This paper investigates the homogeneity of United States aircraft reconnaissance data and the impact of these data on the homogeneity of the tropical cyclone(TC)best track data for the seasons 1949-1987 generated by t...This paper investigates the homogeneity of United States aircraft reconnaissance data and the impact of these data on the homogeneity of the tropical cyclone(TC)best track data for the seasons 1949-1987 generated by the China Meteorological Administration(CMA).The evaluation of the reconnaissance data shows that the minimum central sea level pressure(MCP)data are relatively homogeneous,whereas the maximum sustained wind(MSW)data show both overestimations and spurious abrupt changes.Statistical comparisons suggest that both the reconnaissance MCP and MSW were well incorporated into the CMA TC best track dataset.Although no spurious abrupt changes were evident in the reconnaissance-related best track MCP data,two spurious changepoints were identified in the remainder of the best-track MCP data.Furthermore,the influence of the reconnaissance MSWs seems to extend to the best track MSWs unrelated to reconnaissance,which might reflect the optimistic confidence in making higher estimates due to the overestimated extreme wind“observations”.In addition,the overestimation of either the reconnaissance MSWs or the best track MSWs was greater during the early decades compared to later decades,which reflects the important influence of reconnaissance data on the CMA TC best track dataset.The wind-pressure relationship(WPR)used in the CMA TC best track dataset is also evaluated and is found to overestimate the MSW,which may lead to inhomogeneity within the dataset between the aircraft reconnaissance era and the satellite era.展开更多
This study investigates the activity of tropical cyclones(TCs)in the Bay of Bengal(BOB)from 1979 to 2018 to discover the mechanism affecting the contribution rate to the meridional moisture budget anomaly(MMBA)over th...This study investigates the activity of tropical cyclones(TCs)in the Bay of Bengal(BOB)from 1979 to 2018 to discover the mechanism affecting the contribution rate to the meridional moisture budget anomaly(MMBA)over the southern boundary of the Tibetan Plateau(SBTP).May and October–December are the bimodal phases of BOB TC frequency,which decreases month by month from October to December and is relatively low in May.However,the contribution rate to the MMBA is the highest in May.The seasonal variation in the meridional position of the westerlies is the key factor affecting the contribution rate.The relatively southern(northern)position of the westerlies in November and December(May)results in a lower(higher)contribution rate to the MMBA.This mechanism is confirmed by the momentum equation.When water vapor enters the westerlies near the trough line,the resultant meridional acceleration is directed north.It follows that the farther north the trough is,and the farther north the water vapor can be transported.When water vapor enters the westerlies from the area near the ridge line,for Type-T(Type-R)TCs,water vapor enters the westerlies downstream of the trough(ridge).Consequently,the direction of the resultant meridional acceleration is directed south and the resultant zonal acceleration is directed east(west),which is not conducive to the northward transport of water vapor.This is especially the case if the trough or ridge is relatively south,as the water vapor may not cross the SBTP.展开更多
The present study aims to examine the suitability of two commonly used assumptions that simplify modelling metoceanconditions for designing offshore wind turbines in the South China Sea (SCS). The first assumption ass...The present study aims to examine the suitability of two commonly used assumptions that simplify modelling metoceanconditions for designing offshore wind turbines in the South China Sea (SCS). The first assumption assumes thatjoint N-year extreme wind and wave events can be independently estimated and subsequently combined. The secondone assumes peak wind and waves can be modelled as occurring simultaneously during a tropical cyclone (TC) event.To better understand the potential TC activity, a set of 10000 years synthetic TC events are generated. The wind fieldmodel and the Mike 21 spectral wave model are employed to model the TC-induced hazards. Subsequently, theeffect of the assumptions is evaluated by analyzing the peak structural response of both monopile and semisubmersibleoffshore wind turbines during TC events. The results demonstrate that the examined assumptions are generally accurate.By assessing the implications of these assumptions, valuable insights are obtained, which can inform andimprove the modelling of TC-induced hazards in the SCS region.展开更多
Recent studies on tropical cyclone(TC)intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification(RI),however,understanding how vortex alignment ...Recent studies on tropical cyclone(TC)intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification(RI),however,understanding how vortex alignment occurs remains a challenging topic in TC intensity change research.Based on the simulation outputs of North Atlantic Hurricane Wilma(2005)and western North Pacific Typhoon Rammasun(2014),vortex track oscillations at different vertical levels and their associated role in vortex alignment are examined to improve our understanding of the vortex alignment during RI of TCs with initial hurricane intensity.It is found that vortex tracks at different vertical levels oscillate consistently in speed and direction during the RI of the two simulated TCs.While the consistent track oscillation reduces the oscillation tilt during RI,the reduction of vortex tilt results mainly from the mean track before RI.It is also found that the vortex tilt is primarily due to the mean vortex track before and after RI.The track oscillations are closely associated with wavenumber-1 vortex Rossby waves that are dominant wavenumber-1 circulations in the TC inner-core region.This study suggests that the dynamics of the wavenumber-1 vortex Rossby waves play an important role in the regulation of the physical processes associated with the track oscillation and vertical alignment of TCs.展开更多
Explosive cyclones(ECs)occur frequently over the Kuroshio/Kuroshio Extension region.The most rapidly intensified EC over the Kuroshio/Kuroshio Extension region during the 42 years(1979-2020)of cold seasons(October-Apr...Explosive cyclones(ECs)occur frequently over the Kuroshio/Kuroshio Extension region.The most rapidly intensified EC over the Kuroshio/Kuroshio Extension region during the 42 years(1979-2020)of cold seasons(October-April)was studied to reveal the variations of the key factors at different explosive-developing stages.This EC had weak low-level baroclinicity,mid-level cyclonic-vorticity advection,and strong low-level water vapor convergence at the initial explosive-developing stage.The low-level baroclinicity and mid-level cyclonic-vorticity advection increased substantially during the maximum-deepening-rate stage.The diagnostic analyses using the Zwack-Okossi equation showed that diabatic heating was the main contributor to the initial rapid intensification of this EC.The cyclonic-vorticity advection and warm-air advection enhanced rapidly in the middle and upper troposphere and contributed to the maximum rapid intensification,whereas the diabatic heating weakened slightly in the mid-low troposphere.The relative contribution of the diabatic heating decreased from the initial explosive-developing stage to the maximum-deepening-rate stage due to the enhancement of other factors(the cyclonic-vorticity advection and warm-air advection).Furthermore,the physical factors contributing to this EC varied with the explosive-developing stage.The non-key factors at the initial explosive-developing stage need attention to forecast the rapid intensification.展开更多
