湘中一次大暴雨天气的综合诊断分析

利用NCEP的1°×1°再分析资料、FY-2E逐小时TBB资料以及常规气象观测资料,对湘中地区2010年5月12—13日大暴雨过程的环流形势、物理量场以及中尺度系统进行综合分析,试图从多角度揭示这次大暴雨天气的成因。结果表明：高空南支槽,中低层切变以及地面冷空气是这次大暴雨天气过程的主要影响系统;低空急流作为暖湿气流的载体,为暴雨的产生提供了充足的能量条件和水汽条件;冷空气侵入高能不稳定的暖湿气团,是触发暴雨不稳定能量释放的热力机制;z-螺旋度的空间分布能反映暴雨发生时大气的动力特征,中低层强辐合,高层强辐散与低层正涡度的空间结构,有利于高低层形成“抽吸作用”,从而使上升运动得到发展和加强,为暴雨的产生提供有利的动力条件;高分辨率的云顶亮温TBB资料对降水的强度及落区有很好的指示意义。     

川北一次大暴雨过程的物理量诊断分析

利用2005年7月16日至19日的高空地面资料,对当年7月18日至19日发生在川北的一次大暴雨天气过程进行了环流形势分析和物理量诊断分析,得出了产生此次大暴雨过程的环流特点,并利用假相当位温、水汽通量散度和改进的湿Q矢量散度场分析了暴雨的落区、强度和持续时间。     

大气结构特征与雷暴成因

盛夏季节,宜宾雷暴的形成主要与对流层内高温高湿、风及其在对流层的中上部垂直切变小的特点相关联。西宁雷暴的形成主要与上层为深厚的干冷、下层为浅薄的暖湿、对流层的中上层风及其垂直切变大的特点相关联。分析又得到以下结论:西宁雷暴的形成又与高空冷空气加强南移、副热带急流南侧反气旋式切变得到加强和高空出现辐散相关联。     

粤西沿海“4.20”特大暴雨特征分析

根据气象常规观测资料、湛江新一代天气雷达资料、CFL-08风廓线雷达资料及卫星云图,分析2012年4月20日粤西沿海特大暴雨的天气环流形势、能量场、对流不稳定度、水汽输送和辐合辐散等环境特征及物理量场特征。结果表明:这次暴雨过程粤西地区共经历两次强降水过程,分别是受飑线系统、以及高空槽和低空切变影响;西南低空急流的出现有利于粤西暴雨的形成、维持和发展;暴雨过程粤西上空垂直累积液水含量达25~30g/m2;暴雨期间风向随高度明显逆转,有冷平流输送;约2.0 km高度以下低空急流的下传和增强与暴雨的产生有密切关系;短时间内多普勒天气雷达的速度回波低层辐合区域远远大于辐散区域是可能产生强降水的标志。     

高空急流区飞机颠簸的一种形成机制的探讨

作者应用动力学分析方法，结合观测飞机颠簸的事实，对高空急流区飞机颠簸的一种形成机理进行了理论探讨。结果表明，高空急流区温度平流分布的不均匀性，会在急流附近等温线密集区边缘激发出空气垂直运动和湍流，引起飞机颠簸。     

索马里急流和南亚高压对印度夏季风爆发的协同作用

【目的】探讨索马里急流和南亚高压对印度夏季风(Indian Summer Monsoon,ISM)爆发产生的协同作用。【方法】基于ECMWF欧洲中期天气预报中心第五代再分析资料(ERA5)提供的逐日数据,结合印度气象局对ISM爆发日期(即印度次大陆最南端的喀拉拉邦降水骤升的日期)的统计数据采用功率谱分析、偏相关分析和滑动相关等统计学方法,分析索马里急流和南亚高压对ISM爆发的协同作用。【结果】ISM爆发前1候至当候,印度地区对流层高层南亚高压的范围和强度不断扩大,同时对流层低层索马里急流的强度和范围不断增强,使阿拉伯海地区的西南气流不断增强,将阿拉伯海地区大量水汽输送至印度大陆,在这样有利的条件下,印度南部降水量剧增,ISM爆发;当5月下旬的南亚高压、索马里急流以及阿拉伯海地区水汽通量和气旋性环流均显著偏强时,ISM会提前爆发,降水也会异常偏多。【结论】ISM爆发日期受到索马里急流和南亚高压两者协同作用的影响,而并非单独受到某个系统的影响。     

