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1.
Utilizing Eliassen’s concepts, the forcing of the isentropic azimuthally-averaged mass-weighted radial-vertical circulation by diabatic heating and torques within an extratropical cyclone and a typhoon was studied through nu-merical simulations based on the linear diagnostic equation derived previously. The structure of the forcing associated with diabatic heating and torques was determined from quasi-Lagrangian diagnostic analyses of actual case studies. The two cyclones studied were the Ohio extratropical cyclone of 25-27 January 1978 and typhoon Nancy of 18-23 September 1979. The Ohio cyclone, which formed over the Gulf Coast and moved through Ohio and eastern Michigan, was one of the most intense storms with blizzard conditions to ever occur in this region. Typhoon Nancy which occurred over the South China Sea during the FGGE year was selected since relatively high quality assimilated data were available. Within the Ohio cyclone, the dominant internal processes forcing the mean circulation with em-bedded relatively strong hydrodynamic stability were the pressure torque associated with baroclinic (asymmetric) structure and the horizontal eddy angular momentum transport associated with the typical S-shaped thermal and wind structures of self-development. Within typhoon Nancy, the dominant internal process forcing the mean circula-tion with embedded weak hydrodynamic stability was the latent heat release. This analysis shows that the simulated azimuthally-averaged mass-weighted radial motions within these two cy?clones agree quite well with the “observed” azimuthally-averaged mass-weighted radial motions. This isentropic nu?merical study also provides insight into the relatively important internal forcing processes and the trade off between forcing and stability within both extratropical and tropical cyclones.  相似文献   

2.
    
Following the theoretical result of Eliassen, the Sawyer-Eliassen equation for frontal circulations and the equation for forcing the meridional circulation within a circumpolar vortex are extended in isentropic coordinates to des-cribe the forcing of the azimuthally averaged mass-weighted radial-vertical circulation within translating extratropical and tropical cyclones. Several physical processes which are not evident in studies employing isobaric coordinates are isolated in this isentropic study. These processes include the effects of pressure torque, inertial torque and storm translation that are associated with the asymmetric structure in isentropic coordinates. This isentropic study also includes the effects of eddy angular momentum transport, diabatic heating and frictional torque that are common in both isentropic and isobaric studies. All of the processes are modulated by static, inertial and baroclinic stabilities. Consistent with the theoretical result of Eliassen, the numerical solution from this isentropic study shows that the roles of torque, diabatic heating and hydrodynamic stability in forcing the radial-vertical circulation within stable vortices are that 1) positive (negative) torque which results in the counterclockwise (clockwise) rotation of vortices also forces the outflow (inflow) branch of the radial-vertical circulation, 2) diabatic heating (cooling) forces the ascent (descent) branch of the radial-vertical circulation and 3) for given forcing, the weaker hydrodynamic stability results in a stronger radial-vertical circulation. It is the net inflow or convergence (net outflow or divergence), vertical motions and the associated redistribution of properties that favor the evolution of vortices with colorful weather events. Numerical solutions of this isentropic study are given in companion articles. The relatively important contribution of various physical processes to the forcing of the azimuthally-averaged mass-weighted radial-vertical circulation within different translating cyclones and in their different stages of development will be investigated.  相似文献   

3.
The relevance of the midlatitude conveyor belt model to Mediterranean cyclones (MCs) is examined using data from two winters. Eight MCs, which exhibit typical midlatitude cyclone structure, were scrutinized and their conveyor belts were examined. The analysis was based on satellite imagery, isentropic wind maps, vertical cross-sections of potential and equivalent potential temperatures, and air back-trajectories. The conveyor belts found in the studied MCs were similar to the common features of midlatitude cyclones, except for three aspects. First, the warm conveyor belt was not associated with massive organized cloudiness in five of the eight cyclones since it consisted of dry air originated from the Saharan desert. Second, the anticyclonic branch of the cold conveyor belt was not found in half of the MCs. Third, the dry air intrusion originated north of the cyclone and extended southward around it, unlike its common midlatitudinal northwest–southeast orientation. This is consistent with the relatively small baroclinic vertical-westward tilt of the cyclones analyzed.  相似文献   

