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1.
2008-2012年南京短时强降水特征分析   总被引:4,自引:0,他引:4  
利用2008-2012年南京自动气象观测站逐时降水量的观测资料,分析南京短时强降水的发生规律,包括短时强降水的年变化、月变化、日变化和空间分布等特征。结果表明:2008-2012年南京雨强大于50 mm/h-1的致灾性短时强降水过程的发生次数呈显著增长趋势;短时强降水天气主要出现在6-9月,其中7-8月出现日数最多,雨强最大;春雨期短时强降水最易发生在凌晨,梅雨期短时强降水最易发生在上午和傍晚,台汛期短时强降水最易发生在上午;下半夜-凌晨短时强降水出现次数较少,傍晚前后是短时强降水多发时段;短时强降水天气的空间分布具有明显的城郊差异;城市化效应不能引起城区的局地降雨,但在大尺度天气系统过境时,会使城区的对流活动较郊区更活跃,且城市下风向地区的降水也因此增强。  相似文献   

2.
利用乌鲁木齐多普勒天气雷达、风廓线雷达、GPS/MET水汽探测仪以及FY—2E/G卫星、区域加密自动气象站资料和GFS/NCEP 0.5°×0.5°逐6 h再分析资料,对2015年6月9日18:30—20:00出现在乌鲁木齐的短时强降水过程进行分析,重点分析了强降水过程的环境场和中小尺度特征。结果表明:该短时强降水过程有4个降水集中时段,每个时段约为10~15 min。降水发生在高压脊前低槽后部的西北气流控制之下,700 h Paβ中尺度西北急流上γ尺度对流单体是短时强降水直接影响系统。该降水过程水汽来自于乌鲁木齐周围并在2~3 h内快速集中。对流不稳定潜势从午后14 h开始发展,到降水开始仅4.5 h。沿西北低空急流出现多个γ中尺度对流单体以"列车效应"形式依次影响乌鲁木齐造成短时强降水,对流单体组合反射率最强达45~50 d Bz,生命史仅15~20 min。降水发生在局地新生中尺度对流云团西南侧云顶亮温TBB梯度最大处,TBB最低达-44℃,对流云团生命史2~3 h。  相似文献   

3.
近32年长沙市短时强降水的气候变化研究   总被引:1,自引:0,他引:1  
利用长沙市近32 a的1 h、3 h雨量资料,分析了长沙短时强降水年发生次数、月际分布、时段分布、极值分布等气候特征及1 h、3 h雨量极值趋势分析、突变检验。结果表明,长沙市1 h、3 h短时强降水年发生次数的多年平均值为4.4、3.7次,雨强平均为29.2 mm/h、14.8 mm/h。长沙发生1 h短时强降水高峰期为6-8月,3 h短时强降水高峰期为6-7月。1 h短时强降水容易发生在15-17时及20时等时段,3 h短时强降水容易发生在04-08时及01时等时段。1 h、3 h短时强降水年雨量极值大多出现在主汛期。年1 h雨量极值发生在7月最多,6、8月次之;年3h雨量极值发生在6月最多,7月次之。长沙市1 h、3 h短时强降水年雨量极值整体呈弱增加趋势,其长期趋势变化存在明显年代际变化特征和阶段性特征,无突变现象。  相似文献   

