INFLUENCE OF THE VERTICAL SHEAR OF ENVIRONMENTAL FLOWS ON TYPHOON MOTION

Typhoon is regarded as a convergent,modified Rankine vortex.Based on the vorticity equations written at two levels,higher and lower in the troposphere,typhoon motions are discussed in this study.The analytical expressions of vortex motion direction and speed have been derived for simple homogeneous basic flows at two levels.The expressions indicate that in the easterties,vertical wind shear enhances the steering of east flow, causing the vortex moving westward faster,otherwise,in the westerlies,it reduces the steering of the west flow, causing the vortex moving eastward slower.These results explain theoretically that“cyclones in the easterlies move to the right of,and faster than the basic flow;conversely,cyclones in the westerlies move to the left of,and slower than the basic flow.” With derived baroclinic diagnostic equations and a barotropical model,ten cases from 1980 to 1983 have been calculated for 24h typhoon motions.The results show that the baroclinic models are better than the baro- tropic ones.Therefore,the vertical wind shear is one of the important factors affecting typhoon movement.

Effect of the Interaction of Different Scale Vortices on the Structure and Motion of Typhoons

Five numerical experiments have been performed in this paper by using a quasigtostrophic barotropical model to investigate the interaction of different scale vortiCes on the structure and motion of typhoons.Results show that this interaction may arouse the irregular changes of the asymmetric structure of typhoons,thus leading to anomalous Phenomena such as meandering tracks and sudden changes in the motion speed of typhoons;the ￣t Of this interaction on the strucure and motion may be quite different when the smaller vortex is situated in different Posihons of the typhoon circulation.

Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons

Features of near-inertial motions on the shelf （60 m deep） of the northern South China Sea were observed under the passage of two typhoons during the summer of 2009. There are two peaks in spectra at both sub-inertial and super-inertial frequencies. The super-inertial energy maximizes near the surface, while the sub-inertial energy maximizes at a deeper layer of 15 m. The sub-inertial shift of frequency is induced by the negative background vorticity. The super-inertial shift is probably attributed to the near-inertial wave propagating from higher latitudes. The near-inertial currents exhibit a two-layer pattern being separated at mid-depth （25-30 m）, with the phase in the upper layer being nearly opposite to that in the lower layer. The vertical propagation of phase implies that the near-inertial energy is not dominantly downward. The upward flux of the near-inertial energy is more evident at the surface layer （〈17 m）. There exist two boundaries at 17 and 40 rn, where the near-inertial energy is reflected upward and downward. The near-inertial motion is intermittent and can reach a peak of as much as 30 cm/s. The passage of Typhoon Nangka generates an intensive near-inertial event, but Typhoon Linfa does not. This difference is attributed to the relative moor- ing locations, which is on the right hand side of Nangka＇s path （leading to a wind pattern rotating clockwise with time） and is on the left hand side of Linfa＇s path （leading to a wind pattern rotating anti-clockwise with time）.

Steady motion and spiral patterns in typhoon

By using the equations describing typhoons in the atmosphere, the steady three-dimensional stream fieldand the corresponding pressure and temperature fields are obtained. The three-dimensional velocity fields construct anonlinear autonomuos system in the physical space. It is shown that the center of typhoon is a local minimum pressurewith positive vertical vorticity and horizontal convergence in lower levels and a local maximum pressure with negativevertical vorticity and horizontal divergence in the upper levels. Because there exits two saddle-focus points in the autnomous system, there exist the spiral patterns, in which the winds blow spirally in and out of the center in the lowerand upper levels in the Northern Hemisphere and cause the ascending motion near the center and dascending motionnear the edge, respectively . All these are in fair conformity with the observations. It implies that the rotation of earthand the viscosity of air play an important role in the spiral structure of typhoons.

A NUMERICAL ANALYSIS ON TYPHOON ASYMMETRIC STRUCTUREAND MOTION

Five prediction experiments are carried out with two typhoons in 1992 using a limited -arca primitiveequations and two-way interactive model in a movable ,nested mesh. The result indicates good agreementin terms of motion between the prediction and observation. Studying the asymmetric structure in the cas-es selected, a close link is uncovered between the temporal evolutions of the structure and the track of motion in a tropical cyclone. Understanding of real asymmetric structure will help to improve the skill offorecasting tropical cyclones.