民航飞机气象资料的应用及探讨

为了将AMDAR资料应用于常规观测预报中,对天气系统的演变特征进行更细微的监测,利用2011年5月1~3日的AMDAR资料,分析AMDAR时空分布特点;对比气象常规高空观测实际,研究AMDAR资料处理技术,得出具体算法,并结合2011年5月1~3日常规高空观测资料分析天气形势,看出常规高空观测中显示的1日20时移出盆地的高原东部至盆地上空的浅槽于1日14时就已经移出盆地了,延安伸出的槽在14时也已出现。研究结果表明,高空气压的计算可直接用等温大气中的压高方程代替;AMDAR资料应用于常规高空观测可以得到比常规高空观测更为细致的结果。     

基于卫星观测的两例青藏高原低涡结构的初步分析

应用风云2C卫星云图和配有云顶亮温的MTSAT卫星红外云图,描述了两例青藏高原低涡形成、发展及消亡过程,云图清晰显示了高原低涡具有涡眼和暖心结构的特征,并利用水汽图分析揭示了缺乏水汽供应是导致这类低涡不能进一步发展并移出高原的重要原因.最后用1°×1°NCEP分析资料对高原低涡形成眼结构时的基本物理场进行了诊断计算.结果表明:低涡整体为上升气流,而涡眼区在近地层为下沉气流,上层为相对涡区较弱的上升气流;低层辐合,高层辐散.进而印证了动力学研究工作得出的高原低涡具有与热带气旋类低涡(TCLV, tropical cyclone-like vortices)类似的涡眼和暖心结构特征的结论.     

Features of ocean surface winds observed by the QuikSCAT satellite before tropical cyclogenesis over the South China Sea

Ocean surface winds observed by the Quick Scatterometer (QuikSCAT) satellite prior to the geneses of 36 tropical cy- clones (TCs) in the South China Sea (SCS) are investigated in this paper. The results show that there are areas with negative mean horizontal divergence around the TC genesis locations three days prior to TC formation. The divergence term [-(f ζ)( u/ x v/ y)] in the vorticity equation is calculated based upon the QuikSCAT ocean surface wind data. The calculated mean divergence term is about 10.3 times the mean relative vorticity increase rate around the TC genesis position one day prior to TC genesis, which shows the important contributions of the divergence term to the vorticity increase prior to TC formation. It is suggested that criteria related with the divergence and divergence term be applied in early detections of tropical cyclogenesis using the QuikSCAT satellite data.     

Mapping the vegetation distribution of the permafrost zone on the Qinghai-Tibet Plateau

In this paper,an updated vegetation map of the permafrost zone in the Qinghai-Tibet Plateau(QTP) was delineated.The vegetation map model was extracted from vegetation sampling with remote sensing(RS) datasets by decision tree method.The spatial resolution of the map is 1 km×1 km,and in it the alpine swamp meadow is firstly distinguished in the high-altitude areas.The results showed that the total vegetated area in the permafrost zone of the QTP is 1,201,751 km~2.In the vegetated region,50,260 km~2 is the areas of alpine swamp meadow,583,909 km~2 for alpine meadow,332,754 km~2 for alpine steppe,and 234,828 km~2 for alpine desert.This updated vegetation map in permafrost zone of QTP could provide more details about the distribution of alpine vegetation types for studying the vegetation mechanisms in the land surface processes of highaltitude areas.     

RESPONSE OF EQUATORIAL PACIFIC UPPER OCEAN CURRENT TO WESTERLY WIND BURSTS

The characteristics of the response of equatorial Pacific upper ocean current to westerly wind bursts(WWB)were analyzed in the frequency domain by using wind and ADCP data collected by the Shiyan3 during TOGA-COARE IOP,1992-1993.The preliminary results showed that the response consistedof an eastward surface jet at shallower than 60m depth,a westward counter current centering near100m and a shear layer between them,with the variations of all three being nonlinear and nearlysynchronous.The oceanic responses in the frequency domain were characterized by occurrences of a remotely forced mixed Rossby-gravity wave with period of 8-10 days in the surface jet andcountercurrent at shallower than 110 m depth,and two locally forced waves with periods of 24 daysand 4-5 days limited in shallower than 70m depth.These fluctuations of the responses depended much more on zonal wind than meridional wind.The results also revealed that the oceanic response toWWB resulted from momentum transport and energy propagation assoc     

