Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertic...Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertical wind shear(VWS),or both.Results show that rainwater is enhanced to the right of the motion in the outer rainband,but such enhancement occurs in the upshear-left area of the inner-core region.Additionally,due to the asymmetries introduced by environmental flow,wavenumber-1 temperature and height anomalies develop at a radius of~1000 km in the upper levels.A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears,and asymmetric horizontal winds emerge,which,in turn,changes the storm-scale(within 400 km)VWS.Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s^(-1) and is located downshear of the storm-scale VWS in all the experiments with environmental flow.In the outer rainbands,the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant.These results extend upon the findings of previous studies in three aspects:(1)The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS;(2)The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow,resulting in changes in the storm-scale VWS pattern within the TC area;(3)The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS.展开更多
The sensitivity of the simulation of tropical cyclone （TC） size to microphysics schemes is studied using the Advanced Hurricane Weather Research and Forecasting Model （WRF）. Six TCs during the 2013 western North P...The sensitivity of the simulation of tropical cyclone （TC） size to microphysics schemes is studied using the Advanced Hurricane Weather Research and Forecasting Model （WRF）. Six TCs during the 2013 western North Pacific typhoon season and three mainstream microphysics schemes-Ferrier （FER）, WRF Single-Moment 5-class （WSM5） and WRF Single-Moment 6-class （WSM6）-are investigated. The results consistently show that the simulated TC track is not sensitive to the choice of microphysics scheme in the early simulation, especially in the open ocean. However, the sensitivity is much greater for TC intensity and inner-core size. The TC intensity and size simulated using the WSM5 and WSM6 schemes are respectively higher and larger than those using the FER scheme in general, which likely results from more diabatic heating being generated outside the eyewall in rainbands. More diabatic heating in rainbands gives higher inflow in the lower troposphere and higher outflow in the upper troposphere, with higher upward motion outside the eyewall. The lower-tropospheric inflow would transport absolute angular momentum inward to spin up tangential wind predominantly near the eyewall, leading to the increment in TC intensity and size （the inner-core size, especially）. In addition, the inclusion of graupel microphysics processes （as in WSM6） may not have a significant impact on the simulation of TC track, intensity and size.展开更多
This short paper presents an investigation on how human activities may or may not affect precipitation based on numerical simulations of precipitation in a benchmark case with modified lower boundary conditions, repre...This short paper presents an investigation on how human activities may or may not affect precipitation based on numerical simulations of precipitation in a benchmark case with modified lower boundary conditions, representing different stages of urban development in the model. The results indicate that certain degrees of urbanization affect the likelihood of heavy precipitation significantly, while less urbanized or smaller cities are much less prone to these effects. Such a result can be explained based on our previous work where the sensitivity of precipitation statistics to surface anthropogenic heat sources lies in the generation of buoyancy and turbulence in the planetary boundary layer and dissipation through triggering of convection. Thus only mega cities of sufficient size, and hence human-activity-related anthropogenic heat emission, can expect to experience such effects. In other words, as cities grow, their effects upon precipitation appear to grow as well.展开更多
This study investigated the effects of landfall on the structure of a tropical cyclone （TC）. Numerical simulations were performed using the Weather Research and Forecasting Model on a β-plane. Two landfall experime...This study investigated the effects of landfall on the structure of a tropical cyclone （TC）. Numerical simulations were performed using the Weather Research and Forecasting Model on a β-plane. Two landfall experiments, one with an east–west and another with a north–south oriented coastline, were performed. Similar to previous studies on an f-plane, large-scale flows in the low-to-middle troposphere were modified due to friction. A pair of counter rotating gyres was found, which was shown to be consistent with the slight deffection of the TC relative to the control experiment without land. Compared to previous f-plane simulations, because of the inherent asymmetries due to the β-gyres, the large-scale pattern of flows and convergences/divergences related to friction were found to depend on coastline orientations. On the other hand, regardless of the coastline orientation, convergences were found to be stronger to the left for both cases near landfall, as in previous f-plane simulations. Such a convergence pattern subsequently induced a change in convection and rainfall at the eyewall.展开更多
