Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State...Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State Mesoscale Model （MM5）. The finescale rainbands have two types： one intersecting the eyewall and causing damaging wind streaks, and the other distributed azimuthally along the inner edge of the eyewall with a relatively short lifetime. The formation of the high-velocity wind streaks results from the interaction of the azimuthal flow with the banded vertical vorticity structure triggered by tilting of the horizontal vorticity. The vertical advection of azimuthal momentum also leads to acceleration of tangential flow at a relatively high Mtitude. The evolution and structures of the bands are also examined in this study. Further investigation suggests that the boundary inflection points are related tightly to the development of the finescale rainbands, consistent with previous findings using simple symmetric models. In particular; the presence of the level of inflow reversal in the boundary layer is a crucial factor controlling the formation of these bands. The near-surface wavy peaks of vertical vorticity always follow the inflection points in radial flow. The mesoscale vortices and associated convective updrafts in the eyewall are considered to strengthen the activity of finescale bands, and the updrafts can trigger the formation of the bands as they reside in the environment with inflow reversal in the boundary layer.展开更多
Based on reconstructions of precipitation events from the rain and snowfall archives of the Qing Dynasty （1736-1911）, the drought/flood index data mainly derived from Chinese local gazettes from 1736-2000, and the o...Based on reconstructions of precipitation events from the rain and snowfall archives of the Qing Dynasty （1736-1911）, the drought/flood index data mainly derived from Chinese local gazettes from 1736-2000, and the observational data gathered since 1951, the spatial patterns of monsoon rainbands are analyzed at different time scales. Findings indicate that monsoon rainfall in northern China and the middle-lower reaches of the Yangtze River have significant inter-annual （e.g., 5-7-yr and 2-4-yr） as well as inter-decadal （e.g., 20-30-yr and quasi-10-yr） fluctuation signals. The spatial patterns in these areas also show significant cycles, such as on a 60-80-yr time scale, a reversal phase predominates the entire period from 1736-2000; on a quasi-30-yr time scale, a consistent phase was prevalent from 1736 to 2000; and on a 20-yr time scale, the summer monsoon rains show different spatial patterns before and after 1870.展开更多
This article investigates in detail the structure, genesis and development of parallel-type warm sector rainbands from radar observations. By comparing these observations with diagnostic results from temperature, pres...This article investigates in detail the structure, genesis and development of parallel-type warm sector rainbands from radar observations. By comparing these observations with diagnostic results from temperature, pressure, moisture and wind data, which are both actually observed and numerically generated by a mesoscale model, and the theory of symmetric instability, it is found that the conditional symmetric instability might be responsible for the formation and development of these rainbands.展开更多
In this paper, an idealized perturbation following the ＂surge-flow conceptual model＂ for typical Meiyu frontal structure is designed to explain the β meso-scale structure ofrainbands in the Meiyu front using a non-...In this paper, an idealized perturbation following the ＂surge-flow conceptual model＂ for typical Meiyu frontal structure is designed to explain the β meso-scale structure ofrainbands in the Meiyu front using a non-hydrostatic, full-compressible storm-scale model including multi-phase microphysical parameterization. In addition, sensitivity numerical experiment on the vertical distribution of the ambient meridional wind is conducted to investigate the generation mechanism of D meso-scale double rainbands. The results of numerical experiments show that the cool and dry downdraft invading strengthened by the environmental aloft northerly wind plays a very important role to the generation and maintenance of the β meso-scale double rainbands. Moreover, the intensity and scale of the dry and cool downdraft invading are related to the intensity of the second circumfluence induced by mass adjustment when the acceleration of the westerly jet aloft occurs.展开更多
The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the ...The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.展开更多
As a typhoon approaches the continent,the position where anthropogenic aerosols penetrate,the convection competition between the eyewall and peripheral rainbands,and the separate contributions of direct aerosol-radiat...As a typhoon approaches the continent,the position where anthropogenic aerosols penetrate,the convection competition between the eyewall and peripheral rainbands,and the separate contributions of direct aerosol-radiation interactions(ARI)and indirect aerosol-cloud interactions(ACI),yield uncertainties in the convection intensification area and hence the typhoon intensity.Typhoon Lupit(2009)was simulated using the Weather Research and Forecasting Model with Chemistry(WRF-Chem)to investigate and isolate the direct and indirect effects of aerosols on the intensity,convection,and precipitation of the typhoon.Three simulations(CTL,CLEAN,and CTLARIOFF)were designed,representing a polluted case(CTL,considering the ingestion of anthropogenic aerosols with ARI and ACI),a clean maritime case(CLEAN,mainly with sea salt aerosols),and a polluted case without aerosol radiative forcing(CTLARIOFF,as per CTL but without ARI).The results showed that anthropogenic aerosols could penetrate into both the peripheral rainbands and the eyewall when the typhoon was approaching the Asian continent.Owing to the representation of the real aerosol scenario,the simulated typhoon intensity weakened and was closer to observed values in the CTL experiment.The ARI dominated over ACI with the opposite effects.Specifically,the ACI mainly enhanced the formation of ice-phase hydrometeors within the upper level of the eyewall with more freezing latent heat releases,leading to an invigoration of eyewall convection.These excess ice-phase particles melted after they descended into the warm layer below the 0°C level,which accelerated the accretion of cloud droplets by raindrops(Pcacr)and hence the mixed phase precipitation process in the eyewall.The dynamic feedback induced by the ACI enhanced the boundary layer inflow and the upper layer outflow,supporting the maintenance of strong eyewall convection and intensification of the typhoon.Inversely,the ARI heated the distant periphery low-level atmosphere at an altitude of 1-2 km by the absorbing polluted aerosols.The heated air,driven by the radial inflow,firstly went through the periphery rainbands of the typhoon and invigorated convection there due to the low-level warming.Then,the enhanced periphery convection inhibited the further transport of warm moist air into the eyewall,resulting in weakening of the eyewall convection and hence typhoon intensity.In sum,for the polluted scenario,as the typhoon approached the continent,ARI played a dominant role over ACI.The WRF-Chem model with full consideration of aerosol-cloud-radiation interactions is advantageous in terms of reliably simulating typhoon intensity and precipitation distribution.展开更多
