青藏高原与四川盆地夏季降水日变化的对比分析

采用2006-2008年自动气象站和2002-2008年TRMM（Tropical Rainfall Measurement Mis-sion）多卫星降水分析（Munti-satellite Precipitation Analysis,TMPA）的夏季（6～8月）逐时降水量资料,分析了青藏高原（下称高原）及周边地区夏...     

Factors Influencing Diurnal Variations of Cloud and Precipitation in the Yushu Area of the Tibetan Plateau

Using the cloud radar, ground observations, and ECMWF Reanalysis v5 (ERA5) data, we investigate the factors in-fluencing nighttime precipitation during summer i...     

Ka波段毫米波云雷达对青藏高原东南缘降水回波的分析

利用丽江站新建的Ka波段毫米波云雷达获得的高时间分辨率的垂直观测资料,结合同址的地面自动气象站和雨滴谱的分钟数据、常规探空数据和附近C波段天气雷达的强度回波,分析了两次降水过程前后云雷达反射率因子Z、径向速度V_r、速度谱宽S_w的垂直变化规律。分析表明:在发生弱降水时,云雷达Z在垂直方向的变化不明显;但V_r、S_w值在0℃层稍低位置有一个明显的分界层(融化层),粒子通过融化层后V_r、S_w都是快速变大,这个变化主要是粒子的相态由固态变成液态引发的,可以通过V_r、S_w突变值的位置来识别0℃层亮带的高度。从C波段天气雷达回波强度、剖面图及云雷达位置的时间-高度图看,对毛毛雨和小雨的回波,强度和高度差异比较明显,毛毛雨比小雨回波高度低、强度弱,与云雷达相比C波段雷达对高一些的云观测不到,对距离较远的弱降水回波无法观测到;由于相同粒子对不同波长电磁波的散射不一样,造成两种雷达垂直方向观测到的Z变化不同。对比弱降水回波,云雷达在...     

The Seasonal and Interannual Variation of Diurnal Precipitation over the Tibetan Plateau and Its Downstream Regions Observed by the Tropical Rainfall Measuring Mission

Using nine years of Tropical Rainfall Measuring Mission(TRMM)2A25 data,based on the probability density function of rainfall,a comparative analysis of the diurnal cycle and its seasonal and interannual variation for convective rain,stratiform rain,and total rain is made between the Tibetan Plateau and the downstream Yangtze River basin and East China Sea.The diurnal convective rain is stronger than the diurnal stratiform rain over the Yangtze River basin,and the convective rain peaks in the afternoon when the stratiform rain maximum happens in the early morning.Convective rain and stratiform rain both peak in the early morning over the East China Sea.The diurnal total rain over the Tibetan Plateau is stronger than its downstream regions.The diurnal cycle appears quite different among the four seasons over the Yangtze River basin,and the seasonal variation of diurnal convective rain is more apparent than diurnal stratiform rain.The seasonal variation of the diurnal cycle is weak over the East China Sea and Tibetan Plateau.The maximum of total rain happens in the afternoon during1998–2002 over the Yangtze River basin,while it peaks in the early morning during 2003–2006,but no obvious phase differences can be found among years in the diurnal rain over the East China Sea and over the Tibetan Plateau.     

Diurnal Variations of Precipitation over the Steep Slopes of the Himalayas Observed by TRMM PR and VIRS

This study investigates diurnal variations of precipitation during May–August, 1998–2012, over the steep slopes of the Himalayas and adjacent regions(flat Gangetic Plains–FGP, foothills of the Himalayas–FHH, the steep slope of the southern Himalayas–SSSH, and the Himalayas-Tibetan Plateau tableland–HTPT). Diurnal variations are analyzed at the pixel level utilizing collocated TRMM precipitation radar and visible infrared data. The results indicate that rain parameters(including rain frequency, rain rate, and storm top altitude) are predominantly characterized by afternoon maxima and morning minima at HTPT and FGP, whereas, maximum rain parameters at FHH typically occur in the early morning. Rain parameters at SSSH are characterized by double peaks;one in the afternoon and one at midnight. Over HTPT and FGP,convective activity is strongest in the afternoon with the thickest crystallization layer. Over FHH, the vertical structure of precipitation develops most vigorously in the early morning when the most intense collision and growth of precipitation particles occurs. Over SSSH, moist convection is stronger in the afternoon and at midnight with strong mixing of ice and water particles. The results of harmonic analysis show that rain bands move southward from lower elevation of SSSH to FHH with apparent southward propagation of the harmonic phase from midnight to early morning. Moreover, the strongest diurnal harmonic is located at HTPT, having a diurnal harmonic percentage variance of up to 90%. Large-scale atmospheric circulation patterns exhibit obvious diurnal variability and correspond well to the distribution of precipitation.     

