台风螺旋雨带——涡旋Rossby波

台风中的螺旋云雨带是由多种探测手段被观测到的现象 ,是为大家所共识的不争事实。但是 ,对它的形成、维持的理论解释 ,虽有多种学说 ,一直以来人们都倾向于重力惯性波说。而重力惯性波说有一个致命的弱点 ,即波的相速理论值为 10 1m/s量级 ,它要比螺旋云雨带实测移速只有 10 0 m/s几乎大一个量级。于是从前几年开始 ,人们又回到 30多年前提出的涡旋 Rossby波说那里去寻找合适的解释。经典的Rossby波是 β =(df/dy)作用的大尺度波动 ,而适用于台风中螺旋云雨带的涡旋———Rossby波乃是 f平面 (β =0 )上的中尺度波动。那末 ,对这两类尺度不同和成波机理不同的波动 ,何以均冠予Rossby波一词 ?本文试图从动力学等价原理上 ,对此作统一联系的说明。其结果是 :台风基本气流的涡度 ζ随径向 (r)变化的梯度d ζdr=1rr(r vλ) ,在动力学上等价于科氏参数 f随纬度变化的梯度即β=df/dy ;或者说它们在绝对涡度守恒的前提下 ,作为波扰动的成波机理是等价的     

热带气旋定量降水预报的动力相似方案

该文提出一个热带气旋定量降水预报(QPF) 的动力相似方案。方案应用热带气旋初始参数、历史过程的天气形势场和物理量场及数值预报产品, 构造预报区域内当前时刻至未来时刻环境要素场的多元客观相似判据。通过定义非线性的相似指数综合评估历史热带气旋样本与预报热带气旋在多元判据下的连续动态相似程度, 以此找到相似样本。应用相似样本的历史降水量记录进行相似指数的权重综合, 得到热带气旋未来6~48 h降水量的定点、定量预报值。预报试验表明该方案具有一定的预报技巧。     

A numerical modelling study of coastal flooding

Summary A coastal ocean model capable of modelling tides, storm surge and the overland flow of floodwaters has been further developed to include the flux of water from tributaries and the forcing from wave breaking that leads to wave setup in the nearshore zone. The model is set up over the Gold Coast Broadwater on the east coast of Australia. This complex region features a coastal lagoon into which five tributaries flow and is subject to flooding from extreme oceanic conditions such as storm surge and wave setup as well as terrestrial runoff. Weather conditions responsible for storm surge, waves and flooding include cyclones of both tropical and mid-latitude origin. Two events are modelled. The first is an east coast low event that occurred in April 1989. This event verified well against available observations and analysis of the model simulations revealed that wave setup produced a greater contribution to the elevated water levels than the storm surge. The second case to be modelled was tropical cyclone Wanda, responsible for the 1974 floods. Modelled water levels in the Broadwater were reasonably well captured. Sensitivity experiments showed that storm surge and wave setup were only minor contributors to the elevated sea levels and their contribution was confined to the earlier stage of the event before the runoff reached its peak. The contribution due solely to runoff exhibited a tidal-like oscillation that was 180° out-of-phase with the tide and this was attributed to the greater hydraulic resistance that occurs at high tide. A simulation of this event with present day bathymetry at the Seaway produced sea levels that were 0.3–0.4 m lower than the simulation with 1974 bathymetry highlighting the effectiveness of deepened Seaway channel to reduce the impact of severe runoff events in the Broadwater. Received October 16, 2001 Revised December 28, 2001     

INSTABILITY OF THE OCEANIC WAVES IN THE TROPICAL REGION

In this paper,the effects of the large-scale mean sea temperature fields of the tropical ocean and the zonal current field (southern equatorial current) have been comprehensively entered in consideration on the basis of Chao and Ji (1985),and Ji and Chao (1986),the equatorial oceanic waves of the tropical ocean have been discussed by use of linearized primitive equations,then,the significant influence of the climatic background fields of the tropical ocean upon the oceanic waves of this region has been further testified.When very cold water appears in the tropical region,and the southern equatorial current is also relatively strong,the effect of the Rossby wave weakens,as a consequence,there are substitutive slow waves (i.e.thermal waves) which travel in opposite direction (eastward) to the Rossby wave.The characteristics of the slow wave are similar to those of Rossby waves,only the travelling direction is opposite.Under a certain environmental background field,the slow wave and the modified Rossby wave may be instable.With this conclusion,the mechanism of the occurrence,development and propagation of El Nino events has been studied.It is pointed out that the opposite travelling direction of the thermal wave and Rossby wave will bring repectively into action under different marine environmental background fields.The physical causes for that the abnormal warm water inclines to occur along the South American coast have also been explored in this paper.     

