Effect of the Initial Vortex Vertical Structure on Early Development of an Axisymmetric Tropical Cyclone

摘要

With the nonhydrostatic axisymmetric cloud-resolving model CM1,two sets of ensemble runs are conducted to study the influence of initial vortex depth on the early development of an idealized tropical cyclone (TC).It is found that with the shallow initial vortex,the intensification rate (IR) is smaller and the TC takes a longer time to reach a state of slantwise moist neutrality.These behaviors are primarily ascribed to the less active convection in the shallow case.In contrast to the deep initial vortex,the shallow initial vortex is characterized by a more stable stratification in the lower troposphere and a smaller gradient of angular momentum (M) in the mid-to-upper troposphere.The former tends to hinder the occurrence of deep convection in the TC while the latter makes it difficult to intensify the mid-toupper level vortex and to establish a deep vortex.Thus,deep convection bursts intermittently in the early developing stage of the TC originating from the shallow vortex.During the periods of inactive convection,the TC weakens by the decline of M source associated with reduced horizontal advection,which is overwhelmed by sinks of M from moderately decreased vertical advection and nearly-constant dissipation term.Therefore,the IR of the TC is smaller in the early developing stage and the development of TC from the shallow vortex usually needs a longer time to build the steady deep secondary circulation favorable for more rapid intensification.