Diurnal Variability of Precipitation Depth Over the Tibetan Plateau and its Surrounding Regions

The diurnal variability of precipitation depth over the Tibetan Plateau and its surrounding regions is investigated using nine years of Tropical Rainfall Measuring Mission(TRMM) precipitation radar(PR) measurements.The Tibetan Plateau,the plains area,and the East China Sea are selected as the focus regions in this study.The average precipitation depths(PD) are about 4.6 km,5.8 km,and 5.6 km,while convective(stratiform) PDs are about 6.6(4.5) km,7.5(5.7) km,and 6.0(5.6) km over the plateau,the plains,and the...     

青藏高原气温和降水的年际和年代际变化

通过对青藏高原72个地面气象站1962～1999年的气温和降水变化的分析,以唐古拉山脉为界将高原分为青海区和西藏区,分别考察了两区冬春(上年10月～当年5月)和汛期(当年6月～9月)气温与降水的变化趋势、突变及其周期振荡,得出的主要结论为:近38年(1962～1999)来,青藏高原呈升温趋势,冬春大多数台站的升温率为0.02～0.03 ℃ a-1,汛期大多数台站的升温率为0.01～0.02 ℃ a-1;20世纪80年代以来,高原冬春气温的升温更为强烈,汛期青海区的升温变得强烈,但西藏区反呈微弱降温趋势,降温主要发生在西藏的江河谷地;全球性的1980年左右的暖突变在青藏高原是明显存在的;近38年来,青海区冬春降水和西藏区汛期降水存在相同的相位变化,即20世纪60年代基本偏多,20世纪70年代和20世纪80年代初偏少,20世纪80年代中到20世纪90年代偏多;青海区汛期降水与西藏区汛期降水的变化存在反向的关系,但它的转折点要滞后4～5年,青海区汛期降水20世纪60年代偏少,20世纪70年代和20世纪80年代偏多,20世纪90年代偏少;西藏区冬春降水呈现自己独特的变化,20世纪60年代到20世纪70年代初偏少,20世纪70年代中末期到20世纪90年代偏多;高原气温主要存在准3年、5～8年和准11年的周期振荡,高原降水主要存在3～5年、8～11年和准19年的周期振荡,这些周期振荡在高原气候演变的不同阶段显著性不一.     

新疆夏季降水日变化特征

利用1991-2014年新疆16个国家基准气象站逐时降水资料,分析了新疆夏季不同区域降水日变化基本特征,揭示出新疆夏季降水日变化呈现显著的南、北疆区域差异,有别于我国中东部的一些新事实。结果显示:北疆降水量日变化呈现准单峰型特征,峰值主要发生在傍晚前后（16:00-20:00,地方时,下同）;南疆降水量日变化呈现三峰特征,峰值分别出现在傍晚（17:00-18:00）、午夜后（00:00-01:00）和上午（10:00）。新疆夏季降水事件以6 h以内的短历时性质为主（平均为85%,比例明显高于我国中东部）,而持续12 h以上的较长历时降水事件偶有发生;在天山东麓以外的新疆绝大部分地区,6 h以内短历时降水事件对总降水量的贡献率达54%,高于我国中东部地区。新疆西部和北疆北部降水量日变化主峰的贡献者是2~3 h短持续性降水为主的事件;而天山中-东部降水量日变化峰值则是来自于12 h内各不同持续时间降水事件的大致均等贡献。     

