Numerical Study of the Influences of a Monsoon Gyre on Intensity Changes of Typhoon Chan-Hom(2015)

Typhoon Chan-Hom （2015） underwent a weakening in the tropical western North Pacific （WNP） when it interacted with a monsoon gyre, but all operational forecasts failed to predict this intensity change. A recent observational study indicated that it resulted from its interaction with a monsoon gyre on the 15-30-day timescale. In this study, the results of two numerical experiments are presented to investigate the influence of the monsoon gyre on the intensity changes of Typhoon Chan-Hom （2015）. The control experiment captures the main observed features of the weakening process of Chan-Hom （2015） during a sharp northward turn in the Philippine Sea, including the enlargement of the eye size, the development of strong convection on the eastern side of the monsoon gyre, and the corresponding strong outer inflow. The sensitivity experiment suggests that intensity changes of Chan-Hom （2015） were mainly associated with its interaction with the monsoon gyre. When Chan-Horn （2015） initially moved westward in the eastern part of the monsoon gyre, the monsoon gyre enhanced the inertial stability for the intensification of the typhoon. With its coalescence with the monsoon gyre, the development of the strong convection on the eastern side of the monsoon gyre prevented moisture and mass entering the inner core of Chan-Hom （2015）, resulting in the collapse of the eyewall. Thus, the weakening happened in the deep tropical WNP region. The numerical simulations confirm the important effects of the interaction between tropical cyclones and monsoon gyres on tropical cyclone intensity.

Idealized Numerical Simulations of Tropical Cyclone Formation Associated with Monsoon Gyres

Monsoon gyres have been identified as one of the important large-scale circulation patterns associated with tropical cyclone （TC） formation in the western North Pacific.A recent observational analysis indicated that most TCs form near the center of monsoon gyres or at the northeast end of the enhanced low-level southwesterly flows on the southeast-east periphery of monsoon gyres.In the present reported study,idealized numerical experiments were conducted to examine the tropical cyclogenesis associated with Rossby wave energy dispersion with an initial idealized monsoon gyre.The numerical simulations showed that the development of the low-level enhanced southwesterly flows on the southeasteast periphery of monsoon gyres can be induced by Rossby wave energy dispersion.Mesoscale convective systems emerged from the northeast end of the enhanced southwesterly flows with mid-level maximum relative vorticity.The simulated TC formed in the northeast of the monsoon gyre and moved westward towards the center of the monsoon gyre.The numerical experiment with a relatively smaller sized initial monsoon gyre showed the TC forming near the center of the initial monsoon gyre.The results of the present study suggest that Rossby wave energy dispersion can play an important role in TC formation in the presence of monsoon gyres.

IMPACT OF SEA SPRAY ON TROPICAL CYCLONE STRUCTURE AND INTENSITY CHANGE

In this paper,the effects of sea spray on tropical cyclone(TC)structure and intensity variation are evaluated through numerical simulations using an advanced sea-spray parameterization from the National Oceanic and Atmospheric Administration/Earth System Research Laboratory(NOAA/ESRL),which is incorporated in the idealized Advanced Research version of the Weather Research and Forecast (WRF-ARW)model.The effect of sea spray on TC boundary-layer structure is also analyzed.The results show that there is a significant increase in TC intensity when its boundary-layer wind includes the radial and tangential winds,their structure change,and the total surface wind speed change.Diagnosis of the vorticity budget shows that an increase of convergence in TC boundary layer enhances TC vorticity due to the dynamic effect of sea spay.The main kinematic effect of the friction velocity reduction by sea spray produces an increment of large-scale convergence in the TC boundary layer,while the radial and tangential winds significantly increase with an increment of the horizontal gradient maximum of the radial wind, resulting in a final increase in the simulated TC intensity.The surface enthalpy flux enlarges TC intensity and reduces storm structure change to some degree,which results in a secondary thermodynamic impact on TC intensification.Implications of the new interpretation of sea-spray effects on TC intensification are also discussed.

