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1.
由台风低压倒槽引发的山东暴雨过程研究 总被引：4，自引：1，他引：3
2004年8月26-28日发生在山东省的大到暴雨过程主要是由"艾莉"台风减弱的低压和西风带冷空气远距离相互作用造成的,台风倒槽的发展与低空东南气流的加强及台风低压外围热量和动量的向北输送密切相关.采用双向三重嵌套网格非静力模式MM5对这一过程进行了数值模拟,研究了台风倒槽的中尺度结构特征,并通过涡度收支探讨了台风倒槽及中尺度低涡发生发展的物理过程.结果表明,强降水是在台风倒槽顶部强风中心与弱风中心之间的强辐合作用下触发的,台风倒槽的增强和中尺度低涡的形成是低空急流及其动力作用的结果,降水的非绝热加热也起着重要作用.涡度方程的收支诊断表明,对流层低层的散度项、对流层中层的水平平流项和铅直输送项是正涡度的主要贡献者,在同一等压面上散度项和水平平流项的作用是相反的.对流层中层铅直输送项的贡献为正,扭转项为负贡献,涡度变化的总趋势是它们相互作用的净结果.等压面上相对涡度的变化趋势并不是均匀的,中尺度低涡的东南象限相对涡度局地变化较强,这是强降水发生在此的重要原因.低层正涡度的增加是由水平辐合引起的,而高层正涡度的增加是涡度由低层向高层垂直输送的结果.因此台风倒槽的发展和中尺度低涡的形成主要是由于低层的涡度制造,另一方面来自中低层涡度的垂直输送. 相似文献
2.
Vorticity budget investigation of a simulated long-lived mesoscale vortex in South China 总被引：2，自引：0，他引：2
A vorticity budget investigation is performed using the output data from a numerical simulation of a typical MCV (mesoscale convectively generated votex) case in South China. Results suggest that the divergence caused by convection in the low troposphere is the main producer of positive vorticity, while vertical vorticity transferred by the tilting term from the horizontal vorticity compensates the upward output of cyclonic vorticity. Scale analyses of the vorticity equation suggest that the advection of planetary vorticity can be neglected owing to the low latitude, which is different from the larger scale systems in high latitude areas. In addition, the distribution of relative vorticity tendency on pressure level is not uniform. A vortex will move along the vector from the negative to the positive vorticity tendency region. The mechanism of the phenomenon-that nearly all of the convectively ascending region is located southward/southeastward of the vortex center-is also discussed. Convergence with regard to latent heat release would be in favor of the spin-up of meso-vortex, however, the horizontal vorticity caused by windshear is tilted by vertical motion due to convection. Consequently, the negative and positive vorticity tendencies are located symmetrically about the convective center, which suggests that the vortex southward movement is dynamically driven by convection. 相似文献
3.
中尺度涡旋可以持续激发新对流,是造成局地持续性降水的重要系统。基于经典涡度方程的诊断无法描述热力信息对于涡旋发展的贡献。本文采用Boussinesq近似对涡度方程进行整理,将方程唯一强迫项定义为垂直速度位涡,其形式与位涡类似,利用垂直速度替换位温。进一步在垂直速度位涡倾向方程中,以气压水平梯度的形式引入热力过程的间接作用,定量描述动热力配置的贡献。以2021年6月15日发生在南疆的一次极端暴雨为例,利用高分辨率数值模拟资料,初步分析了低层动热力强迫作用向垂直涡度的传递。结果表明,垂直速度位涡的局地变化主要来自热力强迫项中低层垂直风切变与低层冷池的耦合作用,两者在降水区前侧产生大范围的正值区。该区域与垂直速度位涡的正值区重叠,促进垂直速度位涡的增长,进而维持降水前缘的正涡度,有利于产生较强的上升运动,触发新对流并造成持续性降水。 相似文献
4.