Impact of tropical cyclone development on the instability of South Asian High and the summer monsoon onset over Bay of Bengal

This paper analyzes the evolution of the South Asian High (SAH) during and after the development of tropical cyclone Neoguri over the South China Sea (SCS) in mid-April 2008, the formation of tropical storm Nargis over the Bay of Bengal (BOB) in late April, and the Asian summer monsoon onset, as well as their interrelationships. Numerical sensitivity experiments are conducted to explore the underlying mechanism responsible for these seasonal transitions in 2008. It is demonstrated that strong latent heating related with tropical cyclone activities over the SCS can enhance the development of the SAH aloft and generate zonal asymmetric potential vorticity (PV) forcing, with positive vorticity advection to its east and negative advection to its west. Following the decay of the tropical cyclone, this asymmetric forcing leads to instability development of the SAH, presenting as a slowly westward-propagating Rossby wave accompanied by a westward shift of the high PV advection. A strong upper tropospheric divergence on the southwest of the SAH also shifts westward, while positive PV eddies are shed from the high PV advection and eventually arrives in the southern BOB. Such synoptic patterns provide favorable pumping conditions for local cyclonic vorticity to develop. The latent heating release from the cyclogenesis further intensifies the upper-layer divergence, and the lower and upper circulations become phase locked, leading to the explosive development of the tropical cyclone over the southern BOB. Consequently, a tropical storm is generated and the BOB summer monsoon commences.     

The Relationship Between Abnormal Meiyu and Medium-Term Scale Wave Perturbation Energy Propagation Along the East Asian Subtropical Westerly Jet

The East Asian subtropical westerly jet(EASWJ) is one of the most important factors modulating the Meiyu rainfall in the Yangtze-Huaihe River Basin, China. This article analyzed periods of the medium-term EASWJ variation,wave packet distribution and energy propagation of Rossby waves along the EASWJ during Meiyu season, and investigated their possible influence on abnormal Meiyu rain. The results showed that during the medium-term scale atmospheric dynamic process, the evolution of the EASWJ in Meiyu season was mainly characterized by the changes of3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves. The strong perturbation wave packet and energy propagation of the 3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves are mostly concentrated in the East Asian region of 90°-150°E, where the two wave trains of perturbation wave packets and wave-activity flux divergence coexist in zonal and meridional directions, and converge on the EASWJ. Besides, the wave trains of perturbation wave packet and wave-activity flux divergence in wet Meiyu years are more systematically westward than those in dry Meiyu years, and they are shown in the inverse phases between each other. In wet(dry) Meiyu year, the perturbation wave packet high-value area of the 10-15 d low-frequency variability is located between the Aral Sea and the Lake Balkhash(in the northeastern part of China), while over eastern China the wave-activity flux is convergent and strong(divergent and weak), and the high-level jets are strong and southward(weak and northward). Because of the coupling of high and low level atmosphere and high-level strong(weak) divergence on the south side of the jet over the Yangtze-Huaihe River Basin, the low-level southwest wind and vertically ascending motion are strengthened(weakened), which is(is not)conducive to precipitation increase in the Yangtze-Huaihe River Basin. These findings would help to better understand the impact mechanisms of the EASWJ activities on abnormal Meiyu from the perspective of medium-term scale Rossby wave energy propagation.     

