A NUMERICAL STUDY ON THE INFLUENCE OF WIND FIELDS AT UPPER LEVELS IN THE MEIYU PERIOD ON THE DEVELOPMENT OF LOW LEVEL JET AND MESOSCALE SYSTEMS^*     

Zhai Guoqing  Gao Kun  Sun Shuqing 《Acta Meteorologica Sinica》1998,12(1):92-102

Using a mesoscale model,a numerical study on a heavy rainfall case occurring in the Changjiang-Huaihe River Basin is made in this paper.The influence of the intensity of northeasterly wind in front of the Qinghai-Xizang high at upper level on the low level wind field and development of mesoscale systems as well as heavy rainfall is investigated.The model well reproduced the heavy rainfall process and the weather systems associated.And it indicates that the strong northeasterly flow around the high at upper troposphere will bring about not only the strengthening of low level southeasterly wind,but also the appearance of shear-line and mesoscale vortex at low level.The coupling of northerly wind at upper level and southerly wind at lower level constructs a vertical indirect circulation which is most favourable for the development of convective motions.Its ascending branch in the shear-line area is very strong and shows a pronounced mesoscale characteristic.  相似文献   

Intraseasonal oscillations and interannual variability of surface winds over the Indian monsoon region     

B. N. Goswami  D. Sengupta  G. Suresh Kumar 《Journal of Earth System Science》1998,107(1):45-64

The role of intraseasonal oscillations (ISOs) in modulating synoptic and interannual variations of surface winds over the Indian monsoon region is studied using daily averaged National Centers for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalyses for the period 1987–1996. Two dominant ISOs are found in all years, with a period between 30–60 days and 10–20 days respectively. Although the ISOs themselves explain only about 10–25% of the daily variance, the spatial structure of variance of the ISOs is found to be nearly identical to that of high frequency activity (synoptic disturbances), indicating a significant control by the ISOs in determining the synoptic variations. Zonal and meridional propagation characteristics of the two modes and their interannual variability are studied in detail. The synoptic structure of the 30–60 day mode is similar in all years and is shown to be intimately related to the strong (‘active’) or weak (‘break’) phases of the Indian summer monsoon circulation. The peak (trough) phase of the mode in the north Bay of Bengal corresponds to the ‘active’ (‘break’) phase of monsoon strengthening (weakening) the entire large scale monsoon circulation. The ISOs modulate synoptic activity through the intensification or weakening of the large scale monsoon flow (monsoon trough). The peak wind anomalies associated with these ISOs could be as large as 30% of the seasonal mean winds in many regions. The vorticity pattern associated with the 30–60 day mode has a bi-modal meridional structure similar to the one associated with the seasonal mean winds but with a smaller meridional scale. The spatial structure of the 30–60 day mode is consistent with fluctuations of the tropical convergence zone (TCZ) between one continental and an equatorial Indian Ocean position. The 10–20 day mode has maximum amplitude in the north Bay of Bengal, where it is comparable to that of the 30–60 day mode. Elsewhere in the Indian Ocean, this mode is almost always weaker than the 30–60 day mode. In the Bay of Bengal region, the wind curl anomalies associated with the peak phases of the ISOs could be as large as 50% of the seasonal mean wind curl. Hence, ISOs in this region could drive significant ISOs in the ocean and might influence the seasonal mean currents in the Bay. On the interannual time scale, the NCEP/NCAR reanalysed wind stress is compared with the Florida State University monthly mean stress. The seasonal mean stress as well as interannual standard deviation of monthly stress from the two analyses agree well, indicating absence of any serious systematic bias in the NCEP/NCAR reanalysed winds. It is also found that the composite structure of the 30–60 day mode is strikingly similar to the dominant mode of interannual variability of the seasonal mean winds indicating a strong link between the ISOs and the seasonal mean. The ISO influences the seasonal mean and its interannual variability either through increased/decreased residence time of the TCZ in the continental position or through occurrence of stronger/weaker active/break spells. Thus, the ISOs seem to modulate all variability in this region from synoptic to interannual scales.  相似文献   

两种风场分解方法计算动能收支对比研究     

汪钟兴  霍义强  段旭 《气象》1996,22(7):3-5

使用两种风场分解方法，计算了旋转风和辐散风功能收支方程各项时空平均值，结果表明两者差异不大，具有一定程度的可比性。  相似文献   

半空间非水平层状介质瑞雷面波的频散方程   总被引：2，自引：0，他引：2  

牛滨华  何继善 《物探与化探》1996,20(5):345-350,358

由于工程勘察中的一些特殊情况,使面波以往的一些理论和结论受到了不同程度的限制。本文从弹性动力学虚功变分原理出发,在重点分析自由表面外力提供的能量来源时,引入了等效面波(能量)震源概念。然后用有限元法建立了半空间多个非水平层状介质瑞雷西波的频散方程。这项工作有助于面波理论和应用技术的发展完善。  相似文献   

梅雨期高层流场对低层急流及中尺度系统影响的数值试验   总被引：3，自引：1，他引：3  

翟国庆  高坤  孙淑清 《气象学报》1997,55(6):714-725

用中尺度模式对一次江淮流域暴雨过程进行了数值试验，并研究了对流层高层青藏高压东侧偏北大风的强弱与低层流场及中尺度系统发生及至降水过程的影响。试验不仅较成功地模拟了本次暴雨过程及相应的系统，而且揭示出较强的高空偏北大风将引起对低空急流的加强。而更为重要的是低层切变线的出现以及其上中尺度涡旋的发生。上下风场所构成的垂直反环流圈大大有利于对流的发展，特别是在切变线地区的上升支，带有明显的中尺度特征。  相似文献   

