This study examines the modulation of tropical cyclogenesis over the South China Sea （SCS） by the E1 Nifio-Southem Oscillation （ENSO） Modoki during the boreal summer. Results reveal that there were more tropical c...This study examines the modulation of tropical cyclogenesis over the South China Sea （SCS） by the E1 Nifio-Southem Oscillation （ENSO） Modoki during the boreal summer. Results reveal that there were more tropical cyclones （TCs） formed over the SCS during central Pacific warming years and less TC frequency during central Pacific cooling years. How different environmental factors （including low-level relative vorticity, mid-level relative humidity, vertical wind shear, and potential intensity） contribute to this influence is investigated, using a genesis potential （GP） index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for central Pacific warming and cooling years separately, which could account for the changes of TC frequency over the SCS in different ENSO Modoki phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results suggest that the vertical wind shear and low-level relative vorticity, which are associated with the ENSO Modold-induced anomalous circulations in Matsuno-Gill patterns, make the largest contributions to the ENSO Modoki modulation of tropical cyclogenesis over the SCS as implied by the GP index. These results highlight the important roles of dynamic factors in the modulation of TC fre-quency over the SCS by the ENSO Modold during the boreal summer.展开更多
Threatening millions of people and causing billions of dollars in losses,tropical cyclones(TCs)are among the most severe natural hazards in the world,especially over the western North Pacific.However,the response of T...Threatening millions of people and causing billions of dollars in losses,tropical cyclones(TCs)are among the most severe natural hazards in the world,especially over the western North Pacific.However,the response of TCs to a warming or changing climate has been the subject of considerable research,often with conflicting results.In this study,the abilities of Coupled Model Intercomparison Project(CMIP)Phase 6(CMIP6)models to simulate TC genesis are assessed through historical simulations.The results indicate that a systematic humidity bias persists in most CMIP6 models from corresponding CMIP Phase 5 models,which leads to an overestimation of climatological TC genesis.However,the annual cycle of TC genesis is well captured by CMIP6 models.The abilities of 25 models to simulate the geographical patterns of TC genesis vary significantly.In addition,seven models are identified as well simulated models,but seven models are identified as poorly simulated ones.A comparison of the environmental variables for TC genesis in the well-simulated group and the poorly simulated group identifies moisture in the mid-troposphere as a key factor in the realistic simulation of El Niño-Southern Oscillation(ENSO)impacts on TC genesis.In contrast with the observations,the poorly simulated group does not reproduce the suppressing effect of negative moisture anomalies on TC genesis in the northwestern region(20°–30°N,120°–145°E)during El Niño years.Given the interaction between TC and ENSO,these results provide a guidance for future TC projections under climate change by CMIP6 models.展开更多
The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows ...The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows an asymmetric bimodal pattern with the maximum genesis number appearing in late October and the second largest in early May. The two peaks correspond to the withdrawal and onset of the BoB summer monsoon, respectively. The semimonthly GP index calculated without TC days over the BoB is consistent with TC genesis frequency, indicating that the index captures the monsoon-induced changes in the environment that are responsible for the seasonal variation of TC genesis frequency. Of the four environmental variables (i.e., low-level vorticity, mid-level relative humidity, potential intensity, and vertical wind shear) that enter into the GP index, the potential intensity makes the largest contribution to the bimodal distribution, followed by vertical wind shear due to small wind speed during the summer monsoon onset and withdrawal. The difference in TC genesis frequency between autumn and late spring is mainly owing to the relative humid-ity difference because a divergence (convergence) of horizontal moisture flux associated with cold dry northerlies (warm wet wester-lies) dominates the BoB in late spring (autumn).展开更多
Joint Typhoon Warning Center(JTWC) Best Track data from 1995 to 2014 are processed to examine some specific patterns and trends shown by Typhoons over the Western North Pacific. With a multivariate dataset of 588 TC c...Joint Typhoon Warning Center(JTWC) Best Track data from 1995 to 2014 are processed to examine some specific patterns and trends shown by Typhoons over the Western North Pacific. With a multivariate dataset of 588 TC cases in hand, we carry out a sub-domain analysis by dividing the Western North Pacific region into domains of 2°x2° and find the preferred regions of genesis, favourable direction of movement, steep recurvature, rapid intensification, and rapid decay. The region from longitude 132°E to 134°E and latitude 16°N to 18°N showed the highest number of cases(19) for rapid intensification(RI) and a general pattern is found that the RI systems occurred mostly in the later half of the year with a negative Pacific Decadal Oscillation(PDO) index. Similarly, the domain from longitude 114°E to 116°E and latitude 26°N to 28°N had the highest probability of 0.857 for rapid decay. The probabilities of recurvature for each sub-domain were calculated for angles 30°, 45°, 60°, 90°, 120° and 150°. The sub-domain around longitude 118°E and latitude 12°N had the steepest recurve of 168.69°. It also had a high probability of 0.714 for a recurvature of greater than 90°. The most taken direction of movement of typhoons around the Western North Pacific were analysed in different ways and along the 16 points of compass, the direction from 270° to 292.5° was found to be the most preferred direction of movement.展开更多