4.
湖北省夏季降水日变化特征   总被引:3,自引:2,他引:1       下载免费PDF全文
利用2001—2014年湖北省77个气象观测站的整点逐时降水数据,通过划分不同区域和三种量级降水的方法,分析了夏季(6—8月)降水日变化特征。结果表明:1)湖北省夏季降水日变化特征非常明显,降水量曲线呈双峰结构,峰值出现在08时和17时(北京时间,下同),降水频次与降水强度均呈现"一主一次"的双峰结构,这主要与青藏高原东移来的天气系统自西向东的滞后性以及局地热力强迫有关,发生在傍晚(15—18时)的降水强度有明显的年际增强趋势。2)湖北省降水日变化特征区域差异显著,鄂西北与鄂西南降水峰值主要出现在傍晚和夜间,谷值出现在正午,鄂东三个区域的降水峰值出现在上午和傍晚,谷值出现在午夜。3)近14 a强度为0~20 mm/h的降水呈现减少趋势,主要发生在鄂西地区。其日变化曲线为"一主一次"的双峰结构,主(次)峰值出现在07(17)时。与之相反,短时强降水(≥20 mm/h)的发生概率东部大于西部,平原大于山区,有增加趋势的站点占总站点数的53.24%,峰(谷)值出现在17(12)时。短时特大强降水(≥50 mm/h)峰值出现在15—20时,03—14时出现概率较低。  相似文献   

5.
利用1985-2018年汛期(5-9月)豫东地区20个国家站小时降水资料和2011-2018年同期豫东地区区域自动站观测数据、NCEP(1°×1°)再分析资料、高空地面观测资料等,统计分析了该区域小时雨强分别≥20mm/h、≥30mm/h和≥50mm/h的短时强降水时空分布特征,结果发现:豫东地区近34年汛期平均年降水量为458.9~577.5 mm/a,短时强降水次数为72.8次/a;2000年是短时强降水多发年份,≥20mm/h的雨强出现158次,是常年平均次数的1.17倍;主汛期的7-8月是不同强度短时强降水多发时期,34年来共计发生≥20mm/h的短时强降水1821次,占同强度短时强降水总次数(2476次)的近74.0%;在短时强降水的日变化中,05时是不同强度短时强降水多发时段,20时为次多发时段。对不同环流背景影响下短时强降水过程的水汽、动力、热力及能量等物理量作统计分析,低槽型短时强降水过程的动力条件优于其他两个类型的,850hPa涡度平均值达3.8×10~(-5)s~(-1),700hPa垂直速度平均值达-0.36 Pa·s~(-1);副高边缘型短时强降水过程不稳定能量条件优势显著,850hPa假相当位温平均值达354.1 K,500-850hPa假相当位温差的平均值达-17.80℃,K指数平均值为38.1℃、CAPE值平均值为2075.0 J·kg~(-1);而台风倒槽型短时强降水过程则在水汽输送方面更具优势,850 hPa比湿平均值为15.5g·kg~(-1),整层可降水量达70.0 mm。  相似文献   

6.
7·13郑州大暴雨成因与可预报性分析   总被引:5,自引:5,他引:0  
2008年7月13-14日郑州市出现局地大暴雨,24 h降雨量达174 mm,为1951年以来第二高值.这次大暴雨主要由两个时段的强降水累计而成,具有明显的中尺度特征.通过对常规气象资料分析发现:第一时段的强降水由副热带高压内部产生的局地对流云团加强造成,对流层底层东风气流的加强提供的水汽输送和动力抬升作用,促进了对流发展;新生云团进入潮湿的大气环境中能够得到迅速的发展.针对降水具有的明显中尺度特征,综合分析卫星、雷达、自动站等资料发现:利用新一代天气雷达的组合风廓线拼图可以很好地监测中尺度系统的演变趋势;区域自动站的10 min极大风速场上显示,地面中尺度辐合线和郑州附近的气旋中心维持时段,与对流云团影响郑州及强降水时段对应.因此具有中尺度特征的局地强降水,可由雷达、自动站等信息作出短时临近预报.  相似文献   

