2008年西北太平洋热带气旋活动特征分析

对2008年西北太平洋及我国南海热带气旋的活动特征进行总结,并从多方面分析其成因.结果指出:2008年西北太平洋热带气旋活动的主要特征为生成总数少,源地集中,位置偏西;登陆数多、时间早;登陆地点偏南、时间集中等.其原因主要在于:在热带气旋的多发期副热带高压面积偏大、强度偏强、西伸脊点异常偏西,且脊线偏南,造成西北太平洋热带地区盛行偏东风,不利于热带扰动的生成和发展;同时,也使得在其南侧生成的热带气旋易在偏东气流的引导下登陆我国南方.另外,季风槽、垂直风切变、海表温度和热带辐合带上的对流活动等因子的异常分布都不利于热带气旋在西北太平洋东部海域生成,直接导致这一年热带气旋生成总数明显偏少,源地显著偏西.     

201208号热带气旋“韦森特”影响南宁机场天气过程分析

通过对2012年第8号热带气旋"韦森特"天气气候特征的分析,得出:热带气旋的前期移动受季风槽影响,后期副热带高压西伸加强引导"韦森特"移动。     

2013年影响广西热带气旋频数偏多的成因分析

使用1951—2013年NOAA OLR、NCEP/NCAR风场和高度场再分析资料、中国气象局热带气旋资料,分析2013年影响广西热带气旋数量偏多的原因。结果表明：2013年6—9月西太平洋副热带高压明显偏强,西伸脊点明显偏西,脊线略偏北,同时副热带高压南侧对流活跃,降水过程潜热释放有助于副热带高压位置偏北,这种形势非常有利于热带气旋向广西移动。索马里越赤道气流强劲,在南海及菲律宾与北太平洋反气旋西南侧的东南气流相遇,形成季风槽,非常有利于热带气旋生成频数偏多。热带低频强对流带在印度洋和西太平洋活动频繁,并分别向东向西移动;赤道东太平洋海温偏低;哈得来和沃克环流较常年偏强,沃克环流上升支位置偏西,这些也可能是2013年影响广西热带气旋数量偏多的原因之一。     

两个移速快、强度强、路径相似的台风过程分析

0814强台风"HAGUPIT"和9615台风"SALLY"具有移速快、强度强、路径相似的特点,通过分析得出,500 hPa不断加强的大陆副热带高压,南侧偏东引导气流加强,使热带气旋移速不断加快,而且与热带气旋同向移动增强的副热带高压,使其移速更快。越赤道气流增强和维持,给热带气旋不断输送能量,对流层高层强辐散,弱纬向风垂直切变都有利于热带气旋显著加强和维持。     

1994年8月亚洲季风区水汽的源汇分布和输送

用正压原始方程模式,对热带气旋穿越副热带高压的异常路径进行了数值试验,揭示出热带气旋自身特征及其与副高中心的经向距离、副高的位置和强度变化是直接影响热带气旋移动路径的敏感因子。也反映出热带气旋与其邻近的天气尺度的副热带高压以及β效应三者之间非线性相互作用的复杂机制。     

鞍型场对热带气旋移动路径影响的研究

鞍型场是一种特殊的流场,鞍点附近气压梯度很小,风场很弱,引导气流不明显。当热带气旋进入鞍型场时,会表现为停滞、打转、突然转向等异常路径。采用NCEP资料对2011年热带气旋"梅花"路径和大尺度形势场分析结果表明,在其整个生命史中出现三次移动路径转折,热带气旋进入鞍型场后,出现在鞍点附近停滞、移动缓慢、突然转向等异常路径。利用理想变形场和兰金涡旋相结合的鞍型场作为背景场,用梯度风平衡构造了理想热带气旋,分别考虑了科氏参数为常数和β平面近似两种情况,利用二维浅水模式对热带气旋处于鞍点和收缩轴附近不同位置的情况进行了数值对比试验。当科氏参数为常数时,处于鞍点位置的热带气旋在鞍点停滞;而当采用β平面近似时,处于鞍点位置的热带气旋向东北低压一侧移动,并和低压合并。当初始热带气旋处于鞍点南侧的收缩轴上以及偏东或偏西100 km时,会出现三种截然不同的移动路径。试验结果表明:鞍型场对热带气旋有"陷阱"作用。当热带气旋进入到鞍型场区并接近鞍点时,在β漂移和弱引导气流作用下,可能陷入鞍点附近区域,移动缓慢,出现异常路径,也可能沿着膨胀轴向偏东或偏西方向移动,使得热带气旋突然转向。热带气旋的移动对其和收缩轴的相对位置十分敏感,数十千米的偏差可能会导致截然相反的移动路径。     

