12号热带风暴"北冕"造成江西暴雨的成因分析(摘要)

对2002年12号热带风暴的北上路径及造成江西暴雨的成因进行了分析,发现12号热带风暴形成后路径北上的主要原因是华北大陆副高明显减弱西退造成,而西太平洋上另外1个副高西伸,使得热带风暴与副高之间的偏南风加强,有利于引导热带风暴北上.当热带风暴周围无明显切变,外围又无弱冷空气时,暴雨主要落在热带风暴中心附近;当热带风暴周围出现切变时,暴雨落在切变附近;当有弱冷空气侵入热带风暴时,暴雨会落在热带风暴与弱冷空气的交汇处.当热带低压强度不强,但有弱冷空气侵入时,降水会明显加强.因此,在考虑台风降水预报时,弱冷空气是一个不可忽视的重要因素.高层辐散的加强,有利于热带低压降水加强.     

湖北省咸宁市台风低压暴雨预报方法初探

分析2003～2006年在我国登陆的21个台风的低压移动路径及与之相对应的地面及高空实况资料表明：湖北省咸宁市台风（含热带风暴）低压暴雨的出现与台风登陆区域及登陆后低压的移动路径和强度密切相关,当在闽、浙登陆的台风低压经江西到达咸宁市或江西西北部和湖南省境内,并且有较强风场相配合时,咸宁市才有可能出现暴雨。欧洲中心850 hPa 24～48 h风场预报与台风低压演变的风场基本吻合,可以作为咸宁市台风低压暴雨预报的依据。     

登陆北上热带气旋的特大暴雨落区探讨

由台风降水资料分析发现,登陆北上热带气旋在我国北方地区造成的特大暴雨,集中出现在华北平原西北部和山东￣辽东半岛东南部两个相距较远的区域内。对比分析表明,这两个特大暴雨落区的形成,除地形增幅因素外,主要与前期副热带高压位置、热带气旋北上路径及物理量场的分布状况直接相关。同时,相应给出了判别上述两个特大暴雨落区的预报指标和方法。     

秋季台风“彩虹”引发的清远暴雨过程分析

为研究1522号台风"彩虹"影响过程中清远地区的暴雨产生机制,利用高空常规气象资料、FY2E红外云图、区域加密自动气象站等资料,应用天气动力学诊断分析方法,对台风"彩虹"的移动路径、环流形势、物理量场和卫星云图特征进行分析。结果表明:该次暴雨过程,副高和低空急流的作用十分显著。低空急流生成于热带气旋右侧,不断将低层高能暖湿空气向暴雨区输送,是暴雨区低空不稳定层结的建立者和维持者,再加上多支低层气流辐合,为暴雨的产生提供了充足的水汽条件和不稳定条件。另外,台风牵引西南季风北上,螺旋云系源源不断北上影响同一区域是暴雨产生的重要原因。     

“环高”热带风暴登陆后路径分析及其对辽宁暴雨影响

2003年第11号热带风暴"环高"在浙江省南部登陆后强度迅速减弱,但其残余云系及水汽仍然继续北上,为辽宁8月22-23日区域性暴雨提供了动力、热力、水汽及充分的能量.本文在分析热带气旋维持、北上条件的基础上,对此次暴雨的成因和物理量进行分析,指出北上热带气旋携带的暖湿空气为暴雨提供了热力条件;热带气旋北上使低空偏南急流加强并维持,为暴雨提供了必要的动力条件;热带气旋为这次暴雨过程提供了充足的能量;热带气旋是这次暴雨过程重要水汽来源.     

2016年三个相似路径台风影响江西的暴雨落区差异成因

利用常规气象观测数据、台风路径资料和FNL再分析资料,对2016年三个路径相似台风(01号Nepartak、14号Meranti和17号Megi)在江西的暴雨落区差异进行分析。结果表明:三者移动路径相似,登陆后副热带高压强度、水汽输送条件、台风与冷空气结合等差异共同导致在江西暴雨落区不同。台风Megi在江西形成暴雨范围最广,Nepartak次之,Meranti最小。台风Megi登陆后江西地区水汽通量和天气尺度上升运动最强,天气尺度持续稳定性降水以及后期台风环流与低层冷空气相结合,导致降水累计值最大。台风Nepartak影响江西期间无冷空气与之作用,形成的降水以中尺度对流性降水为主,强的对流有效位能释放加剧中尺度对流上升运动,造成以短时强降雨为主的暴雨。台风Meranti影响时江西东北部天气尺度上升运动相对前两者较弱,影响时间相对较短,形成的暴雨较前两者偏弱。     

