In 2021,Cempaka,a tiny tropical cyclone,made landfall in China.As the TC intensified prior to landfall,the tropical cyclone size measured with precipitation decreased significantly.A numerical simulation was conducted...In 2021,Cempaka,a tiny tropical cyclone,made landfall in China.As the TC intensified prior to landfall,the tropical cyclone size measured with precipitation decreased significantly.A numerical simulation was conducted to examine the possible processes modulating the storm size.Azimuthally mean potential vorticity(PV)was found to decrease mainly in the middle to upper troposphere between 50-and 80-km radii.The PV budget results indicate that the advection and generation of mean PV associated with asymmetric processes,rather than the symmetric processes,primarily contributed to the decrease in mean PV.These asymmetric processes leading to a negative PV tendency were likely associated with inactive outer rainbands.In contrast,the tangential winds simultaneously expanded radially outward,possibly related to inner-core diabatic heating.The findings here emphasize the importance of outer rainband activity in tropical cyclone size change.展开更多
Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertic...Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertical wind shear(VWS),or both.Results show that rainwater is enhanced to the right of the motion in the outer rainband,but such enhancement occurs in the upshear-left area of the inner-core region.Additionally,due to the asymmetries introduced by environmental flow,wavenumber-1 temperature and height anomalies develop at a radius of~1000 km in the upper levels.A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears,and asymmetric horizontal winds emerge,which,in turn,changes the storm-scale(within 400 km)VWS.Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s^(-1) and is located downshear of the storm-scale VWS in all the experiments with environmental flow.In the outer rainbands,the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant.These results extend upon the findings of previous studies in three aspects:(1)The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS;(2)The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow,resulting in changes in the storm-scale VWS pattern within the TC area;(3)The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS.展开更多
The influence of outer-core surface entropy fluxes （SEFs） on tropical cyclone （TC） outer rainband activity is investigated in this study with a fully compressible,nonhydrostatic model.A control simulation and two ...The influence of outer-core surface entropy fluxes （SEFs） on tropical cyclone （TC） outer rainband activity is investigated in this study with a fully compressible,nonhydrostatic model.A control simulation and two sensitivity experiments with the outer-core SEF artificially increased and decreased by 20% respectively were conducted to examine the quasi-periodic outer rainband behavior.Larger negative horizontal advection due to the greater radial wind and the positive contribution by asymmetric eddies leads to a longer period of outer-rainband activity in the SEF-enhanced experiment.The well-developed outer rainbands in the control and SEF-reduced simulations significantly limit the TC intensity,whereas such an intensity suppression influence is not pronounced in the SEF-enhanced experiment.As diabatic heating in outer rainbands strengthens the outer-core tangential wind,the quasi-periodic activity of outer rainbands contributes to the quasi-periodic variations of the inner-core size of the TCs.展开更多
The characteristics and dynamics associated with the distribution, intensity, and triggering factors of local severe precipitation in Zhejiang Province induced by Super Typhoon Soudelor(2015) were investigated using m...The characteristics and dynamics associated with the distribution, intensity, and triggering factors of local severe precipitation in Zhejiang Province induced by Super Typhoon Soudelor(2015) were investigated using mesoscale surface observations, radar reflectivity, satellite nephograms, and the final(FNL) analyses of the Global Forecasting System(GFS) of the National Center for Environmental Prediction(NCEP). The rainfall processes during Soudelor's landfall and translation over East China could be separated into four stages based on rainfall characteristics such as distribution, intensity, and corresponding dynamics. The relatively less precipitation in the first stage resulted from interaction between the easterly wind to the north flank of this tropical cyclone(TC) and the coastal topography along the southeast of Zhejiang Province, China. With landfall of the TC in East China during the second stage, precipitation maxima occurred because of interaction between the TC's principal rainbands and the local topography from northeastern Fujian Province to southwestern Zhejiang Province. The distribution of precipitation presented significant asymmetric features in the third stage with maximal rainfall bands in the northeast quadrant of the TC when Soudelor's track turned from westward to northward as the TC decayed rapidly. Finally, during the northward to northeastward translation of the TC in the fourth stage, the interaction between a mid-latitude weather system and the northern part of the TC resulted in transfer of the maximum rainfall from the north of Zhejiang Province to the north of Jiangsu Province,which represented the end of rainfall in Zhejiang Province. Further quantitative calculations of the rainfall rate induced by the interaction between local topography and TC circulation(defined as "orographic effects") in the context of a one-dimensional simplified model showed that orographic effects were the primary factor determining the intensity of precipitation in this case,and accounted for over 50% of the total precipitation. The asymmetric distribution of the TC's rainbands was closely related to the asymmetric distribution of moisture resulted from changes of the TC's structure, and led to asymmetric distribution of local intense precipitation induced by Soudelor. Based on analysis of this TC, it could be concluded that local severe rainfall in the coastal regions of East China is closely related to changes of TC structure and intensity, as well as the outer rainbands. In addition, precipitation intensity and duration will increase correspondingly because of the complex interactions between the TC and local topography, and the particular TC track along large-scale steering flow. The results of this study may be useful for the understanding, prediction, and warning of disasters induced by local extreme rainfall caused by TCs, especially for facilitating forecasting and warning of flooding and mudslides associated with torrential rain caused by interactions between landfalling TCs and coastal topography.展开更多
基金jointly supported by the National Natural Science Foundation of China[grant numbers U2342202 and 42175005]the Qing Lan Project[grant number R2023Q06]。
文摘In 2021,Cempaka,a tiny tropical cyclone,made landfall in China.As the TC intensified prior to landfall,the tropical cyclone size measured with precipitation decreased significantly.A numerical simulation was conducted to examine the possible processes modulating the storm size.Azimuthally mean potential vorticity(PV)was found to decrease mainly in the middle to upper troposphere between 50-and 80-km radii.The PV budget results indicate that the advection and generation of mean PV associated with asymmetric processes,rather than the symmetric processes,primarily contributed to the decrease in mean PV.These asymmetric processes leading to a negative PV tendency were likely associated with inactive outer rainbands.In contrast,the tangential winds simultaneously expanded radially outward,possibly related to inner-core diabatic heating.The findings here emphasize the importance of outer rainband activity in tropical cyclone size change.