台风“查帕卡”(2021)在粤西陆架上产生的近惯性运动研究

近惯性运动是海洋中广泛存在的一种频率接近局地惯性频率的海水运动,热带气旋是产生近惯性运动的主要动力之一。本文基于COAWST(Coupled Ocean-Atmosphere-Wave-Sediment Transport)数值模型系统,构建了一个覆盖南海北部陆架的波浪-海流耦合三维水动力模型,并对模型进行了充分验证。利用该模型模拟了2021年第7号台风“查帕卡”在粤西近海陆架上激发的近惯性运动。结果表明,近惯性动能在水平分布上有两个能量高值中心,一个在台风风速最大的近岸区域,另一个在离岸约130 km处,且第二个能量高值中心持续时间更久。在水深40 m以浅的近岸区域,近惯性运动以正压模态为主,表底层流速的相位相同,能量从表层向底层递减。随着水深逐渐增加,在水深70 m到100 m的区域,近惯性运动呈明显的两层结构,表底层近惯性运动的流速方向相反,垂向上出现两个能量高值中心,呈明显的一阶斜压模态特征。通过动力模态分解,发现部分两层结构明显的区域由一阶斜压模态和二阶斜压模态共同主导。随着水深继续增加,更高模态的近惯性运动在总的近惯性动能中占据越来越大的比重。动量平衡分析表明,在水深较浅、风速较大的近岸区域,整个水层内的动量平衡都是由垂向湍流黏性力和压强梯度力主导。而在水深较深、风速较小的离岸区域,垂向湍流黏性力集中在表层和底层,水体内部的动量平衡主要由压强梯度力、科氏力和局地加速度主导。这些结果说明近岸区域主要是风应力驱动的正压波动,而陆架区域,上混合层内的近惯性运动由风应力驱动,混合层以下的近惯性运动则是由正压的压强梯度力驱动的。

A Diagnostic Study of the Asymmetric Distribution of Rainfall during the Landfall of Typhoon Haitang(2005)

The precipitation during landfall of typhoon Haitang （2005） showed asymmetric structures （left side/right side of the track）. Analysis of Weather Research and Forecasting model simulation data showed that rainfall on the right side was more than 15 times stronger than on the left side. The causes were analyzed by focusing on comparing the water vapor flux, stability and upward motion between the two sides. The major results were as follows： （1） Relative humidity on both sides was over 80%, whereas the convergence of water vapor flux in the lower troposphere was about 10 times larger on the right side than on the left side. （2） Both sides featured conditional symmetric instability [MPV （moist potential vorticity） 〈0], but the right side was more unstable than the left side. （3） Strong （weak） upward motion occurred throughout the troposphere on the right （left） side. The Q vector diagnosis suggested that large-scale and mesoscale forcing accounted for the difference in vertical velocity. Orographic lift and surface friction forced the development of the asymmetric precipitation pattern. On the right side, strong upward motion from the forcing of different scale weather systems and topography caused a substantial release of unstable energy and the transportation of water vapor from the lower to the upper troposphere, which produced torrential rainfall. However, the above conditions on the left side were all much weaker, which led to weaker rainfall. This may have been the cause of the asymmetric distribution of rainfall during the landfall of typhoon Haitang.

台风海况下半潜式钻井平台动力性能监测与分析

半潜式钻井平台在海洋油气资源开发中发挥着重要作用,目前主要采用模型试验和数值模拟方法对其动力性能进行研究,非常缺乏台风等极端海况下半潜式平台动力响应的实海域监测数据。以某半潜式钻井平台为研究对象,构建了一套比较完善的平台动力性能监测系统,并对台风“杜苏芮”过境阶段的监测数据进行了分析。根据平台艏部气隙及运动监测数据推算了平台吃水及环境波高;采用随机波浪的统计分析方法,计算得到短期海况的有效波高、谱峰周期、能量谱等信息,通过与多种典型海浪谱对比发现Jonswap谱与所测波谱吻合较好;对平台的横摇、纵摇及垂荡运动进行了时域统计分析和频域谱分析,得到了台风海况下被测平台波频运动的实际响应特征,对于指导平台抗台作业具有重要意义。

深中通道管节港内系泊动力响应试验研究(Ⅱ:双管节试验)