Climatologically,among all ocean basins,the western North Pacific(WNP)has the largest annual number of tropical cyclones(TCs)of around 26 while the Atlantic has around 13,yielding a difference of 13.However,the differ...Climatologically,among all ocean basins,the western North Pacific(WNP)has the largest annual number of tropical cyclones(TCs)of around 26 while the Atlantic has around 13,yielding a difference of 13.However,the difference is-7 in 2020,with 30 TCs in the Atlantic and 23 in the WNP,which is the most negative difference within the last 46 years.In fact,during the last 26 years,the difference in TC number is below 10 in ten years,with four years being negative.Such a decreasing difference in TC number can be attributed to the natural multidecadal variation of the Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation,as well as other external forcings such as anthropogenic aerosol forcing and increased greenhouse gases,with the additional impact from the La Niña condition.This result has significant implications on climate model projections of future TC activity in the two ocean basins.展开更多
Numerical simulations are carried out for the disturbed flow caused by three six-story buildings and a twenty-story tall tower respectively, as well as the distribution of automobile exhaust gas from a nearby road, ba...Numerical simulations are carried out for the disturbed flow caused by three six-story buildings and a twenty-story tall tower respectively, as well as the distribution of automobile exhaust gas from a nearby road, based on the Peking University Model of Atmospheric Environment. The results show that the ventilation is better around the tall tower than around the three six-story residential buildings for the same number of households in the same urban region.展开更多
This study examines the long-term change in the threat of landfalling tropical cyclones(TCs) in East Asia over the period 1975–2020 with a focus on rapidly intensifying(RI) TCs. The increase in the annual number of R...This study examines the long-term change in the threat of landfalling tropical cyclones(TCs) in East Asia over the period 1975–2020 with a focus on rapidly intensifying(RI) TCs. The increase in the annual number of RI-TCs over the western North Pacific and the northwestward shift of their genesis location lead to an increasing trend in the annual number of landfalling RI-TCs along the coast of East Asia. The annual power dissipation index(PDI), a measure of the destructive potential of RI-TCs at landfall, also shows a significant increasing trend due to increases in the annual frequency and mean landfall intensity of landfalling RI-TCs. The increase in mean landfall intensity is related to a higher lifetime maximum intensity(LMI) and the LMI location of the landfalling RI-TCs being closer to the coast. The increase in the annual PDI of East Asia is mainly associated with landfalling TCs in the southern(the Philippines, South China, and Vietnam) and northern parts(Japan and the Korean Peninsula) of East Asia due to long-term changes in vertical wind shear and TC heat potential. The former leads to a northwestward shift of favorable environments for TC genesis and intensification, resulting in the northwestward shift in the genesis, RI, and LMI locations of RI-TCs. The latter provides more heat energy from the ocean for TC intensification, increasing its chances to undergo RI.展开更多
An atmosphere-only model system for making seasonal prediction and projecting future intensities of landfalling tropical cyclones(TCs)along the South China coast is upgraded by including ocean and wave models.A total ...An atmosphere-only model system for making seasonal prediction and projecting future intensities of landfalling tropical cyclones(TCs)along the South China coast is upgraded by including ocean and wave models.A total of 642 TCs have been re-simulated using the new system to produce a climatology of TC intensity in the South China Sea.Detailed comparisons of the simulations from the atmosphere-only and the fully coupled systems reveal that the inclusion of the additional ocean and wave models enable differential sea surface temperature responses to various TC characteristics such as translational speed and size.In particular,interaction with the ocean does not necessarily imply a weakening of the TC,with the coastal bathymetry possibly playing a role in causing a near-shore intensification of the TC.These results suggest that to simulate the evolution of TC structure more accurately,it is essential to use an air-sea coupled model instead of an atmosphere-only model.展开更多