This study investigated the effects of upper-level descending inflow(ULDI)associated with inner-eyewall convection on the formation of the moat in tropical cyclones(TCs)with secondary eyewall formation(SEF).In our num...This study investigated the effects of upper-level descending inflow(ULDI)associated with inner-eyewall convection on the formation of the moat in tropical cyclones(TCs)with secondary eyewall formation(SEF).In our numerical experiments,a clear moat with SEF occurred in TCs with a significant ULDI,while no SEF occurred in TCs without a significant ULDI.The eyewall convection developed more vigorously in the control run.A ULDI occurred outside the inner-eyewall convection,where it was symmetrically unstable.The ULDI was initially triggered by the diabatic warming released by the inner eyewall and later enhanced by the cooling below the anvil cloud.The ULDI penetrated the outer edge of the inner eyewall with relatively dry air and prevented excessive solid-phase hydrometeors from being advected further outward.It produced extensive sublimation cooling of falling hydrometeors between the eyewall and the outer convection.The sublimation cooling resulted in negative buoyancy and further induced strong subsidence between the eyewall and the outer convection.As a result,a clear moat was generated.Development of the moat in the ongoing SEF prevented the outer rainband from moving farther inward,helping the outer rainband to symmetrize into an outer eyewall.In the sensitivity experiment,no significant ULDI formed since the eyewall convection was weaker,and the eyewall anvil developed relatively lower,meaning the formation of a moat and thus an outer eyewall was less likely.This study suggests that a better-represented simulation of inner-eyewall convective structures and distribution of the solid-phase hydrometeors is important to the prediction of SEF.展开更多
Based on the Regional Specialized Meteorological Center(RSMC)Tokyo-Typhoon Center best-track data and the NCEP-NCAR reanalysis dataset,extratropical transitioning(ET)tropical cyclones(ETCs)over the western North Pacif...Based on the Regional Specialized Meteorological Center(RSMC)Tokyo-Typhoon Center best-track data and the NCEP-NCAR reanalysis dataset,extratropical transitioning(ET)tropical cyclones(ETCs)over the western North Pacific(WNP)during 1951–2021 are classified into six clusters using the fuzzy c-means clustering method(FCM)according to their track patterns.The characteristics of the six hard-clustered ETCs with the highest membership coefficient are shown.Most tropical cyclones(TCs)that were assigned to clusters C2,C5,and C6 made landfall over eastern Asian countries,which severely threatened these regions.Among landfalling TCs,93.2%completed their ET after landfall,whereas 39.8%of ETCs completed their transition within one day.The frequency of ETCs over the WNP has decreased in the past four decades,wherein cluster C5 demonstrated a significant decrease on both interannual and interdecadal timescales with the expansion and intensification of the western Pacific subtropical high(WPSH).This large-scale circulation pattern is favorable for C2 and causes it to become the dominant track pattern,owning to it containing the largest number of intensifying ETCs among the six clusters,a number that has increased insignificantly over the past four decades.The surface roughness variation and three-dimensional background circulation led to C5 containing the maximum number of landfalling TCs and a minimum number of intensifying ETCs.Our results will facilitate a better understanding of the spatiotemporal distributions of ET events and associated environment background fields,which will benefit the effective monitoring of these events over the WNP.展开更多
Tropical cyclone(TC) genesis forecasting is essential for daily operational practices during the typhoon season.The updated version of the Tropical Regional Atmosphere Model for the South China Sea(CMA-TRAMS) offers f...Tropical cyclone(TC) genesis forecasting is essential for daily operational practices during the typhoon season.The updated version of the Tropical Regional Atmosphere Model for the South China Sea(CMA-TRAMS) offers forecasters reliable numerical weather prediction(NWP) products with improved configurations and fine resolution. While traditional evaluation of typhoon forecasts has focused on track and intensity, the increasing accuracy of TC genesis forecasts calls for more comprehensive evaluation methods to assess the reliability of these predictions. This study aims to evaluate the effectiveness of the CMA-TRAMS for cyclogenesis forecasts over the western North Pacific and South China Sea. Based on previous research and typhoon observation data over five years, a set of localized, objective criteria has been proposed. The analysis results indicate that the CMA-TRAMS demonstrated superiority in cyclogenesis forecasts, predicting 6 out of 22 TCs with a forecast lead time of up to 144 h. Additionally, over 80% of the total could be predicted 72 h in advance. The model also showed an average TC genesis position error of 218.3 km, comparable to the track errors of operational models according to the annual evaluation. The study also briefly investigated the forecast of Noul(2011). The forecast field of the CMA-TRAMS depicted thermal and dynamical conditions that could trigger typhoon genesis, consistent with the analysis field. The 96-hour forecast field of the CMA-TRAMS displayed a relatively organized threedimensional structure of the typhoon. These results can enhance understanding of the mechanism behind typhoon genesis,fine-tune model configurations and dynamical frameworks, and provide reliable forecasts for forecasters.展开更多
This study investigates the effect of the initial tropical cyclone(TC)vortex structure on the intensity change during the eyewall replacement cycle(ERC)of TCs based on two idealized simulations using the Weather Resea...This study investigates the effect of the initial tropical cyclone(TC)vortex structure on the intensity change during the eyewall replacement cycle(ERC)of TCs based on two idealized simulations using the Weather Research and Forecasting(WRF)model.Results show that an initially smaller TC with weaker outer winds experienced a much more drastic intensity change during the ERC than an initially larger TC with stronger outer winds.It is found that an initially larger TC vortex with stronger outer winds favored the development of more active spiral rainbands outside the outer eyewall,which slowed down the contraction and intensification of the outer eyewall and thus prolonged the duration of the concentric eyewall and slow intensity evolution.In contrast,the initially smaller TC with weaker outer winds corresponded to higher inertial stability in the inner core and weaker inertial stability but stronger filamentation outside the outer eyewall.These led to stronger boundary layer inflow,stronger updraft and convection in the outer eyewall,and suppressed convective activity outside the outer eyewall.These resulted in the rapid weakening during the formation of the outer eyewall,followed by a rapid re-intensification of the TC during the ERC.Our study demonstrates that accurate initialization of the TC structure in numerical models is crucial for predicting changes in TC intensity during the ERC.Additionally,monitoring the activity of spiral rainbands outside the outer eyewall can help to improve short-term intensity forecasts for TCs experiencing ERCs.展开更多
For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency...For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency. In this study, experimental and computational fluid dynamics simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop. Generally, the optimal cyclone height should be closely related to the natural vortex length. While, when the vortex end contracts into the separation space in the cyclone with an exceeded height, severe back-mixing of particles always occurs, which will result in the decrease of separation efficiency. Herein, it is found that when an apex cone is installed at the dust outlet, the vortex end can be grasped by the cone so as to weaken the back-mixing of particles.Meanwhile, the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency. In addition, it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.展开更多
In weather sciences,the two specific terms“storm”and“cyclone”frequently appear in literature and usually refer to the violent nature of a number of weather systems characterized by central low pressure,strong wind...In weather sciences,the two specific terms“storm”and“cyclone”frequently appear in literature and usually refer to the violent nature of a number of weather systems characterized by central low pressure,strong winds,large precipitation amounts in the form of rain,freezing rain,or snow,as well as thunder and lightning.But what is the connection between these two specific terms?In this paper,the historic evolutions of the terms“storm”and“cyclone”are reviewed from the perspective of weather science.The earliest recorded storms in world history are also briefly introduced.Then,the origin of the term“meteorological bomb”,which is the nickname of the“explosive cyclone”is introduced.Later,the various definitions of explosive cyclones given by several researchers are discussed.Also,the climatological features of explosive cyclones,as well as the future trends of explosive cyclones under global climate change,are discussed.展开更多
