Accurate prediction of tropical cyclone(TC)intensity is challenging due to the complex physical processes involved.Here,we introduce a new TC intensity prediction scheme for the western North Pacific(WNP)based on a ti...Accurate prediction of tropical cyclone(TC)intensity is challenging due to the complex physical processes involved.Here,we introduce a new TC intensity prediction scheme for the western North Pacific(WNP)based on a time-dependent theory of TC intensification,termed the energetically based dynamical system(EBDS)model,together with the use of a long short-term memory(LSTM)neural network.In time-dependent theory,TC intensity change is controlled by both the internal dynamics of the TC system and various environmental factors,expressed as environmental dynamical efficiency.The LSTM neural network is used to predict the environmental dynamical efficiency in the EBDS model trained using besttrack TC data and global reanalysis data during 1982–2017.The transfer learning and ensemble methods are used to retrain the scheme using the environmental factors predicted by the Global Forecast System(GFS)of the National Centers for Environmental Prediction during 2017–21.The predicted environmental dynamical efficiency is finally iterated into the EBDS equations to predict TC intensity.The new scheme is evaluated for TC intensity prediction using both reanalysis data and the GFS prediction data.The intensity prediction by the new scheme shows better skill than the official prediction from the China Meteorological Administration(CMA)and those by other state-of-art statistical and dynamical forecast systems,except for the 72-h forecast.Particularly at the longer lead times of 96 h and 120 h,the new scheme has smaller forecast errors,with a more than 30%improvement over the official forecasts.展开更多
There is limited understanding regarding the formation of multiple tropical cyclones(MTCs).This study explores the environmental conditions conducive to MTC formation by objectively determining the atmospheric circula...There is limited understanding regarding the formation of multiple tropical cyclones(MTCs).This study explores the environmental conditions conducive to MTC formation by objectively determining the atmospheric circulation patterns favorable for MTC formation over the western North Pacific.Based on 199 MTC events occurring from June to October 1980–2020,four distinct circulation patterns are identified:the monsoon trough(MT)pattern,accounting for 40.3%of occurrences,the confluence zone(CON)pattern at 26.2%,the easterly wave(EW)pattern at 17.8%,and the monsoon gyre(MG)pattern at 15.7%.The MT pattern mainly arises from the interaction between the subtropical high and the monsoon trough,with MTCs forming along the monsoon trough and its flanks.The CON pattern is affected by the subtropical high,the South Asian high,and the monsoon trough,with MTCs emerging at the confluence zone where the prevailing southwesterly and southeasterly flows converge.The EW pattern is dominated by easterly flows,with MTCs developing along the easterly wave train.MTCs in the MG pattern arise within a monsoon vortex characterized by strong southwesterly flows.A quantitative analysis further indicates that MTC formation in the MT pattern is primarily governed by mid-level vertical velocity and low-level vorticity,while mid-level humidity and vertical velocity are significantly important in the other patterns.The meridional shear and convergence of zonal winds are essential in converting barotropic energy from the basic flows to disturbance kinetic energy,acting as the primary source for eddy kinetic energy growth.展开更多
Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over...Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over the western North Pacific(WNP)remains unknown.In this study,we examined the impact of the TEJ on the interannual variability of TC genesis frequency over the WNP in the TC season(June-September)during 1980-2020.The results show a significant positive correlation between TC genesis frequency over the WNP and the jet intensity in the entrance region of the TEJ over the tropical western Pacific(in brief WP_TEJ),with a correlation coefficient as high as 0.66.The intensified WP_TEJ results in strong ageostrophic northerly winds in the entrance region and thus upper-level divergence to the north of the jet axis over the main TC genesis region in the WNP.This would lead to an increase in upward motion in the troposphere with enhanced low-level convergence,which are the most important factors to the increases in low-level vorticity,mid-level humidity and low-level eddy kinetic energy,and the decreases in sea level pressure and vertical wind shear in the region.All these changes are favorable for TC genesis over the WNP and vice versa.Further analyses indicate that the interannual variability of the WP_TEJ intensity is likely to be linked to the local diabatic heating over the Indian Ocean-western Pacific and the central Pacific El Ni?o-Southern Oscillation.展开更多
