CHARACTERISTICS OF THE MERIDIONALLY ORIENTED SHEAR LINES OVER THE TIBETAN PLATEAU AND ITS RELATIONSHIP WITH RAINSTORMS IN THE BOREAL SUMMER HALF-YEAR

In this paper, European Center for Medium-Range Weather Forecasts(ECMWF) Reanalysis-Interim(ERAInterim) data and daily precipitation data in China from May to October during 1981-2016 are used to study the climatic characteristics of the meridionally oriented shear lines(MSLs) over the Tibetan Plateau(TP). The relationship between the MSL and rainstorms in the eastern TP and neighboring areas of the TP during the boreal summer half-year is also investigated. An objective method, which uses a combination of three parameters, i.e. the zonal shear of the meridional wind, the relative vorticity and the zero line of meridional wind, is adopted to identify the shear line. The results show that there are two high-occurrence centers of MSL. One is over the central TP(near 90°E) and the other is over the steep slope area of the eastern TP. Fewer MSLs are found along the Yarlung Zangbo River over the western TP and the southern Tibet. There are averagely 42.2 MSL days in each boreal summer half-year. The number of MSL days reaches the maximum of 62 in 2014 and the minimum of 22 in 2006. July and October witness the maximum of 10.2 MSL days/year and the minimum of 4.2 MSL days/year, respectively. The annual number of the MSL days shows periodicities of 2-4 and 4-6 years, which is quite similar to those of the MSL rainstorm days. In the neighboring areas of the TP, nearly56% of the MSLs lead to rainstorms, and nearly 40% of rainstorms are caused by the MSLs, indicating a close relationship between the MSLs and rainstorms in this region.     

广西西江流域致洪暴雨过程中尺度特征及机制分析

利用广西逐站逐小时降水量、1°×1°逐小时FY-2C的TBB资料和1°×1°逐6 h NCEP/NCAR再分析资料,应用空间25点平滑滤波方法,分析了2005年6月18~22日西江流域致洪暴雨过程的中尺度特征及其发生、发展的机制。结果表明:这次致洪暴雨过程的降水时空分布不均,具有明显的中尺度特征。雨团集中出现在TBB值的低值中心、低值中心北侧等值线密集的地方以及等值线曲率大的地方。镶嵌于大尺度西南气流中的中尺度涡旋系统在西江流域反复生成,导致对流云团不断生成和加强,是此次暴雨产生的直接原因。暴雨区上空中尺度经向垂直环流圈的存在对中尺度涡旋和对流云团的发生和发展具有促进作用。中低层弱的对流不稳定与强的水平风垂直切变和湿斜压性共存是此次暴雨产生和持续发展的重要机制。     

“96.8”暴雨过程的尺度分离动能方程的诊断

用尺度分离的动能平衡方程,对1996年8月3～5日华北地区台风暴雨过程雨区内的动能制造和转换进行诊断。结果表明:动能在暴雨发展过程逐渐减小,动能转换项也是逐渐减小的。暴雨发生前,尺度相互作用制造项GKMS起最重要的作用,大尺度动能制造项次之,中尺度动能制造项消耗少量的动能;暴雨发生时,尺度相互作用和天气尺度运动仍制造动能,只是比发生前明显减少,中尺度运动由消耗动能转变为制造动能,动能转换主要来源于低层且数值明显减少;暴雨发生后,动能制造项数值仍为正,此时天气尺度动能制造最重要,但数值比前两阶段小,动能的转换主要出现于高层。可见,此次暴雨过程总动能的制造项一直为正,主要出现于高层,只是其制造量逐渐减小;动能转换是从低层向高层进行的,水平转换项起主要作用,是一种尺度减小的动能转换过程。     

Thermodynamic Characteristics of Tropical Cyclones with RapidIntensity Change over the Coastal Waters of China

In order to investigate the different thermodynamic mechanisms between rapid intensifying (RI) and rapid weakening (RW) tropical cyclones (TCs),the thermodynamic structures of two sets of composite TCs are analyzed based on the complete-form vertical vorticity tendency equation and the NCEP/NCAR reanalysis data.Each composite is composed of five TCs,whose intensities change rapidly over the coastal waters of China.The results show that the maximum apparent heating source Q1 exists in both the upper and lower troposphere near the RI TC center,and Q1 gets stronger at the lower level during the TC intensification period.But for the RW TC,the maximum Q1 exists at the middle level near the TC center,and Q1 gets weaker while the TC weakens.The maximum apparent moisture sink Q2 lies in the mid troposphere.Q2 becomes stronger and its peak-value height rises while TC intensifies,and vice versa.The increase of diabatic heating with height near the TC center in the mid-upper troposphere and the increase of vertical inhomogeneous heating near the TC center in the lower troposphere are both favorable to the TCs' rapid intensification; otherwise,the intensity of the TC decreases rapidly.     

