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1.
The contribution of tropical cyclones(TCs)to the East Asia–Pacific(EAP)teleconnection pattern during summer was investigated using the best track data of the Joint Typhoon Warning Center and NCEP-2 reanalysis datasets from 1979 to2018.The results showed that the TCs over the western North Pacific(WNP)correspond to a strengthened EAP pattern:During the summers of strong convection over the tropical WNP,TC days correspond to a stronger cyclonic circulation anomaly over the WNP in the lower troposphere,an enhanced seesaw pattern of negative and positive geopotential height anomalies over the subtropical WNP and midlatitude East Asia in the middle troposphere,and a more northward shift of the East Asian westerly jet in the upper troposphere.Further analyses indicated that two types of TCs with distinctly different tracks,i.e.,westward-moving TCs and northward-moving TCs,both favor the EAP pattern.The present results imply that TCs over the WNP,as extreme weather,can contribute significantly to summer-mean climate anomalies over the WNP and East Asia.  相似文献   

2.
This study compares the atmosphere-only HighResMIP simulations from FGOALS-f3-H(FGOALS) and MRIAGCM3-2-S(MRI) with respect to tropical cyclone(TC) characteristics over the Western North Pacific(WNP) for the July–October months of 1985–2014. The focus is on investigating the role of the tropical easterly jet over the Western Pacific(WP＿TEJ) in modulating the simulation biases in terms of their climatological distribution and interannual variability of WNP TC genesis frequency(TCGF) based on the a...  相似文献   

3.
The features of the MJO during two types of El Ni no events are investigated in this paper using the daily NCEP-2reanalysis data, OLR data from NOAA, and Real-time Multivariate MJO index for the period 1979–2012. The results indicate that the MJO exhibits distinct features during eastern Pacific(EP) El Ni no events, as compared to central Pacific(CP) El Ni no events. First, the intensity of the MJO is weakened during EP El Ni no winters from the tropical eastern Indian Ocean to the western Pacific, but enhanced during CP El Ni no winters. Second, the range of the MJO eastward propagation is different during the two types of El Ni no events. During EP El Ni no winters, the MJO propagates eastwards to 120?W, but only to 180?during CP El Ni no winters. Finally, the frequency in eight phases of the MJO may be affected by the two types of El Ni no. Phases 2 and 3 display a stronger MJO frequency during EP El Ni no winters, but phases 4 and 5 during CP El Ni no winters.  相似文献   

4.
In summer 2018, a total of 18 tropical cyclones(TCs) formed in the western North Pacific(WNP) and South China Sea(SCS), among which 8 TCs landed in China, ranking respectively the second and the first highest since 1951.Most of these TCs travelled northwest to northward, bringing in heavy rainfall and strong winds in eastern China and Japan. The present study investigates the impacts of decaying La Ni?a and intraseasonal oscillation(ISO) on the extremely active TCs over the WNP and SCS in summer 2018 by use of correlation and composite analyses. It is found that the La Ni?a episode from October 2017 to March 2018 led to above-normal sea surface temperature(SST) over central–western Pacific, lower sea level pressure and 500-hPa geopotential height over WNP, and abnormally strong convective activities over the western Pacific in summer 2018. These preceding oceanic thermal conditions and their effects on circulation anomalies are favorable to TC genesis in summer. Detailed examination reveals that the monsoon trough was located further north and east, inducing more TCs in northern and eastern WNP; and the more eastward WNP subtropical high as well as the significant wave train with a "-+-+" height anomaly pattern over the midlatitude Eurasia–North Pacific region facilitated the northwest to northward TC tracks. Further analyses reveal that two successively active periods of Madden–Julian Oscillation(MJO) occurred in summer 2018 and the boreal summer intraseasonal oscillation(BSISO) was also active over WNP, propagating northward significantly, corresponding to the more northward TC tracks. The MJO was stagnant over the Maritime Continent to western Pacific,leading to notably enhanced convection in the lower troposphere and divergence in the upper troposphere, conducive to TC occurrences. In a word, the extremely active TC activities over the WNP and SCS in summer 2018 are closely linked with the decaying La Ni?a, and the MJO and BSISO; their joint effects result in increased TC occurrences and the TC tracks being shifted more northwest to northward than normal.  相似文献   