A Case study of a snowstorm at the Great Wall Station,Antarctica

A case of a snowstorm at the Great Wall Station was studied using data of NCEP (National Centers for Environmental Prediction) analysis, in situ observations and surface weather charts. The storm occurred on August 29th,2006, and brought high winds and poor horizontal visibility to the region.It was found that the storm occurred under the synoptic situation of a high in the south and a low in the north. A low-level easterly jet from the Antarctic continent significantly decreased the air temperature and humidity.Warm air advection at high level brought sufficient vapor from lower latitudes for the snowstorm to develop.The dynamic factors relating to strong snowfall and even the developmentof a snowstorm were deep cyclonic vorticity at middle and low levels,the configuration of divergence at high level and convergence at low level, and strong verticaluplift. There was an inversion layer in the low-level atmosphere during the later phase of the storm.This vertical structure of cold air at low levels and warm air at high levels may have been important to the longevity of the snowstorm.     

FLUID EXCHANGE ACROSS THE EQUATORIAL FRONT

In this paper, the cusp-shaped wave pattern (Legeckis wave) along the Equatorial Front (EF) is modeled by a meandering jet, and the motion of fluid parcels in a two-dimensional kine-matic model of the meandering jet along EF is studied using Melnikov‘s method. Results indicated that the velocity field of the cusp-shaped wave pattern can indeed be modeled by a meandering jet; that the EF will act as a barrier to fluid exchange if there is no variability, but that it is just the variability that moves the buoy across the EF.     

2011年春夏长江中下游旱涝急转的低频环流系统变化

为研究2011年春夏长江中下游地区旱涝急转现象与低频环流的关系,利用国家气象信息中心的753站逐日降水、NCEP/NCAR再分析资料和带通滤波的方法,得到如下结果：（1）2011年5-6月,长江中下游地区存在明显旱涝急转现象,5月的降水较同期偏少40％以上,6月的降水较同期偏多60％。（2）5-6月的旱涝急转前后,长江中下游地区的500hPa的垂直速度变化不仅与降水有很好的关系,而且其低频振荡的强度也显著加强,垂直速度由正（下沉运动）转负（上升运动）的转换时间几乎对应由旱转涝的时间。（3）对旱涝急转过程的500hPa低频变化垂直速度下沉运动最强、下沉运动向上升运动转换、上升运动最强3个位相的低频散度场分析发现,在5月干旱期间,长江中下游地区维持对流层低层（850hPa）辐散、高层（200hPa）辐合的低频环流系统,不利于降水。到6月强降水期,长江中下游地区则迅速转为对流层低层辐合、高层辐散的低频环流系统,有利于降水的发生。这种对流层低层-高层低频环流系统的变化是导致旱涝急转的重要原因之一。     

Response of upper ocean currents to typhoons at two ADCP moorings west of the Luzon Strait

We deployed two ADCP mooring systems west of the Luzon Strait in August 2008, and measured the upper ocean currents at high frequency. Two typhoons passed over the moorings during approximately one-month observation period. Using ADCP observations, satellite wind and heat flux measurements, and high-resolution model assimilation products, we studied the response of the upper ocean to typhoons. The first typhoon, Nuri, passed over one of the moorings, resulting in strong Ekman divergence and significant surface cooling. The cooling of surface water lagged the typhoon wind forcing about one day and lasted about five days. The second typhoon, Sinlaku, moved northward east of the Luzon Strait, and did not directly impact currents near the observation regions. Sinlaku increased anomalous surface water transport exchange across the Luzon Strait, which modulated the surface layer current of the Kuroshio.     

浙中金华地区“2013.3.20”春季雷暴天气过程研究分析

为了探索春季强对流发生发展的机制,利用常规观测资料、MICAPS资料以及新一代多普勒天气雷达资料,采用天气学诊断方法,对2013年3月20日凌晨发生在浙中金华地区的一次大范围的强雷暴天气过程进行分析。结果表明:(1)高空槽和地面倒槽是此次强对流天气过程的主要影响系统;(2)高空三层为一致的西南急流,水汽输送强;(3)中低层急流附近存在强的垂直上升运动中心且几乎重合,500hPa到地面存在强的垂直风切变,动力条件好;(4)中低层深厚的暖平流与高层弱冷平流相互作用形成了上干冷、下暖湿的不稳定层结;(5)中层冷空气渗透,促使强对流进一步发展,风暴发展为中-β尺度飑线系统,但前沿无阵风锋产生;(6)飑线南段的超级单体风暴发展为非超级单体强风暴,在雷达图上表现为"弓形"回波,其顶点经过武义站时造成27.4m/s(10级)的瞬时大风;(7)VIL高值维持时间较短,不利于冰雹出现。     

Bofedal response to climate variability,local management,and water extraction:A case study of Chucuyo,Northern Chile

Andean high-altitude wetlands are important ecosystems that serve a range of social-ecological functions.In the Andes,bofedales,a specific type of peat-producin...     