1949—2015年北上热带气旋特征

利用1949—2015年CMA STI热带气旋(TC：Tropical Cyclone)最佳路径数据集、NCEP25°×25°再分析资料及常规资料,对北上TC特征进行研究。结果表明：1949—2015年进入北上定义区的TC共计91个,占西北太平洋（包含南海）TC总数41%,年平均14个;进入定义区最早5月,最晚9月,最多8月,但7月北上几率最大。依据TC运动形态特征将北上TC路径分为转向北上和直接北上两大类,其中转向北上TC转向之后路径与转向点密切联系,这对北上TC路径预报有重要意义。北上TC生成源地主要在8°~25°N,122°~155°E,不同路径北上TC源地纬度、经度分布有差异,源地偏北的TC未来转向点偏北和直接北上的可能性大。北上TC一般在定义区外20°N左右达到生命史最大强度,进入定义区后强度大多减弱为热带风暴,强度越强减弱速度越快;进入影响区后发生变性的TC明显增加。北上TC路径与西太平洋副热带高压的主体位置、形态和强度有关,副高西端高脊的引导气流决定北上TC未来路径是转向还是北上,西脊点的位置决定北上TC未来转向点的位置。不同路径北上TC暴雨和大风天气区分布存在差异,中纬转向、高纬转向和直接北上路径是造成北方强烈降水和大风的主要路径。     

台风“风神”路径、强度及引发江西降水诊断分析

利用NCEP 1°×1°再分析资料、T213分析资料和常规观测资料,从水汽条件、热力条件、动力条件等方面,对2008年第6号台风“风神”路径、强度变化的原因,及其对江西的影响进行分析。结果表明,台风路径与副高的强度和位置变化密切相关,台风移动方向与风场结构中强风速的风向一致。台风在海上强度减弱主要与水汽来源不足有关,登陆后还与冷空气侵入暖中心有关。由于强度减弱且西南季风不强,造成水汽来源不足,从而导致“风神”没有给江西造成大范围暴雨天气。其中的局地强降水天气发生在台风环流高能梯度锋区,这主要是由于干侵入引发对流性不稳定造成的。     

2012年两次台风造成黑龙江省大范围暴雨的成因对比分析

用常规观测资料和红外卫星云图资料对2012年台风"布拉万"和"三巴"登陆后变性北上给黑龙江省造成大范围暴雨天气过程成因进行了对比分析。结果表明台风"布拉万"、"三巴"受不同大气环流背景影响导致台风北上的路径不同;登陆北上后与冷空气结合形成不同的温压场结构、垂直上升运动大值区及云系导致降水落区和强度的不同。     

台风"碧利斯"特点及动力成因分析

利用常规观测资料、T213资料、FY-2C卫星资料和多普勒雷达资料等,对0604号台风“碧利斯“进行了综合研究,并与历史上相似路径的台风进行了对比分析.分析结果表明,“碧利斯“造成的暴雨出现在江西中南部,与历史上进入赣南的热带气旋一般特点相一致;“碧利斯“路径与副高的位置和演变有关;“碧利斯“造成的江西暴雨落区,与辐合上升运动中心及高层辐散中心对应较好,并与台风不对称环流、地形、不稳定能量等因素有关;暴雨与湿位涡呈反位相相关,且在暴雨较强时相关性更好.     

台风移速突变的数值研究

用准地转正压模式，在无环境气流的情况下，实施了８组时间积分大于５个模式日的试验。在模式大气台风移动的过程中，清楚地显示了移速突然变化的现象。台风移速突然变化与前期台风环流的非对称结构之间存在着密切的联系。最后分析了台风环流非规则结构对路径的影响。     

Local and remote impacts of a tropical Atlantic salinity anomaly

The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean–atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector after ten years. It has the form of a robust wave-like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the Amazonian basin. Meanwhile, the salt anomaly is carried northward by the mean oceanic circulation. It is traced up to the convection sites and then on its return path at depth towards lower latitudes. Consistent with the density increase, deep convection is enhanced after the arrival of the salt anomaly and the Atlantic meridional overturning circulation (AMOC) intensifies about 20 years after the beginning of the perturbation. The adjustment of the tropical Atlantic to the AMOC intensification then modifies its initial response to the freshwater forcing, leading to a weaker cooling in the northern tropical Atlantic than in the southern tropical Atlantic, a slight northward shift of the tropical Atlantic precipitation pattern and an intensification of the North Brazil current. On the other hand, no significant anomalous precipitations are found in the Pacific. The initial remote atmospheric response is also modulated, by an NAO-like response to the AMOC intensification.     