青藏高原东侧四川地区夜雨时空变化特征

本文利用四川地区1971～2012年29个气象站逐小时降水资料,计算四川地区雨季(5～9月)夜雨比例、夜雨强度和夜雨频次,并通过区域平均与趋势分析等统计方法,分析了其空间差异与时间变化特征,结果表明:(1)四川地区雨季夜雨占日降水量的比例较大,且具有显著的区域性差异,盆地西南部的夜雨占日降水量的比例最大,川西高原东北与川东北则为明显的两个低值区;(2)川东北地区雨季具有夜雨占日降水量的比例较小、夜雨发生概率也较低、但其夜雨强度却较大的特征,川西高原则与之相反,而盆地西南部的夜雨发生频次虽然不是很高,但夜雨强度和夜雨比例都较大;(3)42年平均四川地区雨季逐日变化,夜雨占日降水量的比例表现为先下降、后上升的特征,夜雨强度与夜雨比例相反,呈先上升、后下降的波动趋势,而夜雨频次的逐日变化呈现出明显的双峰特征;(4)四川地区夜雨比例、夜雨强度和夜雨频次的年变化具有一定差异。20世纪70、80年代,其夜雨频次和夜雨比例均较大,但呈减少趋势,而夜雨强度20世纪70年代较小,80年代较大,呈增大趋势。20世纪90年代,夜雨强度、频次和比例都处于较低状态;21世纪,夜雨强度和夜雨比例都开始明显增大,而夜雨频次增大相对滞后,其中,21世纪夜雨频次和夜雨比例波动明显。     

青藏高原及其下游地区降水厚度季、日变化的气候特征分析

利用10年的TRMM卫星降水雷达观测资料, 首次对青藏高原及其下游平原及海洋地区降水厚度的地区差异进行了对比分析, 并对青藏高原及其周边地区对流和层云降水厚度的水平分布及其日变化和季节变化进行了统计分析, 结果表明: (1) 青藏高原地区对流和层云降水厚度都要比下游平原地区更为浅薄, 东部海洋地区对流降水厚度比平原地区小, 而层云降水厚度与平原地区相当。青藏高原及其下游平原地区对流降水厚度的日变化特征非常明显, 海洋地区对流降水厚度日夜差异则不大。层云降水厚度在各地区的日变化特征都不明显。青藏高原、下游平原及海洋地区对流和层云降水厚度的季节变化都非常明显, 从冬至夏, 对流和层云降水逐渐变得深厚, 而从夏入冬, 对流和层云降水则逐渐变得浅薄。(2) 青藏高原及其周边地区对流和层云平均降水厚度的分布形式和降水量分布具有较好的对应关系, 降水量大的地区其降水厚度一般较为深厚, 降水少的地区则降水厚度比较浅薄。对流和层云降水厚度存在明显差异, 对流降水一般要比层云降水深厚。青藏高原及其周边地区降水厚度水平分布的日夜差距不大, 但季节变化非常明显, 且与气候系统的季节变化紧密相关。     

湖南夏季降水日变化特征

利用湖南96个测站13年的逐时自记降水资料, 分析了夏季（6~8月）降水日变化特征。结果表明, 湖南夏季降水日变化呈现显著的区域差异。湘东南降水量、 降水频次峰值主要出现在午后到傍晚, 而其它地区的降水峰值一般出现在清晨。进一步分析显示, 降水频次峰值出现时次分布更集中, 区域特征更鲜明。湘西北、 湘东南区域平均的累积降水量、 降水频次及降水强度的日变化在清晨和午后均呈双峰型特征。湘西北主（次）峰值出现的时间大致与湘东南次（主）峰值出现的时间对应。同时, 降水日变化与降水持续时间密切相关。持续5~10 h降水事件是持续1~4 h事件与持续10 h以上事件降水量峰值出现时间发生显著变化的过渡降水事件。持续1~4 h（10 h以上）的降水事件的极值降水始发时间为午后至傍晚（夜间）。在不同持续时间的降水事件中, 持续2 h降水的累积量最大。     

基于雷达回波的贵阳地区对流性降水特征分析

为了深入理解贵阳地区对流性降水的时空分布特征,本文利用贵州省贵阳站2014—2016年5—8月CINRAD/CD回波资料,首先挑选出符合对流性降水回波特征的551个样本,然后从对流性降水的回波形态、发生频次、位置、日变化、生命史以及大尺度环境场六个方面进行统计与分析。结果表明:对流性降水回波形态可分为单体型、线状型和区域型,其中线状型接近50%,是贵阳地区最常见的对流组织形式;与线状型和区域型相比,单体型对流生命史最短且局地性特征明显;超过七成对流性降水发生在西南涡或西南气流存在的天气背景下;对流多发生在贵阳市西南和东南面,而北面最少;对流初始时刻存在午后和午夜两个峰值区。最后,还以三类对流性降水过程为例,对比分析其生消过程、降水范围和强度等特点。     

Application of Multi-Scale Tracking Radar Echoes Scheme in Quantitative Precipitation Nowcasting