Numerical Simulation of the Rapid Intensification of Hurricane Katrina(2005):Sensitivity to Boundary Layer Parameterization Schemes

Accurate forecasting of the intensity changes of hurricanes is an important yet challenging problem in numerical weather prediction. The rapid intensification of Hurricane Katrina（2005） before its landfall in the southern US is studied with the Advanced Research version of the WRF（Weather Research and Forecasting） model. The sensitivity of numerical simulations to two popular planetary boundary layer（PBL） schemes, the Mellor–Yamada–Janjic（MYJ） and the Yonsei University（YSU） schemes, is investigated. It is found that, compared with the YSU simulation, the simulation with the MYJ scheme produces better track and intensity evolution, better vortex structure, and more accurate landfall time and location. Large discrepancies（e.g.,over 10 hPa in simulated minimum sea level pressure） are found between the two simulations during the rapid intensification period. Further diagnosis indicates that stronger surface fluxes and vertical mixing in the PBL from the simulation with the MYJ scheme lead to enhanced air–sea interaction, which helps generate more realistic simulations of the rapid intensification process. Overall, the results from this study suggest that improved representation of surface fluxes and vertical mixing in the PBL is essential for accurate prediction of hurricane intensity changes.

NUMERICAL SIMULATION ON RE-INTENSIFICATION OF TROPICAL REMNANT RE-ENTERING THE SEA:A CASE STUDY

When Typhoon Toraji(2001)reached the Bohai Gulf during 1-2 August 2001,a heavy rainfall event occurred over Shandong province in China along the gulf.The Advanced Research version of the Weather Research and Forecast(WRF-ARW)model was used to explore possible effects of environmental factors,including effects of moisture transportation,upper-level trough interaction with potential vorticity anomalies,tropical cyclone(TC)remnant circulation,and TC boundary-layer process on the re-intensification of Typhoon Toraji,which re-entered the Bohai Gulf after having made a landfall.The National Centers for Environmental Prediction(NCEP)global final(FNL)analysis provided both the initial and lateral boundary conditions for the WRF-ARW model.The model was initialized at 1200 UTC on 31 July and integrated until 1200 UTC on 3 August 2001,during which Toraji remnant experienced the extratropical transition and re-intensification.Five numerical experiments were performed in this study,including one control and four sensitivity experiments.In the control experiment,the simulated typhoon had a track and intensity change similar to those observed.The results from three sensitivity experiments showed that the moisture transfer by a southwesterly lower-level jet,a low vortex to the northeast of China,and the presence of Typhoon Toraji all played important roles in simulated heavy rainfall over Shandong and remnant re-intensification over the sea,which are consistent with the observation.One of the tests illustrated that the local boundary layer forcing played a secondary role in the TC intensity change over the sea.

Effects of Land-Sea Distribution, Topography and Diurnal Change on Summer Monsoon Modeling

The effects of the land-sea distribution, the topography and the diurnal change of the solar radiation on the summer monsoon modelings are studied by use of a coupled modeling system with a 5-layer primitive equation model of the atmosphere and a 2-layer soil or ocean thermodynamic model which are all solved in a zonal model domain between 60°S and 60°N. The results of numerical simulations show that the quasi-stationary patterns of the mean monsoon circulations are mainly affected by the land-sea distribution and the topography, the effect of the diurnal change is the secondary. However, the inclusion of the diurnal change into the model system may improve the intensity of the simulated monsoon circulation, it can influence the distributive pattern of precipitation to a larger extent,without the diurnal change precipitation in the interior of land would decrease and in the coastal regions it would increase.