Projected future changes in tropical cyclone-related wave climate in the North Atlantic

Tropical cyclones are a major hazard for numerous countries surrounding the tropical-to-subtropical North Atlantic sub-basin including the Caribbean Sea and Gulf of Mexico. Their intense winds, which can exceed 300 km h⁻¹, can cause serious damage, particularly along coastlines where the combined action of waves, currents and low atmospheric pressure leads to storm surge and coastal flooding. This work presents future projections of North Atlantic tropical cyclone-related wave climate. A new configuration of the ARPEGE-Climat global atmospheric model on a stretched grid reaching ~ 14 km resolution to the north-east of the eastern Caribbean is able to reproduce the distribution of tropical cyclone winds, including Category 5 hurricanes. Historical (1984–2013, 5 members) and future (2051–2080, 5 members) simulations with the IPCC RCP8.5 scenario are used to drive the MFWAM (Météo-France Wave Action Model) spectral wave model over the Atlantic basin during the hurricane season. An intermediate 50-km resolution grid is used to propagate mid-latitude swells into a higher 10-km resolution grid over the tropical cyclone main development region. Wave model performance is evaluated over the historical period with the ERA5 reanalysis and satellite altimetry data. Future projections exhibit a modest but widespread reduction in seasonal mean wave heights in response to weakening subtropical anticyclone, yet marked increases in tropical cyclone-related wind sea and extreme wave heights within a large region extending from the African coasts to the North American continent.

     

热带气旋内中尺度波动的不稳定机理研究进展

在回顾了近年来热带气旋波动动力学研究的基础上,介绍了热带气旋内中尺度波动不稳定机理研究方面的进展,分别对热带气旋三类中尺度特征波动的不稳定,即经典重力惯性波、涡旋Rossby波和具有物理性质不可分的混合波的不稳定进行了物理分析,给出了热带气旋内对称不稳定、横波不稳定、对流对称不稳定、涡旋Rossby波正压不稳定及混合波不稳定的动力解释,进一步说明热带气旋内中尺度扰动发展是与基本气流的动力(水平和垂直切变)及热力状态之间的相互作用密切相关。     

IPO调节大西洋纬向模对澳大利亚秋季降水年际变动的影响

采用1900-2014年115 a的观测和再分析资料,使用滤波、线性相关等方法,研究太平洋年代际振荡(Interdecadal Pacific Oscillation,IPO)调节大西洋纬向模(Atlantic Zonal Mode,AZM)对澳大利亚秋季降水年际变动的调节作用及机制.结果 表明,当IPO位于正位相时,...     

Intensity of the Trough over the Bay of Bengal and Its Impact on the Southern China Precipitation in Winter

In this study, the intensity of the trough over the Bay of Bengal (BBT) and its association with the southern China precipitation, the Madden-Julian Oscillation (MJO) and the Rossby wave propagation along the African-Asian subtropical Jet stream (AASJ) are investigated on the intraseasonal time scale. The results show that the intensity of the BBT affects the southern China precipitation more directly and to a greater degree than the MJO. The peak amplitude of the BBT tended to occur in phase-3 of the MJO. The strong BBT was substantially modulated by the Rossby wave propagation along the AASJ, which was triggered by the anomalous upstream circulation similar to the pattern of the North Atlantic Oscillation (NAO). Therefore, from the perspective of medium- and extended-range weather forecasts, the NAO- like pattern may be regarded as a precursory signal for the strong BBT and thus the southern China precipitation.     

THE INTERLINKAGE OF LARGE-SCALE SYSTEMS BETWEEN HIGH AND LOW LATITUDES RELATED TO PROPAGATION OF THE PLANETARY WAVE AROUND EAST ASIA IN SUMMER*

This study has reviewed recent studies about impact of the Rossby wave propagation on the weather of East Asia.Then,we have focused on the northward progression of the subtropical high affected by the propagations and their interaction.The following results are obtained:(1) The two kinds of meridional Rossby wave propagations often affect the East Asian weather in summer,which propagate in two conflicting directions(northwest-southeastward and southwest-northeast-ward).This is considered as the interaction of the large-scale systems between high and low latitudes with wave propagation,especially to the circulation systems around East Asia.(2) The northward progression of the subtropical high is largely restrained,aecompanied by the southward shift of the convective activity in middle latitudes,under the strong and persistent Rossby wave propagation from high to low latitudes.And the opposite role could be found in the Rossby wave propagation from low to high latitudes.     