5.
Interannual variability of landfalling tropical cyclones(TCs) in China during 1960-2010 is investigated.By using the method of partial least squares regression(PLS-regression),canonical ENSO and ENSO Modoki are identified to be the factors that contribute to the interannual variability of landfalling TCs.El Ni o Modoki years are associated with a greater-than-average frequency of landfalling TCs in China,but reversed in canonical El Ni o years.Significant difference in genesis locations of landfalling TCs in China for the two kinds of El Ni o phases occurs dominantly in the northern tropical western North Pacific(WNP).The patterns of low-level circulation anomalies and outgoing longwave radiation(OLR) anomalies associated with landfalling TC genesis with different types of El Ni o phases are examined.During canonical El Ni o years,a broad zonal band of positive OLR anomalies dominates the tropical WNP,while the circulation anomalies exhibit a meridionally symmetrical dipole pattern with an anticyclonic anomaly in the subtropics and a cyclonic anomaly near the tropics.In El Ni o Modoki years,a vast region of negative OLR anomalies,roughly to the south of 25°N with a strong large-scale cyclonic anomaly over the tropical WNP,provides a more favorable condition for landfalling TC genesis compared to its counterpart during canonical El Ni o years.For more landfalling TCs formed in the northern tropical WNP in El Ni o Modoki years,there are more TCs making landfall on the northern coast of China in El Ni o Modoki years than in canonical El Ni o years.The number of landfalling TCs is slightly above normal in canonical La Ni a years.Enhanced convection is found in the South China Sea(SCS) and the west of the tropical WNP,which results in landfalling TCs forming more westward in canonical La Ni a years.During La Ni a Modoki years,the landfalling TC frequency are below normal,owing to an unfavorable condition for TC genesis persisting in a broad zonal band from 5°N to 25°N.Since the western North Pacific subtropical high(WNPSH) in La Ni a Modoki years is located in the westernmost region,TCs mainly make landfall on the south coast of China.  相似文献   

6.
In this work,an index of tropical 20-90 d oscillation(intra-seasonal oscillation;ISO)in the western North Pacific(WNP)was determined via the combined empirical orthogonal function(EOF)method using daily outgoing longwave radiation(OLR)field data from the National Oceanic and Atmospheric Administration(NOAA),daily wind field data(at 850 hPa)from the European Centre for Medium-Range Weather Forecasts(ECMWF)and referencing the Madden-Julian oscillation(MJO)index proposed by Wheeler and Hendon.An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone(TC)tracks in the WNP during different ISO phases.The research results indicate that during the easterly phase of the ISO,under the impact of the northeastern airflow of anti-cyclonic ISO circulation,the easterly airflow south of the western Pacific subtropical high is relatively weak,and TCs generated in the subtropical high tend to change their tracks east of 140°E;during the westerly phase,there is a relatively high probability that TCs change their tracks west of 140°E.This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic(anti-cyclonic)circulation coincides with that of the cyclone.  相似文献   

7.
Tropical cyclone(TC) genesis over the western North Pacific(WNP) is analyzed using 23 CMIP5(Coupled Model Intercomparison Project Phase 5) models and reanalysis datasets. The models are evaluated according to TC genesis potential index(GPI). The spatial and temporal variations of the GPI are first calculated using three atmospheric reanalysis datasets(ERA-Interim, NCEP/NCAR Reanalysis-1, and NCEP/DOE Reanalysis-2). Spatial distributions of July–October-mean TC frequency based on the GPI from ERA-interim are more consistent with observed ones derived from IBTr ACS global TC data. So, the ERA-interim reanalysis dataset is used to examine the CMIP5 models in terms of reproducing GPI during the period 1982–2005. Although most models possess deficiencies in reproducing the spatial distribution of the GPI, their multimodel ensemble(MME) mean shows a reasonable climatological GPI pattern characterized by a high GPI zone along 20?N in the WNP. There was an upward trend of TC genesis frequency during 1982 to 1998, followed by a downward trend. Both MME results and reanalysis data can represent a robust increasing trend during 1982–1998, but the models cannot simulate the downward trend after 2000. Analysis based on future projection experiments shows that the GPI exhibits no significant change in the first half of the 21 st century, and then starts to decrease at the end of the 21 st century under the representative concentration pathway(RCP) 2.6 scenario. Under the RCP8.5 scenario, the GPI shows an increasing trend in the vicinity of20?N, indicating more TCs could possibly be expected over the WNP under future global warming.  相似文献   

