A Numerical Study of Convective-Scale Structures in the Outer Cores of Sheared Tropical Cyclones: 1. Updraft Traits in Different Vertical Wind Shear Magnitudes

摘要

abstract_textpThis study investigates the outer-core convective-scale updraft features of numerically simulated tropical cyclones under vertical wind shear of different magnitudes. Updrafts in the outer core were weighted in favor of downshear formation, and the increase in the shear value led to more short-lived updrafts. The tops of detected updrafts tended to cluster at either 4- to 6-km or 12- to 14-km height. Downshear-left updrafts mostly moved radially inward, and updrafts on the left side of the shear vector moved more rapidly azimuthally. Longer-lived updrafts gained greater vertical mass fluxes during their life cycles, with those in strongly sheared tropical cyclones having larger vertical mass fluxes for the same updraft life span. The height of stronger vertical velocity in convective bursts decreased as shear increased, whereas larger vertical velocity within nonconvective-burst cells held between 3 and 4 km. The values of several environmental parameters (such as the supercell composite parameter and the energy-helicity index) associated with updrafts in the downshear-left quadrant were larger than those in the downshear-right quadrant for the weakly sheared tropical cyclone, whereas they became much larger in the downshear-right quadrant for highly sheared vortices. There were no relationships between the parameters and updraft mean mass fluxes, so the use of these parameters for predicting the likelihood of updraft strength in tropical cyclones requires caution./ppPlain Language Summary As a tropical cyclone approaches the coasts, high-impact weathers, such as thunderstorms and tornadoes, are usually observed far away from the tropical cyclone center. These weathers are closely related to the activity of isolated convective cells in the outer rainbands. This study investigates the statistical characteristics of updrafts embedded in the convective cells to give insights into the behavior of the updrafts under environmental vertical wind shears. We find that the larger the shear, the shorter-lived updrafts become. The updrafts tend to crest at either 4- to 6-km or 12- to 14-km height. The height of larger vertical velocity in more intense convection decreases as shear increases. Several environmental parameters have been indicated to successfully predict midlatitude supercell development, which are also examined here. These environmental parameters associated with updrafts are much larger in the downshear-right quadrant under larger environmental shears. It is found that there are no relationships between the parameters and updraft strength, so these parameters are applied to predicting updraft strength in tropical cyclones with caution./p/abstract_text