THE INTERLINKAGE OF LARGE-SCALE SYSTEMS BETWEEN HIGH AND LOW LATITUDES RELATED TO PROPAGATION OF THE PLANETARY WAVE AROUND EAST ASIA IN SUMMER

This study has reviewed recent studies about impact of the Rossby wave propagation on theweather of East Asia.Then,we have focused on the northward progression of the subtropical highaffected by the propagations and their interaction.The following results are obtained:(1)The twokinds of meridional Rossby wave propagations often affect the East Asian weather in summer,which propagate in two conflicting directions(northwest-southeastward and southwest-northeast-ward).This is considered as the interaction of the large-scale systems between high and lowlatitudes with wave propagation,especially to the circulation systems around East Asia.(2)Thenorthward progression of the subtropical high is largely restrained,aecompanied by the southwardshift of the convective activity in middle latitudes,under the strong and persistent Rossby wavepropagation from high to low latitudes.And the opposite role could be found in the Rossby wavepropagation from low to high latitudes.     

中国东部夏季季节内降水异常及其伴随的热带和中高纬度大气环流演变特征

利用1981—2020年夏季(5—8月)CPC(Climate Prediction Center)逐日降水资料、NCEP/NCAR逐日再分析资料以及NOAA的向外长波辐射资料,通过经验正交函数(EOF)分解、超前滞后合成等方法,分析了中国东部夏季季节内降水异常的主要模态(即南方型和江淮型降水异常)及其伴随的热带和中高...     

Idealized Numerical Simulations of Tropical Cyclone Formation Associated with Monsoon Gyres简

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.     

Forced Rossby wave packets in barotropic shear flows with critical layers

In this paper, we investigate the meridional propagation of a forced Rossby wave packet towards a critical layer in a zonal shear flow by solving the linearized barotropic vorticity equation. The forcing is applied north of the critical layer. Two approaches are employed for solving this problem. First, an analytic solution valid for large time is derived, using Fourier and Laplace transform techniques and asymptotic approximations. This solution exhibits the modification due to the wave packet of the solution obtained by Warn and Warn (1976) [Warn, T., Warn H., 1976. On the development of a Rossby wave critical level. J. Atmos. Sci., 33, 2021–2024.] in the monochromatic case. A numerical investigation is then carried out using a finite difference scheme and a time-dependent radiation condition. It is found that the forced wave packet is absorbed at the critical layer and the total momentum transferred to the mean flow as a result of the absorption is observed to be proportional to the length scale of the wave packet. We also consider the case of a north–south mean flow with a longitudinally propagating wave packet forced to the east or west of the critical layer. The monochromatic version of this problem has been used before (Geisler, J.E., Dickinson, R.E., 1975. Critical level absorption of barotropic Rossby waves in a north–south flow. J. Geophys. Res., 80, 3805–3811.) to examine the interaction of western boundary currents and oceanic Rossby waves.     

北大西洋涛动对新疆夏季降水异常的影响

利用1961~2003年NCEP/NCAR再分析和新疆75个气象站月降水资料,分析新疆夏季降水与沿西亚副热带西风急流Rossby波和北大西洋涛动（NAO）的关系,研究表明,夏季斯堪的纳维亚半岛-中欧—西亚和中亚的准静止波传播是联系NAO与沿西亚副热带西风急流波活动和新疆夏季降水变化的纽带。通过波作用量的动力学诊断分析,讨论了夏季NAO正、负位相异常年准静止波传播特征和差异,夏季NAO强弱活动影响斯堪的纳维亚半岛EP通量散度强度和位置异常,该区EP通量散度强度和位置异常导致强辐散中心在中高纬向东传播的准静止波和沿副热带西风急流准静止波活动变化,从而影响新疆夏季降水。     

