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991.
992.
针对长治市2008年2月24日大~暴雪天气过程,从500hPa环流形势、700hPa影响系统、地面气压场、物理量场的相对湿度垂直空间分布、Fy-2c云图演变特征进行了综合分析,给出了该次大~暴雪的主要成因,为今后强降雪预报提供重要参考。 相似文献
993.
994.
995.
大暴雨是浙江省乐清水库致洪的直接原因。利用NCEP 1 °×1 °全球再分析资料、常规资料、雷达资料和地面中尺度自动站资料,详细分析了2004—2008年乐清四中型水库大暴雨过程的发生、发展机制。水库大暴雨是在有利的大尺度环流背景下,不断有中小尺度系统的发生发展而产生。主要影响系统为登陆台风、西风低槽和低空急流。物理量诊断分析表明,低层强辐合,高层辐散、旺盛的上升运动以及强大的低空急流和充沛的水汽供给,为水库大暴雨的发生发展提供了极为有利的动力条件。台风强降水出现在台风螺旋雨带或者台风眼周围的密闭云团中的强降雨中心内。业务预报中可利用新一代天气雷达的基本反射率叠加风暴跟踪信息和冰雹指数,结合基本速度和垂直积分液态含水量等指标来跟踪台风强降雨中心,对水库大暴雨的监测和预警有重要意义。 相似文献
996.
DIAGNOSIS OF WAVE ACTIVITY OVER RAINBAND OF LANDFALL TYPHOON 总被引:1,自引:0,他引:1
A generalized wave-activity density, which is defined as an absolute value of production of
three-dimensional vorticity vector perturbation and gradient of general potential temperature perturbation,
is introduced and its wave-activity law is derived in Cartesian coordinates. Constructed in an agoestrophic
and nonhydrostatic dynamical framework, the generalized wave-activity law may be applicable to diagnose
mesoscale weather systems leading to heavy rainfall. The generalized wave-activity density and
wave-activity flux divergence were calculated with the objective analysis data to investigate the character
of wave activity over heavy-rainfall regions. The primary dynamical processes responsible for disturbance
associated with heavy rainfall were also analyzed. It was shown that the generalized wave-activity density
was closely correlated to the observed 6-h accumulative rainfall. This indicated that the wave activity or
disturbance was evident over the frontal and landfall-typhoon heavy-rainfall regions in middle and lower
troposphere. For the landfall-typhoon rainband, the portion of generalized wave-activity flux divergence,
denoting the interaction between the basic-state cyclonic circulation of landfall typhoon and mesoscale
waves, was the primary dynamic process responsible for the evolution of generalized wave-activity density. 相似文献
997.
This paper tests the impacts of cloud-induced mass forcing on the moist potential vorticity
(MPV) anomaly associated with torrential rains caused by Typhoon No.9914 (Dan) by using fine model
simulation data outputted by the Fifth-Generation NCAR / Penn State Mesoscale Model (MM5). The
diagnostic results show that the positive MPV anomaly region, which is obtained by integrating the MPV
from 600 hPa to 300 hPa in the vertical, roughly coincides with the precipitation at their synchronous
stages either in position or in the distribution pattern, and the maximum positive MPV area of Dan is
located mainly between 600 hPa and 300 hPa, which is much higher than torrential rain cases. Further
analyses also showed that the value of positive MPV anomaly increased or decreased with the development
of Dan, and the positive MPV anomaly may also be served as a tracer to indicate the evolution of tropical
cyclone intensity. 相似文献
998.
第二类热成风螺旋度对登陆台风降水的诊断能力分析台风泰利个例研究 总被引:2,自引:0,他引:2
文中利用中尺度数值模式MM5模拟了台风泰利的登陆过程,模拟的台风路径、天气形势和降水都与观测基本一致,能够很好地反映出真实的天气过程.再利用数值模拟结果,研究了第二类热成风螺旋度(H_2)对登陆台风泰利降水的诊断能力,结果表明它对深入内陆的台风强降水具有较好的诊断能力,而对刚登陆前后的台风降水诊断能力不如经典螺旋度.特别地,H_2在提前1 h时与泰利降水达到最高相关系数,且在提前1-5 h时,它与降水的相关性比经典螺旋度的高,表现出十分显著的预示降水增幅的能力.进一步分析表明,在刚登陆前后,泰利台风中心850-200 hPa的风场垂直切变较小(约5 m/s),其最强降水出现在路径右侧300 km半径范围以内,与低空的正温度平流、低空辐合、高空辐散等无明显的关系,而低空相对涡度能够很好地反映降水的变化,这是经典螺旋度与降水在这一阶段相关性优于H_2的主要原因.而在深入内陆后,台风泰利本体环流减弱,受北部西风槽的影响逐渐增强,环境风场垂直切变迅速增大,发生强降水的庐山和大别山区处于顺垂直风切变方向左侧.在东北向的垂直风切变情况下,庐山和大别山强降水区上空有向东的高空急流出流,强高空辐散诱发垂直次级环流,从而激发对流,形成强上升运动区,因此H_2的诊断优势在这一阶段表现得最清楚. 相似文献
999.
A numerical simulation of a torrential rain event occurring in the Jiang-Huai Valley of China from 22-24 June 1999 is performed and analyzed by using the PSU/NCAR MM5 mesoscale non-hydrostatic model. The high-resolution model output data are utilized to diagnose the double front structure, and the distributions of potential temperature, equivalent potential temperature, and specific humidity in the vicinity of the Meiyu Front System (MYFS) in the Jiang-Huai Valley. The results show that both the potential temperature gradient and the specific humidity gradient have important impacts on the two strong equivalent potential temperature gradient zones associated with the double front structure of the MYFS, but the latter (moisture gradient) is more important. In addition, the tendency equation of specific humidity gradient is theoretically derived. It shows that variations of the specific humidity gradient are related to the advection, convergence/divergence, horizontal and vertical vorticities (secondary circulation) effects and the gradient of water vapor source/sink. As an example, the budget of the meridional component of the tendency equation is selected and diagnosed by using the above model simulation data of the torrential rain event. It is shown that the variation of the specific humidity gradient averaged throughout the simulation is mainly controlled by the convergence/divergence effect, the secondary circulation effect associated with the horizontal vorticities, and the water vapor source/sink effect. Since the water vapor source/sink is often formed from the phase change processes of water vapor in the air and thus directly associated with cloud and precipitation microphysics processes, the variation of the specific humidity gradient is closely related with cloud and precipitation microphysics and the distribution, development and evolution of cloud and rainfall systems. The double front structure of the MYFS provides an advantageous environmental condition for the development and movement of the mesoscale torrential rain system nearby. In turn, the development of the torrential rain exerts a signifiant impact on the MYFS through changing the thermal and moisture distributions. 相似文献
1000.