NUMERICAL SIMULATION STUDY ON THE RAPID INTENSIFICATION OF TYPHOON HAIKUI(1211) OFF THE SHORE OF CHINA

Forecasting the rapid intensification of tropical cyclones over offshore areas remains difficult. In this article,the Weather Research and Forecast(WRF) model was used to study the rapid intensification of Typhoon Haikui(1211)off the shore of China. After successful simulation of the intensity change and track of the typhoon, the model output was further analyzed to determine the mechanism of the rapid change in intensity. The results indicated that a remarkable increase in low-level moisture transportation toward the inner core, favorable large-scale background field with low-level convergence, and high-level divergence played key roles in the rapid intensification of Typhoon Haikui in which high-level divergence could be used as an indicator for the rapid intensity change of Typhoon Haikui approximately 6 h in advance. An analysis of the typhoon structure revealed that Typhoon Haikui was structurally symmetric during the rapid intensification and the range of the eyewall was small in the low level but extended outward in the high level. In addition, the vertically ascending motion, the radial and tangential along wind speeds increased with increasing typhoon intensity, especially during the process of rapid intensification. Furthermore, the intensity of the warm core of the typhoon increased during the intensification process with the warm core extending outward and toward the lower layer. All of the above structural changes contributed to the maintenance and development of typhoon intensity.

基于简单台风模型的台风“海马”强度变化机制研究

台风强度预报误差较大,相关物理机制有待深入研究。针对台风“海马”个例,利用台风最佳路径数据集和欧洲中心再分析资料设定台风特征参数,使用基于海-气相互作用理论的简单台风模型对台风“海马”进行数值模拟,并针对焓交换系数与拖曳系数比值开展敏感性试验。控制试验结果表明,在台风的成熟期,台风的切向动能主要存在于眼壁外侧的云下层和对流层中下层,而径向动能主要集中在对流层上部和眼壁外侧的云下层,这些结果描述了台风成熟期的基本特征。敏感性试验表明,当海洋表面焓交换系数与拖曳系数的比值增大时,台风的主级环流与次级环流明显增强,台风边界层的平均径向风速度分布更趋向中心,且风速明显增加,同时,垂直上升速度增加,台风切向动能明显增加,台风强度增强。研究结果有助于理解海气交换对台风强度的影响。

超强台风“桑美”(2006)近海急剧增强过程数值模拟试验

应用PSU/NCAR非静力平衡中尺度模式MM5(V3.5)设计试验方案,对超强台风"桑美"(2006)在我国近海的急剧增强和减弱过程进行数值模拟研究,模式较好地再现了台风的路径和强度变化;通过地形敏感性试验,着重研究了地形对近海台风强度变化的影响。结果表明:(1)"桑美"强度变化与南亚高压、副热带高压的强度变化呈反相变化关系,当南亚高压和副热带高压减弱时,台风急剧增强;台风中心附近对流层高层辐散的增强导致"桑美"急剧增强,对流层中低层辐散的增强以及中层辐合的增大与"桑美"的减弱密切相关;来自海洋的暖湿气流是"桑美"发展的关键条件;低层气旋性涡旋并入台风环流是"桑美"近海急剧增强的重要原因。(2)凝结加热过程对"桑美"的近海维持和发展增强非常重要,尤其是对流层中上层凝结潜热的突然增强有利于台风在近海的急剧增强。(3)小范围地形对"桑美"在近海的强度和路径有一定影响,但作用相对较小,而且主要表现在台风登陆前后;大范围地形导致水平风场的非对称分布和台风中心附近垂直运动的异常,最终影响到台风的强度变化。