The authors document the interaction of the atmosphere and ocean during the formation and passage of an Extra-Tropical Cyclone, which is a Nor-Easter, winter storm that formed in the southern apex of the Middle Atlant...The authors document the interaction of the atmosphere and ocean during the formation and passage of an Extra-Tropical Cyclone, which is a Nor-Easter, winter storm that formed in the southern apex of the Middle Atlantic Bight near Cape Hatteras North Carolina, between February 15 and 18, 1996. While Nor-Easters per se, which have formed along the Atlantic Eastern Seaboard of the United States have been studied for decades, the actual atmospheric-oceanic mechanics and thermodynamics in the formation of a Nor-Easter has never been documented. We report on having done so with in-situ observations and data-based calculations and a numerical model. The in-situ observations were made via a Control Volume consisting of an array of Eulerian Oceanic-Atmospheric Moorings with current meters, temperature and salinity sensors and meteorological towers. We find that Gulf Stream waters were located surrounding the mooring array, and that with the invasion of cold dry atmospheric air, there was a rapid loss of heat from the ocean to the atmosphere via latent and sensible surface heat flux during the cyclogenesis onset of the storm. A unique feature of this storm was that neither satellite nor buoy data showed significant sea surface cooling in the control volume. The findings indicate that storm winds drove warm saline waters from the Gulf Stream across the continental shelf into the control volume, accounting for a 51 cm rise in water level along the coast. This lateral heat advection provided heat to the control volume of 3.4e+18 Joules. On average, the heat loss at the surface of the control volume, via sensible and latent heat fluxes and radiation, was 0.7e+18 Joules, corresponding to a surface heat flux of -600 Watts per Meter2 (W/m<sup>2</sup>). However, the heat lost by the control volume as latent and sensible heat fluxes was less than the heat it received via lateral heat advection, resulting in the lack of an often-observed sea surface cooling during other winter storms. The serendipitous and detailed observations and calculations reveal a climatological flywheel in this region, documenting the role of ETCs in the global heat balance.展开更多
This study compares the atmosphere-only HighResMIP simulations from FGOALS-f3-H(FGOALS)and MRIAGCM3-2-S(MRI)with respect to tropical cyclone(TC)characteristics over the Western North Pacific(WNP)for the July-October m...This study compares the atmosphere-only HighResMIP simulations from FGOALS-f3-H(FGOALS)and MRIAGCM3-2-S(MRI)with respect to tropical cyclone(TC)characteristics over the Western North Pacific(WNP)for the July-October months of 1985-2014.The focus is on investigating the role of the tropical easterly jet over the Western Pacific(WP_TEJ)in modulating the simulation biases in terms of their climatological distribution and interannual variability of WNP TC genesis frequency(TCGF)based on the analysis of the genesis potential index(GPI).Results show that the two models reasonably capture the main TC genesis location,the maximum center of frequency,and track density;however,their biases mainly lie in simulating the intense TCs and TCGF distributions.The MRI better simulates the windpressure relationship(WPR)but overestimates the proportion of super typhoons(SSTYs).At the same time,FGOALS underestimates the WPR and the proportion of SSTYs but better simulates the total WNP TC precipitation.In particular,FGOALS overestimates the TCGF in the northeastern WNP,which is strongly tied to an overestimated WP_TEJ and the enhanced vertical circulation to the north of its entrance region.In contrast,the MRI simulates a weaker WP_TEJ and vertical circulation,leading to a negative TCGF bias in most of the WNP.Both models exhibit comparable capability in simulating the interannual variability of WP_TEJ intensity,but the composite difference of large-scale atmospheric factors between strong and weak WP_TEJ years is overestimated,resulting in larger interannual anomalies of WNP TCGF,especially for FGOALS.Therefore,accurate simulations of the WP_TEJ and the associated oceanic and atmospheric factors are crucial to further improving WNP TC simulations for both models.展开更多
Tropical cyclone(TC)activities in the North Indian Ocean(NIO)peak in May during the pre-monsoon period,but the TC frequency shows obvious inter-annual variations.By conducting statistical analysis and dynamic diagnosi...Tropical cyclone(TC)activities in the North Indian Ocean(NIO)peak in May during the pre-monsoon period,but the TC frequency shows obvious inter-annual variations.By conducting statistical analysis and dynamic diagnosis of long-term data from 1948 to 2016,the relationship between the inter-annual variations of Indian Ocean SST and NIO TC genesis frequency in May is analyzed in this paper.Furthermore,the potential mechanism concerning the effect of SST anomaly on TC frequency is also investigated.The findings are as follows:1)there is a broadly consistent negative correlation between NIO TC frequency in May and SST in the Indian Ocean from March to May,with the key influencing area located in the southwestern Indian Ocean(SWIO);2)the anomalies of SST in SWIO(SWIO-SST)are closely related to a teleconnection pattern surrounding the Indian Ocean,which can significantly modulate the high-level divergence,mid-level vertical motion and other related environmental factors and ultimately influence the formation of TCs over the NIO;3)the increasing trend of SWIO-SST may play an essential role in the downward trend of NIO TC frequency over the past 69 years.展开更多
The flow regimes of GLCC with horizon inlet and a vertical pipe are investigated in experiments,and the velocities and pressure drops data labeled by the corresponding flow regimes are collected.Combined with the flow...The flow regimes of GLCC with horizon inlet and a vertical pipe are investigated in experiments,and the velocities and pressure drops data labeled by the corresponding flow regimes are collected.Combined with the flow regimes data of other GLCC positions from other literatures in existence,the gas and liquid superficial velocities and pressure drops are used as the input of the machine learning algorithms respectively which are applied to identify the flow regimes.The choosing of input data types takes the availability of data for practical industry fields into consideration,and the twelve machine learning algorithms are chosen from the classical and popular algorithms in the area of classification,including the typical ensemble models,SVM,KNN,Bayesian Model and MLP.The results of flow regimes identification show that gas and liquid superficial velocities are the ideal type of input data for the flow regimes identification by machine learning.Most of the ensemble models can identify the flow regimes of GLCC by gas and liquid velocities with the accuracy of 0.99 and more.For the pressure drops as the input of each algorithm,it is not the suitable as gas and liquid velocities,and only XGBoost and Bagging Tree can identify the GLCC flow regimes accurately.The success and confusion of each algorithm are analyzed and explained based on the experimental phenomena of flow regimes evolution processes,the flow regimes map,and the principles of algorithms.The applicability and feasibility of each algorithm according to different types of data for GLCC flow regimes identification are proposed.展开更多