Using the best-track dataset from the Shanghai Typhoon Institute/China Meteorological Administration,the paper presents a detailed summary and analysis of tropical cyclone(TC)activities in the Western North Pacific(WN...Using the best-track dataset from the Shanghai Typhoon Institute/China Meteorological Administration,the paper presents a detailed summary and analysis of tropical cyclone(TC)activities in the Western North Pacific(WNP)and the South China Sea(SCS)during 2023.Based on historical records from 1951 to 2020 as the climatology benchmark,we examine anomalies in TC frequency,origin locations,tracks,intensity,and duration,as well as landfall events across the Asia-Pacific region.TC frequency in 2023 is found to be lower than climatology,with a marked decrease during the autumn months.Origin locations of TCs,which mark the starting points of their paths,are generally consistent with climatology,although there is a noticeable northwestward shift in the origins of the intense TCs.Track density of named TCs is anomalously high within the 0-20°N and 110°E to 125°E longitude box,and offshore areas covering northwestern to southern Japan and around the Korean Peninsula.Comparisons of the means,medians,upper and lower quartiles all indicate that TC intensity is generally stronger than usual,with 8 out of 17 named TCs reaching super typhoon status.The duration of TCs maintaining tropical storm intensity or above also surpasses climatological norms.In terms of landfall,6 TCs made landfall in China,totaling 11 events,while 11 TCs accounted for 20 landfall instances across the Asia-Pacific.The key anomalous annual TC activities are influenced by atmospheric and oceanic conditions modulated by a concurrent El Niño event,a positive North Pacific Mode,a negative Pacific Meridional Mode on the interannual scale,and the negative Pacific Decadal Oscillation phase and positive Atlantic Multidecadal Oscillation phase on the interdecadal scale.展开更多
Based on the best-track dataset from the Shanghai Typhoon Institute/China Meteorological Administration,the paper provides a compre-hensive summary and analysis of tropical cyclone(TC)activities in the Western North P...Based on the best-track dataset from the Shanghai Typhoon Institute/China Meteorological Administration,the paper provides a compre-hensive summary and analysis of tropical cyclone(TC)activities in the Western North Pacific(WNP)and the South China Sea(SCS)for 2022.Using the historical climatology from 1951 to 2020,the anomalous conditions during 2022 in TC frequency,origin locations,tracks,intensity,and duration for the entire ocean basin as well as landfall events in China are examined.Results show that the overall TC frequency is slightly lower than normal,but the multiple TC events have a very high frequency of occurrence.Origin locations of TCs,which mark the starting points of their paths,show a large westward and northward deviation from climatology.Around 40%of the named TCs exhibit a shift in their direction of movement from westerly to easterly.Additionally,comparisons of the means,medians,upper and lower quartiles all indicate that the intensity of TCs in 2022 is generally lower than the climatology,with the duration of TCs at tropical storm intensity or above being shorter than usual.A notable observation is the fewer incidence of TC landfalls in China,but with a geographical concentration in Guangdong Province.These anomalous annual TC activities are influenced by related atmospheric and oceanic environmental conditions modulated by multi-scale climate variability.Thefindings provide useful information for enhancing disaster mitigation strategies in the Asia-Pacific region.展开更多
This study reveals the possible future changes in tropical cyclone(TC)landfalling activity along the East Asian coast under different climate change scenarios based on global circulation model(GCM)simulations.Wefirst i...This study reveals the possible future changes in tropical cyclone(TC)landfalling activity along the East Asian coast under different climate change scenarios based on global circulation model(GCM)simulations.Wefirst identify those GCMs that have the“best”performance in simulating the TC activity over the western North Pacific(WNP)during the current climate(1979–2014)by examining the simulated TCs in each of the GCMs and then compare these simulated TCs with the observed TC climatological features of annual frequency,track densities and genesis locations.Based on such comparisons,we have identifiedfive(TaiESM1,EC-Earth3,ACCESS-CM2,ACCESS-ESM1-5 and HadGEM3-GC31-LL)models among all the available GCMs.A multi-model ensemble gives a further improvement when compared with