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51.
北京“7.21”特大暴雨过程中尺度系统的模拟及演变特征分析 总被引:3,自引:1,他引:2
在2012年7月21日北京特大暴雨过程天气尺度环流背景分析的基础上,主要用WRF模式对该次暴雨过程进行了高分辨率的模拟。利用模拟资料分析了影响此次北京特大暴雨的辐合线及辐合线上生成的中尺度低涡的热动力结构及其演变。从热力场来看,来自于西北和东北方向的强冷空气与西南和东南暖湿气流的长时间对峙形成的辐合以及中低层冷空气从西北和东北方向向西南的入侵迫使整层暖湿空气抬升,以及低空急流的暖湿平流与低空弱冷空气之间形成的"西冷东暖"的结构,对对流不稳定的触发有一定作用,有助于该次特大暴雨的发生。对流层低层的西(东)南风与西北风之间形成了一条持续时间长的辐合切变线,切变线上不断有中尺度低涡生成并沿切变线发展移动,模拟资料分析表明,低涡不断沿切变线生成并移动经过北京从而对该次暴雨造成影响,这与"列车效应"现象类似。切变线上生成的中尺度低涡位置也同时处于急流左前侧和山前,低涡加强和发展时对应有暴雨的明显增强,是直接造成北京特大暴雨的中尺度系统,其生成与低层辐合、低空急流及地形均有关系。低层辐合引发的垂直运动在地形迎风坡附近得到加强,低层辐合及地形抬升共同导致了强垂直运动的发展和维持,是暴雨持续的重要原因。大气中层有下沉气流与低层上升气流相互作用,在大气中低层形成一系列中尺度环流,房山附近一直有中尺度环流的垂直上升支维持,也是暴雨中心出现在房山的原因之一。 相似文献
52.
The sensitivity of precipitation to sea surface temperature(SST) and its diurnal variation is investigated through a rainfall partitioning analysis of two-dimensional cloud-resolving model experiments based on surface rainfall budget.For all experiments,the model is set up using zero vertical velocity and a constant zonal wind and is integrated over 40 days to reach quasi-equilibrium states.The 10-day equilibrium grid-scale simulation data and a time-invariant SST of 29°C are used in the control experiment.In the sensitivity experiments,time-invariant SSTs are 27°C and 31°C with an average value of 29°C when the minimum and maximum values of diurnal SST differences are 1°C and 2°C,respectively.The results show that the largest contribution to total rainfall is from the rainfall with water vapor convergence and local atmospheric drying and hydrometeor gain/divergence(~30%) in all experiments.When SST increases from 27°C to 29°C,the contribution from water vapor convergence decreases.The increase of SST reduces the contribution of the rainfall with water vapor convergence primarily through the decreased contribution of the rainfall with local atmospheric drying and hydrometeor gain/divergence and the rainfall with local atmospheric moistening and hydrometeor loss/convergence.The inclusion of diurnal variation of SST with the diurnal difference of 1°C decreases the rainfall contribution from water vapor convergence primarily through the decreased contribution of the rainfall with local atmospheric moistening and hydrometeor loss/convergence.The contribution of the rainfall from water vapor convergence is barely changed as the diurnal difference of SST increases from 1°C to 2°C. 相似文献
53.
利用观测资料和高分辨率数值模拟资料对2014年6月26日发生在辽东湾北部的一次飑线过程进行了分析。本次飑线发生发展期间,对流层中层存在正在发展加深的槽,近地面则是偏南暖湿气流和西北干冷气流交汇形成的辐合线,天气尺度环境强迫较强,有利于强对流的触发和发展。此次飑线发生发展于地面辐合线的南段。对比分析表明模拟结果和实况观测较为一致。对辐合线北段对流较快消散,而南段对流得以继续发展成为飑线的原因进行了分析。结果表明,与北段相比,南段环境水汽更为丰富,对流有效位能大,水平风的垂直切变适宜。此外,南段环境还受海风锋导致的增湿、降温以及辐合带来的弱上升气流的影响。以上因素是导致辐合线北段对流较快消散而南段对流可以较长时间维持,并发展成为飑线系统的主要原因。本次飑线在成熟时期的气压场成显著的“高—低”结构分布。对流云区中部存在一个中高压,而尾流低压区位于对流云区后部与层状云区交界处。高压后部是一个强烈的地面辐散区,风速较大。飑线成熟时期中主要存在两支气流,前向入流在飑线前方低层流入,带入暖湿空气并在对流云区抬升,随后分成两支在飑线高层向前向后流出。后向入流在飑线后方中层流入,带入干冷空气并下沉,随后在近地面辐散流出。对飑线的对流云区、尾流低压区、层状云区及飑线后方的模拟探空展现了飑线不同区域的环境场特征。 相似文献
54.