东亚冬季风及其影响的进一步研究Ⅰ.东亚冬季风变化及异常的特征

东亚冬季风是北半球冬季最活跃的大气环流系统，其活动有重要影响，其向南爆发可以越过赤道对澳大利亚夏季风起作用。但相对夏季风，人们对东亚冬季风的研究一直较少。作者首先利用Hadley中心近百年的北半球海平面气压场资料，改进提出了一个能更好表征东亚冬季风强度的指数，进一步分析研究了东亚冬季风的年际和年代际变化及其异常特征。其结果表明，东亚冬季风不仅存在着明显的年际变化，主要有准两年的振荡周期和5～7年左右的周期，还存在周期为25～30年左右以及周期为十几年的年代际变化。利用NCEP／NCAR再分析资料，采用相关分析、合成分析的方法，还系统研究了东亚冬季风异常时的大气环流特征。对比分析表明，对应强、弱东亚冬季风，大尺度环流系统（蒙古高压、阿留申低压、500hPa位势高度场等）的变化特征基本上呈反相分布；并且在强、弱东亚冬季风年，赤道地区的Hadley环流和Walker环流也出现基本反相的异常分布特征；而且赤道西太平洋有西（东）风异常出现，菲律宾以东有异常气旋（反气旋）性环流。在对异常东亚冬季风诊断分析的基础上，用一个大气环流模式（GCM）模拟了异常东亚冬季风的活动。通过对数值模拟结果的强、弱东亚冬季风进行对比分析发现，在强、弱东亚冬季风时，北半球中高纬度大气环流的结构会出现明显的变化和调整；同时，热带地区大气环流也有显著的差异。数值模拟和资料分析结果有较好的一致性，从而进一步揭示了东亚冬季风的变化和异常特征。

中国东部城市下垫面变化对南海夏季风爆发影响的数值模拟

本文利用美国国家大气研究中心(NCAR)开发的公用大气环境模式(CAM5.1)进行了中国东部大规模城市下垫面变化对南海夏季风爆发影响的数值模拟研究.结果表明:CAM5.1模式能够很好地模拟出东亚夏季风系统季节演变过程中大尺度环流场和降水分布的变化.敏感性试验结果表明中国东部大规模城市群的发展会使得南海夏季风提前1侯爆发;控制试验中5月中旬南海地区东南风向西南风的转变,以及降水量激增现象的出现,均较无城市试验中提前.同时,城市化快速发展阶段与南海夏季风爆发的年代际变化存在时间段的吻合,初步推断城市下垫面发展可能是1993年之后南海季风提前爆发的原因之一.对南海季风爆发影响的原因分析可以看出,城市化引起的下垫面物理属性变化,使得从春至夏的季节转变中,东部(110°-120°E)中高纬度陆地对大气的感热加热增强,减小了海陆之间的热力对比,加快陆地低层大气降压,从而引导南海季风提前爆发.

对1991年全球越赤道气流的分析和数值模拟

利用１９９１年国家气象中心全年分析资料，对全球各层（５０～１０００ｈＰａ）越赤道气流（ＣＥＦ）进行了分析。指出：主要季风区和１９７９年的相同，但在南美北部为弱季风区，而１９７９年为信风区。除南美北部外，主要信风区与１９７９年相同。还比较了这两类地区的特点，特别是非绝热加热分布随季节变化的特点，还用Ｔ２１Ｌ５模式进行了数值模拟。结果表明：考虑地形和加热的方案最优，除个别情况外，ＣＥＦ与实况很接近；单纯加热方案次之，能定性地模拟ＣＥＦ沿赤道的分布，但强度相差较大；单纯地形方案最差。为了进行解释，还作了简单情况的理论分析。分析显示：考虑加热和地形作用，并不等于单纯地形和单纯加热的叠加，其间有非线性作用；而且，这种非线性作用对ＣＥＦ的产生是直接的、重要的；单纯加热只有通过其对地面气压场的影响才能产生ＣＥＦ。