Among 33 cold frontal systems passed over the Beijing-Tianjin-Tangshan area from May to August during 1963—1979,there existed mesoscale rainbands in the warm sectors ahead of 31 cold fronts.These rainbands, according...Among 33 cold frontal systems passed over the Beijing-Tianjin-Tangshan area from May to August during 1963—1979,there existed mesoscale rainbands in the warm sectors ahead of 31 cold fronts.These rainbands, according to their orientation,movement,formation and development,can be divided into three types:parallel, angulate and perpendicular type.The basic characteristics,sources and propagation of the three types of rainbands and the severe convective weather associated with the bands are presented.The possible mechanis- ms responsible for the formation and development of the bands are also briefly discussed.展开更多
To better understand how severe storms form and evolve in the outer rainbands of typhoons, in this study, we in- vestigate the evolutionary characteristics and possible formation mechanisms for severe storms in the ra...To better understand how severe storms form and evolve in the outer rainbands of typhoons, in this study, we in- vestigate the evolutionary characteristics and possible formation mechanisms for severe storms in the rainbands of Typhoon Mujigae, which occurred during 2-5 October 2015, based on the NCEP-NCAR reanalysis data, conventional observations, and Doppler radar data. For the rainbands far from the inner core （eye and eyewall） of Mujigae （dis- tance of approximately 70-800 kin）, wind speed first increased with the radius expanding from the inner core, and then decreased as the radius continued to expand. The Rankine Vortex Model was used to explore such variations in wind speed. The areas of strong stormy rainbands were mainly located in the northeast quadrant of Mujigae, and overlapped with the areas of high winds within approximately 300-550 km away from the inner core, where the strong winds were conducive to the development of strong storms. A severe convective cell in the rainbands de- veloped into waterspout at approximately 500 km to the northeast of the inner core, when Mujigae was strengthening before it made landfall. Two severe convective cells in the rainbands developed into two tornadoes at approximately 350 km to the northeast of the inner core after Mujigae made landfall. The radar echo bands enhanced to 60 dBZ when mesocyclones occurred in the rainbands and induced tornadoes. The radar echoes gradually weakened after the mesocyclones weakened. The tops of parent clouds of the mesocyclones elevated at first, and then suddenly dropped about 20 min before the tornadoes appeared. Thereby, the cloud top variation has the potential to be used as an early warning of tornado occurrence.展开更多
As one of the most devastating tropical cyclones over the western North Pacific Ocean,Super Typhoon Lekima(2019)has caused a wide range of heavy rainfall in China.Based on the CMA Multi-source merged Precipitation Ana...As one of the most devastating tropical cyclones over the western North Pacific Ocean,Super Typhoon Lekima(2019)has caused a wide range of heavy rainfall in China.Based on the CMA Multi-source merged Precipitation Analysis System(CMPAS)-hourly data set,both the temporal and spatial distribution of extreme rainfall is analyzed.It is found that the heavy rainfall associated with Lekima includes three main episodes with peaks at 3,14 and 24 h after landfall,respectively.The first two rainfall episodes are related to the symmetric outburst of the inner rainband and the persistence of outer rainband.The third rainfall episode is caused by the influence of cold,dry air from higher latitudes and the peripheral circulation of the warm moist tropical storm.The averaged rainrate of inner rainbands underwent an obvious outburst within 6 h after landfall.The asymmetric component of the inner rainbands experienced a transport from North(West)quadrant to East(South)quadrant after landfall which was related to the storm motion other than the Vertical Wind Shear(VWS).Meanwhile the outer rainband in the vicinity of three times of the Radius of Maximum Wind(RMW)was active over a 12-h period since the decay of the inner rainband.The asymmetric component of the outer rainband experienced two significant cyclonical migrations in the northern semicircle.展开更多
Understanding the factors that control typhoon rainfall distribution is critical for improving rainfall forecasting,especially for landfall typhoons. This study investigated the impact of typhoon size on rainfall char...Understanding the factors that control typhoon rainfall distribution is critical for improving rainfall forecasting,especially for landfall typhoons. This study investigated the impact of typhoon size on rainfall characteristics at landfall in eastern coast of China. Typhoons Ampil(2018) and Rumbia(2018), which had similar intensities, were investigated to explore the connection between storm size and rainfall. The larger cyclonic wind field in Typhoon Rumbia led to greater vorticity and broader convergence compared to Typhoon Ampil, along with an ascending region outside the eyewall, which promoted more vigorous rainbands. Rumbia′s larger size exhibited greater outer-core radial vorticity advection relative to Ampil. This maintained its extensive outer-core wind field and intensified outer rainband development. Consequently,Rumbia generated more extensive and prolonged rainfall post-landfall compared to Ampil. A composite analysis of typhoons making landfall in eastern China(2001-2021) further examines the statistical correlation between typhoon size and rainfall distribution. Results indicate that larger typhoons are more likely to generate heavier and more spatially extensive rainfall in regions beyond their eyewalls. These findings highlight that typhoon size significantly regulates rainfall evolution during landfall, underscoring the necessity of incorporating this parameter into operational rainfall forecasting models for landfalling typhoons.展开更多
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