Hong Kong is often affected by tropical cyclones.The Hong Kong observatory issues warning signals based on the impact of tropical cyclones on the region.The joint frequency analysis of tropical cyclones in Hong Kong c...Hong Kong is often affected by tropical cyclones.The Hong Kong observatory issues warning signals based on the impact of tropical cyclones on the region.The joint frequency analysis of tropical cyclones in Hong Kong can provide a scientific basis for disaster reduction and prevention and post-disaster reconstruction of tropical cyclones.First,the maximum hourly mean wind speed(W),warning signal duration(D),maximum sea level(L),and total rainfall(R)of each tropical cyclone that affected Hong Kong from 1985 to 2019 are selected and fitted using the Gumbel,Weibull,Pearson type 3,and lognormal distributions.Then,bivariate copula functions,such as the Clayton,Frank,Gumbel-Hougaard,and Gaussian copulas,are applied to construct the joint probability models of W,D,L,and R,respectively.The joint return periods of W and D and those of L and R are defined as the meteorological and hydrological intensities of tropical cyclones,respectively.The results show that the joint return periods are good indicators of the comprehensive effect of the meteorological and hydrological intensities of tropical cyclones.No necessary correlation between meteorological and hydrological intensities of tropical cyclones exists.The meteorological and hydrological intensities of tropical cyclones show an upward trend in recent years.展开更多
Coastal urban areas are prone to serious disasters caused by landfalling tropical cyclones(TCs). Despite the crucial role of urban forcing in precipitation, how fine-scale urban features impact landfalling TC precipit...Coastal urban areas are prone to serious disasters caused by landfalling tropical cyclones(TCs). Despite the crucial role of urban forcing in precipitation, how fine-scale urban features impact landfalling TC precipitation remains poorly understood. In this study, high-resolution ensemble simulations of Typhoon Rumbia(2018), which crossed the Yangtze River Delta urban agglomeration, were conducted to analyze the potential urban impact on TC precipitation. Results show that the inner-core rainfall of Rumbia is strengthened by approximately 10% due to the urban impact near the landfall,whereas minor differences in outer-core rainfall are found when the urban impact is excluded. Further diagnostic analyses indicate that low-level upward motion is crucial for precipitation evolution, as both co-vary during landfall. Moreover, the frictionally induced upward motion plays a decisive role in enhancing the rainfall when the urban impacts are included.Urban surface friction can decelerate the tangential wind and therefore destroy the gradient balance and strengthen the radial wind within the boundary layer and thus can enhance upward motion. This study demonstrates that urban surface friction and related physical processes make the most significant contribution to landfalling TC rainfall enhancement.展开更多
The main hazard-causing factors of tropical cyclones are strong wind,heavy rainfall,and storm surge.Evaluation of the hazard-causing degree of a tropical cyclone requires a joint intensity analysis of these hazard-cau...The main hazard-causing factors of tropical cyclones are strong wind,heavy rainfall,and storm surge.Evaluation of the hazard-causing degree of a tropical cyclone requires a joint intensity analysis of these hazard-causing factors.According to the maximum hourly mean wind speed,total rainfall,and maximum tide level at various observation stations in Hong Kong during these tropical cyclones,three hazard-causing indices for tropical cyclones are introduced:the strong-wind index(VI),total-rainfall index(RI),and tide-level index(LI).Through a joint probability analysis of VI,RI,and LI for a tropical cyclone affecting Hong Kong,the joint return period is calculated to evaluate its joint hazard-causing intensity.A limit state function of Hong Kong’s resistance to tropical cyclones is developed and used to evaluate the regional risk of tropical cyclones affecting Hong Kong.The results indicate that the joint return period of VI,RI,and LI can reflect the joint hazard-causing intensity of strong wind,heavy rain,and storm surge caused by tropical cyclones;if the overall design return periods of the regional structures decrease,the regional ability to defend against tropical cyclone disasters is degraded.展开更多
In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examine...In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method.Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward,resulting in the lowestθ_(e)in the downshear-left boundary layer.Quantitative estimations ofθ_(e)recovery indicate that air parcels,especially those originating from the downshear-left outer core,can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically.As a result,the maximumθ_(e)is observed in the downshear-right quadrant of a highly sheared TC.The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement ofθ_(e)in the downshear-left outer core.In particular,the former plays a leading role in suchθ_(e)enhancements,while the latter plays a secondary role.As a result,moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.展开更多
The accurate forecasting of tropical cyclones(TCs)is a challenging task.The purpose of this study was to investigate the effects of a dry-mass conserving(DMC)hydrostatic global spectral dynamical core on TC simulation...The accurate forecasting of tropical cyclones(TCs)is a challenging task.The purpose of this study was to investigate the effects of a dry-mass conserving(DMC)hydrostatic global spectral dynamical core on TC simulation.Experiments were conducted with DMC and total(moist)mass conserving(TMC)dynamical cores.The TC forecast performance was first evaluated considering 20 TCs in the West Pacific region observed during the 2020 typhoon season.The impacts of the DMC dynamical core on forecasts of individual TCs were then estimated.The DMC dynamical core improved both the track and intensity forecasts,and the TC intensity forecast improvement was much greater than the TC track forecast improvement.Sensitivity simulations indicated that the DMC dynamical core-simulated TC intensity was stronger regardless of the forecast lead time.In the DMC dynamical core experiments,three-dimensional winds and warm and moist cores were consistently enhanced with the TC intensity.Drier air in the boundary inflow layer was found in the DMC dynamical core experiments at the early simulation times.Water vapor mixing ratio budget analysis indicated that this mainly depended on the simulated vertical velocity.Higher updraft above the boundary layer yielded a drier boundary layer,resulting in surface latent heat flux(SLHF)enhancement,the major energy source of TC intensification.The higher DMC dynamical core-simulated updraft in the inner core caused a higher net surface rain rate,producing higher net internal atmospheric diabatic heating and increasing the TC intensity.These results indicate that the stronger DMC dynamical coresimulated TCs are mainly related to the higher DMC vertical velocity.展开更多
文摘This paper investigates the homogeneity of United States aircraft reconnaissance data and the impact of these data on the homogeneity of the tropical cyclone(TC)best track data for the seasons 1949-1987 generated by the China Meteorological Administration(CMA).The evaluation of the reconnaissance data shows that the minimum central sea level pressure(MCP)data are relatively homogeneous,whereas the maximum sustained wind(MSW)data show both overestimations and spurious abrupt changes.Statistical comparisons suggest that both the reconnaissance MCP and MSW were well incorporated into the CMA TC best track dataset.Although no spurious abrupt changes were evident in the reconnaissance-related best track MCP data,two spurious changepoints were identified in the remainder of the best-track MCP data.Furthermore,the influence of the reconnaissance MSWs seems to extend to the best track MSWs unrelated to reconnaissance,which might reflect the optimistic confidence in making higher estimates due to the overestimated extreme wind“observations”.In addition,the overestimation of either the reconnaissance MSWs or the best track MSWs was greater during the early decades compared to later decades,which reflects the important influence of reconnaissance data on the CMA TC best track dataset.The wind-pressure relationship(WPR)used in the CMA TC best track dataset is also evaluated and is found to overestimate the MSW,which may lead to inhomogeneity within the dataset between the aircraft reconnaissance era and the satellite era.