observations.Future projections from some of these models are then used to identify the frequency of TC activity over the entire WNP as well as landfalling TCs in six East Asia coastal regions under two climate change scenarios(SSP2-4.5 and SSP5-8.5)for two periods,2041-70 and 2071-2100.A bias-correction method is also applied to the projected intensity of these landfalling TCs to estimate the landfall intensity.In general,these GCMs project a possible decrease in TC genesis frequency over the entire WNP,consistent with the results of most of the other studies.At mid-century,decreases in TC genesis frequency are projected to be around 10%for both scenarios.Towards the end of the century,the decreases will be more significant,with the percentage changes of 14.9%(SSP2-4.5)and 22.4%(SSP5-8.5).For landfalling TCs,the northern part of the East Asian coast will likely have an increase in frequency,ranging from 17 to 60%but a decrease of 14–27%in the southern part.In general,the average intensity of landfalling TCs will likely increase although the percentages are not large,ranging from 2 to 14%.展开更多
This paper summarizes the forecast methods,outputs and skill offered by twelve agencies for seasonal tropical cyclone(TC)activity around the world.These agencies use a variety of techniques ranging from statistical mo...This paper summarizes the forecast methods,outputs and skill offered by twelve agencies for seasonal tropical cyclone(TC)activity around the world.These agencies use a variety of techniques ranging from statistical models to dynamical models to predict basinwide activity and regional activity.In addition,several dynamical and hybrid statistical/dynamical models now predict TC track density as well as landfall likelihood.Realtime Atlantic seasonal hurricane forecasts have shown low skill in April modest skill in June and good skill in August at predicting basinwide TC activity when evaluated over 2003-2018.Real-time western North Pacific seasonal TC forecasts have shown good skill by July for basinwide intense typhoon numbers and the ACE index when evaluated for 2003-2018.Both hindcasts and real-time forecasts have shown skill for other TC basins.A summary of recent research into forecasting TC activity beyond seasonal(e.g.,multi-year)timescales is included.Recommendations for future areas of research are also discussed.展开更多
Although tropical cyclone track forecast errors have substantially decreased in recent decades,there are still cases each season with large uncertainties in the forecasts and/or very large track errors.As such cases a...Although tropical cyclone track forecast errors have substantially decreased in recent decades,there are still cases each season with large uncertainties in the forecasts and/or very large track errors.As such cases are challenging for forecasters,it is important to understand the mechanisms behind the low predictability.For this purpose the research community has developed a number of tools.These tools include ensemble and adjoint sensitivity models,ensemble perturbation experiments and nudging experiments.In this report we discuss definitions of difficult cases for tropical cyclone track forecasts,diagnostic techniques to understand sources of errors,lessons learnt in recent years and recommendations for future work.展开更多
Although tropical cyclone(TC)track forecast errors(TFEs)of operational warning centres have substantially decreased in recent decades,there are still many cases with large TFEs.The International Grand Global Ensemble(...Although tropical cyclone(TC)track forecast errors(TFEs)of operational warning centres have substantially decreased in recent decades,there are still many cases with large TFEs.The International Grand Global Ensemble(TIGGE)data are used to study the possible reasons for the large TFE cases and to compare the performance of different numerical weather prediction(NWP)models.Forty-four TCs in the western North Pacific during the period 2007-2014 with TFEs(+24 to+120 h)larger than the 75 th percentile of the annual error distribution(with a total of 93 cases)are identified.Four categories of situations are found to be associated with large TFEs.These include the interaction of the outer structure of the TC with tropical weather systems,the intensity of the TC,the extension of the subtropical high(SH)and the interaction with the westerly trough.The crucial factor of each category attributed to the large TFE is discussed.Among the TIGGE model predictions,the models of the European Centre for Medium-Range Weather Forecasts and the UK Met Office generally have a smaller TFE.The performance of different models in different situations is discussed.展开更多
基金supported by the National Natural Science Foundation of China(Grant number 42075072)support from The Startup Foundation for Introducing Talent of the Nanjing University of Information Science and Technology.