印度洋海温异常对西太平洋副热带高压的影响——大气中的两级热力适应

利用热力适应理论讨论了印度洋海温异常影响中国天气和西太平洋副热带高压异常的物理机制。结果表明 :通过第一级热力适应 ,印度洋上的海温异常形成低层气旋式环流 ,并在其东侧的偏南气流中产生对流性降水 ;然后通过第二级热力适应 ,在 50 0 h Pa上导致西太平洋副热带高压加强西伸、2 0 0 h Pa上南亚高压异常增强。从而证明两级热力适应是导致印度洋海温异常影响中国天气气候异常的重要物理机制。     

影响辽东半岛的热带气旋降水分析

选取移动路径和转向趋势极为相似的两个热带气旋——9711（Winnie）和9406（Tim）为例，对其路径、降水量、移动速度进行对比分析，结果表明，Winnie路径偏东，转向后移动速度增幅大，在辽东半岛地区的降水量大；Tim路径偏西，转向后移动速度增幅小，强降水偏西。并针对其在辽东半岛造成的降水量的差异，采用NCEP全球分析资料，诊断分析其环境流场和结构特征，分析表明，除了地形和海洋的影响，副热带高压位置、高低空急流和锋区与辽东半岛地区的强降水有直接关系。Winnie影响期间，有利、稳定的副高位置使来自东南和西南的暖湿空气输送到辽东半岛上空，并阻挡着低压系统东移出海，使降水持续增加；高低空急流在高空急流人口区上升支环流圈内耦合，对流层上层强辐散场的抽吸作用及高位涡的向下输送，有利于气旋的发展加强；东、西两侧冷空气作用使其变性加强，形成温带气旋，引起强降水。Tim影响期问，副高中心偏西、偏北，高低空急流在高空急流出口区下沉支环流圈内相互作用，其上空辐散强度较弱，只是Winnie的八分之一，不利于气旋的发展加强；Tim位于高空槽后，获得负涡度平流，在东部弱冷空气作用下，引起台风弱变性，并没有形成气旋，在东北地区被西风槽合并后消失，辽东半岛只出现10mm以下的降水。     

热带西南季风对0214号热带气旋“黄蜂”的影响

采用中国数值预报创新基地最新开发的三维变分同化系统(Grapes 3DVAR)的分析场为模式初值场,利用广州热带海洋气象研究所开发的南海热带气旋业务预报模式,在模拟试验(控制试验)的基础上,对强、弱热带西南季风作对比试验(异常试验)研究.试验结果表明除环境引导气流外,"黄蜂"偏心结构变化引起的偏心运动变化对热带气旋移向、移速的变化起了一定的作用;西南季风对热带气旋"黄蜂"的动力结构、热力结构和移动路径都有一定的影响;热带西南季风通过改变热带气旋的不对称结构和削弱副热带高压西侧这两个途径,造成热带气旋路径右偏.     

PDO对西北太平洋热带气旋活动与大尺度环流关系的影响

利用NCEP再分析资料和上海台风研究所整编的热带气旋资料,研究了在太平洋年代际振荡(PDO)冷暖位相中西北太平洋热带气旋频数与太平洋海表温度(SST)年际相关的分布差异,以及500 hPa高度场对热带气旋频数和生成源地的影响.结果表明,在PDO冷位相时期,热带气旋频数与赤道东太平洋SST存在显著相关,副热带高压位置偏东...     

Subseasonal Zonal Oscillation of the Western Pacific Subtropical High during Early Summer

This study examines the features and dynamical processes of subseasonal zonal oscillation of the western Pacific subtropical high (WPSH) during early summer, by performing a multivariate empirical orthogonal function (MVEOF) analysis on daily winds and a diagnosis on potential vorticity (PV) at 500 hPa for the period 1979–2016. The first MV-EOF mode is characterized by an anticyclonic anomaly occupying southeastern China to subtropical western North Pacific regions. It has a period of 10–25 days and represents zonal shift of the WPSH. When the WPSH stretches more westward, the South Asian high (SAH) extends more eastward. Above-normal precipitation is observed over the Yangtze–Huaihe River (YHR) basin. Suppressed convection with anomalous descending motion is located over the subtropical western North Pacific. The relative zonal movement of the SAH and the WPSH helps to establish an anomalous local vertical circulation of ascending motion with upper-level divergence over the YHR basin and descending motion with upper-level convergence over the subtropical western Pacific. The above local vertical circulation provides a dynamic condition for persistent rainfall over the YHR basin. An enhanced southwest flow over the WPSH’s western edge transports more moisture to eastern China, providing a necessary water vapor condition for the persistent rainfall over the YHR basin. A potential vorticity diagnosis reveals that anomalous diabatic heating is a main source for PV generation. The anomalous cooling over the subtropical western Pacific produces a local negative PV center at 500 hPa. The anomalous heating over the YHR basin generates a local positive PV center. The above south–north dipolar structure of PV anomaly along with the climatological southerly flow leads to northward advection of negative PV. These two processes are conducive to the WPSH’s westward extension. The vertical advection process is unfavorable to the westward extension but contributes to the eastward retreat of the WPSH.     