基金supported by the National Natural Science Foundation of China(Grant No.42288101)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(2019QZKK010201-02)+4 种基金GuangDong Basic and Applied Basic Research Foundation(2022A1515010945)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDA20060503)National Natural Science Foundation of China(Grant Nos.92158204,42176026,42005035,41906181)Lei YANG is also supported by Science and Technology Program of Guangdong Province(2022B1212050003)Special fund of South China Sea Institute of Oceanology of the Chinese Academy of Sciences(SCSIO2023QY01).
文摘This study investigates the activity of tropical cyclones(TCs)in the Bay of Bengal(BOB)from 1979 to 2018 to discover the mechanism affecting the contribution rate to the meridional moisture budget anomaly(MMBA)over the southern boundary of the Tibetan Plateau(SBTP).May and October–December are the bimodal phases of BOB TC frequency,which decreases month by month from October to December and is relatively low in May.However,the contribution rate to the MMBA is the highest in May.The seasonal variation in the meridional position of the westerlies is the key factor affecting the contribution rate.The relatively southern(northern)position of the westerlies in November and December(May)results in a lower(higher)contribution rate to the MMBA.This mechanism is confirmed by the momentum equation.When water vapor enters the westerlies near the trough line,the resultant meridional acceleration is directed north.It follows that the farther north the trough is,and the farther north the water vapor can be transported.When water vapor enters the westerlies from the area near the ridge line,for Type-T(Type-R)TCs,water vapor enters the westerlies downstream of the trough(ridge).Consequently,the direction of the resultant meridional acceleration is directed south and the resultant zonal acceleration is directed east(west),which is not conducive to the northward transport of water vapor.This is especially the case if the trough or ridge is relatively south,as the water vapor may not cross the SBTP.
基金supported by the Guangdong Provincial Key Research and Development Program(Grant No.2022B0101100001).
文摘The present study aims to examine the suitability of two commonly used assumptions that simplify modelling metoceanconditions for designing offshore wind turbines in the South China Sea (SCS). The first assumption assumes thatjoint N-year extreme wind and wave events can be independently estimated and subsequently combined. The secondone assumes peak wind and waves can be modelled as occurring simultaneously during a tropical cyclone (TC) event.To better understand the potential TC activity, a set of 10000 years synthetic TC events are generated. The wind fieldmodel and the Mike 21 spectral wave model are employed to model the TC-induced hazards. Subsequently, theeffect of the assumptions is evaluated by analyzing the peak structural response of both monopile and semisubmersibleoffshore wind turbines during TC events. The results demonstrate that the examined assumptions are generally accurate.By assessing the implications of these assumptions, valuable insights are obtained, which can inform andimprove the modelling of TC-induced hazards in the SCS region.
基金National Natural Science Foundation of China(Grant Nos:42150710531,42192551,61827901)supported this study.
文摘Recent studies on tropical cyclone(TC)intensity change indicate that the development of a vertically aligned TC circulation is a key feature of its rapid intensification(RI),however,understanding how vortex alignment occurs remains a challenging topic in TC intensity change research.Based on the simulation outputs of North Atlantic Hurricane Wilma(2005)and western North Pacific Typhoon Rammasun(2014),vortex track oscillations at different vertical levels and their associated role in vortex alignment are examined to improve our understanding of the vortex alignment during RI of TCs with initial hurricane intensity.It is found that vortex tracks at different vertical levels oscillate consistently in speed and direction during the RI of the two simulated TCs.While the consistent track oscillation reduces the oscillation tilt during RI,the reduction of vortex tilt results mainly from the mean track before RI.It is also found that the vortex tilt is primarily due to the mean vortex track before and after RI.The track oscillations are closely associated with wavenumber-1 vortex Rossby waves that are dominant wavenumber-1 circulations in the TC inner-core region.This study suggests that the dynamics of the wavenumber-1 vortex Rossby waves play an important role in the regulation of the physical processes associated with the track oscillation and vertical alignment of TCs.
基金jointly funded by the State Key Program of the National Natural Science Foundation of China(No.42130605)the Major Program of the National Natural Science Foundation of China(No.72293604)+5 种基金the Youth Innovative Talents Program of Guangdong Colleges and Universities(No.2022KQNCX026)the Natural Science Foundation of Shandong(No.ZR2022MD038)the Project of Enhancing School with Innovation of Guangdong Ocean University(No.230419106)the State Key Program of the National Natural Science Foundation of China(No.42130605)the National Natural Science Foundation of China(Nos.42275001,42276019,42205014,and 42275017)the Guangdong Ocean University Ph.D.Scientific Research Program(No.R19045).
文摘Explosive cyclones(ECs)occur frequently over the Kuroshio/Kuroshio Extension region.The most rapidly intensified EC over the Kuroshio/Kuroshio Extension region during the 42 years(1979-2020)of cold seasons(October-April)was studied to reveal the variations of the key factors at different explosive-developing stages.This EC had weak low-level baroclinicity,mid-level cyclonic-vorticity advection,and strong low-level water vapor convergence at the initial explosive-developing stage.The low-level baroclinicity and mid-level cyclonic-vorticity advection increased substantially during the maximum-deepening-rate stage.The diagnostic analyses using the Zwack-Okossi equation showed that diabatic heating was the main contributor to the initial rapid intensification of this EC.The cyclonic-vorticity advection and warm-air advection enhanced rapidly in the middle and upper troposphere and contributed to the maximum rapid intensification,whereas the diabatic heating weakened slightly in the mid-low troposphere.The relative contribution of the diabatic heating decreased from the initial explosive-developing stage to the maximum-deepening-rate stage due to the enhancement of other factors(the cyclonic-vorticity advection and warm-air advection).Furthermore,the physical factors contributing to this EC varied with the explosive-developing stage.The non-key factors at the initial explosive-developing stage need attention to forecast the rapid intensification.