The characteristics of helicity in a hurricane are presented by calculating the MM5 model output in addition to theoretical analysis. It is found that helicity in a hurricane mainly depends on its horizontal component...The characteristics of helicity in a hurricane are presented by calculating the MM5 model output in addition to theoretical analysis. It is found that helicity in a hurricane mainly depends on its horizontal component, whose magnitude is about 100 to 1000 times larger than its vertical component. It is also found that helicity is approximately conserved in the hurricane. Since the fluid has the intention to adjust the wind shear to satisfy the conservation of helicity, the horizontal vorticity is even larger than the vertical vorticity, and the three-dimensional vortices slant to the horizontal plane except in the inner eye. There are significant horizontal vortices and inhomogeneous helical flows in the hurricane. The formation of the spiral rainband is discussed by using the law of horizontal helical flows. It is closely related to the horizontal strong vortices and inhomogeneous helical flows.展开更多
Idealized numerical simulations are conducted in this study to comparatively investigate the characteristics of the stratiform sector in the outer rainbands of tropical cyclones(TCs)in lower-and upper-layer vertical w...Idealized numerical simulations are conducted in this study to comparatively investigate the characteristics of the stratiform sector in the outer rainbands of tropical cyclones(TCs)in lower-and upper-layer vertical wind shear(VWS)with moderate magnitude.Consistent with the results in previous studies,the outer rainband stratiform sector of the TCs simulated in both experiments is generally located downshear left.Upper-layer VWS tends to produce stronger asymmetric outflow at upper levels in the downshear-left quadrant than lower-layer shear.This stronger asymmetric outflow transports more water vapor radially outward from the inner core to the outer core at upper levels in the downshear-left quadrant in the upper-layer shear experiment.More depositional growth of both graupel and cloud ice thus occurs downshear left in upper layers in the outer core,yielding more diabatic heating and stronger upward motions,particularly in the stratiformdominated part of the stratiform sector in the upper-layer shear experiment.Resultingly,a better-organized stratiform sector in the outer rainbands is found in the upper-layer VWS experiment than in the lower-layer VWS experiment.The diabatic heating associated with the stratiform sector produces strong midlevel outflow on the radially inward side of,and weak midlevel inflow on the radially outward side of,the heating core,with lower-level inflow beneath the midlevel outflow and upper-level inflow above.The upper-layer VWS tends to produce a deeper asymmetric inflow layer in the outer rainband stratiform sector,with more significant lower-level inflow and tangential jets in the upper-layer VWS experiment.展开更多
As the first leading mode of upper-tropospheric circulation in observations, the meridional displacement of the East Asian westerly jet (EAJ) varies closely with the East Asian rainfall in summer. In this study, the i...As the first leading mode of upper-tropospheric circulation in observations, the meridional displacement of the East Asian westerly jet (EAJ) varies closely with the East Asian rainfall in summer. In this study, the interannual variation of the EAJ meridional displacement and its relationship with the East Asian summer rainfall are evaluated, using the historical simulations of CMIP5 (phase 5 of the Coupled Model Intercomparison Project). The models can generally reproduce the meridional displacement of the EAJ, which is mainly manifested as the first principal mode in most of the simulations. For the relationship between the meridional displacement of the EAJ and East Asian rainfall, almost all the models depict a weaker correlation than observations and exhibit considerably large spread across the models. It is found that the discrepancy in the interannual relationship is closely related to the simulation of the climate mean state, including the climatological location of the westerly jet in Eurasia and rainfall bias in South Asia and the western North Pacific. In addition, a close relationship between the simulation discrepancy and intensity of EAJ variability is also found: the models with a stronger intensity of the EAJ meridional displacement tend to reproduce a closer interannual relationship, and vice versa.展开更多
Polarimetric radar and 2D video disdrometer observations provide new insights into the precipitation microphysical processes and characteristics in the inner rainband of tropical cyclone(TC)Kajiki(2019)in the South Ch...Polarimetric radar and 2D video disdrometer observations provide new insights into the precipitation microphysical processes and characteristics in the inner rainband of tropical cyclone(TC)Kajiki(2019)in the South China Sea for the first time.The precipitation of Kajiki is dominated by high concentrations and small(<3 mm)raindrops,which contribute more than 98%to the total precipitation.The average mass-weighted mean diameter and logarithmic normalized intercept are 1.49 mm and 4.47,respectively,indicating a larger mean diameter and a lower concentration compared to the TCs making landfall in eastern China.The ice processes of the inner rainband are dramatically different among different stages.The riming process is dominant during the mature stage,while during the decay stage the aggregation process is dominant.The vertical profiles of the polarimetric radar variables together with ice and liquid water contents in the convective region indicate that the formation of precipitation is dominated by warm-rain processes.Large raindrops collect cloud droplets and other raindrops,causing reflectivity,differential reflectivity,and specific differential phase to increase with decreasing height.That is,accretion and coalescence play a critical role in the formation of heavy rainfall.The melting of different particles generated by the ice process has a great influence on the initial raindrop size distribution(DSD)to further affect the warm-rain processes.The DSD above heavy rain with the effect of graupel has a wider spectral width than the region without the effect of graupel.展开更多
Typhoon Rananim （2004） was one of the severest typhoons landfalling the Chinese mainland from 1996 to 2004. It brought serious damage and induced prodigious economical loss. Using a new generation of mesoscale model...Typhoon Rananim （2004） was one of the severest typhoons landfalling the Chinese mainland from 1996 to 2004. It brought serious damage and induced prodigious economical loss. Using a new generation of mesoscale model, named the Weather Research and Forecasting （WRF） modeling system, with 1.667 km grid horizontal spacing on the finest nested mesh, Rananim was successfully simulated in terms of track, intensity, eye, eyewall, and spiral rainbands. We compared the structures of Rananim to those of hurricanes in previous studies and observations to assess the validity of simulation. The three-dimensional （3D） dynamic and thermal structures of eye and eyewall were studied based on the simulated results. The focus was investigation of the characteristics of the vortex Rossby waves in the inner-core region. We found that the Rossby vortex waves propagate azimuthally upwind against the azimuthal mean tangential flow around the eyewall, and their period was longer than that of an air parcel moving within the azimuthal mean tangential flow. They also propagated outward against the boundary layer inflow of the azimuthal mean vortex. Puthermore, we studied the connection between the spiral potential vorticity （PV） bands and spiral rainbands, and found that the vortex Rossby waves played an important role in the formation process of spiral rainbands.展开更多