近30年影响我国东南沿海的热带气旋降水强度变化特征分析

利用中国地面台站逐日降水资料和中国气象局上海台风研究所整编的热带气旋最佳路径资料研究了1978～2007年影响我国热带气旋降水强度的变化及其对我国东南沿海盛夏降水变化的影响.近30年影响我国东南沿海盛夏的热带气旋降水增加是导致我国东南沿海盛夏降水显著增加的主要原因.仅从热带气旋降水来看,东南沿海和内陆(包括江西、湖南东部和湖北南部)热带气旋降水强度显著增加,而影响热带气旋降水频次略有增加.通过对雨量站与引起降水热带气旋的中心距离的变化分析发现:内陆地区影响热带气旋距离显著下降,近距离热带气旋引起降水的增加,是该区域热带气旋降水强度增加的主要来源;而东南沿海地区近距离热带气旋降水增加不明显,热带气旋降水强度的增加主要由于同距离热带气旋降水强度的增加.热带气旋经过频次的空间的变化结果证实,近30年经过中国沿海的TC个数变化不大,仅福建沿海一带略有增加,而内陆地区则增加明显,且经过该区域时热带气旋移动速度变慢,这均与该区域近距离热带气旋降水的增加一致.     

Influence of the tropical cyclone Omar on the weather in Europe

A case of the Atlantic tropical cyclone influence on the weather of Europe is considered. It is demonstrated on the basis of computations of the numerical mesoscale ETA model that one of the reasons of the positive air temperature anomaly in fall 2008 was the tropical cyclone Omar. The detailed analysis was carried out of the computation results of the movement and evolution of the tropical cyclone Omar and of the atmospheric structures surrounding it. The energy characteristics, the explicit and latent heat fluxes, and the precipitation in the tropical cyclone were computed. The computations revealed that starting since the certain moment, the tropical storm Omar actively interacted with the polar front which shifted to the low latitudes and with the extratropical disturbance of synoptic scale which originated on this front. It was obtained that this interaction resulted in the transfer of the huge tropical cyclone energy to the extratropical pole-front cyclone and in the intensification of the latter one. It is demonstrated that the air which circulated in the tropical cyclone and possessed high the thermohygrometric characteristics entered the warm sector of extratropical cyclone and was carried out to Europe.     

On the direction of Rossby wave breaking in blocking

The direction of Rossby wave breaking at the onset of large-scale atmospheric blocking events is shown to relate closely to its position relative to the location of the climatological storm tracks. Using ERA-Interim reanalysis data from October 1989 to March 2009 and a dynamically-based blocking index, Rossby wave breaking is shown to occur preferentially cyclonically to the north, and anticyclonically to the south of the average storm tracks location. Therefore the results support existing theory on the relation between Rossby wave breaking direction and barotropic shear of the background wind. The further away from the storm tracks the breaking occurs, the stronger this preference in breaking direction. Regional differences can also be explained. For the European region on average 70?% of the detected blocking took place after anticyclonic Rossby wave breaking event that occurred on average 6° south of the climatological storm tracks position. Over Western Pacific wave breaking prior to blocking occurs predominantly cyclonically and on average 6° north of the storm tracks. Differences in blocking duration and intensity are found to be within estimated error margins at most longitudes, except for the Atlantic-Europe sector where the blocking events following anticyclonic blocking are also the strongest.     

热带气旋强度变化研究进展

自20世纪90年代后期以来,热带气旋强度变化研究越来越受到人们的重视,随着研究的不断深入,热带气旋强度变化研究取得了可喜的进展,文中总结近年来热带气旋强度变化的主要研究成果,主要包括(1)热带气旋的发生、发展和最大可能强度的研究;(2)行星涡度梯度、环境均匀流、环境流场垂直切变以及热带气旋外流与环境流的相互作用对热带气旋强度的影响及物理机制;(3)热带气旋结构与强度的变化关系,着重总结环境流场导致的非对称结构变化而引起的热带气旋强度变化以及对涡旋倾斜发展理论验证,分析了涡旋Rossby波的最新研究;(4)海洋热状况变化以及海洋飞沫对热带气旋强度的影响研究成果。分析指出,今后进一步开展用现代化卫星探测资料研究热带气旋强度变化外,还应加强热带气旋外流与环境流场的相互作用,海-气交界面的参数化问题,热带气旋结构变化与TC强度变化关系以及这种关系的物理本质的研究,通过深入研究,认识热带气旋强度变化的物理机制,提高热带气旋强度变化的预报能力。