8.
Climatologically, August is the month with the most tropical cyclone(TC) formation over the western North Pacific(WNP) during the typhoon season. In this study, the reason for abnormal TC activity during August is discussed—especially August 2014, when no TCs formed. The large-scale background of August 2014 is presented, with low-level large-scale easterly anomalies and anticyclonic anomalies dominating over the main TC genesis region, a weak monsoon trough system,and a strong WNP subtropical high(WPSH), leading to significantly reduced low-level convergence, upper-level divergence,and mid-level upward motion. These unfavorable large-scale conditions suppressed convection and cyclogenesis. In August2014, equatorial waves were inactive within the negative phase of the Madden–Julian Oscillation(MJO), with fewer tropical disturbances. Although the low-level vorticity and convection of those disturbances were partly promoted by the convective envelopes of equatorial waves, the integral evolution of disturbances, as well as the equatorial waves, were suppressed when propagating into the negative MJO phase. Moreover, the upper-level potential vorticity(PV) streamers associated with anticyclonic Rossby wave breaking events imported extratropical cold and dry air into the tropics. The peripheral tropospheric dryness and enhanced vertical wind shear by PV streamer intrusion combined with the negative MJO phase were responsible for the absence of TC formation over the WNP in August 2014.  相似文献   

9.
The present study investigates modulation of western North Pacific(WNP) tropical cyclone(TC) genesis in relation to different phases of the intraseasonal oscillation(ISO) of ITCZ convection during May to October in the period 1979-2008.The phases of the ITCZ ISO were determined based on 30-80-day filtered OLR anomalies averaged over the region(5-20 N,120-150 E).The number of TCs during the active phases was nearly three times more than during the inactive phases.The active(inactive) phases of ISO were characterized by low-level cyclonic(anticyclonic) circulation anomalies,higher(lower) midlevel relative humidity anomalies,and larger(smaller) vertical gradient anomalies of relative vorticity associated with enhanced(weakened) ITCZ convection anomalies.During the active phases,TCs tended to form in the center of the ITCZ region.Barotropic conversion from the low-level mean flow is suggested to be the major energy source for TC formation.The energy conversion mainly depended on the zonal and meridional gradients of the zonal flow during the active phases.However,barotropic conversion weakened greatly during the inactive phases.The relationship between the meridional gradient of absolute vorticity and low-level zonal flow indicates that the sign of the absolute vorticity gradient tends to be reversed during the two phases,whereas the same sign between zonal flow and the absolute vorticity gradient is more easily satisfied in the active phases.Thus,the barotropic instability of low-level zonal flow might be an important mechanism for TC formation over the WNP during the active phases of ISO.  相似文献   

10.
The quasi-biweekly oscillation (QBWO) is the second most dominant intraseasonal mode for circulation over the Northwestern Pacific (WNP) during boreal summer. In this study, we investigated how the QBWO modulates tropical cyclone (TC) activities over the WNP from dynamic and thermodynamic perspectives. The propagation of the QBWO can be divided into four phases through empirical orthogonal function analysis of the vorticity at 850 hPa, which was proven to be effective in extracting the QBWO signal. TC generation and landings are significantly enhanced during the active period (phases 1 and 2) relative to the inactive period (phases 3 and 4). Composite analyses show the QBWO could significantly modulate TC activity as it propagates northwestward by changing the atmospheric circulation at both high and low levels. Cumulus convection provides an important link between TCs and the QBWO. The major component of the atmosphere heat source is found to be the latent heat release of convection. The condensation latent heat centers, vertical circulation, and water vapor flux divergence cooperate well during different phases of the QBWO. The vertical profile of the condensation latent heat indicates upper-level heating (cooling) during the active (inactive) phases of the QBWO. Thus, the northwestward propagation of the QBWO can modulate TC activity by affecting the configuration of atmospheric heating over the WNP.  相似文献   