利用WRF中尺度数值模式,NCEP/NCAR分析资料,多普勒雷达观测资料等,对2016年7月25日一次东北冷涡下的飑线过程进行数值模拟,研究了飑线形成和维持与水平涡度的关系及飑线过程中中尺度对流涡旋(MCV)的形成机制,分析发现,高低层水平涡度逆时针旋转对本次飑线的形成和维持有很好的指示意义。(1)飑线发生前,高层渤海湾西侧出现水平涡度的逆时针旋转中心,并有较强的辐散配合,低层水平涡度为逆时针弯曲,为飑线产生提供了有利的上升运动条件。随后高层多个对流单体的水平涡度气旋式涡旋合并形成较大范围的气旋式涡旋结构,触发低层的上升运动,同时低层对流区前部形成一致的气旋式弯曲使得对流单体组织成带状结构,形成飑线。(2)飑线成熟时期高层水平涡度表现为统一大范围气旋式涡旋结构,低层则呈现典型的S型弯曲结构,水平涡度x方向的分量沿对流带从南至北表现为正负正,y方向的分量始终为正,并由对流带的中心向两侧减小,显示出水平涡度矢量旋转的方向对飑线影响的重要性。(3)由垂直涡度方程的分析得出,在飑线发展中期,MCV形成前,雷达反射率回波在500 hPa左右表现出明显的旋转,此时主要与500 hPa以上强的正涡度水平平流项及中层倾侧项和水平散度项有关,之后,在这几项的作用下使得中层风场产生气旋式旋转,形成MCV。 相似文献
5.
Three typhoons, Goni, Morakot and Etau which were generated in Western Pacific in
2009, are successfully simulated by the WRF model. The horizontal and vertical vorticity and
their interaction are analyzed and diagnosed by using the simulation results. It is shown that
their resultant vectors had a fixed pattern in the evolution process of the three typhoons:
The horizontal vorticity converged to the tropical cyclone (TC) center below 900 hPa level,
flowed out from it at around 900 to 800 hPa, and flowed in between 800 hPa and 700 hPa. If
multiple maximum wind speed centers showed up, the horizontal vorticity converged to the
center of the typhoon below the maximum wind speed center and diverged from the TC center
above the maximum wind speed center. At low levels, the three typhoons interacted with each
other through vertical circulation generated by the vortex tube. This circulation was mainly
generated by the eastward or westward horizontal vorticity vectors. Clouds and precipitation
were generated on the ascending branch of the vertical circulation. The vortex tubes often
flowed toward the southwest of the right TC from the northeast of the left TC. According to
the full vorticity equation, the horizontal vorticity converted into the vertical vorticity
near the maximum wind speed center below 850 hPa level, and the period of most intense
conversion was consistent with the intensification period of TC, while the vorticity advection
was against the intensification. The vertical vorticity converted into the horizontal
vorticity from 800 hPa to 600 hPa, and the wind speed decreased above the maximum wind speed
region at low levels. 相似文献
6.
覃皓 《沙漠与绿洲气象(新疆气象)》2024,18(2):68-75
利用常规观测、卫星数据及ERA5再分析数据,从动力和热力角度对引发2020年5月24-25日广西北部暴雨过程的低涡发展维持机制进行了诊断分析。结果表明：低涡在滇黔桂交界一带生成,随后逐渐发展东移,对流云团及降水落区主要分布在低涡东侧及南侧。涡度方程诊断表明,低涡的发展维持主要受涡度平流项和水平散度项影响。水平风场对涡度的输送使得局地涡度减小,而水平风场的辐合效应使得局地涡度增大。将原始风场分解为地转风和非地转风分量后发现,非地转风分量主导了局地涡度的变化,非地转风水平散度项正贡献最大,扭转项次之,两者是造成低涡发展维持的主要原因。在热力作用方面,低涡发展移动过程中对流层中层附近的潜热加热正反馈也有利于低层低涡的发展维持。 相似文献
7.
将包含水汽潜热和摩擦因子的平衡模式ω方程适当简化,形式上与准地转方程相似,在简单谐波分布的假定下,由此求得各标准气压层上垂直运动和涡度倾向的近似解析解,它是包含所有各气压层上涡度源变和温度源变(或称“广义平流”)以及地形强迫作用的一组线性多项式。各项的系数分别表现出该项源变或地形强迫作用对某一气压层上垂直运动或涡度倾向的影响。针对几种典型情况,计算出这些影响系数,这有助于定性地诊断天气尺度和次天气尺度系统短期演变的物理过程,适用于副热带情况。 相似文献
8.