7.
利用国家基本站、区域站资料,分析了2006—2016年池州市短时强降水时空分布特征,建立3种天气学概念模型,并总结了短时强降水的中尺度系统、相关物理量和雷达回波的一般特征。结果表明:池州市短时强降水主要发生在汛期(5—8月),其中7月最活跃,其次分别是6、8月。强度≥20 mm/h和≥30 mm/h的短时强降水日变化呈现双峰型特征,强度≥50 mm/h的短时强降水则呈现单峰型特征。东至县中南部是短时强降水的易发区域,其次是贵池南部山区和九华山东、西两侧区域。池州市短时强降水天气类型可分为副热带高压边缘型、西北气流型和台风型,其中副热带高压边缘型是短时强降水的易发天气类型。中小尺度天气系统在不同天气类型中的作用存在差异,但相关物理量差异不明显。副热带高压边缘型、台风型强降水过程中雷达反射率因子多表现低质心结构特征,西北气流型呈现高质心结构特征。  相似文献   

8.
基于1991-2013年呼伦贝尔市汛期(6-8月)16站逐小时降水资料,分别定义各站点小时降水量的短时强降水阈值,同时利用经验正交函数(EOF)分析方法揭示呼伦贝尔市短时强降水变化特征。分析结果表明:短时强降水阈值、强降水事件以及汛期年平均总降水量和强降水雨强均呈现自西向东部偏南方向递增的空间分布,最强中心位于东南部阿荣旗,其形成与地形关系密切。短时强降水占汛期总降水量百分比低于1/5,短时强降水发生频率最低的地区出现84.2mm/h的强降水事件。短时强降水事件具有明显年代际变化, 21世纪以来,短时强降水事件发生频率表现增加趋势,空间分布表现为自东北向西南方向传播。7月下旬是短时强降水事件频发的时段。短时强降水有明显日变化特征,主峰出现在17时。EOF分析结果显示短时强降水事件在空间上表现出全市强降水具有同步性以及南部和北部地区反相位的特征。  相似文献   

9.
乔琪 《贵州气象》2011,35(4):15-17
该文应用NCEP 1°×1°资料,从中尺度系统及物理量的角度对2008年8月15日夜间到16日贵州的一次暴雨天气过程进行分析,得出这次过程强降水时段集中在15日22时—16日02时,雨强达23~56 mm/h,降水强度强、时间短,表现出了中尺度系统的特征,在省中部及东部均有能够引起很大雨强的东北风与东南风构成的中尺度切变线,云图上沿地面切变形成一对流云带,在云带上有MCS云团发展;贵州省处于南亚高压前部的强辐散区,对低层产生强的抽吸作用,加强了对流上升运动;强降水发生前高温高湿主要集中在中低层以下,为强降水的发生积聚了充足的潜在不稳定能量,短时强降水时段过后θse高能舌跃到了500 hPa,不稳定能量向上扩散,能量的快速耗散使得降水的强度趋于减弱;短时强降水发生前,垂直上升运动高度高,对流发展旺盛,而短时强降水过后,垂直上升运动速度虽增强,但高度明显降低,对流主要在中低层;CAPE值的猛增可视为产生短时强降水的一个指标。  相似文献   

10.
2016年夏末南疆地区短时强降水天气频发,中尺度对流系统活动频繁。利用强降水频发时段2016年8月8日至9月16日逐时FY-2G红外亮温(TBB)资料对南疆地区中尺度对流系统(MCS)进行分析,共获得92个生命史≥3小时的中-β尺度对流系统(MβCS),包括β中尺度对流复合体(MβCCS)和β中尺度持续拉长状对流系统(MβECS)。根据南疆地区的极端干旱气候背景,本文中-β尺度对流系统的尺度判定标准为云顶亮温(TBB)≤-32℃的连续冷云区直径≥20 km。对MCS的分布和活动特征进行了分析,结果表明:圆状MCS和带状MCS发生的频次相当。天山南坡和昆仑山北坡是MCS活跃区,MCS移动方向主要以偏东或东北方向为主,南疆地区活动最频繁的MCS生命史为3~4个小时。南疆地区MCS具有明显不同的日变化特征,午后和傍晚是MCS最活跃的时段。与MβCCS相比,MβECS具有更明显的夜发性特征。昆仑山北坡MCS的最活跃时段早于天山南坡MCS,而天山南坡MCS夜间和凌晨形成的特征更为显著。生命史为3~5小时的短生命史MCS主要在午后和傍晚形成发展,并在形成后2小时达到成熟,生命史超过6小时的长生命史MCS多发于午后和凌晨,并且其发展阶段更长。本文给出了1个引发短时强降水的MβCCS和1个MβECS的云团演变特征。  相似文献   