Stream-coordinate structure of oceanic jets based on merged altimeter data

The jet structure of the Southern Ocean front south of Australia is studied in stream-coordinate with a new altimeter product—Absolute Dynamic Topography (ADT) from AVISO. The accuracy of the ADT data is validated with the mooring data from a two-year subantarctic-front experiment. It is demonstrated that the ADT is consistent with in-situ measurements and captures the meso-scale activity of the Antarctic Circumpolar Current (ACC). Stream-coordinate analysis of ADT surface geostrophic flows finds that ACC jets exhibit large spatio-temporal variability and do not correspond to particular streamfunction values. In the circumpolar scope ACC jets display a transient fragmented pattern controlled by topographic features. The poleward shift of jet in streamfunction space, as revealed by a streamwise correlation method, indicates the presence of meridional fluxes of zonal momentum. Such cross-stream eddy fluxes concentrate the broad ACC baroclinic flow into narrow jets. Combined with a recent discovery of gravest empirical mode (GEM) in the thermohaline fields, the study clarifies the interrelationship among front, jet and streamfunction in the Southern Ocean.     

东亚副热带西风急流的时间演变特征及其与中国东部夏季降水的关系

为深入了解东亚副热带西风急流与中国天气系统之间的联系,利用1961-2007年美国国家环境预报中心（NCAR／NCEP）再分析月资料和同期中国596站的降水资料,运用经一纬向急流轴和区域平均两种定义方法分析了西风急流的时间演变特征及其与中国东部降水型的关系,结果表明：（1）两种方法对西风急流东西、南北位置转折时段的分析很接近,分别出现在20世纪80年代和70年代;对西风急流强度、南北位置周期的表征也很一致,分别为10-15年和5-10年。（2）当西风急流位置偏北（南）时,东部地区整层大气环流呈“南北上升中间下沉（南北下沉中间上升）”的形势,850hPa的流场和水汽通量输送都有利于华北地区（江淮河流）的降水,易于形成“南北多中间少（南北少中间多）”的雨带分布,推测这两种反相位雨型的间隔时间为2．5-5年;相比之下,急流东西位置和强度的周期性变化与东部局地降水存在一定联系。     

Numerical simulation of the genesis of typhoon Durian (2001) over the South China Sea: The effect of sea surface temperature

Typhoon Durian (2001),which formed over the South China Sea (SCS),was simulated by using the Weather Research and Forecasting (WRF) model. The genesis of typhoon Durian which formed in the monsoon trough was reproduced by numerical simulations. The simulated results agree reasonably well with observations. Two numerical experiments in which the sea surface temperature (SST) was either decreased or increased were performed to investigate the impact of the SST on the genesis of the ty-phoon. When the SST was decreased by 5℃ uniformly for all grids in the model,the winds calculated became divergent in the lower troposphere and convergent in the upper troposphere,creating conditions in which the amount of total latent heat release (TLHR) was low and the tropical cyclone (TC) could not be formed. This simulation shows the importance of the convergence in the lower tropo-sphere and the divergence in the upper troposphere for the genesis of the initial vortex. When the SST was increased by 1℃ uni-formly for all grids,a stronger typhoon was generated in the results with an increase of about 10 m s-1 in the maximum surface wind speed. Only minor differences in intensity were noted during the first 54 h in the simulation with the warmer SST,but apparent dif-ferences in intensity occurred after 54 h when the vortex began to strengthen to typhoon strength. This experiment shows that warmer SST will speed the strengthening from tropical storm strength to typhoon strength and increase the maximum intensity reached,while only minor impact can be seen during the earlier stage of genesis before the TC reaches the tropical storm strength. The results sug-gest that the amount of TLHR may be the dominant factor in determining the formation and the intensification of the TC.