dynamics. However, the convective clouds in the genesis stage exhibit differences from ordinary cumulonimbus, including very intense “convective bursts” and rotating convective cells called “vortical hot towers.” This chapter describes the special characteristics of the cumulonimbus observed in the tropical cyclogenesis stage. Then, the chapter details the various clouds of a fully formed tropical cyclone. Once the tropical cyclone takes shape, it is characterized by a strong vortex that achieves force balance via a vertically overturning secondary circulation, which produces an eyewall cloud that is unique to tropical cyclones. This chapter details the observed structure and dynamics of the eyewall cloud. The rising branch of the secondary circulation producing the eyewall cloud connects the energy of the warm ocean boundary layer to the intense storm vortex. Observations show that the eyewall cloud is dominated by the secondary circulation of the vortex but may contain intense embedded subvortices and intermittent occurrences of deep cumulonimbus. In intense tropical cyclones, a secondary eyewall cloud forms as the storm undergoes an eyewall replacement cycle. Outside the eyewall are rainband clouds, which have a spiral configuration distinct from the circular eyewall shape. The rainband clouds lie outside the eyewall and have a more cumulonimbus-like behavior than the eyewall.