基于动态期望的航空器滑行路径更新模型仿真

滑行路径优化是提升机场场面运行效率与安全水平的有效途径。为研究管制意图、监控范围对航空器滑行路径优化的影响,基于实际管制规定,同时考虑冲突和拥堵影响,定义优先级反映滑行道通行能力,定义动态期望值量化管制员意图,设计航空器滑行路径变更机制及实施步骤,构造基于动态期望的航空器滑行路径变更模型。采用Visual C++及Mathlab混合编程仿真,得到航空器分布密度、监控范围等参数改变时,不同模型的仿真结果对比及关键统计分析值的变化趋势。结果表明,上述模型能对低密度下的滑行道变更进行抑制,能提高中密度下的滑行道变更比例,并减少滑行速度变化幅度。扩大监控范围能有效增加航空器滑行路径变更比例,减少滑行速度标准差,提高机场场面运行保障能力。

高原夏季风强弱和南亚高压的关系研究

为进一步认识高原夏季风和南亚高压的关系,利用1948~2013年NCEP/NCAR日平均再分析资料,采用相关分析和合成分析,探讨高原夏季风异常对南亚高压活动的影响。研究表明,高原夏季风强时,南亚高压中心位置偏东偏南,呈＂青藏高压模态＂,高原夏季风弱时,南亚高压中心偏西偏北,呈＂伊朗高压模态＂。在非绝热加热场上,高原夏季风强时,青藏高原南侧感热偏强,青藏高原以西到伊朗高原东部感热偏弱。高原夏季风弱时,青藏高原南侧及西南侧为感热偏弱,高原西北部感热偏强。值得注意的是,地表感热的正负异常分布与南亚高压中心位置的分布较一致,夏季南亚高压中心位置的变化可能与地表感热加热密切联系。

极板截面椭圆化对圆柱形电容器耐压能力的影响

极板截面椭圆化对圆柱形电容器耐压能力的影响的研究,可利用复坐标系上的儒可夫斯基变换,分析椭圆柱形电容器内的电场分布,并在其场强分布矢量式的基础上,给出了圆柱形电容器极板椭圆化前后其耐压能力改变量的计算公式,结合MATLAB数据处理软件的数值计算功能进行数值模拟,得到圆柱形电容器的耐压能力随极板截面椭圆焦距增大而降低的结论,并给出理论数据用以指导对椭圆化程度的控制,供电容器生产工艺中使用和参考。

中国东部城市群发展对南海夏季风爆发影响的模拟研究

本文利用NCAR开发的CAM5.1(Community Atmosphere Model Version 5.1)模式,针对我国东部大规模城市下垫面发展对南海夏季风爆发的影响进行了数值模拟研究。结果表明我国东部大规模城市群发展可能使得南海夏季风提前1候爆发;机理分析表明:在南海夏季风爆发之前,中国东部城市群发展引起的陆面增温,使得南海及其附近地区南北温差提前逆转、中国东部区域海平面气压降低,导致中南半岛到南海地区西南气流加强,中南半岛到南海地区降水增加,而凝结潜热垂直变化强迫出的异常环流,促进了南亚高压的加强及提前北跳,相伴随的高层抽吸作用有助于季风对流的建立和西太平洋副高的减弱东撤,从而形成了有利于南海夏季风爆发的高低层环流条件,导致南海夏季风提前爆发。另外,观测结果表明1993年之后南海夏季风爆发的日期相对上一个年代明显提前约2候,城市化快速发展阶段与南海夏季风爆发的年代际变化存在时间段的吻合,表明城市下垫面发展可能是南海夏季风提前爆发的原因之一。

强台风“海葵”(1211)近海急剧增强的数值研究

近海台风强度急剧增强是预报中的难点。使用新一代中尺度WRF模式对台风"海葵"(1211)近海强度急剧增强过程进行数值模拟,并对数值模拟结果展开分析,研究引起台风强度突变的可能机理及相应结构变化。模拟结果表明,台风"海葵"的急剧增强与低层水汽输入的突然增加以及有利的高、低层辐散、辐合流场配置密切相关,且在"海葵"台风强度迅速增强的前6 h其高低层辐合、辐散流场呈现同时增强。台风结构变化的分析表明,在台风急剧增强时段台风结构趋于对称化,且低层眼壁范围小,高层眼壁范围向外扩展。伴随着台风强度增强,径向风速和切向风速也处在增大过程中,特别是台风急剧增强阶段,径向风速和切向风速增大更明显。另外,暖心强度逐渐加强,且暖心范围明显扩大并向低层扩展。同时随着台风强度的增强,垂直上升运动也逐渐增强。台风的这些结构变化都有利于其强度的维持和发展。