11.
Diurnal variations of the vertical profiles of wind and temperature have been surveyed, and the diffusivity and the dimensionless gradient function in the atmospheric boundary layer have been estimated. Even in the middle of the atmospheric boundary layer (e.g., below a height of 442 m), the vertical wind profile normalized by the surface friction velocity has approximately a universal profile function different from that in the surface boundary layer. Under strong stability conditions, the dimensionless gradient function has a value of about 9.  相似文献   

12.
Atmospheric peroxides and formaldehyde were measured at two sites in Sweden; inside a Scots pine stand (Jädraås) and on top of Mt. Åreskutan (1250 msl). Peroxide levels at Jädraås were highest during the day and lowest during the night. Mid-day concentrations of H2O2 varied between 0.05 and 2 ppbv. Isentropic trajectories together with local O3 measurements indicated the importance of long range transport on surface H2O2 lévels. Large diurnal variations and vertical profiles showed the importance of turbulent mixing processes and dry deposition. A comparison of H2O2 and O3 diurnal variations indicated a more rapid dry deposition of H2O2 to the forest. It would appear that terpenes emitted from the forest play a minor role in controlling the H2O2 levels. Formaldehyde at Jädraås had a different diurnal variation than peroxides; highest levels were observed in the early evening indicating chemical production of CH2O. Diurnal variations of peroxides on Mt Åreskutan were opposite to those at Jädraås, highest concentrations were observed during the night. This result is to be expected if during the day air from inside the valley, with lower peroxide levels relative to the free troposphere, rises to the mountain top. In the evening, subsidence brings free tropospheric air with higher peroxides levels to the mountain.  相似文献   

13.
The present study focuses on spatial patterns of diurnal variability in winter precipitation across the Indian subcontinent. Hourly precipitation data during the months of January and February from 1980 to 2002 were procured for 80 stations spread across the subcontinent. The methodology consisted of calculation of the first harmonics by harmonic analysis for three variables that included frequency, total amount, and intensity of precipitation events. There were substantial variations in the strength of the diurnal cycle prevailing over the subcontinent, with most of the peninsular region and eastern part of the northern Gangetic Plain showing relatively stronger diurnal cycles. The variance explained by the first harmonic was significant at the 90% confidence level for larger parts of the peninsular region and northern plains. The weakest patterns were observed in the interior of the continent over central India. The times of maximum for hourly frequency, total amount, and intensity of precipitation were predominantly during the latter half of the 24–hour period, during late evening hours to just before sunrise hours. This was due to the enhanced warm front lifting during the late night to early morning hours as a result of nighttime inversions in the warm sector. Further, along the foothills of the Himalayas, the times of maximum were observed during predawn hours just before sunrise, caused by the downslope movement of katabatic winds and their convergence with the cyclonic storms in the low-lying areas, leading to enhanced precipitation. Along the west coast, the times of maxima were also concentrated in the midnight to early-morning hours due to the convergence of inland moving seas breeze fronts with the northeast trades.  相似文献   