中国省级粮食产量的风险区划研究 总被引:6,自引:2,他引:6
以全国各省份历年粮食单产资料为基础,通过适当的处理,定义了三个反映中国粮食产量风险水平的指标:历年平均减产率,历年减产变异系数和风险概率。这三个指标分别从不同角度刻画了中国粮食产量的风险状况。进而以这三个指标为基础采用迭代自组织动态聚类分析方法分别卉分了全国省级粮食生产单元的风险风,分区的结果反映了近五十年来中国粮食生产的基本状况和风险水平。最后从中国各地孕灾环境、致灾因子和生产力水平差异等方面探讨了风险水平的区域分异的原因。风险区划可为决策部门进行粮食生产布局和风险决策提供依据。 相似文献
55.
56.
The momentum advection vorticity equation in the form of cross multiplication is introduced, in
which the divergence term in the classic vorticity equation does not appear explicitly. This equation
includes the rotation effect of the horizontal wind advection, which are not explicitly included in the classic
vorticity equation. The vorticity and its tendency of Typhoon Fung-Wong (0808) that occurred in July 2008
are analyzed. The computed results show that the rotation effect of the advection of the horizontal wind is a
leading factor in determining the change of vertical vorticity for Fung-Wong during its life cycle, especially
in the period leading up to landfall. The advection term represents the tendency variation of the vertical
vorticity, and the positive-value region of the vertical vorticity tendency is almost in accord with the track
of Fung-Wong, which may be taken as a factor to locate the key observational region of Fung-Wong. The
equation provides a supplementary diagnostic tool for the systems related with strong advection of
horizontal wind. 相似文献
57.
2003年7月8~9日江淮流域暴雨过程中涡旋的结构特征分析 总被引:10,自引:4,他引:6
2003年淮河流域梅雨期 (6月29日~7月11日) 的强降水过程有三次: 6月29日~7月1日、 7月3~5日及7月8~11日。本文对7月8日12时~9日12时期间湖南、 安徽和江苏发生的强降水过程的中尺度数值模式MM5的输出资料进行了诊断分析。分析结果表明: 除大尺度系统的配置有利于此次降水的发生以外, 此次降水主要发生在由西南及偏南暖湿气流与偏北气流辐合形成的梅雨锋切变线上, 切变线上辐合中心处生成并发展的两个中尺度低涡是造成降水的直接系统。低空西南风急流形成了从孟加拉湾、 南海至华东地区的强水汽输送带以及湖南、 安徽和江苏的水汽辐合中心, 为暴雨创造了十分有利的水汽条件。在低层切变线的辐合中心处有两个低涡分别生成或发展, 并沿切变线向东北方向移动, 这两个低涡生成的位置是低空急流左前侧急流达到极值的区域 (也是正涡度中心区), 其生成可能与低空急流的加强有关。在低涡附近, 低层水汽辐合较强, 且对流层中低层形成了强正涡度中心和强散度中心相耦合的动力结构, 并有强上升运动维持, 使得低层辐合的水汽被抬升到对流层高层, 有利于暴雨的发生。 相似文献
58.