Comparison of geostrophic and nonlinear balanced winds from LIMS data and implications for derived dynamical quantities     

T. Miles  W. L. Grose 《Pure and Applied Geophysics》1989,130(2-3):319-342

Nimbus 7 LIMS geopotential height data are utilized to infer the rotational wind distribution in the Northern Hemisphere stratosphere and lower mesosphere during a period of substantial wave-mean flow interaction in January, 1979. Rotational winds are derived from the application of a successive relaxation numerical procedure which incorporates the spherical polar coordinate iterative algorithm ofPaegle andTomlinson (1975) for the nondivergent nonlinear balance equation. Optimum convergence of the numerical solutions is found to occur when under-relaxation is utilized. The LIMS height analyses were also latitudinally smoothed and constrained to obey the ellipticity criterion for spherical coordinates. The balanced winds are compared with geostrophically derived values and within situ radiosonde reports for 100 mb to 10 mb over Berlin.From a localized perspective, the Berlin-LIMS comparison indicates that radiosonde and balanced wind vectors exhibit somewhat closer agreement in direction than is associated with the geostrophic estimates. However, substantial quantitative differences between radiosonde, balanced, and geostrophic wind speeds are also evident, suggesting that caution should be exercised in the local application of derived winds, as for example in the quantitative interpretation of trajectories derived from satellite height analyses during periods of enhanced stratospheric wave activity.On a longitudinally averaged basis, balanced zonal-mean wind speeds are typically 20% weaker than geostrophic values in polar latitudes, and as much as 50% weaker in tropical and midlatitude regions. Meridional balanced wind velocities, at a given longitude, are generally within ±10% of geostrophic values. Although these alterations in horizontal wind components result in only modest differences between balanced and geostrophic meridional eddy heat fluxes, a more substantial change appears in the meridional eddy momentum flux analysis. The corresponding patterns of Eliassen-Palm flux divergence are found to be somewhat more (less) intense for the balanced wind case in the stratosphere (lower mesosphere) in polar latitudes.  相似文献   

Statistics of Wind and Waves off Tsuyazaki, Fukuoka, in the Eastern Tsushima Strait     

Akira Masuda  Tadao Kusaba  Kenji Marubayashi  Michiyoshi Ishibashi 《Journal of Oceanography》1999,55(2):289-305

The variability of the sea surface wind and wind waves in the coastal area of the Eastern Tsushima Strait was investigated based on the hourly data from 1990 to 1997 obtained at a station 2 km off Tsuyazaki, Fukuoka. The annual mean wind speed was 4.84 m s⁻¹, with strong northwesterly monsoon in winter and weak southwesterly wind in summer. Significant wave heights and wave periods showed similar sinusoidal seasonal cycles around their annual means of 0.608 m and 4.77 s, respectively. The seasonal variability relative to the annual mean is maximum for wave heights, medium for wind speeds, and minimum for wave periods. Significant wave heights off Tsuyazaki turned out to be bounded by a criterion, which is proportional to the square of the significant wave period corresponding to a constant steepness, irrespective of the season or the wind speed. For terms shorter than a month, the significant wave height and the wave period were found to have the same spectral form as the inshore wind velocity: white for frequencies less than 0.2 day⁻¹ and proportional to the frequency to the −5/3 power for higher frequencies, where the latter corresponds to the inertial subrange of turbulence. The spectral levels of wave heights and wave periods in that inertial range were also correlated with those of the inshore wind velocity, though the scatter was large. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

台风影响下渤海及邻域海面风场演变过程的MM5模拟分析   总被引：5，自引：1，他引：5  

高山红  谢红琴  吴增茂  林行  吴伟 《中国海洋大学学报(自然科学版)》2001,31(3):325-338

在装有 L inux操作系统的 PC机上运行美国大气研究中心 ( NCAR)的非静力中尺度大气模式 MM5。运用 MM5的嵌套功能 ,以 30 km水平分辨率对台风 KAI- TAK( 2 0 0 0年第 4号 )影响渤海海区的时段进行数值模拟 ,同时给出了水平分辨率为 10 km的嵌套区内逐时的渤海海面风场。通过对台风中心位置、中心气压、风速分布与雨区分布等要素的模拟结果与实况的比较 ,证实该实验对台风过程的模拟较为成功。嵌套区内渤海海面风场也明显体现出了地形影响的特征。并尝试以T10 6格点资料的三维客观分析场结合高空及地面观测为模式提供初值场 ,6h/次预报场为模式提供时变边界条件 ,对渤海海面风场进行了 2 4 h时预报  相似文献   

Magnetar-driven bubbles and the origin of collimated outflows in gamma-ray bursts     

N. Bucciantini  E. Quataert  J. Arons  B. D. Metzger  T. A. Thompson 《Monthly notices of the Royal Astronomical Society》2007,380(4):1541-1553

  相似文献   

The Relationship between El Niño and the Duration and Frequency of the Santa Ana Winds of Southern California     

Jason Finley  Marilyn Raphael 《The Professional geographer》2007,59(2):184-192

This study examines the variability of the duration and frequency of Santa Ana winds due to El Niño over a thirty‐three‐year period. Daily Weather Maps and NCEP/NCAR Reanalysis were used to study large‐scale upper‐level and surface circulation patterns during wind events. A Student's t‐test was used to determine statistically significant changes in the winds during March of El Niño winters. A significant decrease in the duration and frequency of wind events was found in March during El Niño. This can be attributed to the decrease in strength and frequency of the Great Basin high pressure and the increase in wintertime cyclones in southern California.  相似文献