Anomalous Western Pacific Subtropical High during Late Summer in Weak La Nia Years: Contrast between 1981 and 2013

Both 1981 and 2013 were weak La Niña years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the western Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak.     

2013年盛夏中国中东部高温天气的成因分析

为了研究2013年盛夏中国中东部地区异常高温天气的成因,根据中国191个站地面观测资料和NCEP/NCAR再分析资料,利用热力学方程进行了诊断分析。结果表明,非绝热加热(主要是长波净辐散)是夏季中国中东部地区升温最为主要的因子,但2013年盛夏中国中东部地区温度异常偏高(距平)主要是由中低层异常偏强(相对常年平均)的下沉运动造成的,偏强的非绝热加热也有一定的贡献,而异常的温度平流(冷平流)则起着负贡献。结合天气形势分析发现,500 hPa西太平洋副热带高压(西太副高)偏强、偏西、偏北和200 hPa南亚高压偏强、偏东、偏北是造成2013年盛夏中国中东部地区中低层下沉运动偏强的主要原因,偏强的下沉运动又会使空中云雨减少,地表吸收的太阳短波辐射偏强,地表温度偏高,地表向上的感热通量和长波辐射也随之增大。结合海表温度的分析发现,2013年盛夏西太副高偏强、偏西、偏北主要是由赤道西太平洋地区、黑潮地区和北半球西风漂流区海面温度异常偏高造成的。     

气候变暖背景下西太平洋副热带高压体形态变异及热力原因

采用美国NCEP/NCAR再分析资料,利用相关、合成分析、大气热源的计算等方法,研究了气候变暖背景下西太平洋副热带高压（副高）空间形态的变异及热力原因。结果表明,气候变暖前、后各层副高形态特征有很大的差异,副高体的空间形态从850—700 hPa开始显著西伸南扩,到500 hPa最为明显。各层副高在冷、暖期的形态差异与其周围大气热源和涡度的变化相对应。随着气候变暖,副高西侧和南侧的大气热源在850—700 hPa上开始有明显的加强,500 hPa热源加强最明显,且副高体南侧热源中心有所南移;同时,其西侧和南侧从对流层低层至中高层有反气旋涡度的增大,西侧的反气旋涡度在850—700 hPa增大最明显,南侧的反气旋涡度在500 hPa增大最明显,且反气旋中心整体南移。表明气候变暖后,副高体西侧和南侧大气热源的加强,导致相应区域反气旋涡度增大,副高体向反气旋涡度增大的方向发展,从而使副高西脊点西伸,南边界南扩,整体南移。      

Sensitivity Experiments on the Poleward Shift of Tropical Cyclones over the Western North Pacific under Warming Ocean Conditions

Recent studies found that in the context of global warming, the observed tropical cyclones (TCs) exhibit significant poleward migration trend in terms of the mean latitude where TCs reach their lifetime-maximum intensity in the western North Pacific (WNP). This poleward migration of TC tracks can be attributed to not only anthropogenic forcing (e.g., continuous increase of sea surface temperature (SST)), but also impacts of other factors (e.g., natural variability). In the present study, to eliminate the impacts of other factors and thus focus on the impact of unvaried SST on climatological WNP TC tracks, the mesoscale Weather Research and Forecasting (WRF) model is used to conduct a suite of idealized sensitivity experiments with increased SST. Comparisons among the results of these experiments show the possible changes in climatological TC track, TC track density, and types of TC track in the context of SST increase. The results demonstrate that under the warmer SST conditions, the climatological mean TC track systematically shifts poleward significantly in the WNP, which is consistent with the previous studies. Meanwhile, the ocean warming also leads to the decreased (increased) destructive potential of TCs in low (middle) latitudes, and thus northward migration of the region where TCs have the largest impact. Further results imply the possibility that under the ocean warming, the percentage of TCs with westward/northwestward tracks decreases/increases distinctly.     

