气象2025，Vol.51Issue(6)：645-659,15.DOI:10.7519/j.issn.1000-0526.2024.122602
热带气旋外雨带长生命史对流尺度上升运动的演变机制
Evolution Mechanism of a Long Lifespan Convective-Scale Updraft in Outer Rainband of Sheared Tropical Cyclone
摘要
Abstract
This study investigates the evolution mechanism of a long-life convective-scale updraft in outer rainband of numerically simulated sheared tropical cyclone(TC).The updraft originates from the down-shear right quadrant of outer rainband within a sheared TC with a lifespan of 2.5 h.This updraft under-goes two strengthening processes and displays complex evolutionary characteristics with two peaks in verti-cal mass transport.The results show that strong localized vertical wind shear and low-level high-value equivalent potential temperature are the main favorable ambient factors for an updraft long lifespan.The strengthening and weakening of neighboring convective cells lead to different responses to updraft intensity by adjusting the variation of local equivalent potential temperature.The vertical momentum budget sug-gests that an updraft grows when it is dominated by positive buoyancy pressure gradient acceleration and positive thermal buoyancy,but there exist differences between the two strengthening mechanisms.In the first strengthening stage,the development of neighboring convective cells causes the rise in the equivalent potential temperature at lower levels.Moreover,the increase in updraft tilt and the latent heating lead to a significant increase in thermal buoyancy,resulting in a larger vertical velocity.In the early second strengthening stage,the occurrence and development of new convective cells in the vicinity of the focused updraft induce the rise in localized equivalent potential temperature.Subsequently,however,the mature and dissipation of these neighboring convective cells lead to the strengthened downward motion and the de-creased localized equivalent potential temperature,which makes smaller thermal buoyancy and smaller ver-tical velocity.Analogous to the weakening mechanism of convective cells in mid-latitudes,during the weakening phase,the focused updraft exhibits a decrease in tilt,and then forces a downdraft directly be-neath it.This downdraft and downdrafts of neighboring convective cells carry low-value equivalent poten-tial temperature toward the lower layers,forming a surface cold pool.Consequently,thermal buoyancy tends to decrease suppressing the growth of the focused updraft.In addition,the negative contribution of water loading is harmful to the development of the focused updraft.The imbalance among thermal buoyan-cy,buoyancy pressure gradient acceleration,and water loading constitutes the primary physical mechanism responsible for the prolonged evolution of updraft.At the same time,a tilted updraft structure can also in-fluence the development of updraft.关键词
热带气旋/外雨带/上升运动/长生命史/演变机制Key words
tropical cyclone/outer rainband/updraft/long lifespan/evolution mechanism分类
大气科学引用本文复制引用
方俏娴,李青青,伍红雨,程晶晶,梁秀姬..热带气旋外雨带长生命史对流尺度上升运动的演变机制[J].气象,2025,51(6):645-659,15.基金项目
国家自然科学基金项目(U2342202、42175005)、广东省气象局科技项目(GRMC2023Q41)和广东省气候中心科研项目(QH202403)共同资助 （U2342202、42175005）