Precipitation in Heilongjiang Province of China increased slightly from 1960 to 2000. Adopting the method proposed by Arthur N. Samel, we separated monsoon rainband rain and calculated the initial and final date of mo...Precipitation in Heilongjiang Province of China increased slightly from 1960 to 2000. Adopting the method proposed by Arthur N. Samel, we separated monsoon rainband rain and calculated the initial and final date of monsoon rainband of each year and each station, For the period of 1960-2000, the change of annual precipitation in Heilongjiang Province, with an increasing trend of 2.229 mm per decade, is not significant; the duration and total monsoon rain decreased significantly, with a decreasing trend of -6.9 day per decade and -17,5 mm per decade separately. That change comes from early leaving date of summer monsoon rainband for the period of 1960- 1975 and later arriving date of summer monsoon rainband for the period of 1990-2000, The weakening of summer monsoon makes ils contribution to the annual precipitation decreased significantly, with a decreasing trend of 4.4 % per decade.展开更多
The Advanced Weather Research and Forecasting Model （ARW） is used to simulate the local heavy rainstorm process caused by Typhoon Matsa over the northeastern coast of Zhejiang Province in 2005. The results show that...The Advanced Weather Research and Forecasting Model （ARW） is used to simulate the local heavy rainstorm process caused by Typhoon Matsa over the northeastern coast of Zhejiang Province in 2005. The results show that the rainstorm was caused mainly by the secondary spiral rainband of the Stationary Band Complex （SBC） structure. Within the secondary spiral rainband there was a strong meso-β-scale convergence line generated in the boundary layer, corresponding very well to the Doppler radar echo band. The convergence line comprised several smaller convergence centers, and all of these convergence columns inclined outward. Along the convergence line there was precipitation greater than 20 mm occurring during the following one hour. During the heavy rainstorm process, the Doppler radar echo band, convergence line, and the precipitation amount during the following one hour, moved and evolved synchronously. Further study reveals that the vertical shear of radial wind and the low-level jet of tangential wind contributed to the genesis and development of the convergence columns. The combined effect of the ascending leg of the clockwise secondary circulation of radial wind and the favorable environment of the entrance region of the low-level jet of tangential wind further strengthened the convergence. The warm, moist inflow in the lower levels was brought in by the inflows of the clockwise secondary circulation and uplifted intensely at the effect of convergence. In the convectively instable environment, strong convection was triggered to produce the heavy rainstorm.展开更多
Using the WRF(Weather Research Forecast)model,this work performed analysis and simulation on the rainband change during the landfall of Typhoon Haitang(2005)and found that breaking may occur over land and oceans leads...Using the WRF(Weather Research Forecast)model,this work performed analysis and simulation on the rainband change during the landfall of Typhoon Haitang(2005)and found that breaking may occur over land and oceans leads to distinct asymmetric precipitation.The breaking is related to the topographic effect as well as interactions between the typhoon and midlatitude systems at upper levels.During the landfall,divergent flows at the 200-hPa level of the South-Asian high combined with divergent flows at the periphery of the typhoon to form a weak,inverted trough in the northwest part of the storm,with the mid- and low-level divergence fields on the west and northwest side of the typhoon center maintaining steadily.It intensifies the upper-level cyclonic flows,in association with positive vorticity rotating counterclockwise together with air currents that travel stepwise into a vorticity zone in the vicinity of the typhoon core, thereby forming a vorticity transfer belt in 22–25°N that extends to the eastern part of the storm.It is right here that the high-level vorticity band is subsiding so that rainfall is prevented from developing,resulting in the rainbelt breaking,which is the principal cause of asymmetric precipitation occurrence.Migrating into its outer region,the banded vorticity of Haitang at high levels causes further amplification of the cyclonic circulation in the western part and transfer of positive vorticity into the typhoon such that the rainband breaking is more distinct.展开更多
基金supported by the National Basic Research Program of China (2009CB421505)the National Natural Science Foundation of China under Grants Nos.40730948+5 种基金the National Natural Science Foundation of China under Grants Nos.40575030the National Natural Science Foundation of China under Grants Nos.40705024the Shanghai Typhoon Foundation (2009ST09)supported by the National Nature Science Foundation of China under the Grant No.40675060the program of the Ministry of Science and Technology of the People's Republic of China (2006AA09Z151)the program of China Meteorological Administration(GYHY200706031)
文摘Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State Mesoscale Model （MM5）. The finescale rainbands have two types： one intersecting the eyewall and causing damaging wind streaks, and the other distributed azimuthally along the inner edge of the eyewall with a relatively short lifetime. The formation of the high-velocity wind streaks results from the interaction of the azimuthal flow with the banded vertical vorticity structure triggered by tilting of the horizontal vorticity. The vertical advection of azimuthal momentum also leads to acceleration of tangential flow at a relatively high Mtitude. The evolution and structures of the bands are also examined in this study. Further investigation suggests that the boundary inflection points are related tightly to the development of the finescale rainbands, consistent with previous findings using simple symmetric models. In particular; the presence of the level of inflow reversal in the boundary layer is a crucial factor controlling the formation of these bands. The near-surface wavy peaks of vertical vorticity always follow the inflection points in radial flow. The mesoscale vortices and associated convective updrafts in the eyewall are considered to strengthen the activity of finescale bands, and the updrafts can trigger the formation of the bands as they reside in the environment with inflow reversal in the boundary layer.