11.
利用中国气象局热带气旋（TC）资料、NCEP/NCAR 再分析资料和美国 NOAA 向外长波辐射（OLR）等资料,分析了2010年西北太平洋（WNP）及南海（SCS）热带气旋活动异常的可能成因,讨论了同期大气环流配置和海温外强迫对TC生成和登陆的动力和热力条件的影响。结果表明,2010年生成TC频数明显偏少,生成源地显著偏西,而登陆TC频数与常年持平。导致7～10月TC频数明显偏少的大尺度环境场特征为：副热带高压较常年异常偏强、西伸脊点偏西,季风槽位置异常偏西,弱垂直风切变带位置也较常年偏西且范围偏小,南亚高压异常偏强,贝加尔湖附近对流层低高层均为反气旋距平环流,这些关键环流因子的特征和配置都不利于 TC 在WNP的东部生成。影响TC活动的外强迫场特征为：2010年热带太平洋经历了El Ni?o事件于春末夏初消亡、La Ni?a事件于7月形成的转换;7～10月,WNP海表温度维持正距平,140°E以东为负距平且对流活动受到抑制;暖池次表层海温异常偏暖,对应上空850 hPa为东风距平,有利于季风槽偏西和TC在WNP的西北侧海域生成。WNP海表温度和暖池次表层海温的特征是2010年TC生成频数偏少、生成源地异常偏西的重要外强迫信号。有利于7～10月热带气旋西行和登陆的500 hPa风场特征为：北太平洋为反气旋环流距平,其南侧为东风异常,该东风异常南缘可到25°N,并向西扩展至中国大陆地区;南海和西北太平洋地区15°N以南的低纬也为东风异常;在这样的风场分布型下,TC容易受偏东气流引导西行并登陆我国沿海地区。这是2010年生成TC偏少但登陆TC并不少的重要环流条件。  相似文献   

12.
应用NOAA气候预测中心提供的热带大气季节内振荡(MJO)客观业务指数及中国气象局上海台风研究所提供的西北太平洋热带气旋(TC)最佳路径资料集,定量统计榆验了MJO对夏季西北太平洋TC活动的调制作用.结果表明:MJO对TC的生成、强度、路径和登陆活动都有显著的调节作用.当高空辐合中心位于120°E～160°E(MJO位相3～5)时,西北太平洋TC生成偏少,且生成位置偏北;而当高空辐合中心位于10°W～70°E(MJO位相8～10)时,西北太平洋TC生成偏多,且生成位置偏南;随着TC强度加强,能达到显著调节作用的MJO位相逐渐减少,当高空辐合辐散中心位于70°E(MJO位相10)时,对TC强度调制最显著.在路径调节方面,MJO位相1～4和10时,TC活跃于菲律宾以东的西北太平洋上,主要路径为西北偏北行,可能登陆华东、华北;而位相5～8时,TC主要活跃在菲律宾附近及以西到南海,以偏西行路径为主,可能登陆华南.MJO对登陆华南TC也有显著影响.该定量统计检验结果可为TC活动季节内预测提供依据.  相似文献   

13.
利用1979—2012年西北太平洋热带气旋最佳路径资料,Hadley中心的海温资料和NCEP/NCAR再分析资料等,研究了夏季(6—10月)热带北大西洋海温异常与西北太平洋热带气旋(Tropical Cyclone,TC)生成的关系及其可能机制。结果表明,夏季热带北大西洋海温异常与同期西北太平洋TC生成频次之间存在显著的负相关关系。热带北大西洋海温的异常增暖可产生一对东—西向分布的偶极型低层异常环流,其中气旋性异常环流位于北大西洋/东太平洋地区,反气旋异常环流位于西北太平洋地区。该反气旋环流异常使得TC主要生成区的对流活动受到抑制、低层涡度正异常、中低层相对湿度负异常、中层下沉气流异常,这些动力/热力条件均不利于TC生成。此外,西北太平洋地区低层涡旋动能负异常,同时来自大尺度环流的涡旋动能的正压转换也受到抑制,不能为TC的生成和发展提供额外能量源。反之亦然。  相似文献   