To understand the impacts of large-scale circulation during the evolution of E1 Nifio cycle on tropical cyclones （TC） is important and useful for TC forecast. Based on best-track data from the Joint Typhoon Warning ...To understand the impacts of large-scale circulation during the evolution of E1 Nifio cycle on tropical cyclones （TC） is important and useful for TC forecast. Based on best-track data from the Joint Typhoon Warning Center and reanalysis data from National Centers for Environmental Prediction for the period 1975- 2014, we investigated the influences of two types of E1 Nifio, the eastern Pacific E1 Nifio （EP-E1 Nifio） and central Pacific E1 Nifio （CP-E1 Nifio）, on global TC genesis. We also examined how various environmental factors contribute to these influences using a modified genesis potential index （MGPI）. The composites reproduced for two types of E1 Nifio, from their developing to decaying phases, were able to qualitatively replicate observed cyclogenesis in several basins except for the Arabian Sea. Certain factors of MGPI with more influence than others in various regions are identified. Over the western North Pacific, five variables were all important in the two E1Nifio types during developing summer （July-August-September） and fall （October- November-December）, and decaying spring （April-May-June） and summer. In the eastern Pacific, vertical shear and relative vorticity are the crucial factors for the two types of El Nifio during developing and decaying summers. In the Atlantic, vertical shear, potential intensity and relative humidity are important for the opposite variation of EP- and CP-EI Nifios during decaying summers. In the Southern Hemisphere, the five variables have varying contributions to TC genesis variation during peak season （January-February-March） for the two types of E1 Nifio. In the Bay of Bengal, relative vorticity, humidity and omega may be responsible for clearly reduced TC genesis during developing fall for the two types and slightly suppressed TC cyclogenesis during EP-E1 Nifio decaying spring. In the Arabian Sea, the EP-E1 Nifio generates a slightly positive anomaly of TC genesis during developing falls and decaying springs, but the MGPI failed to c展开更多
This study investigates the global performance of the tropical cyclone(TC)genesis potential index based on oceanic parameters(GPI_(ocean))proposed by Zhang et al.(2016).In six major TC formation basins,GPI_(ocean)can ...This study investigates the global performance of the tropical cyclone(TC)genesis potential index based on oceanic parameters(GPI_(ocean))proposed by Zhang et al.(2016).In six major TC formation basins,GPI_(ocean)can represent the seasonal variations of TC genesis over most basins,except for the North Indian Ocean(NIO).The monthly climatological GPI_(ocean)shows only a single peak in the NIO,which cannot describe the bimodal pattern of the annual cycle of TC genesis.To determine the cause of the poor performance of GPI_(ocean)in the NIO,the relative contributions of different parameters related to GPI_(ocean)are calculated and compared with those related to the genesis potential index developed by Emanuel and Nolan(2004)(GPI04).Results show that the net longwave radiation on the sea surface is responsible for the single peak of TC genesis in the NIO in boreal summer.Compared with GPI04,vertical wind shear is not involved in GPI_(ocean).Vertical wind shear is the dominant factor inhibiting TC genesis in the NIO in boreal summer.Therefore,the absence of vertical wind shear in GPI_(ocean)results in the failure of the annual cycle of TC genesis in the NIO.展开更多
In this study,the differences in spatial distribution and controlling parameters for the formation of near-equatorial tropical cyclones(NETCs)between the western North Pacific(WNP)and the North Atlantic(NA)are investi...In this study,the differences in spatial distribution and controlling parameters for the formation of near-equatorial tropical cyclones(NETCs)between the western North Pacific(WNP)and the North Atlantic(NA)are investigated.NETCs exhibit distinctive spatial variabilities in different basins.Over the past few decades,the majority of NETCs took place in WNP while none was observed in NA.The mechanism behind such a distinguishing spatial distribution difference is analyzed by using statistical methods.It is noted that the dynamical variables such as low-level relative vorticity and vertical wind shear(VWS)are likely the primary controlling parameters.Compared with NA,larger low-level vorticity and smaller VWS appear over WNP.The increase of vorticity attributes a lot to the turning of northeast trade wind.NETCs in WNP tend to occur in the areas with VWS less than 9 m s^(-1),while the VWS in NA generally exceeds 10 m s^(-1).On the other hand,the sea surface temperature in the near-equatorial region of both of the two oceans exceeds 26.5℃and the difference of mid-level moisture is not significant;thus,thermal factors have little contribution to the distinction of NETC activities between WNP and NA.Intraseasonal oscillation(ISO)and synoptic-scale disturbances in WNP are also shown to be more favorable for NETC genesis.More NETCs were generated in ISO active phase.Synoptic-scale disturbances in WNP obtain more energy from the mean flows through the barotropic energy conversion process.The overall unfavorable thermal and dynamic conditions lead to the absence of NETCs in NA.展开更多