基金supported by grants from the Chinese Academy of Sciences(KZCX2-YW-315-2)the National Natural Science Foundation of China(Grant Nos40701021,40625002)
文摘Based on reconstructions of precipitation events from the rain and snowfall archives of the Qing Dynasty （1736-1911）, the drought/flood index data mainly derived from Chinese local gazettes from 1736-2000, and the observational data gathered since 1951, the spatial patterns of monsoon rainbands are analyzed at different time scales. Findings indicate that monsoon rainfall in northern China and the middle-lower reaches of the Yangtze River have significant inter-annual （e.g., 5-7-yr and 2-4-yr） as well as inter-decadal （e.g., 20-30-yr and quasi-10-yr） fluctuation signals. The spatial patterns in these areas also show significant cycles, such as on a 60-80-yr time scale, a reversal phase predominates the entire period from 1736-2000; on a quasi-30-yr time scale, a consistent phase was prevalent from 1736 to 2000; and on a 20-yr time scale, the summer monsoon rains show different spatial patterns before and after 1870.
文摘This article investigates in detail the structure, genesis and development of parallel-type warm sector rainbands from radar observations. By comparing these observations with diagnostic results from temperature, pressure, moisture and wind data, which are both actually observed and numerically generated by a mesoscale model, and the theory of symmetric instability, it is found that the conditional symmetric instability might be responsible for the formation and development of these rainbands.
基金State Key Basic Program (Project 973, 2004CB18301)Doctorate-Supervisor Foundation,MOE under Grant (20050284035)Project of Natural Science Foundation of Jiangsu Province (BK99020,BK2005081)
文摘In this paper, an idealized perturbation following the ＂surge-flow conceptual model＂ for typical Meiyu frontal structure is designed to explain the β meso-scale structure ofrainbands in the Meiyu front using a non-hydrostatic, full-compressible storm-scale model including multi-phase microphysical parameterization. In addition, sensitivity numerical experiment on the vertical distribution of the ambient meridional wind is conducted to investigate the generation mechanism of D meso-scale double rainbands. The results of numerical experiments show that the cool and dry downdraft invading strengthened by the environmental aloft northerly wind plays a very important role to the generation and maintenance of the β meso-scale double rainbands. Moreover, the intensity and scale of the dry and cool downdraft invading are related to the intensity of the second circumfluence induced by mass adjustment when the acceleration of the westerly jet aloft occurs.
文摘The characteristics of the South Asia high (SAH) and subtropical westerly jets in the summer of 2010 and their relationship with the changes in rainband in China were analyzed. As shown by the results, the SAH in the upper troposphere extended northward relatively late in June 2010. Correspondingly, the subtropical westerly jets on the north side of the SAH jumped northward comparatively late, thus delaying the formation of a strong divergence field in the upper air over the Yangtze-Huaihe River valley. This was one of the main causes for the late onset of plum rains in the Yangtze-Huaihe River valley. In July, there was a vertical structure consisting of upper-level divergence and low-level convergence near the subtropical westerly jets on the north side of the SAH and in the air stream dispersal area on the northeast side of the eastward-extending SAH, which was the dynamic mechanism bringing about frequent and extremely heavy rainstorms during the plum rain period in this year. The SAH in the upper troposphere affected the subtropical high in the lower stratosphere, and thereby led to changes in the main rainband location in China.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41775017&41675058).