THE RELATIONSHIP BETWEEN HORIZONTAL VORTICITY INDUCED BY
VERTICAL SHEAR AND VERTICAL MOTION DURING A SQUALL LINE
PROCESS 总被引：2，自引：0，他引：2
The horizontal vorticity equation used in this study
was obtained using the equations of motion in the pressure
coordinate system without considering friction, to reveal its
relationship with vertical shear. By diagnostically analyzing
each term in the horizontal vorticity equation during a squall
line process that occurred on 19 June 2010, we found that the
non-thermal wind term had a negative contribution to the local
change of upward movement in the low-level atmosphere, and that
its impact changed gradually from negative to positive with
altitude, which could influence upward movement in the mid- and
upper-level atmosphere greatly. The contribution of upward
vertical transport to vertical movement was the largest in the
low-level atmosphere, but had negative contribution to the
upper-level atmosphere. These features were most evident in the
development stage of the squall line. Based on analysis of
convection cells along a squall line, we found that in the
process of cell development diabatic heating caused the
subsidence of constant potential temperature surface and non-
geostrophic motion, which then triggered strong convergence of
horizontal acceleration in the mid-level atmosphere and
divergence of horizontal acceleration in the upper-level
atmosphere. These changes of horizontal wind field could cause a
counterclockwise increment of the horizontal vorticity around
the warm cell, which then generated an increase of upward
movement. This was the main reason why the non-thermal wind term
had the largest contribution to the strengthening of upward
movement in the mid- and upper-level atmosphere. The vertical
transport of large value of horizontal vorticity was the key to
trigger convection in this squall line process. 相似文献
9.
Quadrant-Averaged Structure and Evolution Mechanisms of a Northeast Cold Vortex during Its Mature Stage 
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下载免费PDF全文 A Northeast China cold vortex(NCCV) that maintained from 0200 UTC 3 July to 0500 UTC 3 July 2013 and caused several heavy rainfall events was analyzed in detail to reveal its quadrant-averaged structure and main maintaining mechanisms during its mature stage. Results indicated the vortex’s intensity, divergence, ascending motions, precipitable water(PW), and thermal structures were all characterized by significant unevenness, and their main pattern changed gradually during the mature stage. Mechanisms accounting for the maintenance of the NCCV were also characterized by remarkable unevenness. Within different quadrants, dominant factors for the vortex’s evolution may have differed from each other significantly. The NCCV-averaged vorticity budget revealed that the vertical advection of vorticity, which is closely related to convective activities, was the most favorable factor for maintaining the NCCV, whereas the tilting effect, which is closely related to the vertical shear of the horizontal wind(horizontal vorticity), was the most detrimental factor. 相似文献
10.
强降水过程中热力切变平流参数的诊断分析 总被引：3，自引：3，他引：0
在以往研究的基础上, 本文把对流涡度矢量的垂直分量、水平散度和广义位温的垂直梯度有机地结合起来, 引入热力切变平流参数的概念。本文针对两次强降水过程, 利用NCEP/NCAR全球最终分析资料对热力切变平流参数进行诊断分析, 结果表明, 热力切变平流参数能够比较准确地综合表征雨区上空水平风场切变和湿等熵面漏斗状向下伸展等动力学和热力学典型的垂直结构特征, 因而该参数与降水系统的发展演变密切相关, 与观测的6小时累积地面降水区存在一定的对应关系; 在空间水平分布和时间演变趋势上, 热力切变平流参数的异常值区覆盖着观测的6小时累积地面降水区; 该参数在降水区内表现为强信号, 而在非降水区表现为弱信号。影响热力切变平流参数发展演变的因素分析表明, 该参数倾向方程中通量散度项的异常值区覆盖着观测的6小时累积地面降水区, 表明雨区内通量散度项导致的热力切变平流参数变化比较明显, 其中纬向风速与经向风速相互作用的贡献是不容忽略的。 相似文献
11.
A Study on a Heavy Rainfall Event Triggered by an Inverted Typhoon Trough in Shandong Province 总被引：2，自引：0，他引：2 下载免费PDF全文
下载免费PDF全文 A heavy rainfall event that occurred in Shandong Province in 26 28 August 2004 was caused mainly by Typhoon Acre and cold air activities related to a westerly trough. The event was triggered by an inverted typhoon trough, which was closely associated with the intensification of the low-level southeasterly flow and the northward transport of heat and momentum in the periphery of the typhoon low. A numerical simulation of this event is performed using the nonhydrostatic mesoscale model MM5 with two-way interactive and triply-nested grids, and the structure of the inverted typhoon trough is studied. Furthermore, the formation and development mechanism of the inverted typhoon trough and a mesoscale vortex are discussed through a vorticity budget analysis. The results show that the heavy rainfall was induced by the strong convergence between the strong and weak winds within the inverted typhoon trough. Dynamic effects of the low-level jet and the diabatic heating of precipitation played an important role in the development of the inverted typhoon trough and the formation of the mesoscale vortex. The vorticity budget analysis suggests that the divergence term in the low troposphere, the horizontal advection term, and the convection term in the middle troposphere were main contributors to positive vorticity. Nonetheless, at the same pressure level, the effect of the divergence term and that of the adveetion term were opposite to each other. In the middle troposphere, the vertical transport term made a positive contribution while the tilting term made a negative contribution, and the total vorticity tendency was the net result of their counteractions. It is found that the change tendency of the relative vorticity was not uniform horizontally. A strong positive vorticity tendency occurred in the southeast of the mesoscale vortex, which is why the heavy rainfall was concentrated there. The increase of positive vorticity in the low （upper） troposphere was caused by horizontal convergence （upward transport of vorticity from the lower troposphere）. Therefore, the development of the inverted typhoon trough and the formation of the mesoscale vortex were mainly attributed to the vorticity generated in the low troposphere, and also the vertical transport of vorticity from the low and middle troposphere. 相似文献
12.