基金supported by the National Natural Science Foundation of China(Grant Nos.42192552,42192551,42150710531,42175016,and 42075072)the Shanghai Typhoon Research Fund(Grant No.TFJJ202207)the Basic Research Fund of CAMS(Grant No.2023Y010)。
文摘This study investigated the effects of upper-level descending inflow(ULDI)associated with inner-eyewall convection on the formation of the moat in tropical cyclones(TCs)with secondary eyewall formation(SEF).In our numerical experiments,a clear moat with SEF occurred in TCs with a significant ULDI,while no SEF occurred in TCs without a significant ULDI.The eyewall convection developed more vigorously in the control run.A ULDI occurred outside the inner-eyewall convection,where it was symmetrically unstable.The ULDI was initially triggered by the diabatic warming released by the inner eyewall and later enhanced by the cooling below the anvil cloud.The ULDI penetrated the outer edge of the inner eyewall with relatively dry air and prevented excessive solid-phase hydrometeors from being advected further outward.It produced extensive sublimation cooling of falling hydrometeors between the eyewall and the outer convection.The sublimation cooling resulted in negative buoyancy and further induced strong subsidence between the eyewall and the outer convection.As a result,a clear moat was generated.Development of the moat in the ongoing SEF prevented the outer rainband from moving farther inward,helping the outer rainband to symmetrize into an outer eyewall.In the sensitivity experiment,no significant ULDI formed since the eyewall convection was weaker,and the eyewall anvil developed relatively lower,meaning the formation of a moat and thus an outer eyewall was less likely.This study suggests that a better-represented simulation of inner-eyewall convective structures and distribution of the solid-phase hydrometeors is important to the prediction of SEF.
基金supported by the National Natural Science Foundation of China(Grant Nos.42075053 and 41975128)。
文摘Based on the Regional Specialized Meteorological Center(RSMC)Tokyo-Typhoon Center best-track data and the NCEP-NCAR reanalysis dataset,extratropical transitioning(ET)tropical cyclones(ETCs)over the western North Pacific(WNP)during 1951–2021 are classified into six clusters using the fuzzy c-means clustering method(FCM)according to their track patterns.The characteristics of the six hard-clustered ETCs with the highest membership coefficient are shown.Most tropical cyclones(TCs)that were assigned to clusters C2,C5,and C6 made landfall over eastern Asian countries,which severely threatened these regions.Among landfalling TCs,93.2%completed their ET after landfall,whereas 39.8%of ETCs completed their transition within one day.The frequency of ETCs over the WNP has decreased in the past four decades,wherein cluster C5 demonstrated a significant decrease on both interannual and interdecadal timescales with the expansion and intensification of the western Pacific subtropical high(WPSH).This large-scale circulation pattern is favorable for C2 and causes it to become the dominant track pattern,owning to it containing the largest number of intensifying ETCs among the six clusters,a number that has increased insignificantly over the past four decades.The surface roughness variation and three-dimensional background circulation led to C5 containing the maximum number of landfalling TCs and a minimum number of intensifying ETCs.Our results will facilitate a better understanding of the spatiotemporal distributions of ET events and associated environment background fields,which will benefit the effective monitoring of these events over the WNP.
基金Science and Technology Innovation Project of Guangdong Provincial Water Resources Department (2022-01)Science and Technology Program of Guangdong Province(2022A1515011870)+1 种基金China Meteorological Administration Key Innovation Team of Tropical Meteorology (CMA2023ZD08)Open Research Program of the State Key Laboratory of Severe Weather (2022LASW-B18)。
文摘Tropical cyclone(TC) genesis forecasting is essential for daily operational practices during the typhoon season.The updated version of the Tropical Regional Atmosphere Model for the South China Sea(CMA-TRAMS) offers forecasters reliable numerical weather prediction(NWP) products with improved configurations and fine resolution. While traditional evaluation of typhoon forecasts has focused on track and intensity, the increasing accuracy of TC genesis forecasts calls for more comprehensive evaluation methods to assess the reliability of these predictions. This study aims to evaluate the effectiveness of the CMA-TRAMS for cyclogenesis forecasts over the western North Pacific and South China Sea. Based on previous research and typhoon observation data over five years, a set of localized, objective criteria has been proposed. The analysis results indicate that the CMA-TRAMS demonstrated superiority in cyclogenesis forecasts, predicting 6 out of 22 TCs with a forecast lead time of up to 144 h. Additionally, over 80% of the total could be predicted 72 h in advance. The model also showed an average TC genesis position error of 218.3 km, comparable to the track errors of operational models according to the annual evaluation. The study also briefly investigated the forecast of Noul(2011). The forecast field of the CMA-TRAMS depicted thermal and dynamical conditions that could trigger typhoon genesis, consistent with the analysis field. The 96-hour forecast field of the CMA-TRAMS displayed a relatively organized threedimensional structure of the typhoon. These results can enhance understanding of the mechanism behind typhoon genesis,fine-tune model configurations and dynamical frameworks, and provide reliable forecasts for forecasters.
基金National Key R&D Program of China (2022YFC3004200)National Natural Science Foundation of China (42305007,41730960,41875057)National Science Foundation (AGS-1834300)。
文摘This study investigates the effect of the initial tropical cyclone(TC)vortex structure on the intensity change during the eyewall replacement cycle(ERC)of TCs based on two idealized simulations using the Weather Research and Forecasting(WRF)model.Results show that an initially smaller TC with weaker outer winds experienced a much more drastic intensity change during the ERC than an initially larger TC with stronger outer winds.It is found that an initially larger TC vortex with stronger outer winds favored the development of more active spiral rainbands outside the outer eyewall,which slowed down the contraction and intensification of the outer eyewall and thus prolonged the duration of the concentric eyewall and slow intensity evolution.In contrast,the initially smaller TC with weaker outer winds corresponded to higher inertial stability in the inner core and weaker inertial stability but stronger filamentation outside the outer eyewall.These led to stronger boundary layer inflow,stronger updraft and convection in the outer eyewall,and suppressed convective activity outside the outer eyewall.These resulted in the rapid weakening during the formation of the outer eyewall,followed by a rapid re-intensification of the TC during the ERC.Our study demonstrates that accurate initialization of the TC structure in numerical models is crucial for predicting changes in TC intensity during the ERC.Additionally,monitoring the activity of spiral rainbands outside the outer eyewall can help to improve short-term intensity forecasts for TCs experiencing ERCs.
基金sponsored by the National Natural Science Foundation of China (21506139 and U1710101)。
文摘For a cyclone, it is possible to improve separation efficiency and reduce pressure drop by increasing the cyclone height. However, an exceeded height increase could result in a dramatical drop in separation efficiency. In this study, experimental and computational fluid dynamics simulation results exhibit that the introduction of an apex cone at the dust outlet could avoid the risk of separation efficiency drop but lead to a continuous reducing of the pressure drop. Generally, the optimal cyclone height should be closely related to the natural vortex length. While, when the vortex end contracts into the separation space in the cyclone with an exceeded height, severe back-mixing of particles always occurs, which will result in the decrease of separation efficiency. Herein, it is found that when an apex cone is installed at the dust outlet, the vortex end can be grasped by the cone so as to weaken the back-mixing of particles.Meanwhile, the introduction of this apex cone can enhance the secondary separation to capture the back-mixed particles again so as to protect the efficiency. In addition, it is found that the enhanced secondary separation could come from either the stagnant current of axial velocity in the center or the improved tangential velocity of inner vortex whereas the forcibly extending the length of vortex to exceed its natural length will not significantly increase efficiency.