14.
使用Emanuel和Nolan完善的潜在生成指数(GPI)的计算方法,利用美国联合台风警报中心提供的热带气旋(TC)资料和欧洲中期数值天气预报中心提供的全球ERA-40再分析资料,比较了1970-2001年西北太平洋海域的TC生成频数和GPI的气候特征,分析了包含于GPI中的环境要素对西北太平洋TC频数年代际变化空间分布的影响.结果表明:GPI能近似地表述西北太平洋TC频数的季节变化和空间分布.各环境要素对TC、较弱类TC和较强类TC生成频数的影响有显著差异,相对湿度随着TC强度的增强而减弱,风速垂直切变则相反.西北太平洋TC频数年代际变化空间分布的正异常主要分布于130°E以东,(15°N,140°E)附近最大的正异常频数中心主要受绝对涡度和相对湿度正异常变化的影响;负的风速垂直切变和正的相对湿度异常变化引起了(10～15°N,160°E)附近的TC频数正异常.  相似文献   

15.
By analyzing observational data, previous studies have indicated that the tropical Madden-Julian Oscillation (MJO) is active during the boreal winter but relatively weak during the boreal summer. However, the factors that control seasonal MJO variation are not clear. To quantitatively understand the relative contributions of the occurrence frequency of enhanced MJO events and their averaged strength and lifespan to seasonal MJO amplitude, we defined the MJO events of 1979–2014 and analyzed their features in different seasons by using the Real-time Multivariate MJO (RMM) index and the newly proposed RMM-r index. The results indicate that the MJO events show a higher frequency of occurrence, a stronger intensity and a longer duration during the boreal winter (Dec.–Feb.) and spring (Mar.–May). However, the frequency, strength and lifespan of MJO events are all reduced during the boreal summer (Jun.–Aug.) and autumn (Sep.–Nov.). The enhanced MJO events in winter–spring also show a large ratio of variance for eastward to westward components. To elucidate how large-scale background fields affect seasonal MJO variation, a series of sensitivity experiments was conducted by using a 2.5-layer model that can simulate MJO-like features. It is found that the variation in low-level moisture (vertical wind shear) is the key large-scale factor affecting the seasonal variation in MJO strength (in propagation). In comparison with the summer–autumn seasons when the MJO is relatively weakened, the relatively abundant low-level moisture near the equator during boreal winter–spring may strengthen the development of MJO convection and circulation, whereas the relatively weak easterly shear (or the westerly shear anomaly) is conducive to the enhancement of an eastward-propagating MJO component.  相似文献   

16.
The present study identifies a significant influence of the sea surface temperature gradient(SSTG) between the tropical Indian Ocean(TIO; 15°S-15°N, 40°-90°E) and the western Pacific warm pool(WWP; 0°-15°N, 125°-155°E) in boreal spring on tropical cyclone(TC) landfall frequency in mainland China in boreal summer. During the period 1979-2015, a positive spring SSTG induces a zonal inter-basin circulation anomaly with lower-level convergence, mid-tropospheric ascendance and upper-level divergence over the west-central TIO, and the opposite situation over the WWP, which produces lower-level anomalous easterlies and upper-level anomalous westerlies between the TIO and WWP. This zonal circulation anomaly further warms the west-central TIO by driving warm water westward and cools the WWP by inducing local upwelling, which facilitates the persistence of the anomaly until the summer. Consequently, lower-level negative vorticity, strong vertical wind shear and lower-level anticyclonic anomalies prevail over most of the western North Pacific(WNP), which decreases the TC genesis frequency. Meanwhile, there is an anomalous mid-tropospheric anticyclone over the main WNP TC genesis region,meaning a westerly anomaly dominates over coastal regions of mainland China, which is unfavorable for steering TCs to make landfall in mainland China during summer. This implies that the spring SSTG may act as a potential indicator for TC landfall frequency in mainland China.  相似文献   

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