台风“凤凰”和“诺瑞丝”路径与降水分布对比分析 总被引：3，自引：1，他引：2
台风"凤凰"(0808)和"诺瑞丝"(8012)路径相似,但降水分布不同,"凤凰"暴雨分布在路径左右两侧,而"诺瑞丝"暴雨分布在路径左侧。文章从湿位涡和垂直风切变角度对这两个路径相似台风暴雨进行了诊断分析。结果表明:无论是"凤凰",还是"诺瑞丝"台风暴雨与湿位涡和垂直风切变都有较一致对应关系,强降水位于垂直风切变矢量左侧,垂直风切变矢量与移动路径呈不同夹角时,强降水分布在移动路径不同方位。湿位涡正压项(MPV1)负值区和斜压项(MPV2)正值区相叠加对应强降水落区,而且叠加区内MPV2越大,降水强度也越强。因此,在实际台风预报中,可以结合湿位涡和垂直风切变综合分析来提高预测强降水落区准确性。 相似文献
13.
高空急流对青藏高原切变线影响的数值试验与动力诊断 总被引：2，自引：0，他引：2
利用NCEP 1°×1° FNL分析资料和中尺度数值模式WRF对一次青藏高原（简称高原）切变线过程进行了数值试验,主要研究高空急流强度对高原切变线的影响,并结合ω方程分析了影响高原切变线上垂直上升运动的若干因子。研究得出高空急流的强度对低层风场有重要影响,急流增强会使高原切变线上的风切变增大,切变线变长,同时高空急流强度的增强也有利于高原切变线上水汽的辐合。高空急流可通过影响高层辐散、低层辐合的散度场垂直配置对高原切变线上的正涡度柱与辐合上升运动产生作用。ω方程的诊断分析表明,温度平流的拉普拉斯项对高原切变线上的垂直上升运动起主导作用,低层暖平流有利于切变线上产生上升运动。高空急流强度的变化对差动涡度平流项的影响要大于温度平流拉普拉斯项,高空急流强度的增强会放大差动涡度平流项和温度平流项的正贡献,从而更加有利于上升运动及高原切变线的维持。 相似文献
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16.
Horizontal velocity spirals with a clockwise rotation(downward looking) rate of 1.7?m-1, on average, were observed in the western and northern Yellow Sea from December 2006 to February 2007. With the observed thermal wind relation,the beta-spiral theory was used to explain the dynamics of spirals. It was found that the horizontal diffusion of geostrophic vortex stretching is likely to be a major mechanism for generating geostrophic spirals. Vertical advection associated with surface/bottom Ekman pumping and topography-induced upwelling is too weak to support these spirals. Strong wind stirring and large heat loss in wintertime lead to weak stratification and diminish the effects of vertical advection. The cooling effect and vertical diffusion are offset by an overwhelming contribution of horizontal diffusion in connection with vortex stretching. The Richardson number-dependent vertical eddy diffusivity reaches a magnitude of 10-4 m^2 s-1 on average. An eddy diffusivity of 2870 m^2 s-1 is required for dynamic balance by estimating the residual term. This obtained value of 10-4 m^2 s-1 is in good agreement with the estimation in terms of observed eddy activities. The suppressed and unsuppressed diffusivities in the observation region are 2752 and 2881 m^2 s-1, respectively, which supports a closed budget for velocity rotation. 相似文献
17.