文摘Idealized numerical simulations have been carried out to reveal the complexity in the development of asymmetric convection in a tropical cyclone(TC)under the influence of an environment with either uniform flow,vertical wind shear(VWS),or both.Results show that rainwater is enhanced to the right of the motion in the outer rainband,but such enhancement occurs in the upshear-left area of the inner-core region.Additionally,due to the asymmetries introduced by environmental flow,wavenumber-1 temperature and height anomalies develop at a radius of~1000 km in the upper levels.A sub-vortex aside from the TC center encompassing the wavenumber-1 warm center appears,and asymmetric horizontal winds emerge,which,in turn,changes the storm-scale(within 400 km)VWS.Deep convection in the inner core closely follows the changing storm-scale VWS when its magnitude is larger than 2 m s^(-1) and is located downshear of the storm-scale VWS in all the experiments with environmental flow.In the outer rainbands,the maximum boundary layer convergence is mainly controlled by the direction of motion and is located in the rear-right quadrant.These results extend upon the findings of previous studies in three aspects:(1)The discovery of the roughly linear combination effect from the uniform flow and large-scale VWS;(2)The development of upper-level asymmetric winds on a 1000-km scale through the interaction between the TC vortex and environmental flow,resulting in changes in the storm-scale VWS pattern within the TC area;(3)The revelation that TC asymmetric convection closely aligns with the direction-varying storm-scale VWS instead of the initially designated VWS.
基金supported by the Hong Kong Research Grants Council (Grant City U 11300214)
文摘The sensitivity of the simulation of tropical cyclone （TC） size to microphysics schemes is studied using the Advanced Hurricane Weather Research and Forecasting Model （WRF）. Six TCs during the 2013 western North Pacific typhoon season and three mainstream microphysics schemes-Ferrier （FER）, WRF Single-Moment 5-class （WSM5） and WRF Single-Moment 6-class （WSM6）-are investigated. The results consistently show that the simulated TC track is not sensitive to the choice of microphysics scheme in the early simulation, especially in the open ocean. However, the sensitivity is much greater for TC intensity and inner-core size. The TC intensity and size simulated using the WSM5 and WSM6 schemes are respectively higher and larger than those using the FER scheme in general, which likely results from more diabatic heating being generated outside the eyewall in rainbands. More diabatic heating in rainbands gives higher inflow in the lower troposphere and higher outflow in the upper troposphere, with higher upward motion outside the eyewall. The lower-tropospheric inflow would transport absolute angular momentum inward to spin up tangential wind predominantly near the eyewall, leading to the increment in TC intensity and size （the inner-core size, especially）. In addition, the inclusion of graupel microphysics processes （as in WSM6） may not have a significant impact on the simulation of TC track, intensity and size.
基金the support of the Hong Kong Research Grant Councils Early Career Scheme(No.104712)the support of the City University Institutional Post Graduate Studentship
文摘This short paper presents an investigation on how human activities may or may not affect precipitation based on numerical simulations of precipitation in a benchmark case with modified lower boundary conditions, representing different stages of urban development in the model. The results indicate that certain degrees of urbanization affect the likelihood of heavy precipitation significantly, while less urbanized or smaller cities are much less prone to these effects. Such a result can be explained based on our previous work where the sensitivity of precipitation statistics to surface anthropogenic heat sources lies in the generation of buoyancy and turbulence in the planetary boundary layer and dissipation through triggering of convection. Thus only mega cities of sufficient size, and hence human-activity-related anthropogenic heat emission, can expect to experience such effects. In other words, as cities grow, their effects upon precipitation appear to grow as well.
基金supported bythe City University of Hong Kong (Grant No. 7001994)
文摘This study investigated the effects of landfall on the structure of a tropical cyclone （TC）. Numerical simulations were performed using the Weather Research and Forecasting Model on a β-plane. Two landfall experiments, one with an east–west and another with a north–south oriented coastline, were performed. Similar to previous studies on an f-plane, large-scale flows in the low-to-middle troposphere were modified due to friction. A pair of counter rotating gyres was found, which was shown to be consistent with the slight deffection of the TC relative to the control experiment without land. Compared to previous f-plane simulations, because of the inherent asymmetries due to the β-gyres, the large-scale pattern of flows and convergences/divergences related to friction were found to depend on coastline orientations. On the other hand, regardless of the coastline orientation, convergences were found to be stronger to the left for both cases near landfall, as in previous f-plane simulations. Such a convergence pattern subsequently induced a change in convection and rainfall at the eyewall.
