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1.
Total deformation and its role in heavy precipitation events associated with deformation-dominant flow patterns 总被引：6，自引：0，他引：6
In this paper, it is elucidated that the total deformation （TD）, defined as the square root of the sum of squared stretching deformation and squared shearing deformation, is an invariant independent of the coordinate system used. An idealized flow field is then constructed to demonstrate the confluence effect of a non-divergent and irrotational deformation field on moisture transport. To explore the characteristics and role of TD, one heavy rainfall case that occurred in the middle and lower reaches of the Yangtze River （MRYR） over China, associated with a front with shear line, is analyzed using the Weather Research and Forecasting （WRF） model output data. It is found that right before the occurrence of precipitation, the effect of the confluence induced by deformation on moisture transport provides a favorable condition for precipitation. During the precipitation, both location and orientation of the zone of large TD coincide with the confluent shear line. The rainhands are nearly parallel with, and located lightly to the south of the zones of large TD and the confluent shear line. The TD in the lower troposphere increases in value as precipitation persists. When TD approaches its maximal value, the next 6-hour precipitation reaches its peak correspondingly. A tendency equation for TD is derived. The analysis of linear correlation and RMS difference between individual terms in the total deformation equation and the sum of the terms shows that the pressure gradient plays a major role in determining the local change of total deformation. 相似文献
2.
The alternating change of the two meiyu front rain-bands caused by the alternating change between the moist potential vorticities is discussed. The main factors of the change of moist potential vorticity are the vertical and horizontal divergence of moist potential vorticity flux as well as the vertical transport caused by the cumulus mass flux. Also discussed is the possibility that the WAVE-CISK conditional symmetric instability in the baroclinic moist atmosphere leads to the forming of the double rain-bands and their roller-shaped circulation features. Theoretical analyses show that the latitudinal disturbance scale-selection by the primitive moisture model of the latent heat release in cumulus convection depends on the stratification instability parameter (Ri number) and viscous coefficient of eddy. 相似文献
3.
Analysis on the Interaction between Turbulence and Secondary Circulation of the Surface Layer at Jinta Oasis in Summer 总被引：2，自引：0，他引：2
The kinetic energy variations of mean flow and turbulence at three levels in the surface layer were calculated by using eddy covariance data from observations at Jinta oasis in 2005 summer.It is found that when the mean horizontal flow was stronger,the turbulent kinetic energy was increased at all levels,as well as the downward mean wind at the middle level.Since the mean vertical flow on the top and bottom were both negligible at that time,there was a secondary circulation with convergence in the upper half and divergence in the lower half of the column.After consideration of energy conversion,it was found that the interaction between turbulence and the secondary circulation caused the intensification of each other.The interaction reflected positive feedback between turbulence and the vertical shear of the mean flow.Turbulent sensible and latent heat flux anomaly were also analyzed.The results show that in both daytime and at night,when the surface layer turbulence was intensified as a result of strengthened mean flow,the sensible heat flux was decreased while the latent heat flux was increased.Both anomalous fluxes contributed to the cold island effect and the moisture island effect of the oasis. 相似文献
4.
It is generally thought that the influence of comparable track typhoons is approximately similar,
but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a
contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of
a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve
forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared.
The result indicates that these two TCs have similar precipitation distribution before landfall but different
precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is
analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence.
The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang
(0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the
tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of
Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in
the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a
southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea
monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt
south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes
water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much
stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a
north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical
wind shear with water vapor transportation is a good way to predict rainstorms associated with landing
tropical cyclones. 相似文献
5.