A mathematical relation between deformation and vertical vorticity tendency is built by introducing the frontogenesis function and the complete vertical vorticity equation, which is derived by virtue of moist potential vorticity. From the mathematical relation, it is shown that properly configured atmospheric conditions can make deformation exert a positive contribution to vortex development at rates comparable to other favorable factors. The effect of deformation on vortex development is not only related to the deformation itself, but also depends on the current thermodynamic and dynamic structures of the atmosphere, such as the convective stability, moist baroclinicity and vertical wind shear(or horizontal vorticity). A diagnostic study of a heavy-rainfall case that occurred during 20–22 July 2012 shows that deformation has the most remarkable effect on the increase in vertical vorticity during the rapid development stage of the low vortex during its whole life cycle. This feature is mainly due to the existence of an approximate neutral layer(about 700 h Pa) in the atmosphere where the convective stability tends to be zero. The neutral layer makes the effect of deformation on the vertical vorticity increase significantly during the vortex development stage, and thus drives the vertical vorticity to increase. 相似文献
18.
The complete form of the vertical vorticity tendency equation (the complete-form vorticity equation) is derived from the Ertel potential vorticity equation to contain thermodynamic factors. In this study, a new complete-form vorticity equation, which has the same form as the original complete-form vorticity equation, is deduced from the absolute vorticity vector equation combined with the continuity equation and the expression of three-dimensional (3D) entropy gradient. By comparing the complete-form vorticity equation with the classical vertical vorticity equation, it is found that regardless of whether or not the isentropic surface is tilting, the two vorticity equations are in essence the same. The “baroclinic term” of the complete-form vorticity equation is exactly equal to the solenoidal term of the classical one, and there is a significant amount of cancellation between the two baroclinic items (the “slantwise term” and the horizontal vorticity change term) in the complete-form vorticity equation. In operational weather analysis, the tilt of the isentropic surface can be diagnosed according to the density of the isotherm on the upper-level isobaric map. For synoptic-scale motion, the vertical vorticity produced by the tilt of the isentropic surface is due to the contribution of atmospheric baroclinicity, which is measured by the solenoid. The 3D solenoid is parallel to the isentropic surface, so the more tilted the isentropic surface, the bigger the projection of the 3D solenoid in the vertical direction. The baroclinic contribution can be interpreted based on the PV thinking theory, but the relationship between the vorticity field and the potential vorticity field is not immediate. 相似文献
19.
引发暴雨天气的中尺度低涡的数值研究 总被引：1，自引：1，他引：0
2008年7月17—19日发生在山东的大到暴雨天气是由“海鸥”台风和副热带高压共同向山东输送水汽,与弱冷空气相互作用造成的。对流层低层的中尺度低涡是暴雨天气的直接制造者。利用常规观测资料和中尺度模式WRF（Weather Research and Forecasting）的模拟资料对该中尺度低涡的结构及形成机制进行了分析研究。结果表明,数值模拟可以清楚地捕捉到中尺度低涡东移过程中有新的涡旋中心形成,并与原来的涡旋中心合并的过程,而不是简单的沿切变线东移。中尺度低涡形成在增温增湿明显、上升运动为主的对流区内;中尺度低涡形成后其中心转为下沉运动,对流区东移,降水区位于低涡的东北和东南象限。中尺度低涡上空近地面层的冷池、600～400hPa的弱冷空气堆、900～850hPa的弱风区及高低空急流耦合发展是中尺度低涡形成和发展阶段的重要特征。中尺度低涡减弱阶段,下沉运动变强,低空急流和高空出流都明显减弱。涡度方程的收支表明,对流层低层的散度项、倾侧项及对流层中层的水平平流项和铅直输送项是正涡度的主要贡献者。中低层的水平辐合、涡度由低层向高层的垂直输送都有利于中尺度低涡的形成和发展。倾侧项对中尺度低涡的形成也有重要贡献。中尺度低涡形成后期,低层辐合、高层辐散及垂直输送的减弱导致正涡度制造的减弱,从而使中尺度低涡减弱。 相似文献
20.
基于2 km分辨率的ARW-WRF数值模拟资料,讨论了台风"珍珠"(2006)螺旋雨带中对流单体及内雨带的发展机制。结果表明:模式很好地再现了台风的路径和强度。作为雨带中仅仅存在于眼壁外侧的内雨带,其传播机制与重力波、涡旋Rossby波及混合波没有联系,其可能发展机制仅与低层出流、水平风场和变形场有关。低层出流使得内雨带径向向外运动,而低层的水平风场和变形场使其形成螺旋结构。同时,就螺旋雨带中精细对流单体的发展而言,涡度收支方程定量分析表明,其主要通过两种方式获得垂直涡度:水平涡度倾斜为垂直涡度;上升运动拉伸垂直涡度。随着平流输送,对流单体在眼壁附近合并和汇聚。 相似文献