热带气旋生成过程的中尺度涡旋活动数值模拟

热带气旋生成过程中包含不同尺度环流及其相互作用。为此，本文将热带气旋生成数值模拟的起点提前到模拟中尺度涡旋（MCV）的生成，从而利用高分辨率数值试验结果，对热带气旋过程中的不同尺度涡旋活动进行分析。模式首先模拟了季风涡旋的东南侧增强的西南气流中出现低形变旋转性扰动，随着扰动的旋转性增强，中层出现水平尺度为200km左右的MCV。在扰动区内的不同高度上还发现10～20km尺度不等的中γ气旋性涡旋扰动，其中部分涡旋扰动具有热塔的特征，中γ气旋性涡旋扰动在MCV的旋转环境内不断组织化，低层气旋性涡旋扰动的分布比中层更加集中。模拟表明这些较小尺度的气旋性中尺度涡旋扰动对热带气旋的生成有重要作用。

青藏高原隆升气候效应的数值模拟研究进展概述

青藏高原隆升作为新生代的重大地质事件对亚洲乃至全球气候环境变化产生了深远的影响,因而高原隆升的气候环境效应一直是备受关注的重要科学问题。在过去近半个世纪中,国内外学者利用气候数值模式开展了大量高原地形气候效应的数值模拟研究,这些研究结果极大地提升了对地形抬升影响气候的物理机制以及高原隆升对古气候演化驱动作用的认识。本文简要回顾了过去有关青藏高原隆升气候效应数值模拟研究的进展,并按照高原隆升模拟研究发展的3个阶段总结了目前取得的主要研究成果。从数值模拟结果看,新生代以来青藏高原在隆升、生长和北移过程中其动力和热力作用对东亚季风的形成、南亚季风的演化、内陆干旱化的发展以及亚洲季风-干旱环境格局的变迁都具有深远的影响。青藏高原及其周边不同区域地形隆升的气候效应不同,青藏高原隆升的气候效应与大陆漂移背景下海陆分布和古地理格局的变化密切相关。南亚热带季风的建立是由大陆漂移的位置和热带辐合带季节性移动共同决定的,而东亚季风的建立则主要取决于青藏高原的隆升和北移。亚洲副热带干旱区的存在取决于大陆的位置和行星尺度副热带高压的控制,而亚洲内陆中纬度干旱区的形成则是青藏高原隆升的结果。本文最后简要梳理了高原隆升气候效应数值模拟研究目前存在的问题和未来可能的改进。

1991年8月季风涡旋个例形成的模拟研究

季风涡旋对台风活动有重要的影响,因此研究季风涡旋的形成机制有利于提高台风预报的准确性。此研究利用中尺度非静力数值模式WRF-ARW模拟1991年8月季风涡旋的生成过程,并对其生成机制进行分析。模式结果表明,此次季风涡旋个例是由一个中纬度气旋性低压发展而来。初期中纬度高层正位势涡度的强迫作用有利于对流层低层气旋性低压的发展和维持,随后高层动力强迫作用减弱,但中纬度气旋性低压在南移过程中其东南侧对流带逐渐与低纬地区的对流带合并,使得对流潜热释放增强,进而使低压在Gill响应的作用下不断加强并最终形成季风涡旋。同时,涡旋的对流结构表现出明显的非对称性,因而使其得以维持较大尺度。敏感性试验的结果表明对流层高层强迫对于初始低层扰动的发展至关重要,而后期热带地区的潜热释放有利于季风涡旋的增强。