4.
ＯｎｔｈｅＦｏｒｃｉｎｇｏｆｔｈｅＲａｄｉａｌ－ｖｅｒｔｉｃａｌＣｉｒｃｕｌａｔｉｏｎｗｉｔｈｉｎＣｙｃｌｏｎｅｓ—Ｐａｒｔ１：ＣｏｎｃｅｐｔｓａｎｄＥｑｕａｔｉｏｎｓＤ．Ｒ．ＪｏｈｎｓｏｎａｎｄＺｈｕｏｊｉａｎＹｕａｎＳｐａｃｅＳｃｉｅｎｃｅａｎｄ...  相似文献   

5.
一次爆发性气旋的发展与湿位涡关系的研究   总被引：13，自引：3，他引：13  
通过对一次陆地爆发性气旋的数值模拟与湿位涡的诊断分析发现，气旋的爆发与湿位涡的平流关系密切，气旋的发展并不是在湿位涡中心位于气旋上空时才开始，而是当湿位涡中心位于气旋的后部，并在200hPa对下有明显的倒圆锥形下伸区时，才有利于气旋的发展。当湿位涡中心位于气旋上空时，气旋发展开始减慢。湿位涡局地变化的大小与水平方向位涡梯度的大小有关。湿斜压位涡负值区的上下贯通与气旋发展也有明显的关系。  相似文献   

6.
A comparison of two objective climatologies of explosive cyclones in the Mediterranean region is performed. The results are derived from two different mean sea-level pressure reanalysis data resolutions, but from the same assimilation model, in order to quantify the pure impact of higher resolution on the identification and characteristics of explosive cyclones, when the assimilation model is the same. The explosive cyclones were identified with the aid of the Melbourne University automatic cyclone finding and tracking scheme over a 40-year period, using the 6-hourly analyses of ERA-40 mean sea-level pressure (MSLP) on: (a) 2.5?×?2.5 and (b) 1?×?1 latitude–longitude grid. The comparison of the two datasets revealed the significant role of the increase in spatial resolution of MSLP data on the identification and tracking process, and the number of the explosive cyclones in the high-resolution dataset is almost four times greater than the respective one in the lower resolution dataset. However, the comparison of explosive cyclone characteristics, including spatial and temporal variations of explosive deepening, revealed differences in the geographical distribution of the location of the maximum explosive deepening and average explosive cyclone Laplacian of the central pressure. These differences are due to the identification in the higher resolution set of smaller scale and secondary explosives along the strongly baroclinic northern Mediterranean boundaries, south of the Alps and the Pyrenees. Explosive deepening appears a bias to the daytime period from 12 to 18 Coordinated Universal Time (UTC) for both datasets, which is more prominent in the LR dataset. Statistically significant difference of pressure tendency between the two datasets appear for the daytime period from 06 to 12 UTC, accounting for better representation of orographic forcing in the HR dataset.  相似文献   

7.
将Eliassen建立在平面等压柱坐标系中的径向环流强迫理论（用于研究在摩擦力和非绝热加热过程影响下的静止对称涡旋），推广应用到研究移动非对称气旋或反气旋的径向环流，导出了考虑地球曲面影响的准拉格朗日等压柱坐标系的切向平均径向环流诊断方程，并根据Eliassen的解析解所揭示的涡旋径向环流在涡旋演变中的作用，定 性地讨论了各种热力和动力的作用，这些热力和动力因子除了磨擦力和非绝热加热外，还有平均和涡动形式的惯性力，角动量平流（相当涡度平流），角动量的垂直对流，温度平流，温度的垂直对流（相当绝热加热）等。  相似文献   