基金the Research Grants Council of the Hong Kong Grant CityU11303919.
文摘Climatologically,among all ocean basins,the western North Pacific(WNP)has the largest annual number of tropical cyclones(TCs)of around 26 while the Atlantic has around 13,yielding a difference of 13.However,the difference is-7 in 2020,with 30 TCs in the Atlantic and 23 in the WNP,which is the most negative difference within the last 46 years.In fact,during the last 26 years,the difference in TC number is below 10 in ten years,with four years being negative.Such a decreasing difference in TC number can be attributed to the natural multidecadal variation of the Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation,as well as other external forcings such as anthropogenic aerosol forcing and increased greenhouse gases,with the additional impact from the La Niña condition.This result has significant implications on climate model projections of future TC activity in the two ocean basins.
基金The research was supported by the National Natural Science Foundation of China underGrant Nos. 4001161948 and 59895410, and partly supported by the Key Project of Chinese Academy of Sciences under Grant No. KZCX-201.
文摘Numerical simulations are carried out for the disturbed flow caused by three six-story buildings and a twenty-story tall tower respectively, as well as the distribution of automobile exhaust gas from a nearby road, based on the Peking University Model of Atmospheric Environment. The results show that the ventilation is better around the tall tower than around the three six-story residential buildings for the same number of households in the same urban region.
基金supported by the Research Grants Council of Hong Kong Grant City U ECity U101/16。
文摘This study examines the long-term change in the threat of landfalling tropical cyclones(TCs) in East Asia over the period 1975–2020 with a focus on rapidly intensifying(RI) TCs. The increase in the annual number of RI-TCs over the western North Pacific and the northwestward shift of their genesis location lead to an increasing trend in the annual number of landfalling RI-TCs along the coast of East Asia. The annual power dissipation index(PDI), a measure of the destructive potential of RI-TCs at landfall, also shows a significant increasing trend due to increases in the annual frequency and mean landfall intensity of landfalling RI-TCs. The increase in mean landfall intensity is related to a higher lifetime maximum intensity(LMI) and the LMI location of the landfalling RI-TCs being closer to the coast. The increase in the annual PDI of East Asia is mainly associated with landfalling TCs in the southern(the Philippines, South China, and Vietnam) and northern parts(Japan and the Korean Peninsula) of East Asia due to long-term changes in vertical wind shear and TC heat potential. The former leads to a northwestward shift of favorable environments for TC genesis and intensification, resulting in the northwestward shift in the genesis, RI, and LMI locations of RI-TCs. The latter provides more heat energy from the ocean for TC intensification, increasing its chances to undergo RI.
基金supported by Hong Kong Research Grants Council Grant CityU E-CityU101/16supported by the Natural Environment Research Council/UKRI(Grant No.NE/V017756/1).
文摘An atmosphere-only model system for making seasonal prediction and projecting future intensities of landfalling tropical cyclones(TCs)along the South China coast is upgraded by including ocean and wave models.A total of 642 TCs have been re-simulated using the new system to produce a climatology of TC intensity in the South China Sea.Detailed comparisons of the simulations from the atmosphere-only and the fully coupled systems reveal that the inclusion of the additional ocean and wave models enable differential sea surface temperature responses to various TC characteristics such as translational speed and size.In particular,interaction with the ocean does not necessarily imply a weakening of the TC,with the coastal bathymetry possibly playing a role in causing a near-shore intensification of the TC.These results suggest that to simulate the evolution of TC structure more accurately,it is essential to use an air-sea coupled model instead of an atmosphere-only model.
基金supported by the Shanghai Science and Technology Commission Project(23DZ1204701)the National Natural Science Foundation of China(42105042).