基金supports of National Key R&D Program of China(2022YFC3004200)National Natural Science Foundation of China(Grant Nos.42275001 and 41775042)to this study.
文摘In weather sciences,the two specific terms“storm”and“cyclone”frequently appear in literature and usually refer to the violent nature of a number of weather systems characterized by central low pressure,strong winds,large precipitation amounts in the form of rain,freezing rain,or snow,as well as thunder and lightning.But what is the connection between these two specific terms?In this paper,the historic evolutions of the terms“storm”and“cyclone”are reviewed from the perspective of weather science.The earliest recorded storms in world history are also briefly introduced.Then,the origin of the term“meteorological bomb”,which is the nickname of the“explosive cyclone”is introduced.Later,the various definitions of explosive cyclones given by several researchers are discussed.Also,the climatological features of explosive cyclones,as well as the future trends of explosive cyclones under global climate change,are discussed.
文摘The authors document the interaction of the atmosphere and ocean during the formation and passage of an Extra-Tropical Cyclone, which is a Nor-Easter, winter storm that formed in the southern apex of the Middle Atlantic Bight near Cape Hatteras North Carolina, between February 15 and 18, 1996. While Nor-Easters per se, which have formed along the Atlantic Eastern Seaboard of the United States have been studied for decades, the actual atmospheric-oceanic mechanics and thermodynamics in the formation of a Nor-Easter has never been documented. We report on having done so with in-situ observations and data-based calculations and a numerical model. The in-situ observations were made via a Control Volume consisting of an array of Eulerian Oceanic-Atmospheric Moorings with current meters, temperature and salinity sensors and meteorological towers. We find that Gulf Stream waters were located surrounding the mooring array, and that with the invasion of cold dry atmospheric air, there was a rapid loss of heat from the ocean to the atmosphere via latent and sensible surface heat flux during the cyclogenesis onset of the storm. A unique feature of this storm was that neither satellite nor buoy data showed significant sea surface cooling in the control volume. The findings indicate that storm winds drove warm saline waters from the Gulf Stream across the continental shelf into the control volume, accounting for a 51 cm rise in water level along the coast. This lateral heat advection provided heat to the control volume of 3.4e+18 Joules. On average, the heat loss at the surface of the control volume, via sensible and latent heat fluxes and radiation, was 0.7e+18 Joules, corresponding to a surface heat flux of -600 Watts per Meter2 (W/m<sup>2</sup>). However, the heat lost by the control volume as latent and sensible heat fluxes was less than the heat it received via lateral heat advection, resulting in the lack of an often-observed sea surface cooling during other winter storms. The serendipitous and detailed observations and calculations reveal a climatological flywheel in this region, documenting the role of ETCs in the global heat balance.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA19060102)Shanghai 2021“Scientific and technological innovation action plan”Natural Science Foundation(Grant No.21ZR1420400)+2 种基金National Natural Science Foundation of China(Grant No.91958201)International Partnership Program of Chinese Academy of Sciences Grant 183311KYSB20200015the National Natural Science Foundation for Young Scientist of China(Grant No.41605079)。
文摘This study compares the atmosphere-only HighResMIP simulations from FGOALS-f3-H(FGOALS)and MRIAGCM3-2-S(MRI)with respect to tropical cyclone(TC)characteristics over the Western North Pacific(WNP)for the July-October months of 1985-2014.The focus is on investigating the role of the tropical easterly jet over the Western Pacific(WP_TEJ)in modulating the simulation biases in terms of their climatological distribution and interannual variability of WNP TC genesis frequency(TCGF)based on the analysis of the genesis potential index(GPI).Results show that the two models reasonably capture the main TC genesis location,the maximum center of frequency,and track density;however,their biases mainly lie in simulating the intense TCs and TCGF distributions.The MRI better simulates the windpressure relationship(WPR)but overestimates the proportion of super typhoons(SSTYs).At the same time,FGOALS underestimates the WPR and the proportion of SSTYs but better simulates the total WNP TC precipitation.In particular,FGOALS overestimates the TCGF in the northeastern WNP,which is strongly tied to an overestimated WP_TEJ and the enhanced vertical circulation to the north of its entrance region.In contrast,the MRI simulates a weaker WP_TEJ and vertical circulation,leading to a negative TCGF bias in most of the WNP.Both models exhibit comparable capability in simulating the interannual variability of WP_TEJ intensity,but the composite difference of large-scale atmospheric factors between strong and weak WP_TEJ years is overestimated,resulting in larger interannual anomalies of WNP TCGF,especially for FGOALS.Therefore,accurate simulations of the WP_TEJ and the associated oceanic and atmospheric factors are crucial to further improving WNP TC simulations for both models.
基金National Natural Science Foundation of China(41965005,41790471,42075013)Key R&D Plan of Yunnan Province Science and Technology Department(202203AC100006)National Natural Science Foundation of Yunnan Province(202201AS070069)。
文摘Tropical cyclone(TC)activities in the North Indian Ocean(NIO)peak in May during the pre-monsoon period,but the TC frequency shows obvious inter-annual variations.By conducting statistical analysis and dynamic diagnosis of long-term data from 1948 to 2016,the relationship between the inter-annual variations of Indian Ocean SST and NIO TC genesis frequency in May is analyzed in this paper.Furthermore,the potential mechanism concerning the effect of SST anomaly on TC frequency is also investigated.The findings are as follows:1)there is a broadly consistent negative correlation between NIO TC frequency in May and SST in the Indian Ocean from March to May,with the key influencing area located in the southwestern Indian Ocean(SWIO);2)the anomalies of SST in SWIO(SWIO-SST)are closely related to a teleconnection pattern surrounding the Indian Ocean,which can significantly modulate the high-level divergence,mid-level vertical motion and other related environmental factors and ultimately influence the formation of TCs over the NIO;3)the increasing trend of SWIO-SST may play an essential role in the downward trend of NIO TC frequency over the past 69 years.
文摘The flow regimes of GLCC with horizon inlet and a vertical pipe are investigated in experiments,and the velocities and pressure drops data labeled by the corresponding flow regimes are collected.Combined with the flow regimes data of other GLCC positions from other literatures in existence,the gas and liquid superficial velocities and pressure drops are used as the input of the machine learning algorithms respectively which are applied to identify the flow regimes.The choosing of input data types takes the availability of data for practical industry fields into consideration,and the twelve machine learning algorithms are chosen from the classical and popular algorithms in the area of classification,including the typical ensemble models,SVM,KNN,Bayesian Model and MLP.The results of flow regimes identification show that gas and liquid superficial velocities are the ideal type of input data for the flow regimes identification by machine learning.Most of the ensemble models can identify the flow regimes of GLCC by gas and liquid velocities with the accuracy of 0.99 and more.For the pressure drops as the input of each algorithm,it is not the suitable as gas and liquid velocities,and only XGBoost and Bagging Tree can identify the GLCC flow regimes accurately.The success and confusion of each algorithm are analyzed and explained based on the experimental phenomena of flow regimes evolution processes,the flow regimes map,and the principles of algorithms.The applicability and feasibility of each algorithm according to different types of data for GLCC flow regimes identification are proposed.