8.
陶祖钰  周小刚  郑永光 《气象》2012,38(1):28-40
由于从等熵位涡分析引申出来的平流层干侵入（以下简称干侵入）概念造成了当前天气预报思路中一些混乱和违背天气学常识的看法,文中回顾了天气预报原理从着眼气压变化到着眼涡度变化的发展历史和位涡问题的缘起。进而根据位涡的定义、数学表达式、物理意义,并结合实例的计算结果指出,位涡的大小主要取决于位温的垂直梯度;等熵面上的位涡分布形势实质是对流层顶高度的分布,因此可以间接反映极地气团、锋、高空槽和高空急流的形势。轨迹计算和数值预报都证明,低空的高位涡异常是地面气旋强烈加深和潜热反馈的结果,而不是干侵入的结果。指出位涡的守恒性不能替代斜压扰动发展的动力学机理;干侵入的错误概念来源于对位涡守恒性的绝对化和简单的推断,并犯了流体力学原理上混淆流线和轨迹两个不同概念的错误。  相似文献   

9.
Midlatitude cyclones are analyzed on a selected region covering most of southern Europe and the western part of the Mediterranean Sea (35–50°N, 10°W–25°E). On the basis of mean sea level pressure fields of the ECMWF (European Centre for Medium-range Weather Forecast) Reanalysis Dataset (ERA-40), detailed evaluation of Mediterranean cyclones is accomplished for the period between 1957 and 2002 on a 1° horizontal resolution grid. Cyclone centers are identified and their paths are tracked with a 6-h time step (using 00 UTC, 06 UTC, 12 UTC, and 18 UTC). Decadal, annual, and seasonal statistical analysis of cyclone tracks includes the study of the genesis, frequency, and activity of the Mediterranean cyclones as well as the variability of cyclone tracks. The results suggest that the cyclone frequency in the western Mediterranean region increased in summer and autumn, and decreased in winter and spring. A special belt-shaped area is identified, which plays a special role in cyclogenesis, and also, the cyclone tracks often remain within this belt. An overall decreasing trend is detected in winter and spring in the entire Mediterranean belt, while cyclone frequency increased in autumn. The largest positive and negative trend coefficients are identified in summer.  相似文献   

10.
尹尽勇  李泽椿  杜秉玉 《气象》2009,35(8):16-26
利用中尺度模式MM5对西北太平洋9617号热带风暴Tom转变温带气旋的变性过程进行了模拟.通过对其变性过程的模拟分析发现:热带风暴Tom与西风槽相互作用,风暴东侧低层暖湿气流与槽前正涡度平流发生耦合有利于气旋发展;槽前暖平流与槽后冷平流使风暴形成具有西冷东暖的热力分布结构,诱使风暴向斜压转变;高空急流入口处右侧的气旋式切变及出口处右侧的反气旋式切变有利于风暴右侧气流上升和左侧气流下沉运动,有利于风暴由正压向斜压性转变;来自风暴西北侧的干冷空气自700hPa附近向风暴中心侵入,使风暴中心暖柱体发生自低层向高层的西北一东南向的倾斜,其暖性特征遭到破坏;由于干冷空气的侵入,低层700hPa分为南北两个暖中心,北侧暖中心北侧出现了明显的暖锋锋生,西南侧另一个暖心附近有冷锋锋生迹象;平流层高值PV异常下传有利于变性后的热带风暴的再次加强.  相似文献   

11.
The adjoint sensitivity related to explosive cyclogenesis in a conditionally unstable atmosphere is investigated in this study.The PSU/NCAR limited-area,nonhydrostatic primitive equation numerical model MM5 and its adjoint system are employed for numerical simulation and adjoint computation,respectively.To ensure the explosive development of a baroclinic wave,the forecast model is initialized with an idealized condition including an idealized two-dimensional baroclinic jet with a balanced three-dimensional moderateamplitude disturbance,derived from a potential vorticity inversion technique.Firstly,the validity period of the tangent linear model for this idealized baroclinic wave case is discussed,considering different initial moisture distributions and a dry condition.Secondly,the 48-h forecast surface pressure center and the vertical component of the relative vorticity of the cyclone are selected as the response functions for adjoint computation in a dry and moist environment,respectively.The preliminary results show that the validity of the tangent linear assumption for this idealized baroclinic wave case can extend to 48 h with intense moist convection,and the validity period can last even longer in the dry adjoint integration.Adjoint sensitivity analysis indicates that the rapid development of the idealized baroclinic wave is sensitive to the initial wind and temperature perturbations around the steering level in the upstream.Moreover,the moist adjoint sensitivity can capture a secondary high sensitivity center in the upper troposphere,which cannot be depicted in the dry adjoint run.  相似文献   