The Tropical Cyclone Genesis Potential Index （GPI） was employed to investigate possible impacts of global warming on tropical cyclone genesis over the western North Pacific （WNP）. The outputs of 20th century clima...The Tropical Cyclone Genesis Potential Index （GPI） was employed to investigate possible impacts of global warming on tropical cyclone genesis over the western North Pacific （WNP）. The outputs of 20th century climate simulation by eighteen GCMs were used to evaluate the models＇ ability to reproduce tropical cyclone genesis via the GPI. The GCMs were found in general to reasonably reproduce the observed spatial distribution of genesis. Some of the models also showed ability in capturing observed temporal variation. Based on the evaluation, the models （CGCM3.1-T47 and IPSL-CM4） found to perform best when reproducing both spatial and temporal features were chosen to project future GPI. Results show that both of these models project an upward trend of the GPI under the SRES A2 scenario, however the rate of increase differs between them.展开更多
The quasi-biweekly oscillation （QBWO） is the second most dominant intraseasonal mode over the westem North Pacific （WNP） during boreal summer. In this study, the modulation of WNP tropical cyclogenesis （TCG） by ...The quasi-biweekly oscillation （QBWO） is the second most dominant intraseasonal mode over the westem North Pacific （WNP） during boreal summer. In this study, the modulation of WNP tropical cyclogenesis （TCG） by the QBWO and its association with large-scale patterns are investigated. A strong modulation of WNP TCG events by the QBWO is found. More TCG events occur during the QBWO＇s convectively active phase. Based on the genesis potential index （GPI）, we further evaluate the role of environmental factors in affecting WNP TCG. The positive GPI anomalies associated with the QBWO correspond well with TCG counts and locations. A large positive GPI anomaly is spatially correlated with WNP TCG events during a life cycle of the QBWO. The low-level relative vorticity and mid-level relative humidity appear to be two dominant contributors to the QBWO-composited GPI anomalies during the QBWO＇s active phase, followed by the nonlinear and potential intensity terms. These positive contributions to the GPI anomalies are partly offset by the negative contribution from the vertical wind shear. During the QBWO＇s inactive phase, the mid-level relative humidity appears to be the largest contributor, while weak contributions are also made by the nonlinear and low-level relative vorticity terms. Meanwhile, these positive contributions are partly cancelled out by the negative contribution from the potential intensity. The contributions of these environmental factors to the GPI anomalies associated with the QBWO are similar in all five flow patterns--the monsoon shear line, monsoon confluence region, monsoon gyre, easterly wave, and Rossby wave energy dispersion associated with a preexisting TC. Further analyses show that the QBWO strongly modulates the synoptic-scale wave trains （SSWs） over the WNP, with larger amplitude SSWs during the QBWO＇s active phase. This implies a possible enhanced （weakened） relationship between TCG and SSWs during the active （inactive） phase. This study improves our understa展开更多
基金funded by the Strategic Priority Research Program of the Chinese Academy of Sciences with Grant No.XDA11010000the National Natural Science Foundation of China (No.41205026)+6 种基金the National Basic Research Program of China (2011CB403500)the Innovation Group Program of State Key Laboratory of Tropical Oceanography (LTOZZ1201)Dr.Lei Wang was also sponsored by the Knowledge Innovation Program of the Chinese Academy of Sciences (SQ201208)the foundation for returned scholars of Ministry of Education of Chinathe specialized research fund for the doctoral program of Higher Education for Youthsthe foundation of Guangdong Educational Committee for Youths (2012 LYM_0008)the open fund of the Key Laboratory of Ocean Circulation and Waves of Chinese Academy of Sciences (KLOCAW1309)
文摘This study examines the modulation of tropical cyclogenesis over the South China Sea （SCS） by the E1 Nifio-Southem Oscillation （ENSO） Modoki during the boreal summer. Results reveal that there were more tropical cyclones （TCs） formed over the SCS during central Pacific warming years and less TC frequency during central Pacific cooling years. How different environmental factors （including low-level relative vorticity, mid-level relative humidity, vertical wind shear, and potential intensity） contribute to this influence is investigated, using a genesis potential （GP） index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for central Pacific warming and cooling years separately, which could account for the changes of TC frequency over the SCS in different ENSO Modoki phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results suggest that the vertical wind shear and low-level relative vorticity, which are associated with the ENSO Modold-induced anomalous circulations in Matsuno-Gill patterns, make the largest contributions to the ENSO Modoki modulation of tropical cyclogenesis over the SCS as implied by the GP index. These results highlight the important roles of dynamic factors in the modulation of TC fre-quency over the SCS by the ENSO Modold during the boreal summer.
