A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caus...A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is di?erent from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon—that nearly all of the convectively ascending region is located southward/southeastward of the vortex center—is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by wind shear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection.展开更多
Based on a 16-warm-season statistical study on the mesoscale convective systems(MCSs)that were generated over the Tibetan Plateau(TP),11 long-lived eastward propagating MCSs of the same type were selected for a compos...Based on a 16-warm-season statistical study on the mesoscale convective systems(MCSs)that were generated over the Tibetan Plateau(TP),11 long-lived eastward propagating MCSs of the same type were selected for a composite semiidealized simulation and a corresponding no-latent-heating sensitivity run by using the Weather Research and Forecasting(WRF)model.Common evolutionary features and associated mechanisms of this type of long-lived eastward propagating MCS were investigated.Main results are as follows:(i)This type of MCS was generated in a favorable background environment which was characterized by a notable upper-tropospheric divergence south of an upper-level jet,a strong warm advection around a middle-level shortwave trough’s central area,and an instable convective stratification below the trough.Development of the MCS featured rapid increase of cyclonic vorticity in the middle and lower troposphere.The convergence-related vertical stretching and tilting were key factors for the cyclonic-vorticity’s production,and convection-related upward cyclonic-vorticity transport contributed to the upward extending of the MCS.(ii)During the vacating stage of the MCS,it first coupled with a quasistationary Tibetan Plateau vortex(TPV)over the TP’s eastern section,and then decoupled from the vortex.In the former stage,the MCS contributed to maintaining ascending motions and convergence associated with the TPV,which favored its persistence;whereas,in the latter stage,decoupling weakened the TPV-associated convection significantly.This reduced the upward transport of cyclonic vorticity notably,which,together with the negative tilting effect,finally led to the vortex’s dissipation.(iii)After vacating TP,the MCS first weakened due to the disappearance of strong direct sensible heating from the TP on its bottom,and then,under the favorable conditions associated with the shortwave trough over the eastern section of the TP,the MCS redeveloped rapidly.Convergence-related cyclonic-vorticity production in the middle and lower troposphere and upward transport of cyclonic vorticity due to convection governed the MCS’s redevelopment.(iv)Sensitivity simulation shows that latent heating was a necessary condition for the formation and development of the long-lived eastward propagating MCS.On the one hand,this MCS affected the TP’s eastern section and downstream regions directly by inducing precipitation;and on the other hand,it exerted effects on the precipitation over a wider range in the downstream regions by modulating large-scale circulations over and around the TP.展开更多
The Advanced Research WRF(Weather Research and Forecasting) model is used to simulate the evolution of a mesoscale convective vortex(MCV) that formed on the Meiyu front and lasted for more than two days. The simul...The Advanced Research WRF(Weather Research and Forecasting) model is used to simulate the evolution of a mesoscale convective vortex(MCV) that formed on the Meiyu front and lasted for more than two days. The simulation is used to investigate the underlying reasons for the genesis, intensification, and vertical expansion of the MCV. This MCV is of a type of mid-level MCV that often develops in the stratiform regions of mesoscale convective systems. The vortex strengthened and reached its maximum intensity and vertical extent(from the surface to upper levels) when secondary organized convection developed within the mid-level circulation. The factors controling the evolution of the kinetic and thermal structure of the MCV are examined through an analysis of the budgets of vorticity, temperature, and energy. The evolution of the local Rossby radius of deformation reveals the interrelated nature of the MCV and its parent mesoscale convective system.展开更多
文摘A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is di?erent from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon—that nearly all of the convectively ascending region is located southward/southeastward of the vortex center—is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by wind shear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection.
基金This work was supported by the National Key R&D Program of China(Grant No.2018YFC1507606)the National Natural Science Foundation of China(Grant Nos.41775046,42075002,91637211,and 42030611)+1 种基金the Foundation of Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province(Grant No.SZKT202001)the Youth Innovation Promotion Association,Chinese Academy of Sciences.
文摘Based on a 16-warm-season statistical study on the mesoscale convective systems(MCSs)that were generated over the Tibetan Plateau(TP),11 long-lived eastward propagating MCSs of the same type were selected for a composite semiidealized simulation and a corresponding no-latent-heating sensitivity run by using the Weather Research and Forecasting(WRF)model.Common evolutionary features and associated mechanisms of this type of long-lived eastward propagating MCS were investigated.Main results are as follows:(i)This type of MCS was generated in a favorable background environment which was characterized by a notable upper-tropospheric divergence south of an upper-level jet,a strong warm advection around a middle-level shortwave trough’s central area,and an instable convective stratification below the trough.Development of the MCS featured rapid increase of cyclonic vorticity in the middle and lower troposphere.The convergence-related vertical stretching and tilting were key factors for the cyclonic-vorticity’s production,and convection-related upward cyclonic-vorticity transport contributed to the upward extending of the MCS.(ii)During the vacating stage of the MCS,it first coupled with a quasistationary Tibetan Plateau vortex(TPV)over the TP’s eastern section,and then decoupled from the vortex.In the former stage,the MCS contributed to maintaining ascending motions and convergence associated with the TPV,which favored its persistence;whereas,in the latter stage,decoupling weakened the TPV-associated convection significantly.This reduced the upward transport of cyclonic vorticity notably,which,together with the negative tilting effect,finally led to the vortex’s dissipation.(iii)After vacating TP,the MCS first weakened due to the disappearance of strong direct sensible heating from the TP on its bottom,and then,under the favorable conditions associated with the shortwave trough over the eastern section of the TP,the MCS redeveloped rapidly.Convergence-related cyclonic-vorticity production in the middle and lower troposphere and upward transport of cyclonic vorticity due to convection governed the MCS’s redevelopment.(iv)Sensitivity simulation shows that latent heating was a necessary condition for the formation and development of the long-lived eastward propagating MCS.On the one hand,this MCS affected the TP’s eastern section and downstream regions directly by inducing precipitation;and on the other hand,it exerted effects on the precipitation over a wider range in the downstream regions by modulating large-scale circulations over and around the TP.
基金Supported by the National Natural Science Foundation of China (40875028)National Key Basic Research and Development (973) Program of China (2013CB430103)
文摘The Advanced Research WRF(Weather Research and Forecasting) model is used to simulate the evolution of a mesoscale convective vortex(MCV) that formed on the Meiyu front and lasted for more than two days. The simulation is used to investigate the underlying reasons for the genesis, intensification, and vertical expansion of the MCV. This MCV is of a type of mid-level MCV that often develops in the stratiform regions of mesoscale convective systems. The vortex strengthened and reached its maximum intensity and vertical extent(from the surface to upper levels) when secondary organized convection developed within the mid-level circulation. The factors controling the evolution of the kinetic and thermal structure of the MCV are examined through an analysis of the budgets of vorticity, temperature, and energy. The evolution of the local Rossby radius of deformation reveals the interrelated nature of the MCV and its parent mesoscale convective system.