12.
Sensitivity of the warm core of tropical cyclones to solar radiation   总被引：1，自引：0，他引：1  
To investigate the impacts of solar radiation on tropical cyclone (TC) warm-core structure (i.e., the magnitude and height), a pair of idealized simulations are conducted by specifying different strengths of solar shortwave radiation. It is found that the TC warm core is highly sensitive to the shortwave radiative effect. For the nighttime storm, a tendency for a more intense warm core is found, with an elevated height compared to its daytime counterpart. As pointed out by previous studies, the radiative cooling during nighttime destabilizes the local and large-scale environment and thus promotes deep moist convection, which enhances the TC's intensity. Due to the different inertial stabilities, the diabatic heating in the eyewall will force different secondary circulations. For a strong TC with a deeper vertical structure, this promotes a thin upper-level inflow layer. This inflow carries the lower stratospheric air with high potential temperature and descends adiabatically in the eye, resulting in significant upper-level warming. The Sawyer-Eliassen diagnosis further confirms that the height of the maximum temperature anomaly is likely attributable to the balance among the forced secondary circulations.  相似文献   

13.
Considered are long-term features and characteristics of storm activity variability in the North Atlantic based on the method of automatic identification of cyclone centers using the data on sea level pressure as well as the estimates of the maximum speed of the surface wind in the area of cyclones. Integral regional parameters of the variability of storm cyclone frequency for the gradations of the surface wind speed are presented for some areas of the North Atlantic. Investigated is the interrelation between extremely deep and storm cyclones.  相似文献   

14.
Summary  A diagnostic energetics analysis is used to study the effects of moisture-related processes on a developing cyclone over the Mediterranean. This is done by using the moist wind component to calculate the energy budget and then the effect due to wind field changes on the kinetic energy budget is illustrated. The horizontal flux convergence serves as a major energy budget source in both cases (actual and moist wind), although the magnitude values of this term are small in the case of the moist wind. Generation of kinetic energy, is generally (in the case of moist wind), a prominent sink during the life cycle of the cyclone, and its values are greater than the corresponding ones for the actual wind field except at the decay period. Subgrid-scale sources of kinetic energy provide a substantial energy gain throughout the life cycle of the cyclone. The values of the dissipation term differ from using the actual or moist components where its values are influenced by the values of the other terms in the budget. The baroclinic generation due to the divergent moist wind component offsets by 80.8% and 12.1% for the barotropic destruction of kinetic energy by the rotational moist wind component. The divergent moist wind component was found to be very important in the synoptic-scale environments of the cyclogenesis. Both demonstrate that the divergent moist wind component is as important as the rotational moist wind component in producing generation and horizontal flux divergence of kinetic energy. Generation of kinetic energy by the divergent moist wind component seems to be a major factor leading to the creation of upper-level wind maxima north of the storm areas. Thus, these diagnostic findings suggest possible modifications to the wind field by investigating the role of the divergent moist wind component and may also be fruitful in exploring the effects of cyclogensis on the large-scale environment. Received April 27, 1998/Revised April 23, 1999  相似文献   

15.
黄淮气旋引发山东两次暴雨过程的对比分析   总被引：1，自引：0，他引：1  
王玮  王英  黄玉芳 《气象科技》2014,42(6):1057-1063
利用常规天气图资料和NCEP再分析资料,对2002年5月14日和2013年5月26日发生在山东的两次气旋暴雨过程进行对比分析。结果表明:两次过程均是在高空低槽、西南涡及地面气旋共同作用下形成的,但气旋形成方式、高低空急流及空气不稳定层结有明显的差异。前者为倒槽锋生型,空气层结呈对流性稳定,冷暖空气在近地层交汇使得等熵面陡立触发垂直涡度增长和湿对称不稳定能量释放造成暴雨,后者为静止锋上冷暖平流加强形成气旋波,冷空气团叠加在暖湿气流之上通过降低低层稳定度强迫暖空气抬升触发对流不稳定能量释放造成暴雨;前者高空急流偏南,后者高低空急流配合较好激发出次级环流从而使上升运动增强;两次过程暴雨落区均在850hPa高能轴顶端冷暖空气交汇处。  相似文献   