The Webster and Yang monsoon index (WYI)-the zonal wind shear between 850 and 200 hPa was calculated and modified on the basis of NCEP/NCAR reanalysis data. After analyzing the circulation and divergence fields of 150-100 and 200 hPa, however, we found that the 200-hPa level could not reflect the real change of the upper-tropospheric circulation of Asian summer monsoon, especially the characteristics and variation of the tropical easterly jet which is the most important feature of the upper-tropospheric circulation. The zonal wind shear U850-U(150 100) is much larger than U850-U200, and thus it can reflect the strength of monsoon more appropriately. In addition, divergence is the largest at 150 hPa rather than 200 hPa, so 150 hPa in the upper-troposphere can reflect the coupling of the monsoon system. Therefore, WYI is redefined as DHI, i.e., IDH=U850* - U(150 100)*, which is able to characterize the variability of not only the intensity of the center of zonal wind shear in Asia, but also the monsoon system in the upper and lower troposphere. DHI is superior to WYI in featuring the long-term variation of Asian summer monsoon as it indicates there is obvious interdecadal variation in the Asian summer monsoon and the climate abrupt change occurred in 1980. The Asian summer monsoon was stronger before 1980 and it weakened after then due to the weakening of the easterly in the layer of 150-100 hPa, while easterly at 200 hPa did not weaken significantly. After the climate jump year in general, easterly in the upper troposphere weakened in Asia, indicating the weakening of summer monsoon; the land-sea pressure difference and thermal difference reduced, resulting in the weakening of monsoon; the corresponding upper divergence as well as the water vapor transport decreased in Indian Peninsula, central Indo-China Peninsula, North China, and Northeast China, indicating the weakening of summer monsoon as well. The difference between NCEP/NCAR and ERA-40 reanalysis data in studying the intensity and long-term variation of Asian summer monsoon is also compared in the end for reference. 相似文献
6.
The NCEP/NCAR reanalysis, Japan Meteorological Agency(JMA) tropical cyclone tracks and intensive surface observations are used to diagnose the features of moisture transport of tropical storm Bilis(No. 0604), which is simulated by the WRF(weather research and forecasting) mesoscale numerical model. It is shown that the Bilis was linked with the moisture channel in the lower latitudes after its landing. Meanwhile, the cross-equatorial flows over 80°-100°E and Somali were active and brought abundant water vapor into the tropical storm, facilitating the maintenance of the landing storm with intensified heavy rainfall along its path. The simulation suggested that the decreased water vapor from lower latitudes prevents the maintenance of Bilis and the development of rainfall. While the cross-equatorial flows over 80°-100°E and Somali were in favor of keeping the cyclonic circulation over land. If the moisture supply fro m the Somali jet stream was reduced, the strength and area of heavy rainfall in tropical cyclone would be remarkably weakened. Consequently, the decreased water vapor from lower latitudes can remarkably suppress the deep convection in tropical storm, then Bilis was damped without the persistent energy support and the rainfall was diminished accordingly. 相似文献
7.
Non-Acceleration Theorem in a Primitive Equation System: I. Acceleration of Zonal Mean Flow 总被引：2，自引：0，他引：2
Non-acceleration theorem in a primitive equation system is developed to investigate the influences of waves on the mean flow variation against external forcing. Numerical results show that mechanical forcing overwhelms thermal forcing in maintaining the mean flow in which the internal mechanical forcing associated with horizontal eddy flux of momentum plays the most important roles. Both internal forcing and external forcing are shown to be active and at the first place for the mean flow variations, whereas the forcing-induced mean meridional circulation is passive and secondary. It is also shown that the effects on mean flow of external mechanical forcing are concentrated in the lower troposphere, whereas those due to wave-mean flow interaction are more important in the upper troposphere. These act together and result in the vertically easterly shear in low latitudes and westerly shear in mid-latitudes. This vertical shear of mean flow is to some extent weakened by thermal forcing. 相似文献
8.