文摘Using the best-track dataset from the Shanghai Typhoon Institute/China Meteorological Administration,the paper presents a detailed summary and analysis of tropical cyclone(TC)activities in the Western North Pacific(WNP)and the South China Sea(SCS)during 2023.Based on historical records from 1951 to 2020 as the climatology benchmark,we examine anomalies in TC frequency,origin locations,tracks,intensity,and duration,as well as landfall events across the Asia-Pacific region.TC frequency in 2023 is found to be lower than climatology,with a marked decrease during the autumn months.Origin locations of TCs,which mark the starting points of their paths,are generally consistent with climatology,although there is a noticeable northwestward shift in the origins of the intense TCs.Track density of named TCs is anomalously high within the 0-20°N and 110°E to 125°E longitude box,and offshore areas covering northwestern to southern Japan and around the Korean Peninsula.Comparisons of the means,medians,upper and lower quartiles all indicate that TC intensity is generally stronger than usual,with 8 out of 17 named TCs reaching super typhoon status.The duration of TCs maintaining tropical storm intensity or above also surpasses climatological norms.In terms of landfall,6 TCs made landfall in China,totaling 11 events,while 11 TCs accounted for 20 landfall instances across the Asia-Pacific.The key anomalous annual TC activities are influenced by atmospheric and oceanic conditions modulated by a concurrent El Niño event,a positive North Pacific Mode,a negative Pacific Meridional Mode on the interannual scale,and the negative Pacific Decadal Oscillation phase and positive Atlantic Multidecadal Oscillation phase on the interdecadal scale.
基金supported by the Shanghai Science and Technology Commission Project(23DZ1204701)the National Natural Science Foundation of China(42105042)。
文摘Based on the best-track dataset from the Shanghai Typhoon Institute/China Meteorological Administration,the paper provides a compre-hensive summary and analysis of tropical cyclone(TC)activities in the Western North Pacific(WNP)and the South China Sea(SCS)for 2022.Using the historical climatology from 1951 to 2020,the anomalous conditions during 2022 in TC frequency,origin locations,tracks,intensity,and duration for the entire ocean basin as well as landfall events in China are examined.Results show that the overall TC frequency is slightly lower than normal,but the multiple TC events have a very high frequency of occurrence.Origin locations of TCs,which mark the starting points of their paths,show a large westward and northward deviation from climatology.Around 40%of the named TCs exhibit a shift in their direction of movement from westerly to easterly.Additionally,comparisons of the means,medians,upper and lower quartiles all indicate that the intensity of TCs in 2022 is generally lower than the climatology,with the duration of TCs at tropical storm intensity or above being shorter than usual.A notable observation is the fewer incidence of TC landfalls in China,but with a geographical concentration in Guangdong Province.These anomalous annual TC activities are influenced by related atmospheric and oceanic environmental conditions modulated by multi-scale climate variability.Thefindings provide useful information for enhancing disaster mitigation strategies in the Asia-Pacific region.
文摘This study reveals the possible future changes in tropical cyclone(TC)landfalling activity along the East Asian coast under different climate change scenarios based on global circulation model(GCM)simulations.Wefirst identify those GCMs that have the“best”performance in simulating the TC activity over the western North Pacific(WNP)during the current climate(1979–2014)by examining the simulated TCs in each of the GCMs and then compare these simulated TCs with the observed TC climatological features of annual frequency,track densities and genesis locations.Based on such comparisons,we have identifiedfive(TaiESM1,EC-Earth3,ACCESS-CM2,ACCESS-ESM1-5 and HadGEM3-GC31-LL)models among all the available GCMs.A multi-model ensemble gives a further improvement when compared with observations.Future projections from some of these models are then used to identify the frequency of TC activity over the entire WNP as well as landfalling TCs in six East Asia coastal regions under two climate change scenarios(SSP2-4.5 and SSP5-8.5)for two periods,2041-70 and 2071-2100.A bias-correction method is also applied to the projected intensity of these landfalling TCs to estimate the landfall intensity.In general,these GCMs project a possible decrease in TC genesis frequency over the entire WNP,consistent with the results of most of the other studies.At mid-century,decreases in TC genesis frequency are projected to be around 10%for both scenarios.Towards the end of the century,the decreases will be more significant,with the percentage changes of 14.9%(SSP2-4.5)and 22.4%(SSP5-8.5).For landfalling TCs,the northern part of the East Asian coast will likely have an increase in frequency,ranging from 17 to 60%but a decrease of 14–27%in the southern part.In general,the average intensity of landfalling TCs will likely increase although the percentages are not large,ranging from 2 to 14%.