16.
季风低压角动量收支的研究   总被引：1，自引：1，他引：1  
江敦春 《气象学报》1987,45(4):416-425
本文给出移动坐标系中角动量收支方程,并采用FGGE IIIb资料,对发生在印度地区1979年8月6—11日的季风低压作了角动量收支的诊断分析,得到:(i)在低压发展期间,角动量的时间变率为正;低压减弱期为负。(ii)水平侧边界角动量输送是系统角动量的主要来源,而高层东风和低层西风的增强、减弱,则是影响这种输送的重要因素。(iii)在气压场不对称的情况下,侧边界附近的气压力矩是另一个重要的角动量源。(iV)摩擦力矩是主要的角动量汇。据此,可以推论,对于印度季风扰动的发展、维持,水平侧边界输送和边界附近气压力矩的作用最为重要。  相似文献   

17.
Storm tracks play a major role in regulating the precipitation and hydrological cycle in midlatitudes. The changes in the location and amplitude of the storm tracks in response to global warming will have significant impacts on the poleward transport of heat, momentum and moisture and on the hydrological cycle. Recent studies have indicated a poleward shift of the storm tracks and the midlatitude precipitation zone in the warming world that will lead to subtropical drying and higher latitude moistening. This study agrees with this key feature for not only the annual mean but also different seasons and for the zonal mean as well as horizontal structures based on the analysis of Geophysical Fluid Dynamics Laboratory (GFDL) CM2.1 model simulations. Further analyses show that the meridional sensible and latent heat fluxes associated with the storm tracks shift poleward and intensify in both boreal summer and winter in the late twenty-first century (years 2081?C2100) relative to the latter half of the twentieth century (years 1961?C2000). The maximum dry Eady growth rate is examined to determine the effect of global warming on the time mean state and associated available potential energy for transient growth. The trend in maximum Eady growth rate is generally consistent with the poleward shift and intensification of the storm tracks in the middle latitudes of both hemispheres in both seasons. However, in the lower troposphere in northern winter, increased meridional eddy transfer within the storm tracks is more associated with increased eddy velocity, stronger correlation between eddy velocity and eddy moist static energy, and longer eddy length scale. The changing characteristics of baroclinic instability are, therefore, needed to explain the storm track response as climate warms. Diagnosis of the latitude-by-latitude energy budget for the current and future climate demonstrates how the coupling between radiative and surface heat fluxes and eddy heat and moisture transport influences the midlatitude storm track response to global warming. Through radiative forcing by increased atmospheric carbon dioxide and water vapor, more energy is gained within the tropics and subtropics, while in the middle and high latitudes energy is reduced through increased outgoing terrestrial radiation in the Northern Hemisphere and increased ocean heat uptake in the Southern Hemisphere. This enhanced energy imbalance in the future climate requires larger atmospheric energy transports in the midlatitudes which are partially accomplished by intensified storm tracks. Finally a sequence of cause and effect for the storm track response in the warming world is proposed that combines energy budget constraints with baroclinic instability theory.  相似文献   