基金The National Natural Science Foundation of China under contract Nos 42076001,41690121,and 41690120the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)under contract No.311020004the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University under contract No.SL2020PT205.
文摘Threatening millions of people and causing billions of dollars in losses,tropical cyclones(TCs)are among the most severe natural hazards in the world,especially over the western North Pacific.However,the response of TCs to a warming or changing climate has been the subject of considerable research,often with conflicting results.In this study,the abilities of Coupled Model Intercomparison Project(CMIP)Phase 6(CMIP6)models to simulate TC genesis are assessed through historical simulations.The results indicate that a systematic humidity bias persists in most CMIP6 models from corresponding CMIP Phase 5 models,which leads to an overestimation of climatological TC genesis.However,the annual cycle of TC genesis is well captured by CMIP6 models.The abilities of 25 models to simulate the geographical patterns of TC genesis vary significantly.In addition,seven models are identified as well simulated models,but seven models are identified as poorly simulated ones.A comparison of the environmental variables for TC genesis in the well-simulated group and the poorly simulated group identifies moisture in the mid-troposphere as a key factor in the realistic simulation of El Niño-Southern Oscillation(ENSO)impacts on TC genesis.In contrast with the observations,the poorly simulated group does not reproduce the suppressing effect of negative moisture anomalies on TC genesis in the northwestern region(20°–30°N,120°–145°E)during El Niño years.Given the interaction between TC and ENSO,these results provide a guidance for future TC projections under climate change by CMIP6 models.
基金supported by the National Basic Research Program of China(973Program:2012CB955604)National Natural Science Foundation of China(No.40975038,40830106)the CMA Program(GYHY200906008)
文摘The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows an asymmetric bimodal pattern with the maximum genesis number appearing in late October and the second largest in early May. The two peaks correspond to the withdrawal and onset of the BoB summer monsoon, respectively. The semimonthly GP index calculated without TC days over the BoB is consistent with TC genesis frequency, indicating that the index captures the monsoon-induced changes in the environment that are responsible for the seasonal variation of TC genesis frequency. Of the four environmental variables (i.e., low-level vorticity, mid-level relative humidity, potential intensity, and vertical wind shear) that enter into the GP index, the potential intensity makes the largest contribution to the bimodal distribution, followed by vertical wind shear due to small wind speed during the summer monsoon onset and withdrawal. The difference in TC genesis frequency between autumn and late spring is mainly owing to the relative humid-ity difference because a divergence (convergence) of horizontal moisture flux associated with cold dry northerlies (warm wet wester-lies) dominates the BoB in late spring (autumn).
文摘Joint Typhoon Warning Center(JTWC) Best Track data from 1995 to 2014 are processed to examine some specific patterns and trends shown by Typhoons over the Western North Pacific. With a multivariate dataset of 588 TC cases in hand, we carry out a sub-domain analysis by dividing the Western North Pacific region into domains of 2°x2° and find the preferred regions of genesis, favourable direction of movement, steep recurvature, rapid intensification, and rapid decay. The region from longitude 132°E to 134°E and latitude 16°N to 18°N showed the highest number of cases(19) for rapid intensification(RI) and a general pattern is found that the RI systems occurred mostly in the later half of the year with a negative Pacific Decadal Oscillation(PDO) index. Similarly, the domain from longitude 114°E to 116°E and latitude 26°N to 28°N had the highest probability of 0.857 for rapid decay. The probabilities of recurvature for each sub-domain were calculated for angles 30°, 45°, 60°, 90°, 120° and 150°. The sub-domain around longitude 118°E and latitude 12°N had the steepest recurve of 168.69°. It also had a high probability of 0.714 for a recurvature of greater than 90°. The most taken direction of movement of typhoons around the Western North Pacific were analysed in different ways and along the 16 points of compass, the direction from 270° to 292.5° was found to be the most preferred direction of movement.
