Even though Malaysia is relatively safe from the direct path of tropical cyclones nevertheless the passage of such systems over the neighbouring seas and their tail effect present a unique challenge for forecasters. I...Even though Malaysia is relatively safe from the direct path of tropical cyclones nevertheless the passage of such systems over the neighbouring seas and their tail effect present a unique challenge for forecasters. In rare situations, tropical cyclones had made landfall on Malaysian shores such as Typhoon Vamei in 2001 and Tropical Storm Greg in 1996. Hence it is vital to forecast the severity of the heavy rainfall events associated with low pressure systems to assist the disaster management agencies in decision making. Towards this endeavour, the Malaysian Meteorological Department(MMD) utilises a nowcasting system called Radar Integrated Nowcasting System(RaINS) which uses a combination of radar data and Numerical Weather Prediction(NWP) data. RaINS was adapted from SWIRLS(Short-range Warning of Intense Rainstorms in Localised Systems) developed by the Hong Kong Observatory(HKO) and operationalised in MMD in August 2017. This paper studies the cyclonic vortex and synoptic features during the heavy rainfall event that caused major flooding in Penang, Malaysia on 5 November 2017. This paper also investigates the performance of RaINS in predicting the rain cloud distribution and intensity during that event. It is found that RaINS is capable of forecasting the rain cloud distribution and intensity reasonably well in the very short-term period of 1-3 hours. The forecasts are verified by comparing the RaINS forecast data with observed radar echo.展开更多
Since the 2000 s,extratropical extremes have been more frequent,which are closely related to anomalies of planetary-scale and synoptic-scale systems.This study focuses on a key synoptic system,the extratropical cyclon...Since the 2000 s,extratropical extremes have been more frequent,which are closely related to anomalies of planetary-scale and synoptic-scale systems.This study focuses on a key synoptic system,the extratropical cyclonic vortex(ECV)over land,to investigate its relations with extreme precipitation.It was found that ECVs have been more active post-2000,which has induced more extreme precipitation,and such variation is projected to persist along with increasing temperature within 1.5℃of global warming.An enhanced quasi-stationary vortex(QSV)primarily contributes to the ECV,rather than inactive synoptic-scale transient eddies(STEs).Inactive STEs respond to a decline in baroclinicity due to the tendency of the homogeneous temperature gradient.However,such conditions are helpful to widening the westerly jet belt,favoring strong dynamic processes of quasi-resonant amplification and interaction of STEs with the quasi-stationary wave,and the result favors an increasing frequency and persistence of QSVs,contributing to extreme precipitation.展开更多
The dynamics of eastward shifting cyclonic vortices are investigated in terms of a barotropic primitive equation model, and six experiments are performed. Both the interaction of a cyclonic vortex with vorticity lumps...The dynamics of eastward shifting cyclonic vortices are investigated in terms of a barotropic primitive equation model, and six experiments are performed. Both the interaction of a cyclonic vortex with vorticity lumps and the interaction of the vortex with the shearing basic flow may induce the strengthening of the vortex in a short period, however, the vortex intensity still shows a general decreasing tendency over the whole integration time period. The interaction among the shearing basic flow, cyclonic vortex, and multiple vorticity lumps can change the tendency. The merging of the cyclonic vortex with vorticity lumps in the shearing basic flow of positive vorticity is directly responsible for the maintenance and development of the cyclonic vortex.展开更多
In order to suppressing the particle deposition on vortex finder,a series of gas cyclones with the secondary swirling clean gas were developed inspired by the gas purge effect.Effects of the width and extension length...In order to suppressing the particle deposition on vortex finder,a series of gas cyclones with the secondary swirling clean gas were developed inspired by the gas purge effect.Effects of the width and extension length of the flow channel as well as the secondary inlet velocity and running time on the particle deposition pattern,the deposited particle mass and the cyclones'performance were experimentally investigated,respectively.The results show that the ultrafine particles(Stokes number Stk<0.0358)are mainly loose deposited on the walls under the secondary gas.Compare to the conventional cyclone with single tangential inlet,the total deposited particle mass of the improved cyclone has a maximum reduction more than 60%,and the collecting efficiency is increased up to 97.5%under the basically same pressure drop.The corresponding no-deposition area is increased by about 13%,and remains constant in spite of extending the running time.Moreover,an interesting phenomenon named"self-cleaning effect"of the vortex finder was captured for the gas cyclones,and mechanism of the secondary clean gas on the particle deposition is preliminarily analyzed.The results can deepen the understanding of the particle deposition on the vortex finder and guide the design of the anti-coking gas cyclones.展开更多