基金supported by the G.Unger Vetlesen Foundationfinancial support from the European Union’s Horizon 2020 Research and Innovation programme(EUCP+5 种基金grant agreement no.776613)from the Ministerio de Economia y Competitividad(MINECO)as part of the CLINSA(CGL2017-85791-R)and HIATUS(CGL2015-70353-R)projectssupport of JSPS KAKENHI Grant Numbers JP17K14395 and JP17K01223financial support from the National Typhoon Center at the Korea Meteorological Administration("Research and Development for Numerical Weather Prediction and Earthquake Services"project)support from the UK Public Weather Service research programmesupported by the Research Grants Council of the Hong Kong Special Administrative Region of China Grant E-CityU101/16.
文摘This paper summarizes the forecast methods,outputs and skill offered by twelve agencies for seasonal tropical cyclone(TC)activity around the world.These agencies use a variety of techniques ranging from statistical models to dynamical models to predict basinwide activity and regional activity.In addition,several dynamical and hybrid statistical/dynamical models now predict TC track density as well as landfall likelihood.Realtime Atlantic seasonal hurricane forecasts have shown low skill in April modest skill in June and good skill in August at predicting basinwide TC activity when evaluated over 2003-2018.Real-time western North Pacific seasonal TC forecasts have shown good skill by July for basinwide intense typhoon numbers and the ACE index when evaluated for 2003-2018.Both hindcasts and real-time forecasts have shown skill for other TC basins.A summary of recent research into forecasting TC activity beyond seasonal(e.g.,multi-year)timescales is included.Recommendations for future areas of research are also discussed.
基金supported by the Research Grants Council(RGC)of Hong Kong,General Research Fund(CityU11332816)supported by the Chief of Naval Research through the NRL Base Program PE 0601153N and the Office of Naval Research PE 0601153NComputational resources for Doyle’s and Komaromi’s research were supported by a grant of High Performance Computing time from the Department of Defense Major Shared Resource Centers,Stennis Space Center,MS.
文摘Although tropical cyclone track forecast errors have substantially decreased in recent decades,there are still cases each season with large uncertainties in the forecasts and/or very large track errors.As such cases are challenging for forecasters,it is important to understand the mechanisms behind the low predictability.For this purpose the research community has developed a number of tools.These tools include ensemble and adjoint sensitivity models,ensemble perturbation experiments and nudging experiments.In this report we discuss definitions of difficult cases for tropical cyclone track forecasts,diagnostic techniques to understand sources of errors,lessons learnt in recent years and recommendations for future work.
基金supported by the Research Grants Council(RGC)of Hong Kong,General Research Fund(City U11332816)supported by Japan Society for the Promotion of Science KAKENHI Grant 26282111 and 18H01283
文摘Although tropical cyclone(TC)track forecast errors(TFEs)of operational warning centres have substantially decreased in recent decades,there are still many cases with large TFEs.The International Grand Global Ensemble(TIGGE)data are used to study the possible reasons for the large TFE cases and to compare the performance of different numerical weather prediction(NWP)models.Forty-four TCs in the western North Pacific during the period 2007-2014 with TFEs(+24 to+120 h)larger than the 75 th percentile of the annual error distribution(with a total of 93 cases)are identified.Four categories of situations are found to be associated with large TFEs.These include the interaction of the outer structure of the TC with tropical weather systems,the intensity of the TC,the extension of the subtropical high(SH)and the interaction with the westerly trough.The crucial factor of each category attributed to the large TFE is discussed.Among the TIGGE model predictions,the models of the European Centre for Medium-Range Weather Forecasts and the UK Met Office generally have a smaller TFE.The performance of different models in different situations is discussed.