基金Supported by the National Basic Research Program of China(973Program)(No.2012CB417402)the State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,Chinese Academy of Sciences(No.LTO1510)+3 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA11010102)the National Natural Science Foundation of China(No.41106018)the Funds for Creative Research Groups of China(No.41421005)the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1406401)
文摘To understand the impacts of large-scale circulation during the evolution of E1 Nifio cycle on tropical cyclones （TC） is important and useful for TC forecast. Based on best-track data from the Joint Typhoon Warning Center and reanalysis data from National Centers for Environmental Prediction for the period 1975- 2014, we investigated the influences of two types of E1 Nifio, the eastern Pacific E1 Nifio （EP-E1 Nifio） and central Pacific E1 Nifio （CP-E1 Nifio）, on global TC genesis. We also examined how various environmental factors contribute to these influences using a modified genesis potential index （MGPI）. The composites reproduced for two types of E1 Nifio, from their developing to decaying phases, were able to qualitatively replicate observed cyclogenesis in several basins except for the Arabian Sea. Certain factors of MGPI with more influence than others in various regions are identified. Over the western North Pacific, five variables were all important in the two E1Nifio types during developing summer （July-August-September） and fall （October- November-December）, and decaying spring （April-May-June） and summer. In the eastern Pacific, vertical shear and relative vorticity are the crucial factors for the two types of El Nifio during developing and decaying summers. In the Atlantic, vertical shear, potential intensity and relative humidity are important for the opposite variation of EP- and CP-EI Nifios during decaying summers. In the Southern Hemisphere, the five variables have varying contributions to TC genesis variation during peak season （January-February-March） for the two types of E1 Nifio. In the Bay of Bengal, relative vorticity, humidity and omega may be responsible for clearly reduced TC genesis during developing fall for the two types and slightly suppressed TC cyclogenesis during EP-E1 Nifio decaying spring. In the Arabian Sea, the EP-E1 Nifio generates a slightly positive anomaly of TC genesis during developing falls and decaying springs, but the MGPI failed to c
基金the Strategic Priority Re-search Program of the Chinese Academy of Sciences(No.XDA20060502)the National Key Research and Devel-opment Program of China(No.2019YFA0606701)+2 种基金the National Natural Science Foundation of China(Nos.41925024 and 41731173)the Pioneer Hundred Talents Program of the Chinese Academy of Sciences,the Leading Talents of Guangdong Province Program,Innovation Academy of South China Sea Ecology and Environmental Engineering,Chinese Academy of Sciences(No.ISEE2018PY06)the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Lab-oratory(Guangzhou)(No.GML2019ZD0306).
文摘This study investigates the global performance of the tropical cyclone(TC)genesis potential index based on oceanic parameters(GPI_(ocean))proposed by Zhang et al.(2016).In six major TC formation basins,GPI_(ocean)can represent the seasonal variations of TC genesis over most basins,except for the North Indian Ocean(NIO).The monthly climatological GPI_(ocean)shows only a single peak in the NIO,which cannot describe the bimodal pattern of the annual cycle of TC genesis.To determine the cause of the poor performance of GPI_(ocean)in the NIO,the relative contributions of different parameters related to GPI_(ocean)are calculated and compared with those related to the genesis potential index developed by Emanuel and Nolan(2004)(GPI04).Results show that the net longwave radiation on the sea surface is responsible for the single peak of TC genesis in the NIO in boreal summer.Compared with GPI04,vertical wind shear is not involved in GPI_(ocean).Vertical wind shear is the dominant factor inhibiting TC genesis in the NIO in boreal summer.Therefore,the absence of vertical wind shear in GPI_(ocean)results in the failure of the annual cycle of TC genesis in the NIO.