Accurate prediction of tropical cyclone(TC)intensity remains a challenge due to the complex physical processes involved in TC intensity changes.A seven-day TC intensity prediction scheme based on the logistic growth e...Accurate prediction of tropical cyclone(TC)intensity remains a challenge due to the complex physical processes involved in TC intensity changes.A seven-day TC intensity prediction scheme based on the logistic growth equation(LGE)for the western North Pacific(WNP)has been developed using the observed and reanalysis data.In the LGE,TC intensity change is determined by a growth term and a decay term.These two terms are comprised of four free parameters which include a time-dependent growth rate,a maximum potential intensity(MPI),and two constants.Using 33 years of training samples,optimal predictors are selected first,and then the two constants are determined based on the least square method,forcing the regressed growth rate from the optimal predictors to be as close to the observed as possible.The estimation of the growth rate is further refined based on a step-wise regression(SWR)method and a machine learning(ML)method for the period 1982−2014.Using the LGE-based scheme,a total of 80 TCs during 2015−17 are used to make independent forecasts.Results show that the root mean square errors of the LGE-based scheme are much smaller than those of the official intensity forecasts from the China Meteorological Administration(CMA),especially for TCs in the coastal regions of East Asia.Moreover,the scheme based on ML demonstrates better forecast skill than that based on SWR.The new prediction scheme offers strong potential for both improving the forecasts for rapid intensification and weakening of TCs as well as for extending the 5-day forecasts currently issued by the CMA to 7-day forecasts.展开更多
Seasonal tropical cyclone(TC)forecasting has evolved substantially since its commencement in the early 1980s.However,present operational seasonal TC forecasting services still do not meet the requirements of society a...Seasonal tropical cyclone(TC)forecasting has evolved substantially since its commencement in the early 1980s.However,present operational seasonal TC forecasting services still do not meet the requirements of society and stakeholders:current operational products are mainly basin-scale information,while more detailed sub-basin scale information such as potential risks of TC landfall is anticipated for decision making.To fill this gap and make the TC science and services move forward,this paper reviews recent research and development in seasonal tropical cyclone(TC)forecasting.In particular,this paper features new research topics on seasonal TC predictability in neutral conditions of El Ni˜no–Southern Oscillation(ENSO),emerging forecasting techniques of seasonal TC activity including Machine Learning/Artificial Intelligence,and multi-annual TC predictions.We also review the skill of forecast systems at predicting landfalling statistics for certain regions of the North Atlantic,Western North Pacific and South Indian oceans and discuss the gap that remains between current products and potential user's expectations.New knowledge and advanced forecasting techniques are expected to further enhance the capability of seasonal TC forecasting and lead to more actionable and fit-for-purpose products.展开更多
The attempt of this article is to provide a literature review on recent development and progress in seasonal forecasts for tropical cyclone(TC) activity over the western North Pacific(WNP). Since the predictability of...The attempt of this article is to provide a literature review on recent development and progress in seasonal forecasts for tropical cyclone(TC) activity over the western North Pacific(WNP). Since the predictability of seasonal TC activity mainly comes from the slowly-evolving sea surface temperature(SST) conditions and the large-scale atmospheric circulation teleconnection patterns, our current understanding on the relationships between the interannual TC variability and tropical SST forcing and variations of various climate modes is first reviewed. It serves as the scientific basis and gives us ideas how predictable the seasonal TC activity is. The main body of the article focuses on an overview of the forecast approaches and methodologies, including statistical and dynamical models and their combination, currently used in seasonal forecasts for TCs over the WNP, and an initial assessment of their prediction skills in the past decade or so. Some outstanding issues, including the intrinsic limitation of predictability due to various uncertainties and the areas for future developments, are also briefly discussed. It is expected that the quality of the scientifically based seasonal TC forecasts would be steadily improved with the advancement in the forecast techniques and the driving of society needs.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