青藏高原夏季降水研究进展

青藏高原夏季降水是高原气象研究关注的重要领域.受高原夏季各个层次的天气系统的影响,在高原多尺度地形的强迫作用下,高原夏季降水表现出复杂多样的时空分布和演变特征.回顾了国内外学者在高原夏季降水特征和影响机理方面取得的主要研究成果,分为以下三个方面:高原夏季降水的时空分布和演变特征;影响高原夏季降水的高原天气系统,包括南亚...     

AN ANALYSIS OF THE APPLICABILITY OF FUZZY CLUSTERING IN ESTABLISHING AN INDEX FOR THE EVALUATION OF METEOROLOGICAL SERVICE SATISFACTION

An evaluation index is a prerequisite for scientific evaluation of a public meteorological service. This paper aims to explore a technical method for determining and screening evaluation indicators. Based on public satisfaction survey data obtained in Wafangdian (China) in 2010, this study investigates the suitability of the fuzzy clustering analysis method in establishing an evaluation index. Through quantitative analysis of multilayer fuzzy clustering of various evaluation indicators, correlation analysis indicates that if the results of clustering were identical for two evaluation indicators in the same sub-evaluation layer, then one indicator could be removed, or the two indicators merged. For evaluation indicators in different sub-evaluation layers, although clustering reveals attribute correlations, these indicators may not be substituted for one another. Analysis of the applicability of the fuzzy clustering method shows that it plays a certain role in the establishment and correction of an evaluation index.     

Impact of Dynamic and Thermal Forcing on the Intensity Evolution of the Vortices over the Tibetan Plateau in Boreal Summer

The Tibetan Plateau Vortex (TPV) is one of the main weather systems causing heavy rainfall over the Tibetan Plateau in boreal summer. Based on the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) reanalysis datasets provided by the National Aeronautics and Space Administration (NASA), 8 cases of TPV over the Tibetan Plateau generated in June–August with a lifetime of 42 hours are composited and analyzed to reveal the impact of dynamic and thermal forcing on the intensity evolution of TPVs. The results are as follows. (1) The TPVs appear obviously at 500 hPa and the TPVs intensity (TPVI) shows an obvious diurnal variation with the strongest at 00LT and the weakest at 12LT (LT=UTC+6h). (2) A strong South Asia high at 200 hPa as well as a shrunken Western Pacific subtropical high at 500 hPa provide favorable conditions for the TPVI increasing. (3) The vorticity budget reveals that the divergence is indicative of the variation of TPVI. TPVI decreases when the convergence center at 500 hPa and the divergence center at 200 hPa lie in the east of the TPVs center and increases when both centers coincide with the TPVs center. (4) Potential vorticity (PV) increases with the enhancement of TPVI. The PV budget shows that the variation of TPVI is closely related to the diabatic heating over the Tibetan Plateau. The increased sensible heating and radiative heating in the boundary layer intensify the ascent and latent heating release. When the diabatic heating center rises to 400 hPa, it facilitates the development of TPVs.     

高层动力强迫对回流型华南暖区暴雨影响的个例研究

应用NCEP再分析资料,分析了2014年5月8—9日发生在华南的一次暖区暴雨过程,研究高层动力强迫对此次华南暖区暴雨的影响。此次暴雨过程发生在暖湿的西南气流中,无明显天气尺度锋面系统影响,属于华南暖区暴雨过程。根据中尺度对流系统(MCS)的生消发展特征,可以将其分为5月8日与9日两个阶段,第一阶段具有显著的回流型暖区暴雨的特征,主要研究该阶段。研究发现,高PV扰动沿对流层高层南亚高压东北侧的西北气流下滑东移,导致IPV正异常,其东侧的辐散气流显著发展,在高层辐散气流的抽吸作用下,上升运动首先从中上层发展起来。在过程发展前期,IPV正异常主要是由平流作用引起,且在其东侧诱发出南风异常,进而导致辐散气流发展。当降水发生后,潜热加热反馈作用使高层辐散气流进一步加强,此时,辐散增强是对流发展的结果。此外,低层浅薄偏东风是本次暖区暴雨发生的低层背景场,其与西南风气流汇合,提供有利的低层辐合条件。      

爆发性发展台风合成环境场的诊断分析

本文应用合成分析方法对5个台风的平缓演变阶段和爆发性发展阶段的环境场作了对比分析。结果表明，在台风爆发性发展时，副热带高压及其反气旋环流增强，台风东部低层风速加大，高空有东风扰动叠加，低空辐合和高层辐散增强，低层水汽能量辐合及台风外围对流性不稳定性增大，低空垂直环流发展。以上因子导致积云对流发展。在弱垂直切变环境下，通过第二类条件性不稳定(CISK)机制，使台风中心气压急剧下降，气旋性环流显著增强，从而导致台风的爆发性发展。这说明台风爆发性发展是大尺度环流和积云对流相互作用的结果。     

法国气象培训

本文主要介绍在法国气象局为期8周的预报员专项培训的基本情况以及培训过程的收获和体会，涉及教学内容、法国国家气象局的组织结构、法国气象业务系统以及法国气象的人才培养等方面。