文摘As a typhoon approaches the continent,the position where anthropogenic aerosols penetrate,the convection competition between the eyewall and peripheral rainbands,and the separate contributions of direct aerosol-radiation interactions(ARI)and indirect aerosol-cloud interactions(ACI),yield uncertainties in the convection intensification area and hence the typhoon intensity.Typhoon Lupit(2009)was simulated using the Weather Research and Forecasting Model with Chemistry(WRF-Chem)to investigate and isolate the direct and indirect effects of aerosols on the intensity,convection,and precipitation of the typhoon.Three simulations(CTL,CLEAN,and CTLARIOFF)were designed,representing a polluted case(CTL,considering the ingestion of anthropogenic aerosols with ARI and ACI),a clean maritime case(CLEAN,mainly with sea salt aerosols),and a polluted case without aerosol radiative forcing(CTLARIOFF,as per CTL but without ARI).The results showed that anthropogenic aerosols could penetrate into both the peripheral rainbands and the eyewall when the typhoon was approaching the Asian continent.Owing to the representation of the real aerosol scenario,the simulated typhoon intensity weakened and was closer to observed values in the CTL experiment.The ARI dominated over ACI with the opposite effects.Specifically,the ACI mainly enhanced the formation of ice-phase hydrometeors within the upper level of the eyewall with more freezing latent heat releases,leading to an invigoration of eyewall convection.These excess ice-phase particles melted after they descended into the warm layer below the 0°C level,which accelerated the accretion of cloud droplets by raindrops(Pcacr)and hence the mixed phase precipitation process in the eyewall.The dynamic feedback induced by the ACI enhanced the boundary layer inflow and the upper layer outflow,supporting the maintenance of strong eyewall convection and intensification of the typhoon.Inversely,the ARI heated the distant periphery low-level atmosphere at an altitude of 1-2 km by the absorbing polluted aerosols.The heated air,driven by the radial inflow,firstly went through the periphery rainbands of the typhoon and invigorated convection there due to the low-level warming.Then,the enhanced periphery convection inhibited the further transport of warm moist air into the eyewall,resulting in weakening of the eyewall convection and hence typhoon intensity.In sum,for the polluted scenario,as the typhoon approached the continent,ARI played a dominant role over ACI.The WRF-Chem model with full consideration of aerosol-cloud-radiation interactions is advantageous in terms of reliably simulating typhoon intensity and precipitation distribution.
文摘Among 33 cold frontal systems passed over the Beijing-Tianjin-Tangshan area from May to August during 1963—1979,there existed mesoscale rainbands in the warm sectors ahead of 31 cold fronts.These rainbands, according to their orientation,movement,formation and development,can be divided into three types:parallel, angulate and perpendicular type.The basic characteristics,sources and propagation of the three types of rainbands and the severe convective weather associated with the bands are presented.The possible mechanis- ms responsible for the formation and development of the bands are also briefly discussed.
基金Supported by the National Basic Research and Development(973)Program of China(2013CB430102)Open Research Fund of Key Laboratory of Geographic Information Science(KLGIS2015A01)+3 种基金China Meteorological Administration Special Public Welfare Research Fund(GYHY201306040,GYHY201306078,and GYHY201506001)National Natural Science Foundation of China(91537214,41275079,41305077,41405069,91537214,41505078,and 41305031)Research Innovation Program for College Graduates of Jiangsu Province(KYZZ-0246)Open Research Fund of State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences(2016LASW-B12)
文摘To better understand how severe storms form and evolve in the outer rainbands of typhoons, in this study, we in- vestigate the evolutionary characteristics and possible formation mechanisms for severe storms in the rainbands of Typhoon Mujigae, which occurred during 2-5 October 2015, based on the NCEP-NCAR reanalysis data, conventional observations, and Doppler radar data. For the rainbands far from the inner core （eye and eyewall） of Mujigae （dis- tance of approximately 70-800 kin）, wind speed first increased with the radius expanding from the inner core, and then decreased as the radius continued to expand. The Rankine Vortex Model was used to explore such variations in wind speed. The areas of strong stormy rainbands were mainly located in the northeast quadrant of Mujigae, and overlapped with the areas of high winds within approximately 300-550 km away from the inner core, where the strong winds were conducive to the development of strong storms. A severe convective cell in the rainbands de- veloped into waterspout at approximately 500 km to the northeast of the inner core, when Mujigae was strengthening before it made landfall. Two severe convective cells in the rainbands developed into two tornadoes at approximately 350 km to the northeast of the inner core after Mujigae made landfall. The radar echo bands enhanced to 60 dBZ when mesocyclones occurred in the rainbands and induced tornadoes. The radar echoes gradually weakened after the mesocyclones weakened. The tops of parent clouds of the mesocyclones elevated at first, and then suddenly dropped about 20 min before the tornadoes appeared. Thereby, the cloud top variation has the potential to be used as an early warning of tornado occurrence.
基金supported by Postdoctoral Science Foundation of China(No.2019M661342).
文摘As one of the most devastating tropical cyclones over the western North Pacific Ocean,Super Typhoon Lekima(2019)has caused a wide range of heavy rainfall in China.Based on the CMA Multi-source merged Precipitation Analysis System(CMPAS)-hourly data set,both the temporal and spatial distribution of extreme rainfall is analyzed.It is found that the heavy rainfall associated with Lekima includes three main episodes with peaks at 3,14 and 24 h after landfall,respectively.The first two rainfall episodes are related to the symmetric outburst of the inner rainband and the persistence of outer rainband.The third rainfall episode is caused by the influence of cold,dry air from higher latitudes and the peripheral circulation of the warm moist tropical storm.The averaged rainrate of inner rainbands underwent an obvious outburst within 6 h after landfall.The asymmetric component of the inner rainbands experienced a transport from North(West)quadrant to East(South)quadrant after landfall which was related to the storm motion other than the Vertical Wind Shear(VWS).Meanwhile the outer rainband in the vicinity of three times of the Radius of Maximum Wind(RMW)was active over a 12-h period since the decay of the inner rainband.The asymmetric component of the outer rainband experienced two significant cyclonical migrations in the northern semicircle.