This paper presents a review of tropical cyclone(TC) activity over the western North Pacific in 2013 and examines the main factors that influenced the pattern of activity. The 2013 season was characterized by an above...This paper presents a review of tropical cyclone(TC) activity over the western North Pacific in 2013 and examines the main factors that influenced the pattern of activity. The 2013 season was characterized by an abovenormal genesis number of named storms, near-normal total occurrence frequency, and near-normal accumulated cyclone energy. Both the tropical SSTs in the Pacific sector and the East Asian summer monsoon contributed to favorable conditions for active cyclogenesis. The monsoon circulation also controlled the TC track patterns. Three prevailing tracks were identified, along with four stages of track pattern transition that were characterized by different combinations of prevailing tracks. The different track patterns were associated with variations in the regional circulation, which in turn were closely related to the seasonal variation of the monsoon. The regional circulation was also influenced by the intra-seasonal oscillation. In particular, the quasi-biweekly oscillation(QBWO) was important during the early and late seasons, while the 30–60 day oscillation was significant in the active season from late July to early October. The QBWO mainly influenced the circulation in the subtropics and the midlatitudes, while the 30–60 day oscillation was related to the Pacific–Japan pattern, variation in the subtropical high, and tropical cyclonic circulation during the early, main, and late seasons, respectively.展开更多
Tropical cyclone(TC) activity over the western North Pacific(WNP) in 2012 is summarized and the associated large-scale environmental conditions are discussed. In total 25 named storms formed in the WNP basin in 2012, ...Tropical cyclone(TC) activity over the western North Pacific(WNP) in 2012 is summarized and the associated large-scale environmental conditions are discussed. In total 25 named storms formed in the WNP basin in 2012, among them were 3 tropical storms(TSs), 7 severe TSs, 4 typhoons, 6 severe typhoons, and 5 super typhoons. TC activity was close to a 30-year average but above the average active level of recent years since 2005. Total number of TCs formed in the South China Sea(SCS) in 2012 was below normal, with only 40% of the climatological mean. Overall, TC genesis over the WNP was characterized by four active periods. During each period TCs took distinct prevailing tracks. The periodic characteristics in TC genesis were attributed to the activity of the intraseasonal oscillation(ISO), while those in TC tracks were related to the large-scale dynamical and thermodynamic conditions induced by the enhanced WNP monsoon activity and the weak El Ni?o conditions.展开更多
基金supported by the National Key R&D Program of China(Grant No.2017YFC1501604)the National Natural Science Foundation of China(Grant Nos.41875114 and 41875057).
文摘Accurate prediction of tropical cyclone(TC)intensity is challenging due to the complex physical processes involved.Here,we introduce a new TC intensity prediction scheme for the western North Pacific(WNP)based on a time-dependent theory of TC intensification,termed the energetically based dynamical system(EBDS)model,together with the use of a long short-term memory(LSTM)neural network.In time-dependent theory,TC intensity change is controlled by both the internal dynamics of the TC system and various environmental factors,expressed as environmental dynamical efficiency.The LSTM neural network is used to predict the environmental dynamical efficiency in the EBDS model trained using besttrack TC data and global reanalysis data during 1982–2017.The transfer learning and ensemble methods are used to retrain the scheme using the environmental factors predicted by the Global Forecast System(GFS)of the National Centers for Environmental Prediction during 2017–21.The predicted environmental dynamical efficiency is finally iterated into the EBDS equations to predict TC intensity.The new scheme is evaluated for TC intensity prediction using both reanalysis data and the GFS prediction data.The intensity prediction by the new scheme shows better skill than the official prediction from the China Meteorological Administration(CMA)and those by other state-of-art statistical and dynamical forecast systems,except for the 72-h forecast.Particularly at the longer lead times of 96 h and 120 h,the new scheme has smaller forecast errors,with a more than 30%improvement over the official forecasts.
基金supported by the National Natural Science Foundation of China(Grant No.42075015)the Science and Technology Commission of Shanghai Municipality,China(23DZ1204703).