Diabatic heating by convection in the eyewall often produces an annular region of high potential vorticity(PV)around the relatively low PV eye in a strong tropical cyclone(TC).Such a PV ring is barotropically unstable...Diabatic heating by convection in the eyewall often produces an annular region of high potential vorticity(PV)around the relatively low PV eye in a strong tropical cyclone(TC).Such a PV ring is barotropically unstable and can encourage the exponential growth of PV waves.In this study,such instability and the subsequent nonlinear evolution of three TC-like vortices having PV rings with different degrees of hollowness on an f-plane are first examined using an unforced,inviscid shallow-water-equation model.Results show that the simulated eyewalls evolve similarly to those in the nondivergent barotropic model.It is also found that the polygonal eyewall structure can be decomposed into vortex Rossby waves(VRWs)of different wavenumbers with different amplitudes,allowing for wave-wave interactions to produce complicated behaviors of mesovortices in the TC eyewall.The same set of PV rings has been examined on a beta-plane.Although the beta effect has been rendered unimportant to the eyewall evolution due to the relatively small scale of the inner-core circulation,this study shows that the beta effect may erode the coherent structure of mesovortices in the eyewall of an initially hollow PV-ring vortex.Mesovortices modeled on the beta-plane with a greater beta parameter tend to experience an earlier breakdown and enhanced radial gradients of the basic-state(azimuthally mean)angular velocity,followed by wave-wave,wave-flow interactions,leading to earlier merger and axisymmetrization processes.This result implies that the beta effect could be one of the forcings that shorten the lifetime of quasi-steady mesovortices in the eyewall of real TCs.展开更多
文摘Even though Malaysia is relatively safe from the direct path of tropical cyclones nevertheless the passage of such systems over the neighbouring seas and their tail effect present a unique challenge for forecasters. In rare situations, tropical cyclones had made landfall on Malaysian shores such as Typhoon Vamei in 2001 and Tropical Storm Greg in 1996. Hence it is vital to forecast the severity of the heavy rainfall events associated with low pressure systems to assist the disaster management agencies in decision making. Towards this endeavour, the Malaysian Meteorological Department(MMD) utilises a nowcasting system called Radar Integrated Nowcasting System(RaINS) which uses a combination of radar data and Numerical Weather Prediction(NWP) data. RaINS was adapted from SWIRLS(Short-range Warning of Intense Rainstorms in Localised Systems) developed by the Hong Kong Observatory(HKO) and operationalised in MMD in August 2017. This paper studies the cyclonic vortex and synoptic features during the heavy rainfall event that caused major flooding in Penang, Malaysia on 5 November 2017. This paper also investigates the performance of RaINS in predicting the rain cloud distribution and intensity during that event. It is found that RaINS is capable of forecasting the rain cloud distribution and intensity reasonably well in the very short-term period of 1-3 hours. The forecasts are verified by comparing the RaINS forecast data with observed radar echo.
基金supported by the National Natural Science Foundation of China(Grant No.41975083)。
文摘Since the 2000 s,extratropical extremes have been more frequent,which are closely related to anomalies of planetary-scale and synoptic-scale systems.This study focuses on a key synoptic system,the extratropical cyclonic vortex(ECV)over land,to investigate its relations with extreme precipitation.It was found that ECVs have been more active post-2000,which has induced more extreme precipitation,and such variation is projected to persist along with increasing temperature within 1.5℃of global warming.An enhanced quasi-stationary vortex(QSV)primarily contributes to the ECV,rather than inactive synoptic-scale transient eddies(STEs).Inactive STEs respond to a decline in baroclinicity due to the tendency of the homogeneous temperature gradient.However,such conditions are helpful to widening the westerly jet belt,favoring strong dynamic processes of quasi-resonant amplification and interaction of STEs with the quasi-stationary wave,and the result favors an increasing frequency and persistence of QSVs,contributing to extreme precipitation.