The winters of 1997/1998 and 1998/1999,corresponding to El Ni(?)o and La Ni(?)a episodes,respectively, were two typical rain-abundant and-scarce seasons for the southern China.In order to understand the cause of the anomalous precipitation during the two winters,a comparative analysis technique has been employed to investigate the differences in general circulation and moisture transportation between the two seasons. The results show that the abundant rainfall during the winter of 1997/1998 was associated with the ENSO warm episode event,eastward shifted weak westerly trough/ridge,weakened East Asian winter monsoon (EAWM),strengthened subtropical high,and presented two anti-cyclonic circulations over Hokkaido and the Philippine Sea,respectively,as well as one cyclonic circulation over the Yangtze River Basin in the anomalous wind fields of the lower troposphere.During the rain-scarce winter,however,the patterns of equatorial sea surface temperature anomalies and the circulation systems both in upper and lower levels were nearly the opposite of those during the rain-abundant winter.It has also been discovered that the water vapor over southern China during the winters came mainly from the southwesterly flow ahead of troughs in the southern branch of westerlies and the turning flow over the South China Sea-Indo-China Peninsula area;and the moisture transportation channels varied significantly with regard to height.The intensified flow in the southern branch of westerlies and the anti-cyclonic circulation anomaly over the Philippine Sea during the winter of 1997/1998 were favorable for moisture transportation to mainland China,however the two moisture transportation streams were dramatically weakened during the winter of 1998/1999 due to weak westerly flow and the dominance of a cold high system in the lower level over the southeast coast of China.Such a significant inter-annual change of moisture transportation is a key factor resulting in the obvious difference in precipitation between the two winters. 相似文献
9.
Based on the detection of the dynamic and thermodynamic functions of the physical processes in IAP3.0, the equilibrium mechanisms of the temperature, moisture and wind are analyzed. The negative feedback between the longwave radiation and temperature is verified. The cooling regulation of net radiation on temperature is mostly balanced by the heating of precipitation, the leading actions on temperature of other processes such as vertical diffusion, shallow cumulus convection and friction are merely available for lower air. The moisture consumption of precipitation is compensated on the whole by the provision of shallow cumulus convection, which sustains the moisture conservation to a high degree. The wind field is directly regulated by the momentum redistribution of cumulus, the dry adiabatic convection and vertical diffusion. Yet, the prominent influences of these processes are generally confined to the lower level. The east wind at low latitudes and the west wind at high latitudes are both weakened by the regulations and furthermore, by virtue of the transportation of mean meridional circulation, such a variation exactly maintains the angular momentum conservation. 相似文献
10.
AN ANALYSIS OF THE WINTER EXTREME PRECIPITATION EVENTS ON THE BACKGROUND OF CLIMATE WARMING IN SOUTHERN CHINA 总被引：2，自引：1，他引：1
Based on daily precipitation and monthly temperature data in southern China, the winter
extreme precipitation changes in southern China have been investigated by using the Mann-Kendall test
and the return values of Generalized Pareto Distribution. The results show that a winter climate
catastrophe in southern China occurred around 1991, and the intensity of winter extreme precipitation was
strengthened after climate warming. The anomalous circulation characteristics before and after the climate
warming was further analyzed by using the U.S. National Centers for Environmental Prediction/National
Center for Atmospheric Research reanalysis data. It is found that the tropical winter monsoon over East
Asia is negatively correlated with the precipitation in southeastern China. After climate warming the
meridionality of the circulations in middle and high latitudes increases, which is favorable for the
southward movement of the cold air from the north. In addition, the increase of the temperature over
southern China may lead to the decrease of the differential heating between the continent and the ocean.
Consequently, the tropical winter monsoon over East Asia is weakened, which is favorable for the transport
of the warm and humid air to southeastern China and the formation of the anomalous convergence of the
moisture flux, resulting in large precipitation over southeastern China. As a result, the interaction between
the anomalous circulations in the middle and high latitudes and lower latitudes after the climate warming
plays a major role in the increase of the winter precipitation intensity over southeastern China. 相似文献
11.