基金supported by the National Natural Science Foundation of China(Grant number 42075072)support from The Startup Foundation for Introducing Talent of the Nanjing University of Information Science and Technology.
文摘Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertical wind shear(VWS),or both.Results show that rainwater is enhanced to the right of the motion in the outer rainband,but such enhancement occurs in the upshear-left area of the inner-core region.Additionally,due to the asymmetries introduced by environmental flow,wavenumber-1 temperature and height anomalies develop at a radius of~1000 km in the upper levels.A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears,and asymmetric horizontal winds emerge,which,in turn,changes the storm-scale(within 400 km)VWS.Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s^(-1) and is located downshear of the storm-scale VWS in all the experiments with environmental flow.In the outer rainbands,the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant.These results extend upon the findings of previous studies in three aspects:(1)The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS;(2)The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow,resulting in changes in the storm-scale VWS pattern within the TC area;(3)The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2009CB421505)National NaturalScience Foundation of China(40775060,41005033,40975035,and 40921160381)China Meteorological Administration SpecialPublic Welfare Research Fund(GYHY201006008 and GYHY200906002)
文摘The influence of outer-core surface entropy fluxes （SEFs） on tropical cyclone （TC） outer rainband activity is investigated in this study with a fully compressible,nonhydrostatic model.A control simulation and two sensitivity experiments with the outer-core SEF artificially increased and decreased by 20% respectively were conducted to examine the quasi-periodic outer rainband behavior.Larger negative horizontal advection due to the greater radial wind and the positive contribution by asymmetric eddies leads to a longer period of outer-rainband activity in the SEF-enhanced experiment.The well-developed outer rainbands in the control and SEF-reduced simulations significantly limit the TC intensity,whereas such an intensity suppression influence is not pronounced in the SEF-enhanced experiment.As diabatic heating in outer rainbands strengthens the outer-core tangential wind,the quasi-periodic activity of outer rainbands contributes to the quasi-periodic variations of the inner-core size of the TCs.
基金supported by the Huadong Regional Meteorological Science and Technology Innovation Fund Collaborative Project (Grant No. QYHZ201404)the Development of Social Welfare Project of Zhejiang Province (Grant No. 2013C33037)+2 种基金the Science Foundation of Zhejiang Province (Grant No. LY18D050001)United States Office of Naval Research Project (Grant No. N000140910526)the Development of Social Welfare Key Project of Zhejiang Province (Grant No. 2017C03035)
文摘The characteristics and dynamics associated with the distribution, intensity, and triggering factors of local severe precipitation in Zhejiang Province induced by Super Typhoon Soudelor(2015) were investigated using mesoscale surface observations, radar reflectivity, satellite nephograms, and the final(FNL) analyses of the Global Forecasting System(GFS) of the National Center for Environmental Prediction(NCEP). The rainfall processes during Soudelor's landfall and translation over East China could be separated into four stages based on rainfall characteristics such as distribution, intensity, and corresponding dynamics. The relatively less precipitation in the first stage resulted from interaction between the easterly wind to the north flank of this tropical cyclone(TC) and the coastal topography along the southeast of Zhejiang Province, China. With landfall of the TC in East China during the second stage, precipitation maxima occurred because of interaction between the TC's principal rainbands and the local topography from northeastern Fujian Province to southwestern Zhejiang Province. The distribution of precipitation presented significant asymmetric features in the third stage with maximal rainfall bands in the northeast quadrant of the TC when Soudelor's track turned from westward to northward as the TC decayed rapidly. Finally, during the northward to northeastward translation of the TC in the fourth stage, the interaction between a mid-latitude weather system and the northern part of the TC resulted in transfer of the maximum rainfall from the north of Zhejiang Province to the north of Jiangsu Province,which represented the end of rainfall in Zhejiang Province. Further quantitative calculations of the rainfall rate induced by the interaction between local topography and TC circulation(defined as "orographic effects") in the context of a one-dimensional simplified model showed that orographic effects were the primary factor determining the intensity of precipitation in this case,and accounted for over 50% of the total precipitation. The asymmetric distribution of the TC's rainbands was closely related to the asymmetric distribution of moisture resulted from changes of the TC's structure, and led to asymmetric distribution of local intense precipitation induced by Soudelor. Based on analysis of this TC, it could be concluded that local severe rainfall in the coastal regions of East China is closely related to changes of TC structure and intensity, as well as the outer rainbands. In addition, precipitation intensity and duration will increase correspondingly because of the complex interactions between the TC and local topography, and the particular TC track along large-scale steering flow. The results of this study may be useful for the understanding, prediction, and warning of disasters induced by local extreme rainfall caused by TCs, especially for facilitating forecasting and warning of flooding and mudslides associated with torrential rain caused by interactions between landfalling TCs and coastal topography.