以深中通道工程海底隧道为依托,对管节在港内系泊防台开展物理模型试验,量测系缆力以及管节运动响应参数,探究管节在系泊状态下的动力响应特征及规律。研究主要结论有:环抱式港区内泊位系泊条件是对波浪掩护条件最好的位置最优,靠近口门的泊位最差;不同载况下,空载时风场的作用最显著而有沉放驳和测量塔的重载+工况下,风的作用力也要明显大于仅管节的重载情况,与管节半载时接近(重载+沉放驳+测量塔>重载);E32非标准管节系于突堤码头(GC1泊位)时,在各载况条件下,半载时的缆力相对最大,其中尼龙缆的最大张力为773 kN,钢缆的最大张力为1024 kN,不同载况下缆力大小的排序为半载>重载+沉放驳+测量塔>重载。

TCM-90现场试验台风能量频散波列特征

采用ＴＣＭ－９０（台风运动－９０）台风现场科学试验资料，对台风ＦＬＯ，ＥＤ个例进行了诊断分析，并做了有关数值试验研究。分析研究结论揭示了台风涡旋作为一动力、热力强迫源或ＣＩＳＫ不稳定结构，其与环境场相互作用可激发出动能频散波列；台风扰源通过频散机制可构成类似２维Ｒｏｓｓｂｙ波的经向波列；台风涡旋的移动路径与上述能量传播特征有一定的相关关系。

台风的定常运动和螺旋斑图

应用控制台风的大气运动方程组求得了台风的三维定常流场以及相应的气压场和温度场，其中的三维流场构成了物理空间的一个非线性自治动力系统．研究指出：根据台风运动的定常解，台风的下层中心是低气压且是正垂直涡度（气旋式涡度）和水平辐合，上层中心是高气压（反气旋式涡度）和水平辐散；根据台风自治动力系统所获得的两个鞍一焦点很好地说明了台风的螺旋斑图，下层空气螺旋向内，引起台风中心附近的上升运动，上层空气螺旋向外引起台风外围的下沉运动，这些都与实际台风结构相似，文中阐明，地球的旋转和大气粘性对台风的螺旋结构是至关重要的．

高层冷涡的不同结构对台风运动的影响

通过对不同水平和垂直结构的高层冷涡在台风移动中的作用的对比试验,发现高层冷涡的水平和垂直结构变化会影响台风的运动。对总涡度倾向分布和强度的比较分析,发现正压过程主导台风运动的方向,而斜压过程在某些情况下对台风移速有很大影响。通过各动力项对总涡度倾向贡献的讨论,发现涡度平流对总涡度倾向正中心的贡献主要来自引导气流对非对称涡度场的平流。散度场贡献主要来自行星涡度和非对称散度相关场。最后还得到预报性的结论:台风朝对流层上层的辐合中心或对流层中下层辐散中心方向移动。

热带气旋路径集合预报方法研究I——正压模式结果的初步分析

选择1979～1993年间的热带气旋为试验个例,通过扰动热带气旋初始位置和初始结构,构造集合成员, 用正压原始方程模式,进行路径集合预报试验, 并初步探讨预报成员的集合方法。试验结果表明:热带气旋定位误差影响路径预报,但扰动初始位置的集合平均预报与控制试验的预报水平相接近。扰动热带气旋初始结构的集合预报试验表明,约有60 %～70 %个例的集合路径预报得到改进。此外,试验结果还表明,当环境引导气流较弱时,进行扰动热带气旋初始结构的集合预报,预报结果的改善较明显。

斜压大气中环流非对称结构与台风移速关系的数值研究

采用４层准地转斜压模式，在无环境气流的情况下，进行了两次数值试验，研究了台风环流不同方位、不同半径处的非对称程度与其中心移速的关系，以及不同层次台风环流的非对称结构与台风移速的相关性。结果表明：（１）距台风环流中心１００～３００ｋｍ的东一西向和东北一西南向非对称程度与其东西向移速有稳定的强负相关，２００～５００ｋｍ的东南一西北向非对称程度与其南北向移速有稳定的强正相关。（２）模式最下层环流的非对称结构与台风移速的关系最密切。在该层，距中心１００～４００ｋｍ的东一西向和东北一西南向非对称程度与台风沿东西向移速密切相关，１００ｋｍ以外的东南一西北向非对称程度与台风沿南北向移速密切相关。