基金The study was supported by the National Natural Science Foundation of China-Shandong Joint Fund(No.U1706226)the National Natural Science Foundation of China(No.52171284).
文摘Hong Kong is often affected by tropical cyclones.The Hong Kong observatory issues warning signals based on the impact of tropical cyclones on the region.The joint frequency analysis of tropical cyclones in Hong Kong can provide a scientific basis for disaster reduction and prevention and post-disaster reconstruction of tropical cyclones.First,the maximum hourly mean wind speed(W),warning signal duration(D),maximum sea level(L),and total rainfall(R)of each tropical cyclone that affected Hong Kong from 1985 to 2019 are selected and fitted using the Gumbel,Weibull,Pearson type 3,and lognormal distributions.Then,bivariate copula functions,such as the Clayton,Frank,Gumbel-Hougaard,and Gaussian copulas,are applied to construct the joint probability models of W,D,L,and R,respectively.The joint return periods of W and D and those of L and R are defined as the meteorological and hydrological intensities of tropical cyclones,respectively.The results show that the joint return periods are good indicators of the comprehensive effect of the meteorological and hydrological intensities of tropical cyclones.No necessary correlation between meteorological and hydrological intensities of tropical cyclones exists.The meteorological and hydrological intensities of tropical cyclones show an upward trend in recent years.
基金supported by the National Science Foundation of China (Grant Nos. 42088101 and 42175005)by the Postgraduate Research and Practice Innovation Program of Jiangsu Province (KYCX22_1137)。
文摘Coastal urban areas are prone to serious disasters caused by landfalling tropical cyclones(TCs). Despite the crucial role of urban forcing in precipitation, how fine-scale urban features impact landfalling TC precipitation remains poorly understood. In this study, high-resolution ensemble simulations of Typhoon Rumbia(2018), which crossed the Yangtze River Delta urban agglomeration, were conducted to analyze the potential urban impact on TC precipitation. Results show that the inner-core rainfall of Rumbia is strengthened by approximately 10% due to the urban impact near the landfall,whereas minor differences in outer-core rainfall are found when the urban impact is excluded. Further diagnostic analyses indicate that low-level upward motion is crucial for precipitation evolution, as both co-vary during landfall. Moreover, the frictionally induced upward motion plays a decisive role in enhancing the rainfall when the urban impacts are included.Urban surface friction can decelerate the tangential wind and therefore destroy the gradient balance and strengthen the radial wind within the boundary layer and thus can enhance upward motion. This study demonstrates that urban surface friction and related physical processes make the most significant contribution to landfalling TC rainfall enhancement.
基金The National Natural Science Foundation of China—Shandong Joint Fund under contract No.U1706226the National Natural Science Foundation of China under contract No.52171284。
文摘The main hazard-causing factors of tropical cyclones are strong wind,heavy rainfall,and storm surge.Evaluation of the hazard-causing degree of a tropical cyclone requires a joint intensity analysis of these hazard-causing factors.According to the maximum hourly mean wind speed,total rainfall,and maximum tide level at various observation stations in Hong Kong during these tropical cyclones,three hazard-causing indices for tropical cyclones are introduced:the strong-wind index(VI),total-rainfall index(RI),and tide-level index(LI).Through a joint probability analysis of VI,RI,and LI for a tropical cyclone affecting Hong Kong,the joint return period is calculated to evaluate its joint hazard-causing intensity.A limit state function of Hong Kong’s resistance to tropical cyclones is developed and used to evaluate the regional risk of tropical cyclones affecting Hong Kong.The results indicate that the joint return period of VI,RI,and LI can reflect the joint hazard-causing intensity of strong wind,heavy rain,and storm surge caused by tropical cyclones;if the overall design return periods of the regional structures decrease,the regional ability to defend against tropical cyclone disasters is degraded.
基金jointly supported by the National Key Research and Development Program of China under Grant No. 2017YFC1501601the National Natural Science Foundation of China under Grant Nos. 42175005 and 41875054
文摘In this study,the characteristics of azimuthally asymmetric equivalent potential temperature(θ_(e))distributions in the outer core of tropical cyclones(TCs)encountering weak and strong vertical wind shear are examined using a Lagrangian trajectory method.Evaporatively forced downdrafts in the outer rainbands can transport low-entropy air downward,resulting in the lowestθ_(e)in the downshear-left boundary layer.Quantitative estimations ofθ_(e)recovery indicate that air parcels,especially those originating from the downshear-left outer core,can gradually revive from a low entropy state through surface enthalpy fluxes as the parcels move cyclonically.As a result,the maximumθ_(e)is observed in the downshear-right quadrant of a highly sheared TC.The trajectory analyses also indicate that parcels that move upward in the outer rainbands and those that travel through the inner core due to shear make a dominant contribution to the midlevel enhancement ofθ_(e)in the downshear-left outer core.In particular,the former plays a leading role in suchθ_(e)enhancements,while the latter plays a secondary role.As a result,moist potential stability occurs in the middle-to-lower troposphere in the downshear-left outer core.
基金jointly supported by the National Key Research and Development Program of China (2021YFC3101500)the National Natural Science Foundation of China (Grant Nos. 41830964, 42275062)
文摘The accurate forecasting of tropical cyclones(TCs)is a challenging task.The purpose of this study was to investigate the effects of a dry-mass conserving(DMC)hydrostatic global spectral dynamical core on TC simulation.Experiments were conducted with DMC and total(moist)mass conserving(TMC)dynamical cores.The TC forecast performance was first evaluated considering 20 TCs in the West Pacific region observed during the 2020 typhoon season.The impacts of the DMC dynamical core on forecasts of individual TCs were then estimated.The DMC dynamical core improved both the track and intensity forecasts,and the TC intensity forecast improvement was much greater than the TC track forecast improvement.Sensitivity simulations indicated that the DMC dynamical core-simulated TC intensity was stronger regardless of the forecast lead time.In the DMC dynamical core experiments,three-dimensional winds and warm and moist cores were consistently enhanced with the TC intensity.Drier air in the boundary inflow layer was found in the DMC dynamical core experiments at the early simulation times.Water vapor mixing ratio budget analysis indicated that this mainly depended on the simulated vertical velocity.Higher updraft above the boundary layer yielded a drier boundary layer,resulting in surface latent heat flux(SLHF)enhancement,the major energy source of TC intensification.The higher DMC dynamical core-simulated updraft in the inner core caused a higher net surface rain rate,producing higher net internal atmospheric diabatic heating and increasing the TC intensity.These results indicate that the stronger DMC dynamical coresimulated TCs are mainly related to the higher DMC vertical velocity.