基金National Natural Science Foundation of China(42375012)China Meteorological Administration Foundation(CXFZ2025J023)。
文摘Understanding the factors that control typhoon rainfall distribution is critical for improving rainfall forecasting,especially for landfall typhoons. This study investigated the impact of typhoon size on rainfall characteristics at landfall in eastern coast of China. Typhoons Ampil(2018) and Rumbia(2018), which had similar intensities, were investigated to explore the connection between storm size and rainfall. The larger cyclonic wind field in Typhoon Rumbia led to greater vorticity and broader convergence compared to Typhoon Ampil, along with an ascending region outside the eyewall, which promoted more vigorous rainbands. Rumbia′s larger size exhibited greater outer-core radial vorticity advection relative to Ampil. This maintained its extensive outer-core wind field and intensified outer rainband development. Consequently,Rumbia generated more extensive and prolonged rainfall post-landfall compared to Ampil. A composite analysis of typhoons making landfall in eastern China(2001-2021) further examines the statistical correlation between typhoon size and rainfall distribution. Results indicate that larger typhoons are more likely to generate heavier and more spatially extensive rainfall in regions beyond their eyewalls. These findings highlight that typhoon size significantly regulates rainfall evolution during landfall, underscoring the necessity of incorporating this parameter into operational rainfall forecasting models for landfalling typhoons.
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sponsored by the National Natural Science Foundation of China under Grant No.400750112001 PIA 20026 the National Key program for Developing Basic Sciences:CHeRES(G 1998040907).
文摘The characteristics of helicity in a hurricane are presented by calculating the MM5 model output in addition to theoretical analysis. It is found that helicity in a hurricane mainly depends on its horizontal component, whose magnitude is about 100 to 1000 times larger than its vertical component. It is also found that helicity is approximately conserved in the hurricane. Since the fluid has the intention to adjust the wind shear to satisfy the conservation of helicity, the horizontal vorticity is even larger than the vertical vorticity, and the three-dimensional vortices slant to the horizontal plane except in the inner eye. There are significant horizontal vortices and inhomogeneous helical flows in the hurricane. The formation of the spiral rainband is discussed by using the law of horizontal helical flows. It is closely related to the horizontal strong vortices and inhomogeneous helical flows.
基金the National Key Research and Development Program of China(Grant No.2017YFC1501601)the Key Program of the Ministry of Science and Technology of China(Grant No.2017YFE0107700)the National Natural Science Foundation of China(Grant Nos.41875054,41730961,41730960,and 41775065).
文摘Idealized numerical simulations are conducted in this study to comparatively investigate the characteristics of the stratiform sector in the outer rainbands of tropical cyclones(TCs)in lower-and upper-layer vertical wind shear(VWS)with moderate magnitude.Consistent with the results in previous studies,the outer rainband stratiform sector of the TCs simulated in both experiments is generally located downshear left.Upper-layer VWS tends to produce stronger asymmetric outflow at upper levels in the downshear-left quadrant than lower-layer shear.This stronger asymmetric outflow transports more water vapor radially outward from the inner core to the outer core at upper levels in the downshear-left quadrant in the upper-layer shear experiment.More depositional growth of both graupel and cloud ice thus occurs downshear left in upper layers in the outer core,yielding more diabatic heating and stronger upward motions,particularly in the stratiformdominated part of the stratiform sector in the upper-layer shear experiment.Resultingly,a better-organized stratiform sector in the outer rainbands is found in the upper-layer VWS experiment than in the lower-layer VWS experiment.The diabatic heating associated with the stratiform sector produces strong midlevel outflow on the radially inward side of,and weak midlevel inflow on the radially outward side of,the heating core,with lower-level inflow beneath the midlevel outflow and upper-level inflow above.The upper-layer VWS tends to produce a deeper asymmetric inflow layer in the outer rainband stratiform sector,with more significant lower-level inflow and tangential jets in the upper-layer VWS experiment.
基金supported by the National Key Research and Development Program of China (Grant No. 2018YFA0606501)the National Natural Science Foundation of China (Grant Nos. 41721004, U1502233 and 41775083)
文摘As the first leading mode of upper-tropospheric circulation in observations, the meridional displacement of the East Asian westerly jet (EAJ) varies closely with the East Asian rainfall in summer. In this study, the interannual variation of the EAJ meridional displacement and its relationship with the East Asian summer rainfall are evaluated, using the historical simulations of CMIP5 (phase 5 of the Coupled Model Intercomparison Project). The models can generally reproduce the meridional displacement of the EAJ, which is mainly manifested as the first principal mode in most of the simulations. For the relationship between the meridional displacement of the EAJ and East Asian rainfall, almost all the models depict a weaker correlation than observations and exhibit considerably large spread across the models. It is found that the discrepancy in the interannual relationship is closely related to the simulation of the climate mean state, including the climatological location of the westerly jet in Eurasia and rainfall bias in South Asia and the western North Pacific. In addition, a close relationship between the simulation discrepancy and intensity of EAJ variability is also found: the models with a stronger intensity of the EAJ meridional displacement tend to reproduce a closer interannual relationship, and vice versa.
基金This work was primarily supported by the National Key Research and Development Program of China(Grant No.2018YFC1507304)the National Natural Science Foundation of China(Grant Nos.42075080,41975066 and 41865009).
文摘Polarimetric radar and 2D video disdrometer observations provide new insights into the precipitation microphysical processes and characteristics in the inner rainband of tropical cyclone(TC)Kajiki(2019)in the South China Sea for the first time.The precipitation of Kajiki is dominated by high concentrations and small(<3 mm)raindrops,which contribute more than 98%to the total precipitation.The average mass-weighted mean diameter and logarithmic normalized intercept are 1.49 mm and 4.47,respectively,indicating a larger mean diameter and a lower concentration compared to the TCs making landfall in eastern China.The ice processes of the inner rainband are dramatically different among different stages.The riming process is dominant during the mature stage,while during the decay stage the aggregation process is dominant.The vertical profiles of the polarimetric radar variables together with ice and liquid water contents in the convective region indicate that the formation of precipitation is dominated by warm-rain processes.Large raindrops collect cloud droplets and other raindrops,causing reflectivity,differential reflectivity,and specific differential phase to increase with decreasing height.That is,accretion and coalescence play a critical role in the formation of heavy rainfall.The melting of different particles generated by the ice process has a great influence on the initial raindrop size distribution(DSD)to further affect the warm-rain processes.The DSD above heavy rain with the effect of graupel has a wider spectral width than the region without the effect of graupel.