A new radar echo tracking algorithm known as multi-scale tracking radar echoes by cross-correlation(MTREC) was developed in this study to analyze movements of radar echoes at different spatial scales.Movement of radar echoes,particularly associated with convective storms,exhibits different characteristics at various spatial scales as a result of complex interactions among meteorological systems leading to the formation of convective storms.For the null echo region,the usual correlation technique produces zero or a very small magnitude of motion vectors.To mitigate these constraints,MTREC uses the tracking radar echoes by correlation(TREC) technique with a large "box" to determine the systematic movement driven by steering wind,and MTREC applies the TREC technique with a small "box" to estimate small-scale internal motion vectors.Eventually,the MTREC vectors are obtained by synthesizing the systematic motion and the small-scale internal motion.Performance of the MTREC technique was compared with TREC technique using case studies:the Khanun typhoon on 11 September 2005 observed by Wenzhou radar and a squall-line system on 23 June 2011 detected by Beijing radar.The results demonstrate that more spatially smoothed and continuous vector fields can be generated by the MTREC technique,which leads to improvements in tracking the entire radar reflectivity pattern.The new multi-scale tracking scheme was applied to study its impact on the performance of quantitative precipitation nowcasting.The location and intensity of heavy precipitation at a 1-h lead time was more consistent with quantitative precipitation estimates using radar and rain gauges.     

The First Observed Cloud Echoes and Microphysical Parameter Retrievals by China's 94-GHz Cloud Radar

By using the cloud echoes first successfully observed by China's indigenous 94-GHz SKY cloud radar, the macrostructure and microphysical properties of drizzling stratocumulus clouds in Anhui Province on 8 June2013 are analyzed, and the detection capability of this cloud radar is discussed. The results are as follows.(1) The cloud radar is able to observe the time-varying macroscopic and microphysical parameters of clouds,and it can reveal the microscopic structure and small-scale changes of clouds.(2) The velocity spectral width of cloud droplets is small, but the spectral width of the cloud containing both cloud droplets and drizzle is large. When the spectral width is more than 0.4 m s-1, the radar reflectivity factor is larger(over –10 dBZ).(3) The radar's sensitivity is comparatively higher because the minimum radar reflectivity factor is about–35 dBZ in this experiment, which exceeds the threshold for detecting the linear depolarized ratio(LDR) of stratocumulus(commonly –11 to –14 dBZ; decreases with increasing turbulence).(4) After distinguishing of cloud droplets from drizzle, cloud liquid water content and particle effective radius are retrieved. The liquid water content of drizzle is lower than that of cloud droplets at the same radar reflectivity factor.     

基于雷达资料的一次高原涡天气云降水宏微观特征研究

利用常规天气资料,并结合第三次青藏高原大气科学试验(TIPEX-Ⅲ)的毫米波云雷达资料和激光雨滴谱仪雨滴谱资料,对影响那曲地区的一次高原涡天气进行了综合分析,包括天气背景和云-降水水平、垂直结构和演变特征。结果表明:此次高原涡天气形成了涡旋状的云系,从垂直结构看本次过程由对流云演变为积层混合云。对流云阶段,回波多呈小面积的零星稀疏分布,持续时间较短,与此同时还伴有强烈的上升运动,云中正速度区多呈条状或细带状,云顶较高,呈"蘑菇状",此时对应降水强度小,雨滴粒子浓度较低。混合云阶段,回波多呈整齐的片状,回波持续时间较长,云中的正速度区常呈柱状或方块状,近地面1km位置处亮带明显,是由于粒子相态变化造成的,亮带以下降水粒子碰撞破碎,反射率因子明显降低,对应雨滴粒子直径多处于1～3mm,且浓度较大。高原涡过程中不同阶段云所对应的雷达回波结构和降水特征存在明显的差别,本研究可为高原天气预报和物理过程等研究提供一定参考。     

青藏高原西部地表通量的年、日变化特征

利用青藏高原西部地区改则和狮泉河两个自动观测气象站1998年全年每天24个时次的风速、温度和湿度等梯度观测资料,采用湍流相似理论．计算了改则和狮泉河的动量通量、感热通量以及潜热通量。结果表明：改则和狮泉河两地的地表湍流通量都具有明显的季节变化和日变化,且其季节变化的相同点表现在感热通量均在5月份最大,1月份最小：而潜热通量均在8月份最大。不同点表现在改则的潜热通量在12月份最小,狮泉河1～5月平均潜热通量为负,以凝结为主,改则的月平均蒸发及全年的蒸发总量比狮泉河的要大。而其感热通量比后者的都小。日变化幅度随季节变化明显,表现在夏季地表通量的日变化幅度大,冬季要小得多。     