文摘There is limited understanding regarding the formation of multiple tropical cyclones(MTCs).This study explores the environmental conditions conducive to MTC formation by objectively determining the atmospheric circulation patterns favorable for MTC formation over the western North Pacific.Based on 199 MTC events occurring from June to October 1980–2020,four distinct circulation patterns are identified:the monsoon trough(MT)pattern,accounting for 40.3%of occurrences,the confluence zone(CON)pattern at 26.2%,the easterly wave(EW)pattern at 17.8%,and the monsoon gyre(MG)pattern at 15.7%.The MT pattern mainly arises from the interaction between the subtropical high and the monsoon trough,with MTCs forming along the monsoon trough and its flanks.The CON pattern is affected by the subtropical high,the South Asian high,and the monsoon trough,with MTCs emerging at the confluence zone where the prevailing southwesterly and southeasterly flows converge.The EW pattern is dominated by easterly flows,with MTCs developing along the easterly wave train.MTCs in the MG pattern arise within a monsoon vortex characterized by strong southwesterly flows.A quantitative analysis further indicates that MTC formation in the MT pattern is primarily governed by mid-level vertical velocity and low-level vorticity,while mid-level humidity and vertical velocity are significantly important in the other patterns.The meridional shear and convergence of zonal winds are essential in converting barotropic energy from the basic flows to disturbance kinetic energy,acting as the primary source for eddy kinetic energy growth.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(Grant No.2020B0301030004)the National Natural Science Foundation of China(Grant Nos.42075015,41775060,41875114)+1 种基金the Science and Technology Commission of Shanghai MunicipalityChina(Grant No.20dz1200700)。
文摘Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over the western North Pacific(WNP)remains unknown.In this study,we examined the impact of the TEJ on the interannual variability of TC genesis frequency over the WNP in the TC season(June-September)during 1980-2020.The results show a significant positive correlation between TC genesis frequency over the WNP and the jet intensity in the entrance region of the TEJ over the tropical western Pacific(in brief WP_TEJ),with a correlation coefficient as high as 0.66.The intensified WP_TEJ results in strong ageostrophic northerly winds in the entrance region and thus upper-level divergence to the north of the jet axis over the main TC genesis region in the WNP.This would lead to an increase in upward motion in the troposphere with enhanced low-level convergence,which are the most important factors to the increases in low-level vorticity,mid-level humidity and low-level eddy kinetic energy,and the decreases in sea level pressure and vertical wind shear in the region.All these changes are favorable for TC genesis over the WNP and vice versa.Further analyses indicate that the interannual variability of the WP_TEJ intensity is likely to be linked to the local diabatic heating over the Indian Ocean-western Pacific and the central Pacific El Ni?o-Southern Oscillation.
基金This study is supported by the National Key R&D Program of China(Grant Nos.2017YFC1501604 and 2019YFC1509101)the National Natural Science Foundation of China(Grant Nos.41875114,41875057,and 91937302).
文摘Accurate prediction of tropical cyclone(TC)intensity remains a challenge due to the complex physical processes involved in TC intensity changes.A seven-day TC intensity prediction scheme based on the logistic growth equation(LGE)for the western North Pacific(WNP)has been developed using the observed and reanalysis data.In the LGE,TC intensity change is determined by a growth term and a decay term.These two terms are comprised of four free parameters which include a time-dependent growth rate,a maximum potential intensity(MPI),and two constants.Using 33 years of training samples,optimal predictors are selected first,and then the two constants are determined based on the least square method,forcing the regressed growth rate from the optimal predictors to be as close to the observed as possible.The estimation of the growth rate is further refined based on a step-wise regression(SWR)method and a machine learning(ML)method for the period 1982−2014.Using the LGE-based scheme,a total of 80 TCs during 2015−17 are used to make independent forecasts.Results show that the root mean square errors of the LGE-based scheme are much smaller than those of the official intensity forecasts from the China Meteorological Administration(CMA),especially for TCs in the coastal regions of East Asia.Moreover,the scheme based on ML demonstrates better forecast skill than that based on SWR.The new prediction scheme offers strong potential for both improving the forecasts for rapid intensification and weakening of TCs as well as for extending the 5-day forecasts currently issued by the CMA to 7-day forecasts.
基金support of the MEXT program for the advanced studies of climate change projection(SENTAN),Grant Numbers JPMXD0722680395 and JPMXD0722680734Julia Lockwood would like to acknowledge funding from the C3S_34c contract(number:ECMWF/COPERNICUS/2019/C3S_34c_DWD)of the Copernicus Climate Change Service operated by ECMWF.