海表温度对台风移动的影响

运用１９９０－１９９１年西北太平洋上气象卫星的高分辨率ＳＳＴ、天气图和台风路径图，分析了１７个台风移动与ＳＳＴ的关系，发现它们相关密切，即在无较强天气系统引导的情况下，台风沿着前期ＳＳＴ暖区外围的等ＳＳＴ线并与暖轴平行或者沿着暖轴移动，同时避开行进前方的冷ＳＳＴ区。对西行、西北移、北上和抛物线型４种常见台风路径，选取了５个有代表性的台风和相应的ＳＳＴ场，分别较详细地展示了上述关系，并对其机理作了初步探讨。台风移动中造成的ＳＳＴ变化。

西沙海域内潮与近惯性内波的相互作用

通过使用西沙海域锚定潜标的测流数据,分析了距浣熊台风路径100km处海流受浣熊台风影响前后的动能谱、旋转谱和流剪切谱,从而阐明近惯性波,以及近惯性波与全日内潮波的相互作用机制.台风浣熊之后所引起的近惯性波主要在上250m较强,其能量是普通风场所引起的40倍.近惯性波的能量向下传播至450m左右,与此同时,强的近惯性流的剪切驱动着惯性波与全日内潮波之间的相互作用,从而产生强的近惯性波与全日内波的耦合波(f+D1).此三波耦合机制为Davies的波波相互作用理论提供了观测依据,同时,近惯性内波与全日内潮波之间的非线性相互作用,揭示了南海近惯性波能量耗散的一种机制.

环流非对称结构与台风移速关系的数值研究

利用准地转正压模式，在无环境气流的情况下，对初始轴对称和非轴对称理想台风实施两组共13个数值试验，研究台风环流不同区域的非对称性与其移速的关系。结果表明：（1）台风环流某些区域的非对称性与其移速有稳定的强相关，如，大风半径外围50～100KM附近东—西向东北—西南向的非对称性；（2）大风半径的位角，使台风外围环流的非对称性与其移速相关增强，而最大风速和初始非对称方位用的变化对上述相关性几乎没有影响。

TCFM技术的卫星导风数据在台风模拟中的应用初探

利用傅里叶相位分析方法与最大相关法结合的云导风技术TCFM(Technique based on combination of Fourier phase analysis and maximum correlation),对2005-08-05的强热带风暴"麦莎"天气过程中静止气象卫星得到的30min间隔云图时间序列进行导风计算,并将导风结果应用于中尺度数值模式ARPS(The Advanced Regional Prediction System),结合其资料分析系统ADAS(ARPS Data Analysis System),对台风"麦莎"登陆前的过程进行模拟。尽管洋面上常规资料稀缺,但卫星导风数据的同化使用结果表明,TCFM技术得到的导风资料能够显著改善台风眼壁东部区域的垂直气流活动,使台风螺旋雨带更加明显,符合实际。

热带气旋异常运动的曲率变化特征

运用热带气旋曲率理论模型,选择不同环境及移速特征的台风个例,通过动力学诊断分析,揭示了台风异常运动的关键影响因子的物理机制及其规律。研究结果表明,热带气旋曲率理论模型中影响台风移动的相关特征能够在一定程度上描述出天气系统等环境因子对台风异常运动的综合影响规律。诊断分析结果表明,台风移速、涡旋动力结构、外围副热带高压带及西风槽的非定常变化均可影响台风移动轨迹曲率,尤其是对异常路径和转向点的影响,其突变规律符合台风移动规律。台风移动与系统动力结构有关,台风最大风速与中心气压突然增强或减弱时都会导致台风的突然转向。

两种导风方法在台风路径分析中的应用比较研究

基于云导风使用的最大相关法(已经广泛应用)和TCFM法(傅立叶相位分析法和最大相关法相结合)两方法的原理,开发了利用FY-2C静止气象卫星30min间隔卫星云图资料获得云迹风的可视化导风实验系统。利用该系统处理2005年夏季麦莎、卡努、龙王等3个台风期间的卫星云图,对得到的云迹风进行台风路径反演分析。结果表明,TCFM导风方法得到的结果优于最大相关法。