2018年夏季东北极端高温事件物理机制分析

基于观测资料和再分析资料,研究分析了2018年夏季中国东北地区持续多日出现高温异常事件的形成机理。首先分析了整个夏季该地区观测台站逐日的温度资料,计算了观测台站的超热因子（Excess Heat Factor,EHF）指数,发现东北地区出现高温异常的时段主要是7月和8月,异常高温的发生区域集中在东北南部。在此期间,东亚大气环流形势的异常主要表现为南亚高压和西太平洋副热带高压强度异常增强,作用相互重叠和位置持续偏北。进一步的分析可以注意到,二者的重叠造成研究区域内有负涡度异常增强,使得南亚高压和西太平洋副热带高压在北推的过程中不断带动东北南部上空负涡度异常增强,并伴随有异常下沉气流,下沉绝热增温与晴空辐射增温,这可能是东北南部地表增温的一个重要原因。相关分析证实,在整个夏季东北南部地表气温与其上空300 hPa至500 hPa涡度异常都有显著的负相关关系。因此,南亚高压和西太平洋副热带高压之间的相互叠加组合是导致东北南部在2018年夏季7、8月份出现高温异常的主要原因。进一步的研究发现,夏季副热带西风急流中准定常Rossby波能量的传播与南亚高压和西太平洋副热带高压异常增强有密切联系,同时夏季西太平洋暖池的显著增暖导致了菲律宾地区异常旺盛的对流活动,进而在500 hPa高度场上激发出PJ（太平洋—日本涛动）波列,从另一个路径上促进了西太平洋副热带高压偏强偏北。     

热带气旋进入北部湾后强度增强的环流特征分析

利用NCEP/NCAR再分析资料,对1949年以来7个进入北部湾后强度突然增强的热带气旋(TC)环流背景特征及物理量场特征进行分析,结果表明,有利TC进入北部湾后强度增强的环流背景是:(1)西太平洋副热带高压稳定加强西伸,(2)热带辐合带北抬至华南沿海活动,(3)西南季风爆发处于活跃期,(4)东风波西移叠加,(5)有适度的弱冷空气侵入;对物理量场的合成分析表明,TC进入北部湾前和进入北部湾后,环流中心附近500hPa涡度变化极小,200hPa高空散度增大,500hPa垂直上升速度增大,850hPa中南半岛水汽输送量增大。     

Northward Shift in Landfall Locations of Tropical Cyclones over the Western North Pacific during the Last Four Decades

This study analyzes landfall locations of tropical cyclones(TCs)over the western North Pacific during 1979–2018.Results demonstrate that the landfall locations of TCs over this region have shifted northward during the last four decades,primarily due to the shift of landfalling TC tracks,with the decreasing/increasing proportion of westward/northward TC tracks.In particular,the northward shift of the landfalling TCs was not related to their formation locations,which have not markedly changed,whereas"no-landed"TCs have significantly shifted northward.TC movement was significantly and positively correlated to the zonal component of the steering flow,while the correlation between TC movement and the meridional component of the steering flow was relatively unobvious.The westward steering flow in the tropical central Pacific that occurred around the formation and early development of the westward TCs was significantly weakened,which was unfavorable for their westward movement,thereby,causing the higher proportions of northward moving tracks.This weakened westward flow was related to the northward shift of the subtropical high ridge,which was caused by significant weakening of the southern part of the subtropical high.The vertical wind shear,sea surface temperature,and convective available potential energy also showed that the northern region of the western North Pacific became more favorable for TC development,whereas the upper divergence,low-layer relative vorticity,and accumulated water vapor content were not obviously related to the northward shift of TCs.     

用南亚高压和西太副高的周期关系做多雨时段的预报研究

对１００ｈＰａ南亚高压的振荡指数及５００ｈＰａ西太平洋副高的强度指数、西进指数进行了谱分析,着重考察了５天到一个月的振荡周期。通过分析得出,南亚高压的显著周期主要是准两周周期,西太平洋副高的显著周期主要是准一周周期,其次是准 两周周期;在多数情况下,南亚高压东进比西太平洋副高西伸加强提前１￣２天;南亚高压的显著周期与西太平洋副高的显著周期叠加时,陕西地区可出现多雨时段。     

Influence of monsoon over the warm pool on interannual variation on tropical cyclone activity over the western North Pacific

The relationship between the interannual variation in tropical cyclone （TC） activity over the western North Pacific （WNP） and the thermal state over the warm pool （WP） is examined in this paper. The results show that the subsurface temperature in the WP is well correlated with TC geographical distribution and track type. Their relation is linked by the East Asian monsoon trough. During the warm years, the westward-retreating monsoon trough creates convergence and vorticity fields that are favorable for tropical cyclogenesis in the northwest of the WNP, whereas more TCs concentrating in the southeast result from eastward penetration of the monsoon trough during the cold years. The steering flows at 500 hPa lead to a westward displacement track in the warm years and recurving prevailing track in the cold years.
The two types of distinct processes in the monsoon environment triggering tropical cyclogenesis are hypothesized by composites centered for TC genesis location corresponding to two kinds of thermal states of the WP. During the warm years, low-frequency intraseasonal oscillation is active in the west of the WNP such that eastward-propagating westerlies cluster TC genesis in that region. In contrast, during the cold years, the increased cyclogenesis in the southeast of the WNP is mainly associated with tropical depression type disturbances transiting from equatorially trapped mixed Rossby gravity waves. Both of the processes may be fundamental mechanisms for the inherent interannual variation in TC activity over the WNP.