A Numerical Investigation on Microphysical Properties of Clouds and Precipitation over the Tibetan Plateau in Summer 2014

In order to improve our understanding of microphysical properties of clouds and precipitation over the Tibetan Plateau (TP), six cloud and precipitation processes with different intensities during the Third Tibetan Plateau Atmospheric Science Experiment (TIPEX-Ⅲ) from 3 July to 25 July 2014 in Naqu region of the TP are investigated by using the high-resolution mesoscale Weather Research and Forecasting (WRF) model. The results show unique properties of summertime clouds and precipitation processes over the TP. The initiation process of clouds is closely associated with strong solar radiative heating in the daytime, and summertime clouds and precipitation show an obvious diurnal variation. Generally, convective clouds would transform into stratiform clouds with an obvious bright band and often produce strong rainfall in midnight. The maximum cloud top can reach more than 15 km above sea level and the velocity of updraft ranges from 10 to 40 m s-1. The simulations show high amount of supercooled water content primarily located between 0 and -20℃ layer in all the six cases. Ice crystals mainly form above the level of -20℃ and even appear above the level of -40℃ within strong convective clouds. Rainwater mostly appears below the melting layer, indicating that its formation mainly depends on the melting process of precipitable ice particles. Snow and graupel particles have the characteristics of high content and deep vertical distribution, showing that the ice phase process is very active in the development of clouds and precipitation. The conversion and formation of hydrometeors and precipitation over the plateau exhibit obvious characteristics. Surface precipitation is mainly formed by the melting of graupel particles. Although the warm cloud microphysical process has less direct contribution to the formation of surface precipitation, it is important for the formation of supercooled raindrops, which are essential for the formation of graupel embryos through heterogeneous freezing process. The growth of graupel particles mainly relies on the riming process with supercooled cloud water and aggregation of snow particles.     

利用高原积雪信号改进我国南方夏季降水预测的新方法及其在2014年降水预测中的应用试验

2014年夏季我国南方出现严重洪涝、北方大部干旱,国内绝大多数预测模型在三月起报的汛期预测中均未能抓住位于南方地区的异常雨带,导致预测准确率明显偏低。基于模式对东亚地区夏季海平面气压场的高预报技巧和青藏高原冬季积雪与南方地区夏季降水的高相关性,本文提出一个针对我国夏季降水异常的组合统计降尺度预测新方法（Hybrid Statistical Downscaling Prediction,简称HSDP）,该方法综合利用了气候模式输出的高可预报性环流信息和前期观测的高原积雪异常信号,从而实现对我国南方夏季降水进行动力-统计相结合的改进预报。据此方法建立了一个基于国家气候中心气候预测模式的统计降尺度模型。对我国南方夏季降水进行跨季节预测的交叉检验结果显示,HSDP方法对于南方地区多年平均空间距平相关系数从模式原始预报的-0.006提高到0.24,且在大多数年份均有改进。基于HSDP方法于三月份制作的2014年夏季降水预测,能够很好地抓住南涝北旱的基本形势和我国南方的降水大值区,空间距平相关系数达到0.43。这表明,该方法对于我国夏季降水预测具有较好业务应用前景。     

“海棠”影响河南降水雷达回波和中尺度雨团对比分析

使用郑州714CD雷达观测资料，以及2005年刚建立起的河南省乡镇雨量站网资料，配合河南省自动站资料，对0505号台风海棠造成的河南省大范围暴雨、局部特大暴雨过程进行了分析，总结出强降水回波区早于中尺度雨团1个小时左右生成，中尺度雨团早于降水回波减弱消失，稳定少动的强降水回波有利于中尺度雨团的产生和发展；多普勒速度场上，中尺度系统存在的地方有利于强降水回波发展和维持，也有利于中尺度雨团产生和发展；受持续不断45dBz左右强降水回波影响，构成“列车效应”，可造成暴雨甚至是大暴雨过程；对于大范围降水回波，依据乡镇雨量图上中尺度雨团活动规律，分析速度场上中尺度系统如逆风区、辐合区、大风区（低空急流），可以准确预报暴雨落区，发布暴雨预警信号。