文摘Seasonal tropical cyclone(TC)forecasting has evolved substantially since its commencement in the early 1980s.However,present operational seasonal TC forecasting services still do not meet the requirements of society and stakeholders:current operational products are mainly basin-scale information,while more detailed sub-basin scale information such as potential risks of TC landfall is anticipated for decision making.To fill this gap and make the TC science and services move forward,this paper reviews recent research and development in seasonal tropical cyclone(TC)forecasting.In particular,this paper features new research topics on seasonal TC predictability in neutral conditions of El Ni˜no–Southern Oscillation(ENSO),emerging forecasting techniques of seasonal TC activity including Machine Learning/Artificial Intelligence,and multi-annual TC predictions.We also review the skill of forecast systems at predicting landfalling statistics for certain regions of the North Atlantic,Western North Pacific and South Indian oceans and discuss the gap that remains between current products and potential user's expectations.New knowledge and advanced forecasting techniques are expected to further enhance the capability of seasonal TC forecasting and lead to more actionable and fit-for-purpose products.
文摘The attempt of this article is to provide a literature review on recent development and progress in seasonal forecasts for tropical cyclone(TC) activity over the western North Pacific(WNP). Since the predictability of seasonal TC activity mainly comes from the slowly-evolving sea surface temperature(SST) conditions and the large-scale atmospheric circulation teleconnection patterns, our current understanding on the relationships between the interannual TC variability and tropical SST forcing and variations of various climate modes is first reviewed. It serves as the scientific basis and gives us ideas how predictable the seasonal TC activity is. The main body of the article focuses on an overview of the forecast approaches and methodologies, including statistical and dynamical models and their combination, currently used in seasonal forecasts for TCs over the WNP, and an initial assessment of their prediction skills in the past decade or so. Some outstanding issues, including the intrinsic limitation of predictability due to various uncertainties and the areas for future developments, are also briefly discussed. It is expected that the quality of the scientifically based seasonal TC forecasts would be steadily improved with the advancement in the forecast techniques and the driving of society needs.
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the National Science Foundation of China Grants 41375093 and 41075071.
文摘This paper presents a review of tropical cyclone(TC) activity over the western North Pacific in 2013 and examines the main factors that influenced the pattern of activity. The 2013 season was characterized by an abovenormal genesis number of named storms, near-normal total occurrence frequency, and near-normal accumulated cyclone energy. Both the tropical SSTs in the Pacific sector and the East Asian summer monsoon contributed to favorable conditions for active cyclogenesis. The monsoon circulation also controlled the TC track patterns. Three prevailing tracks were identified, along with four stages of track pattern transition that were characterized by different combinations of prevailing tracks. The different track patterns were associated with variations in the regional circulation, which in turn were closely related to the seasonal variation of the monsoon. The regional circulation was also influenced by the intra-seasonal oscillation. In particular, the quasi-biweekly oscillation(QBWO) was important during the early and late seasons, while the 30–60 day oscillation was significant in the active season from late July to early October. The QBWO mainly influenced the circulation in the subtropics and the midlatitudes, while the 30–60 day oscillation was related to the Pacific–Japan pattern, variation in the subtropical high, and tropical cyclonic circulation during the early, main, and late seasons, respectively.
文摘Tropical cyclone(TC) activity over the western North Pacific(WNP) in 2012 is summarized and the associated large-scale environmental conditions are discussed. In total 25 named storms formed in the WNP basin in 2012, among them were 3 tropical storms(TSs), 7 severe TSs, 4 typhoons, 6 severe typhoons, and 5 super typhoons. TC activity was close to a 30-year average but above the average active level of recent years since 2005. Total number of TCs formed in the South China Sea(SCS) in 2012 was below normal, with only 40% of the climatological mean. Overall, TC genesis over the WNP was characterized by four active periods. During each period TCs took distinct prevailing tracks. The periodic characteristics in TC genesis were attributed to the activity of the intraseasonal oscillation(ISO), while those in TC tracks were related to the large-scale dynamical and thermodynamic conditions induced by the enhanced WNP monsoon activity and the weak El Ni?o conditions.