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15.
Coherent structures in turbulent flow above a midlatitude deciduous forest are identified using a wavelet analysis technique. Coupling between motions above the canopy (z/h=1.5, whereh is canopy height) and within the canopy (z/h=0.6) are studied using composite velocity and temperature fields constructed from 85 hours of data. Data are classified into winter and summer cases, for both convective and stable conditions. Vertical velocity fluctuations are in phase at both observation levels. Horizontal motions associated with the structures within the canopy lead those above the canopy, and linear analysis indicates that the horizontal motions deep in the canopy should lead the vertical motions by 90°. On average, coherent structures are responsible for only about 40% of overall turbulent heat and momentum fluxes, much less than previously reported. However, our large data set reveals that this flux fraction comes from a wide distribution that includes much higher fractions in its upper extremes. The separation distanceL s between adjacent coherent structures, 6–10h, is comparable to that obtained in previous observations over short canopies and in the laboratory. Changes in separation between the summer and winter (leafless) conditions are consistent withL s being determined by a local horizontal wind shear scale.  相似文献   

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An analytical framework is proposed for studying variations in the diurnal wind structure in the planetary boundary layer (PBL) and the evolution of the low-level nocturnal jet. A time-dependent eddy-diffusivity coefficient corresponding to solar input is proposed, and an appropriate coordinate transformation ensures that mixing height varies continuously with ground heat-flux changes. The solution exhibits the receding character of the daytime PBL as evening approaches, thereby dividing the PBL into two regimes — the one just above the ground, representing the nocturnal boundary layer, and the region above it. It is assumed that inertial oscillations (IO) are triggered in the upper layer at about the time of sunset when the reversal in the direction of ground heat flux is felt in the upper layer. Two approaches are adopted to determine the characteristic features of IO and the evolution of the nocturnal low-level jet. The first one is based on the physical principle that release of horizontal momentum due to deviation from the geostrophic wind gives rise to the IO. The solution captures all the characteristic features of the IO, such as phase shift and decreasing amplitude of the IO with increasing height. According to this analysis the IO is triggered at a level as soon as the top of the receding boundary layer leaves that level. The solution is discontinuous with respect to the vertical coordinate. In the second approach we solve an initial-value problem to determine the solution in the upper layer, assuming that at about the time of sunset there is a rapid collapse of the daytime PBL to the steady, nocturnal boundary layer. The assumption is based on the mixing-height profiles prepared from climatological data collected at Delhi. The solution for the nocturnal boundary-layer regime is then obtained as a boundary-value problem. The solutions so obtained are continuous throughout the domain of interest and exhibit the characteristic features of an IO. The analysis leads to the conditions under which a low-level nocturnal jet is produced and provides quantitative estimates of the parameters, such as length of night, latitude, mixing height at sunset and nocturnal mixing height, that are conducive to the generation of a jet. The nocturnal wind profile produced by this approach compares well both with typical atmospheric data observed at Delhi and with output from a mesoscale numerical model. There is still some uncertainty related to the time of initiation of the IO as a function of latitude.  相似文献   

19.
Aimed at improving knowledge regarding the diurnal cycle of warm-season rainfall in northwestern China, this study investigated the diurnal variations of warm-season precipitation with different durations in Xinjiang Province, China, using an hourly gauge–satellite merged precipitation product during 2008 to 2019. Results show noticeable diurnal variations with distinctive regional features. The primary peak is in the early evening. Rainfall events with duration less than 3 h occur more often across the whole of Xinjiang and contribute more than half of the precipitation amount over its northern and southern peripheries, while rainfall events with duration more than 7 h over the Tianshan Mountains are responsible for the primary peak in the diurnal variations of warm-season precipitation.摘要降水日变化受大气热力,动力过程以及复杂地形影响, 演变特征复杂且区域差异显著. 本文采用中国气象局发布的中国地面与CMORPH融合逐小时降水产品 (2008–2019年), 分析了新疆省暖季降水日变化特征. 研究结果表明: (1) 新疆大部分地区降水主峰值发生在清晨; (2) 持续时间超过三小时的降水事件是新疆地区主要降水事件, 贡献了南疆和北疆一半以上的降水量; (3) 在新疆中部 (天山地区) , 暖季降水日变化峰值主要由持续时间超过7小时的降水事件贡献.  相似文献   

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