基金Supported by the National Natural Science Foundation of China(42088101)。
文摘In this study,the differences in spatial distribution and controlling parameters for the formation of near-equatorial tropical cyclones(NETCs)between the western North Pacific(WNP)and the North Atlantic(NA)are investigated.NETCs exhibit distinctive spatial variabilities in different basins.Over the past few decades,the majority of NETCs took place in WNP while none was observed in NA.The mechanism behind such a distinguishing spatial distribution difference is analyzed by using statistical methods.It is noted that the dynamical variables such as low-level relative vorticity and vertical wind shear(VWS)are likely the primary controlling parameters.Compared with NA,larger low-level vorticity and smaller VWS appear over WNP.The increase of vorticity attributes a lot to the turning of northeast trade wind.NETCs in WNP tend to occur in the areas with VWS less than 9 m s^(-1),while the VWS in NA generally exceeds 10 m s^(-1).On the other hand,the sea surface temperature in the near-equatorial region of both of the two oceans exceeds 26.5℃and the difference of mid-level moisture is not significant;thus,thermal factors have little contribution to the distinction of NETC activities between WNP and NA.Intraseasonal oscillation(ISO)and synoptic-scale disturbances in WNP are also shown to be more favorable for NETC genesis.More NETCs were generated in ISO active phase.Synoptic-scale disturbances in WNP obtain more energy from the mean flows through the barotropic energy conversion process.The overall unfavorable thermal and dynamic conditions lead to the absence of NETCs in NA.
基金supported by the Chinese Academy of Sciences under (Grant Nos.KZCX2-YW-Q1-02 and KZCX2-YW-Q11-05)the Major State Basic Research Development Program of China (973 Pro-gram) (Grant No.2009CB421407)the National Natural Science Foundation of China (Grant Nos. 40631005,40775049, and 40805029)
文摘The Tropical Cyclone Genesis Potential Index （GPI） was employed to investigate possible impacts of global warming on tropical cyclone genesis over the western North Pacific （WNP）. The outputs of 20th century climate simulation by eighteen GCMs were used to evaluate the models＇ ability to reproduce tropical cyclone genesis via the GPI. The GCMs were found in general to reasonably reproduce the observed spatial distribution of genesis. Some of the models also showed ability in capturing observed temporal variation. Based on the evaluation, the models （CGCM3.1-T47 and IPSL-CM4） found to perform best when reproducing both spatial and temporal features were chosen to project future GPI. Results show that both of these models project an upward trend of the GPI under the SRES A2 scenario, however the rate of increase differs between them.
基金jointly supported by the National Natural Science Foundation of China(Grant Nos.41675072,41305050,41275093,41475091 and 41305039)the National Basic Research Program of China(Grant Nos.2013CB430301,2013CB430103 and 2015CB452803)+5 种基金the Jiangsu Provincial Natural Science Fund Project(Grant No.BK20150910)the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant No.14KJA170005)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the Project of Global Change and Air–Sea Interaction(Grant No.GASI-03-IPOVAI-04)the base funding of the Atlantic Oceanographic and Meteorological Laboratory(AOML)Earth System Modelling Center Contribution Number 117
文摘The quasi-biweekly oscillation （QBWO） is the second most dominant intraseasonal mode over the westem North Pacific （WNP） during boreal summer. In this study, the modulation of WNP tropical cyclogenesis （TCG） by the QBWO and its association with large-scale patterns are investigated. A strong modulation of WNP TCG events by the QBWO is found. More TCG events occur during the QBWO＇s convectively active phase. Based on the genesis potential index （GPI）, we further evaluate the role of environmental factors in affecting WNP TCG. The positive GPI anomalies associated with the QBWO correspond well with TCG counts and locations. A large positive GPI anomaly is spatially correlated with WNP TCG events during a life cycle of the QBWO. The low-level relative vorticity and mid-level relative humidity appear to be two dominant contributors to the QBWO-composited GPI anomalies during the QBWO＇s active phase, followed by the nonlinear and potential intensity terms. These positive contributions to the GPI anomalies are partly offset by the negative contribution from the vertical wind shear. During the QBWO＇s inactive phase, the mid-level relative humidity appears to be the largest contributor, while weak contributions are also made by the nonlinear and low-level relative vorticity terms. Meanwhile, these positive contributions are partly cancelled out by the negative contribution from the potential intensity. The contributions of these environmental factors to the GPI anomalies associated with the QBWO are similar in all five flow patterns--the monsoon shear line, monsoon confluence region, monsoon gyre, easterly wave, and Rossby wave energy dispersion associated with a preexisting TC. Further analyses show that the QBWO strongly modulates the synoptic-scale wave trains （SSWs） over the WNP, with larger amplitude SSWs during the QBWO＇s active phase. This implies a possible enhanced （weakened） relationship between TCG and SSWs during the active （inactive） phase. This study improves our understa
