广东2008年低温雨雪冰冻灾害及气象应急响应

2008年初我国南方遭受了百年一遇低温雨雪冰冻灾害,广东的受灾程度属80年一遇,造成了重大经济损失和严重社会影响.分析发现:灾害过程在近年来最严重的一次"拉尼娜"事件背景下发生的,与欧亚地区持续大气环流异常密切相关.在"北脊南槽"和西太平洋副高偏北偏强的形势下,冷暖气流在我国南方地区频繁交汇,使对流层中低层形成逆温层和局地经向环流产生异常,造成了此次持续低温雨雪冰冻过程.面对灾害引发的公共事件,广东省气象部门打破常规、准确预警,启动预案,通过媒体和"公共事件预警信息发布平台",及时传播权威的公共预警信息,为安定民心、稳定社会、减少灾害起到积极作用.灾后反思发现,山区冰灾的监测、灾害的评估、公共信息发布等的能力和规范均亟待加强.     

一次冷锋南侧对流性暴雨诊断分析

利用常规气象观测资料、NCEP资料、卫星、雷达和地面加密观测等资料,对2008年5月27-28日江西北部一次冷锋南侧(冷锋前)对流性暴雨过程进行天气动力学诊断分析和中尺度分析.结果表明:(1)对流性暴雨出现在冷锋前的主要原因是:各层槽线位置近于垂直,锋面陡峭,并出现前倾槽结构;冷锋前低层暖湿气流异常强盛,下暖湿上干冷使对流不稳定能量增强;当冷锋移近、气旋波发展东移和低空急流加强,触发了冷锋前对流不稳定能量释放.(2)本次暴雨具有明显中小尺度特征,共有4个β中尺度对流系统沿地面冷锋南侧发展东移,850 hPa的中尺度辐合线、地面中低压和中尺度辐合线、云顶亮温低值区、强回波区及雷达速度图上逆风区等均揭示中小尺度扰动系统存在,且中小尺度扰动系统与暴雨雨团对应很好.     

广义Ertel-Rossby不变量在北京“7.21”暴雨过程分析中的应用

在绝热无摩擦大气中,具有守恒性及可反演性的Ertel位涡(PV)在大尺度天气系统分析中有广泛应用。由于忽略了力管项的作用,PV用于分析中小尺度天气系统演变时受到局限。从广义速度推导得到的广义Ertel-Rossby不变量(GERI)除了包含有PV的守恒性,还包含了螺旋度效应及力管项的作用,对于分析研究快变流型的中小尺度系统演变有一定优势。用GERI分析2012年7月21日北京地区的特大暴雨过程,表明GERI在暴雨区有明显的异常出现,其异常基本与暴雨出现时间同位相,表明GERI的定义涵盖了螺旋度和PV,也包含了暴雨发生时的旋转斜压大气的力管项效应,确实能体现暴雨过程中的流型快变的特点,可以作为独立的变量来分析和揭示造成暴雨的低涡系统的动力结构,为诊断和预报暴雨落区提供新的动力物理量。     

2006-06-13贵州省望谟县大暴雨的诊断分析

利用NCEP／NCAR再分析资料、观测资料、FY-2C的红外云图TBB资料以及多普勒雷达的实时监测资料,对2006年6月13日发生在贵州省望谟县的突发大暴雨天气进行了研究,综合分析了此次强降水天气过程的影响系统、中尺度对流云团的发生发展演变、雷达回波特征及物理量场特征。结果表明,望谟县的短时强降水是受河套冷空气快速南下影响而致使贵州中部的辐合线南压锋生诱发β中尺度云团的生成与强烈发展所引起的。强降水区域与低层辐合带直接相关;对流层低层有能量锋出现,锋前积聚较强的潜在湿有效位能,在斜压扰动下,激发了倾斜垂直涡度的发展,导致大气层结对流性不稳定强烈发展,使中尺度对流系统得以发展和维持;雷达回波图反映了典型的中尺度系统特征。     

长江下游地区汛期暴雨气候特征分析

IPCC(1995)第二次科学评估报告指出了极端气象事件变化研究的重要意义[1].长江下游地区地势低平,往往是我国暴雨洪涝的多发区域,造成严重灾害,因此,研究长江下游地区暴雨的规律具有极其重要的意义.选取了长江下游地区52站1960～2003年逐日降水资料,运用EOF分析将其分为3个分区,采用小波分析,Mann-kendall非参数检验法及趋势系数法等分析方法研究各分区汛期暴雨降水的气候统计特征.结果表明:虽然汛期同为暴雨降水的集中时期,但各分区暴雨降水在汛期降水中所占比重略有差异,暴雨降水量、频次所占比例的空间分布为西区较大、东区和北区略小,暴雨平均强度则西区和北区东部强、其他区域小.同一区域中降水量与频次具有显著的正相关,不同区域间仅暴雨降水量的相关性较好.暴雨降水量44 a中呈现了增加的趋势.各区汛期暴雨具有多重时间尺度的周期变化,暴雨降水量和频次的周期在西区与全区的较为一致,主要是6～9 a的周期振荡.东区和北区有着不同尺度的振荡周期.各区的暴雨降水强度都不同程度地存在着3 a的周期振荡.长江下游地区汛期暴雨降水量除北区外,全区及其他分区的突变时刻均发生在1980年代末～1990年代初这一时期,暴雨降水量在1980年代中期～20世纪末出现了一个增长的过程,北区趋势并不显著.全区暴雨平均强度在突变时刻之后有一个减弱的过程,而西区和北区的暴雨平均强度变化并不显著.     