基金supported by the National Key Basic Research and Development Project of China (Grant Nos. 2004CB418301,2009CB421503)National Natural Science Foundation of China (Grant No. 40775033)the Chinese Special Scientific Research Project for Public Interest (Grant No.GYHY200806009)
文摘Typhoon Rananim （2004） was one of the severest typhoons landfalling the Chinese mainland from 1996 to 2004. It brought serious damage and induced prodigious economical loss. Using a new generation of mesoscale model, named the Weather Research and Forecasting （WRF） modeling system, with 1.667 km grid horizontal spacing on the finest nested mesh, Rananim was successfully simulated in terms of track, intensity, eye, eyewall, and spiral rainbands. We compared the structures of Rananim to those of hurricanes in previous studies and observations to assess the validity of simulation. The three-dimensional （3D） dynamic and thermal structures of eye and eyewall were studied based on the simulated results. The focus was investigation of the characteristics of the vortex Rossby waves in the inner-core region. We found that the Rossby vortex waves propagate azimuthally upwind against the azimuthal mean tangential flow around the eyewall, and their period was longer than that of an air parcel moving within the azimuthal mean tangential flow. They also propagated outward against the boundary layer inflow of the azimuthal mean vortex. Puthermore, we studied the connection between the spiral potential vorticity （PV） bands and spiral rainbands, and found that the vortex Rossby waves played an important role in the formation process of spiral rainbands.
文摘Precipitation in Heilongjiang Province of China increased slightly from 1960 to 2000. Adopting the method proposed by Arthur N. Samel, we separated monsoon rainband rain and calculated the initial and final date of monsoon rainband of each year and each station, For the period of 1960-2000, the change of annual precipitation in Heilongjiang Province, with an increasing trend of 2.229 mm per decade, is not significant; the duration and total monsoon rain decreased significantly, with a decreasing trend of -6.9 day per decade and -17,5 mm per decade separately. That change comes from early leaving date of summer monsoon rainband for the period of 1960- 1975 and later arriving date of summer monsoon rainband for the period of 1990-2000, The weakening of summer monsoon makes ils contribution to the annual precipitation decreased significantly, with a decreasing trend of 4.4 % per decade.
基金supported by the State Key Program of the National Natural Science Foundation of China (Grant No 40830958)the Research Project of Serious Oceanic Disasters Alerting and Application Technology (Grant No 2006BAC03B00)+1 种基金the Key Program of the State Key Laboratory of Disaster Weather (Grant No 2008LASW-A03)the National Natural Science Foundation of China(Grant No 40975021)
文摘The Advanced Weather Research and Forecasting Model （ARW） is used to simulate the local heavy rainstorm process caused by Typhoon Matsa over the northeastern coast of Zhejiang Province in 2005. The results show that the rainstorm was caused mainly by the secondary spiral rainband of the Stationary Band Complex （SBC） structure. Within the secondary spiral rainband there was a strong meso-β-scale convergence line generated in the boundary layer, corresponding very well to the Doppler radar echo band. The convergence line comprised several smaller convergence centers, and all of these convergence columns inclined outward. Along the convergence line there was precipitation greater than 20 mm occurring during the following one hour. During the heavy rainstorm process, the Doppler radar echo band, convergence line, and the precipitation amount during the following one hour, moved and evolved synchronously. Further study reveals that the vertical shear of radial wind and the low-level jet of tangential wind contributed to the genesis and development of the convergence columns. The combined effect of the ascending leg of the clockwise secondary circulation of radial wind and the favorable environment of the entrance region of the low-level jet of tangential wind further strengthened the convergence. The warm, moist inflow in the lower levels was brought in by the inflows of the clockwise secondary circulation and uplifted intensely at the effect of convergence. In the convectively instable environment, strong convection was triggered to produce the heavy rainstorm.
基金Natural Foundamental Research and Development Project"973"Program(2009CB421503)Natural Science Foundation of China(4097503740775033)
文摘Using the WRF(Weather Research Forecast)model,this work performed analysis and simulation on the rainband change during the landfall of Typhoon Haitang(2005)and found that breaking may occur over land and oceans leads to distinct asymmetric precipitation.The breaking is related to the topographic effect as well as interactions between the typhoon and midlatitude systems at upper levels.During the landfall,divergent flows at the 200-hPa level of the South-Asian high combined with divergent flows at the periphery of the typhoon to form a weak,inverted trough in the northwest part of the storm,with the mid- and low-level divergence fields on the west and northwest side of the typhoon center maintaining steadily.It intensifies the upper-level cyclonic flows,in association with positive vorticity rotating counterclockwise together with air currents that travel stepwise into a vorticity zone in the vicinity of the typhoon core, thereby forming a vorticity transfer belt in 22–25°N that extends to the eastern part of the storm.It is right here that the high-level vorticity band is subsiding so that rainfall is prevented from developing,resulting in the rainbelt breaking,which is the principal cause of asymmetric precipitation occurrence.Migrating into its outer region,the banded vorticity of Haitang at high levels causes further amplification of the cyclonic circulation in the western part and transfer of positive vorticity into the typhoon such that the rainband breaking is more distinct.