动力因子对2006“碧利斯”台风暴雨的诊断分析 总被引：1，自引：0，他引：1
本文利用2006年登陆台风"碧利斯"暴雨过程高分辨率数值模拟资料, 结合湿热力平流参数、广义对流涡度矢量垂直分量、水汽螺旋度、热力螺旋度、散度垂直通量、热力散度垂直通量、热力切变平流参数和 Q *矢量散度等8个动力因子, 对"碧利斯"台风暴雨进行诊断分析。结果指出:(1)8个动力因子在"碧利斯"台风强降水区均表现为强信号, 其中, 水汽螺旋度、热力螺旋度、散度垂直通量、热力散度垂直通量等动力因子与降水强度的相关系数均达0.99以上, 与总云水物质的相关系数也均达0.97以上, 而热力切变平流参数与上述二者的相关系数最低, 达0.5左右;(2)8个动力因子中, Q *矢量散度随降水强度先增大后减小, 与"霰融化成雨水造成雨水增长"微物理过程随降水强度的变化相似, 热力切变平流参数随降水强度呈现"增大—减小—再增大"的变化特征, 而其他6个动力因子均呈现单调增长趋势, 与"雨水碰并云水造成雨水增长"微物理过程随降水强度的变化相类似;(3)总体看来, 水汽螺旋度、热力螺旋度、散度垂直通量、热力散度垂直通量4个动力因子与降水强度及雨水收支相关的总的云微物理过程转化率对应更好, 因此, 对降水的指示意义也更好。 相似文献
12.
13.
一次高原低涡与高原切变线演变过程与机理分析 总被引：6，自引：1，他引：5
对一次东移高原低涡减弱、高原切变线生成并在有利的环流背景下东南移,进而引发川渝强降水的高原切变线生成机制以及演变过程进行了初步分析。首先引入描写热带气旋的Okubo-Weiss（OW）参数（VOW）来定量表达低涡、切变气流中旋转和变形的相对大小,确定高原切变线的潜在生成区域和发展状况。得出在高原切变线生成阶段,500 hPa等压面上VOW值由正转负,VOW负值带可以很好地指示高原切变线的潜在生成区域。VOW负值强度与高原切变线强度有很好的相关性。高原切变线上以VOW负值中心为主,但也会存在正值中心,说明在切变线上也会有气旋性涡度。此个例高原切变线以伸缩变形为主,高原切变线沿变形场的拉伸轴分布。然后通过涡度方程和总变形方程进一步分析了高原低涡减弱、高原切变线生成的动力机制。高原低涡的减弱、消失主要受散度项的影响,时间演变分析表明系统由强气旋性涡度的高原低涡演变为强辐合性的高原切变线。总变形方程中的扭转项对高原切变线的生成贡献最大,其次为水平气压梯度项,散度项最小;当高原切变线上以拉伸变形为主时,不利于其上高原低涡的发展,切变线可能是影响低涡发展的背景流场。 相似文献
14.
从大气环流，海温，太阳黑子，台风等方面分析了2000，2001两年河南汛期降水差异原因，结果表明，500hPa环流形势的差异是两年降水差异的原因之一；2001年登陆台风较多，且多位于水汽通道上，阻挡水汽向河南输送，这是2001年较2000年干旱的又一原因。 相似文献
15.
登陆热带气旋Bilis（0604）暴雨增幅与风场结构变化 总被引：1，自引：1，他引：0
利用日本气象厅区域谱模式（RSM）20 km再分析资料及改进的调和—余弦算法,对2006年4号台风Bilis登陆后暴雨增幅前后风场的结构变化特征进行了比较分析。Bilis台风登陆西行过程中,于14日18:00（协调世界 时,下同）开始,至15日12:00出现明显的暴雨增幅现象。在暴雨增幅前后时段,暴雨区的全风场及无辐散风分布变化强度小于无旋风。具体表现为:暴雨增幅前,Bilis低层西南部的无旋风速加强,辐合中心与Bilis中心逐步靠近,垂直上升运动加强;在暴雨增幅期间,Bilis西南部的低层和高层的无旋风速都一致持续加强。这种无旋风场上的变化与暴雨强度变化有很好的相关性,即:无旋风在Bilis西南部的增强及辐合增强与该区域暴雨的增强相对应,暴雨增幅的时段与高低层无旋风的风速加大和辐合增强是一致的。对暴雨增幅起主导作用的是无旋风的变化及其引起的散度变化。无旋风速及辐合增强时,暴雨增强并维持;无旋风及辐合减弱后,暴雨强度逐渐减弱。无辐散风强度变化与暴雨强度变化相反,而全风速在暴雨增幅前主要由无旋风决定,暴雨减弱阶段主要由无辐散风决定,对无旋风及无辐散风的分析能更加明显的揭示出暴雨增幅时期风场的具体变化。相对于全风场分析,无辐散风和无旋风能提供更多的风场结构变化与暴雨增幅的关系,这对于预报和分析登陆台风的风雨分布有一定的促进作用。 相似文献
16.