IMPROVEMENT OF NUMERICAL SIMULATION OF TYPHOON RANANIM (0414) BY USING DOPPLER RADAR DATA

Typhoon Rananim (0414) has been simulated by using the non-hydrostatic Advanced Regional Prediction System (ARPS) from Center of Analysis and Prediction of Storms (CAPS). The prediction of Rananim has generally been improved with ARPS using the new generation CINRAD Doppler radar data. Numerical experiments with or without using the radar data have shown that model initial fields with the assimilated radar radial velocity data in ARPS can change the wind field at the middle and high levels of the troposphere; fine characteristics of the tropical cyclone (TC) are introduced into the initial wind, the x component of wind speed south of the TC is increased and so is the y component west of it. They lead to improved forecasting of TC tracks for the time after landfall. The field of water vapor mixing ratio, temperature, cloud water mixing ratio and rainwater mixing ratio have also been improved by using radar reflectivity data. The model’s initial response to the introduction of hydrometeors has been increased. It is shown that horizontal model resolution has a significant impact on intensity forecasts, by greatly improving the forecasting of TC rainfall, and heavy rainstorm of the TC specially, as well as its distribution and variation with time.     

ANALYSIS OF THE CHARACTERISTICS OF SUSTAINED TORRENTIAL RAINS IN JUNES DURING 1958-2000

Day-to-day precipitation data of Junes during the 43 years of 1958-2000 from stations to the south of Yangtze River are used to divide regions and run statistical analysis of sustained torrential rainfall processes. A preliminary analysis is then made based on it and the results show that June is the month in which torrential rains in the southern half of China take place frequently and sustained torrential rains occur at the same time in South China and the area to the south of Yangtze River. In addition, the analysis gives the basic features of sustained torrential rains of June in China and their interannual variability patterns, with the suggestion that the amount of these events increases significantly after the 1990s. Lastly, the sustained torrential rains occurring in Junes of 1994, 1998 and 2005 in the southern half of China are taken as examples in the research on the basic patterns and formation mechanisms of the evolution of double rain-bands during the rain season in South China and the area to the south of Yangtze River. The analysis shows that the large scale environment field in which sustained torrential rains occur is related to the stable sustaining of the South Asia High and upper level jet streams.     

降雪与冻雨天气研究回顾

2008年初,中国南方许多地区出现了历史罕见的持续雨雪、冰冻天气,对电力、交通、农业、林业等造成了极大破坏。分析研究这种在全球气候变化背景下发生的极端天气事件的形成原因,有助于提高预测水平和对类似灾害性天气的防范能力。在对近年来国内外关于冬季降雪和冻雨天气研究进行简略回顾的基础上,对其未来研究方向进行了展望。认为：在全球气候变暖的背景下,要加强雨雪、冰冻天气形成机理与变化规律的研究,特别是要加强其发生的前兆性研究;要充分利用现代先进的探测技术和手段,提高对雨雪、冰冻天气的监测能力;要建立和完善对雨雪、冰冻灾害天气时间发生、发展的预报技术和方法。     

Splash detachment of sand particles under varying contact stress field of wind-driven raindrop impact

The effects of wind-driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two-dimensional experimental set-up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind-free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s⁻¹ and rainfall intensities of 50, 60, 75 and 90-mm h⁻¹ to assess the sand detachment rate (D, in g m⁻² s⁻¹). The effects of sand moisture state (dry and wet) on the detachment of different-sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KE_x and KE_y, respectively, in J m⁻² s⁻¹) along with their vector sum (KE_r, in J m⁻² s⁻¹) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KE_r, KE_x and KE_y with the sand size and three-way interaction of KE_x, sand size and moisture were statistically significant. These results can be explained by size-dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind-driven oblique raindrops (KE_x/KE_y). Further analysis of the variation of the unit sand detachment rate (D_u = D/KE_r = g J⁻¹) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity on D_u that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non-cohesive particle detachment rates, to some extent interacted with size-dependent compressibility and interface shear strength of sand grains.     

乐山地区酸性降水特征、规律及防治对策

酸雨已成为世界性问题之一．它给人们造成了巨大的危害和损失。研究乐山酸雨污染形成机理、特征、变化规律以及防治对策,对于乐山这个优秀旅游城市来说．具有非常重要的意义。