湿大气的广义位温与干大气位温及饱和湿大气相当位温的比较 总被引:5,自引:1,他引:4
实际大气既非完全是干空气,也不是处处达到饱和的湿空气,而是处于含有水汽但又不饱和的湿空气状态。基于这样一种湿大气状态,在湿大气中广义位温定义的基础上,对不同暴雨类型的广义位温与干大气的位温及饱和湿大气的相当位温做了比较。对2003年江淮流域暴雨过程、2004年华北一次暴雨过程以及2006年碧利斯台风中的位温、相当位温和广义位温分布的对比分析表明:即使是在暴雨系统中,湿空气的相对湿度也不一定达到100%,饱和湿空气相当位温的引入条件不能完全满足。而广义位温的定义用一个表达式就可以表示出于大气、未饱和湿大气以及饱和湿大气这3种大气状态的位温,位温和相当位温则是广义位温的特殊情况。当大气比湿为零时,广义位温就变成位温;当大气比湿达到饱和后,广义位温就变成相当位温。除了可以衔接干大气位温和饱和湿大气的相当位温外,广义位温包含了水汽由干到湿再到饱和的变化过程,更好地体现了大气中水汽的实际分布和变化特征。 相似文献
59.
Using real analysis data of 1°×1° resolution of the National Center for Environmental
Prediction/National Center for Atmospheric Research (NCEP/NCAR), the nondivergent wind component
and irrotational wind component obtained by the harmonic-cosine(H-C) method, and the wind structure of
Typhoon Fung-Wong (coded 0808 in China) in 2008 was analyzed. The results indicated that the
irrotational component was advantageous over the total wind in reflecting both the changes in convergent
height and the asymmetrical convergence of Fung-Wong. In Fung-Wong, the nondivergent component was
larger than the irrotational component, but the latter was much more variable than the former, which was
obtained only from the wind partition method. Further analyses on the irrotational component
demonstrated that the location of the convergent center at lower levels was almost the same as the
divergent center during the development of Fung-Wong, and its convergent level was high in its life cycle,
with the most highest up to 400 hPa when it became stronger. After the typhoon landed in the provinces of
Taiwan and Fujian, respectively, its convergent center at lower levels was slowly detached from the
divergent center at high levels and the convergent height was also depressed from high levels to lower
levels. Gradually, this weakened the intensity of Fung-Wong. This kind of weakening was slow and
Fung-Wong maintained its circulation for a long time over land because of its very thick convergent height.
Analyses on wind partitioning provided one possible explanation to why Fung-Wong stayed for a long time
after it landed. Furthermore, the asymmetric vertical ascending motion was induced by the asymmetric
convergence at lower levels. In general, when typhoons (such as Fung-Wong) land, the rainfall region
coincides with that of the convergence region (indicated by the irrotational component at lower layers).
This means that the possible rainfall regions may be diagnosed from the convergent area of the irrotational
component. For an observational experiment on typhoons, the convergent region may be considered as a
key observational region. 相似文献
60.
1410号台风Matmo登陆前后的动热力结构演变和水汽输送特征分析 总被引:2,自引:2,他引:0
利用NCEP/NCAR(美国国家环境预报中心/国家大气研究中心)的全球预报系统(GFS)再分析资料、欧洲气象中心(ERA-interim)资料以及中国气象局观测站点的实况降水观测结合CMORPH卫星反演降水资料,对2014年第10号台风Matmo生成后西北行并登陆台湾及福建过程中的特征进行了分析,揭示出Matmo移动路径主要受西太平洋副热带高压(简称西太副高)外围引导气流影响。动、热力物理量场分析表明,Matmo在登陆福建前后,福建上空一直维持深厚的涡旋结构,福建东南部上空的上升区与台湾海峡及福建西部附近的下沉运动区形成明显的垂直环流圈。同时,南海上空有明显的西南急流(风速大于16 m s-1),Matmo的水汽来源主要有两条,分别为孟加拉湾和南海以及西太副高南侧。充足的水汽输送及低层水汽辐合抬升有利于Matmo登陆后的强降水发生和维持。Matmo登陆福建后仍然保持低层辐合、高层辐散,有利于持续暴雨的发生。Matmo登陆福建期间始终处于风速垂直切变小值区(小于9 m s-1)中,环境风速的弱垂直切变有利于Matmo暖心结构及高空辐散形势的维持,是Matmo在登陆后依然能维持自身强度不衰减的原因之一。 相似文献