18.
A real case study for the transformation of Tropical Storm (TS) Haima (2004) into an extratropical cyclone (EC) is carried out numerically since,after landfall,Haima (2004) (as an EC) brought severe weather to a large area (from the south to the north) in China during 13-16 September 2004.With the linear diagnostic model (derived in a previous study) for the tangentially-averaged radial-vertical circulation within vortices moving on the spherical Earth,Haima’s (2004) life cycle is reconstructed noticeably well.Therefore,the major contributor could be identified confidently for Haima’s (2004) extratropical transition based on the diagnostic model outputs.The quantitative comparison shows that up to a 90% contribution to the innerregion updraft and a 55% contribution to the upper-layer outflow come from latent heating during Haima’s (2004) TS stage.Up to a 90% contribution to the inner-region updraft and nearly a 100% contribution to the upper-layer outflow come from the upper-layer eddy angular momentum advection (EAMA) during Haima’s (2004) EC stage.Representing the asymmetric structure of the storm,the predominantly positive contribution of the upper-layer EAMA to Haima’s (2004) transformation is closely associated with the Sshaped westerlies in the upper layer with two jets.One jet in the cyclonic-curvature area carries cyclonic angular momentum into the storm,and the other jet in the anticyclonic-curvature area carries anticyclonic angular momentum out of the storm.Consequently,the newly-increased cyclonic tangential wind is deflected by the Coriolis force to the right to form the upper-layer outflow accompanied by the central-area rising motion,leading to Haima’s (2004) extratropical transition after its landfall.  相似文献   

19.
A heavy rainfall event during the period from 30th of March to 2nd of April 2009 has been studied using upper air and surface data as well as NOAA HYSPLIT model. This observational study attempts to determine factors responsible for the occurrence of heavy rainfall over Iran induced by Mediterranean cyclone, a western severe sub-tropical storm that made rainfall on most regions of the country. On the surface chart, cyclones, anticyclones and weather fronts were identified. The positions of the cold and warm fronts, which extended from a two-core low pressure center, were quite in good agreements with directions of winds i.e., westerly, southerly and easterly flows as well as the regions of precipitation. The heavy rain event occurred due to a Mediterranean cyclone’s activity over the study area, while other conditions were also responsible for this event such as an unstable atmosphere condition with abundant low-level moisture, which the warm and moist air parcels were brought by the southwesterly low-level jet into the country from Persian Gulf, Oman Sea, Indian Ocean and Caspian Sea at lower levels as well as Mediterranean Sea, Red Sea and Persian Gulf at upper levels over the examined period. A strong low-level convergence zone was observed along the wind-shift line between the southwesterly flow because of the low-level jet and the northeasterly flow due to the Russian high pressure. The amount of precipitable water varied between 20 and 24 kg m?2, surface moisture convergence exceeded 2.5 g kg?1 s?1 and the highest CAPE value in the sounding profiles was observed in Birjand site with 921 J kg?1 during the study period. The HYSPLIT model outputs confirmed the observed synoptic features for the examined system over the country.  相似文献   

20.
An accurate form of the moist potential vorticity(MPV) equation was deduced from a complete set of primitive equations.It was shown that motion in a saturated atmosphere without diabatic heating and friction conserves moist potential vorticity.This property was then used to investigate the development of vertical vorticity in moist baroclinic processes.Results show that in the framework of moist isentropic coordinate,vorticity development can result from reduction of convective stability,or convergence,or latent heat release at isentropic surfaces.However,the application of the usual analysis of moist isentropic potential vorticity is limited due to the declination of moist isentropic surfaces.and a theory of development based on z-coordinate and p-coordinate was then proposed.According to this theory,whether the atmosphere is moist-symmetrically stable or unstable,on convective stable or unstable,the reduction of convective stability,the increase of the vertical shear of horizontal wind or moist baroclinity may result in the increase of vertical vorticity,so long as the moist isentropic surface is slantwise.The larger the declination of the moist isentropic surface,the more vigorous the development of vertical vorticity.In a region with a monsoon front to the north and the warm and moist air to the south,or by the north of the front,the moist isentropes are very steep.The is the region most favorable for development of vorticities and formation of torrential rain.For a case of persistent torrential rain occurring in the middle and lower reaches of the Changjiang and Huaihe Rivers in June 11-15,1991,moist potential vorticity analysis,especially the isobaric analysis of its vertical and horizontal components,i.e.MPV1 and MPV2,respectively,is effective for identifying synoptic systems not only in middle and high latitudes,but also in low latitudes and in the lower troposphere.It can serve as a powerful tool for the diagnosis and prediction of torrential rain.  相似文献   

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