基金the National Natural Science Foundation under Grant No.49775263the project of the Tibetan Plateau Experiment(TIPEX)of Atmospheric Science and the 973 Project onheavy rain in China.
文摘The dynamics of eastward shifting cyclonic vortices are investigated in terms of a barotropic primitive equation model, and six experiments are performed. Both the interaction of a cyclonic vortex with vorticity lumps and the interaction of the vortex with the shearing basic flow may induce the strengthening of the vortex in a short period, however, the vortex intensity still shows a general decreasing tendency over the whole integration time period. The interaction among the shearing basic flow, cyclonic vortex, and multiple vorticity lumps can change the tendency. The merging of the cyclonic vortex with vorticity lumps in the shearing basic flow of positive vorticity is directly responsible for the maintenance and development of the cyclonic vortex.
基金the National Natural Science Foundation of China(grant No.51904088)Scientific Research Project of Colleges and Universities in Hebei Province(grant No.BJ2020042).
文摘In order to suppressing the particle deposition on vortex finder,a series of gas cyclones with the secondary swirling clean gas were developed inspired by the gas purge effect.Effects of the width and extension length of the flow channel as well as the secondary inlet velocity and running time on the particle deposition pattern,the deposited particle mass and the cyclones'performance were experimentally investigated,respectively.The results show that the ultrafine particles(Stokes number Stk<0.0358)are mainly loose deposited on the walls under the secondary gas.Compare to the conventional cyclone with single tangential inlet,the total deposited particle mass of the improved cyclone has a maximum reduction more than 60%,and the collecting efficiency is increased up to 97.5%under the basically same pressure drop.The corresponding no-deposition area is increased by about 13%,and remains constant in spite of extending the running time.Moreover,an interesting phenomenon named"self-cleaning effect"of the vortex finder was captured for the gas cyclones,and mechanism of the secondary clean gas on the particle deposition is preliminarily analyzed.The results can deepen the understanding of the particle deposition on the vortex finder and guide the design of the anti-coking gas cyclones.
基金supported in part by the National Natural Science Foundation of China under Grant No.41730960in part by NSF grant AGS-1834300。
文摘Diabatic heating by convection in the eyewall often produces an annular region of high potential vorticity(PV)around the relatively low PV eye in a strong tropical cyclone(TC).Such a PV ring is barotropically unstable and can encourage the exponential growth of PV waves.In this study,such instability and the subsequent nonlinear evolution of three TC-like vortices having PV rings with different degrees of hollowness on an f-plane are first examined using an unforced,inviscid shallow-water-equation model.Results show that the simulated eyewalls evolve similarly to those in the nondivergent barotropic model.It is also found that the polygonal eyewall structure can be decomposed into vortex Rossby waves(VRWs)of different wavenumbers with different amplitudes,allowing for wave-wave interactions to produce complicated behaviors of mesovortices in the TC eyewall.The same set of PV rings has been examined on a beta-plane.Although the beta effect has been rendered unimportant to the eyewall evolution due to the relatively small scale of the inner-core circulation,this study shows that the beta effect may erode the coherent structure of mesovortices in the eyewall of an initially hollow PV-ring vortex.Mesovortices modeled on the beta-plane with a greater beta parameter tend to experience an earlier breakdown and enhanced radial gradients of the basic-state(azimuthally mean)angular velocity,followed by wave-wave,wave-flow interactions,leading to earlier merger and axisymmetrization processes.This result implies that the beta effect could be one of the forcings that shorten the lifetime of quasi-steady mesovortices in the eyewall of real TCs.