1998年区域性水汽输送及对流活动与副高活动变异的相关特征(英)

根据1998年NCEP逐日资料和TBB逐日资料,探讨了低纬度对流活动和副高周边水汽输送及其对流活动对夏季西太平洋副热带高压季节性北跳、南撤的影响效应。研究表明:低纬热带对流加强,且110°-150°E地区的南北向垂直经圈环流下沉区北移,夏季西太平洋副热带高压有北跳现象。另外,诊断结果亦表明西太平洋副高周边纬向水汽输送的显著减弱亦预示将出现副高的北跳,而西太平洋地区低纬经向水汽输送减少一候之后,副高南撤。研究结果表明西太平洋副高北跳、南撤与低纬度的对流潜热释放、中纬西太平洋副高周边的水汽输送及其对流活动存在密切的关系。数值模拟结果进一步证实上述副高活动变异与前期水汽输送及其对流特征的相关关系。     

我国秋季降水的年际变化及与热带太平洋海温异常分布的关系

利用我国160个站点58年(1951～2008年)的降水资料、NCEP/NCAR再分析环流资料和Hadley海表温度资料,对我国秋季降水年际变化的特征和可能成因进行了分析。结果显示,秋季降水前两模态分别反映长江流域及以南地区和长江以北的江淮、黄淮、华北、四川盆地北部至河套等地降水的变化,两降水模态的变化都以年际尺度为主,年代际变化特征不明显。就环流形势而言,第一模态的年际变化主要与西太平洋副热带高压的强度及相应的对流层低层菲律宾群岛附近的异常气旋/反气旋联系紧密,第二模态的年际变化则可能受到副热带高压的南北位置和相应的日本岛附近的异常气旋/反气旋的影响。同时,两模态及相应的异常环流还分别与热带东印度洋和热带西太平洋附近的异常垂直运动关系密切,热带地区的异常垂直运动可能通过经圈方向的异常环流影响到东亚地区。此外,两降水模态不仅与热带地区的异常环流关系密切,而且与热带海温异常也存在紧密的联系。与两模态相关联的热带太平洋海温异常显示出不同的分布特征,当热带东太平洋偏暖/冷,西太平洋偏冷/暖时,长江以南地区降水偏多/少。而当热带东太平洋和中太平洋一致偏暖/冷时,长江以北地区降水易偏少/多。两降水模态与热带海温及热带地区异常环流之间的密切关系显示热带太平洋海温异常的不同分布可能通过激发不同的热带地区异常垂直环流形势而对降水产生影响。     

江西省夏季降水年际变化的机理研究

通过对观测资料和大气再分析资料的诊断分析,研究了影响江西省夏季降水变率的物理机制。结果表明江西省夏季降水存在显著的年际变率。极端条件下,降水偏多的夏季可达降水偏少的夏季的降水量的三倍。中纬度地区的准静止波列和热带关键海区的海温异常是造成江西夏季降水异常的主要原因。当江西省夏季降水偏多时,欧亚大陆地区存在"正—负—正"的准正压Rossby波列结构,位于贝加尔湖的正活动中心能引导干冷空气南下,从而有利于江南地区的锋生和江西降水的增加。此外,当江西省夏季降水偏多时,前期冬季中东太平洋地区有El Ni1o事件的活动,并能通过大气桥在夏季印度洋地区形成正海温异常。通过"印度洋电容器"机制,印度洋的暖海温能激发向东传播的Kelvin波,引起菲律宾地区降水的减少。菲律宾地区抑制的降水能激发向北传播的EAP/PJ波列,使得西太平洋副热带高压西伸增强,从而有利于水汽向江南地区的输送,并造成江西夏季的降水增加。     

Characteristics of Subtropical Monsoon and Rainfall over Eastern China and Western North Pacific