本文以2000年第10号台风“碧丽斯”为例,得出特殊流场条件下登陆台风后部局域性强降雨产生的原因.它是发生在低层流场中变形场的辐合渐近线的一端附近,由于较强的偏北气流对暖湿的西南气流起到触发抬升作用,使原本水汽充沛、层结不稳定的气层对流发展,形成中尺度强对流云团,从而产生强降水.由于满足这种流场条件的区域很小,暴雨落点附近气流本身不强,因此暴雨范围不大,降雨强度也不太强,但由于流场维持时间较长,降雨历时也较长. 相似文献
17.
It is generally thought that the influence of comparable track typhoons is approximately similar,but in fact their wind and especially their rainstorm distribution are often very different. Therefore,a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604),which are of a similar track,is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainthll of TC itaitang (0505) and Bills (0604) is diagnosed and compared.The result indicates that these two TCs have similar precipitation distribution before landtall but different precipitation characteristics after landthll. Using NCEP/GFS analysis data,the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence.The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bitis (0604) before landlhll results ti'om a peripheral easterly wind,a combination of the tropical cyclone and the terrain. After landthll and moving far inland of the storm,the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing thctors to heavy rainstorms in southeast Zhejiang is a southeast jet stream,which is maintained over the southeast coast. In contrast,the South China Sea monsoon circulation transports large amounts of water vapor into Bills - when a water-vapor transport belt south of the tropical cyclone significantly strengthens - which strengthens the transport. Then,it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland,the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary,combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones. 相似文献
18.
低纬季风涌影响登陆台风“榴莲”（0103）和“碧利斯”（0604）暴雨增幅的比较 总被引：3，自引：1，他引：2
以2001和2006年盛夏登陆中国南方并造成巨大灾害的两次热带气旋过程为例,利用＂CMA-STI热带气旋最佳路径数据集＂、NCEP/NCAR再分析资料及地面加密观测资料,对2001年0103号＂榴莲＂和2006年0604号＂碧利斯＂热带气旋陆上维持和暴雨增幅的大尺度环境场及成因进行了对比分析。结果表明：1）＂榴莲＂登陆后与中纬度西风槽发生相互作用,构成了典型的＂北槽南涡＂天气形势,＂碧利斯＂登陆后受西太平洋副高、北方大陆高压坝和南侧副高向西南方向延伸的高压脊所包围,有利于其环流维持。2）＂榴莲＂和＂碧利斯＂陆上维持期间越赤道气流明显增强,但是在＂榴莲＂活动期间,100°E附近越赤道气流表现突出,而在＂碧利斯＂陆上活动期间,80°E附近越赤道气流尤为显著,它们都增强了当时的西南季风,把大量来自热带海洋的水汽注入登陆后减弱的＂榴莲＂和＂碧利斯＂环流,使其非但没有很快减弱消亡,反而能在登陆后长时间维持不消。3）2001和2006年东亚夏季风存在明显低频振荡,2001年低纬夏季风10～20d低频振荡显著,而2006年则以30～60d低频振荡为主,由不同低频振荡周期表示的低纬季风涌均存在明显的北传特征。当低频振荡处于极端活跃位相时,季风涌最为强盛并侵入＂榴莲＂和＂碧利斯＂环流系统,正好对应着当时的台风暴雨剧烈增幅。此外,低频气流的辐合和低频水汽输送也是＂榴莲＂和＂碧利斯＂暴雨增幅的重要原因。 相似文献