Using the NCAR/NCEP (National Center for Atmospheric Research/National Centers for Environmental Prediction) reanalysis and the NOAA Climate Prediction Center's merged analysis of precipitation (CMAP)during 1981-2000, we investigated the seasonal evolution of the southwesterly wind and associated precipitation over the eastern China-subtropical western North Pacific area and its relationship with the tropical monsoon and rainfall, and analyzed the reasons responsible for the onset and development of the wind. It was found that the persistent southwesterly wind appears over southern China and the subtropical western Pacific the earliest in early spring, and then expands southwards to the tropics and advances northward to the midlatitudes. From winter to summer, the seasonal variation of surface heating over western China and the subtropical western Pacific may result in an earlier reversal of the westward tropospheric temperature gradient over the subtropics relative to the tropics, which may contribute to the earliest beginning of the subtropical southwesterly wind. Additionally, the strengthening and eastward expanding of the trough near the eastern Tibetan Plateau as well as the strengthening and westward moving of the western Pacific subtropical high also exert positive influences on the beginning and development of the subtropical southwesterly wind.In early summer,the northward expansion of the southwesterly wind over southern China is associated with a northward shift of the subtropical high, while the southward stretch of the southwesterly wind is associated with a southward stretch of the trough in the eastern side of the plateau. With the beginning and northward expansion of the subtropical southwesterly wind (namely southwest monsoon), convergences of the low-level air and water vapor and associated upward motion in front of the strongest southwesterly wind core also strengthen and move northward, leading to an increase in rainfall intensity and a northward shift of the rain belt. Accordingly, the subtropical rainy season occurs the earliest over southern China in spring, moves northward to the Yangtze-Huaihe River valley in early summer, and arrives in North China in mid summer.Compared with the subtropical rainy season, the tropical rainy season begins later and stays mainly over the tropics, not pronouncedly moving into the subtropics. Clearly, the Meiyu rainfall over the Yangtze-Huaihe River valley in early summer results from a northward shift of the spring rain belt over southern China,instead of a northward shift of the tropical monsoon rain belt. Before the onset of the tropical monsoon,water vapor over the subtropical monsoon region comes mainly from the coasts of the northern Indo-China Peninsula and southern China. After the onset, one branch of the water vapor flow comes from the Bay of Bengal, entering into eastern China and the subtropical western Pacific via southwestern China and the South China Sea, and another branch comes from the tropical western North Pacific, moving northwestward along the west edge of the western Pacific subtropical high and entering into the subtropics.     

Responses of global monsoon and seasonal cycle of precipitation to precession and obliquity forcing

In this paper, the response of global monsoon to changes in orbital forcing is investigated using a coupled atmosphere–ocean general circulation model with an emphasis on relative roles of precession and obliquity changes. When precession decreases, there are inter-hemispheric asymmetric responses in monsoonal precipitation, featuring a significant increase over most parts of the Northern Hemisphere (NH) monsoon regions and a decrease over the Southern Hemisphere (SH) monsoon regions. In contrast, when obliquity increases, global monsoon is enhanced except for the American monsoon. Dynamic effects (caused by changes in winds with humidity unchanged) dominate the monsoonal precipitation response to both precession and obliquity forcing, while thermodynamic effects (caused by changes in humidity with winds unchanged) is related to the northward extension of the North African summer monsoon. During minimum precession, the seasonal cycle of tropical precipitation is advanced with respect to the maximum precession. The rainfall increase in the transitional season (April-June in the NH and October-December in the SH) is dominated by the dynamic component. From an energetics perspective, the southward (northward) cross-equatorial energy transport during April-June (October-December) corresponds to a northward (southward) shift of tropical precipitation, which results in a seasonal advance in the migration of tropical precipitation. Nonetheless, there is no significant change in the seasonal cycle in response to obliquity forcing.

     

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.     

0605号台风"格美"在江西致灾的气象成因分析

运用常规观测资料、T213资料等,对0605号台风“格美”的移动路径和暴雨成因进行了分析。分析结果表明,“格美”登陆后虽然强度迅速减弱,但由于其减弱后的低气压环流在江西逗留时间长,所携带的水汽和造成的辐合上升条件足以造成江西出现暴雨天气。通过分析探空、地面加密自动站和闪电定位等资料进一步指出,地面中尺度辐合线、对流不稳定和地形抬升的共同作用,加剧了赣西南局地降雨的强度。由于前期台风“碧利斯”已造成赣州市出现较强降水,赣南土壤含水量、地下水位和江河湖库水位均较高,使得“格美”造成的短时强降雨迅速产生有效径流和汇流,导致局地山洪暴发而致灾。