Anomalous Western Pacific Subtropical High during Late Summer in Weak La Nia Years: Contrast between 1981 and 2013     

Feng Xue  Fangxing Fan 《大气科学进展》2016,33(12):1351-1360

Both 1981 and 2013 were weak La Niña years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the western Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak.  相似文献   

京津冀地区中α尺度飑线过程中大风特征分析及成因初探     

吴紫煜  姚雯  李超 《气象与环境科学》2016,39(2):90-98

应用常规天气观测资料、地面加密自动气象站资料、大风灾情报资料、京津冀地区7部多普勒天气雷达组网观测资料及VDRAS资料,从多个角度对2013年8月4日京津冀地区一次飑线过程产生的大范围大风天气过程进行了分析,结果显示:此次过程是在高空冷空气南下、低层暖湿气流北上、系统前倾及位势不稳定的有利层结条件下,由多单体风暴演变为中α尺度的强飑线所致。飑线形成于低层垂直切变加强、冷池合并之后;大风主要发生在飑线主体回波中,其次是主体回波前和中前,主体回波后很少发生。大风发生的位置取决于飑线结构中气流的性质,气流的性质与冷池前进的程度和对流的强度关系密切。大风大部分由下沉冷气流产生,少数为近地面上升暖气流导致。大风发生的范围和强度与低层风垂直切变的强度呈正比,大范围低层风垂直切变的加强增强了飑线入流和出流的强度,是大范围大风、局部强风形成的重要原因。大风发生站次与冷池的强度和范围密切相关,冷池的加强和范围的扩大加强了后侧冷入流和前侧暖入流的强度和范围,也是大范围大风形成的重要因素。  相似文献   

Effects of initial step height on the headcut erosion of bank gullies: a case study using a 3D photo-reconstruction method in the dry-hot valley region of southwest China   总被引：1，自引：0，他引：1  

Baojun Zhang  Zhengan Su  Dan Yang  Yifan Dong  Liang Xiao 《自然地理学》2016,37(6):409-429

Abstract

Headcut erosion has been recognized as one of the main processes involved in gully development in the dry-hot valley region of southwest China. To examine the effect of initial step height on headcut erosion processes, three headcuts were constructed ranging in height from 0.75 to 1.25 m on an active bank gully head, and a series of scouring experiments were conducted under a flow discharge of 120 L min^?1. The morphological evolutions of the plunge pools and soil loss volume were estimated by three-dimensional photo-reconstruction methods (3D-PR). As the step height increased, the experimental results showed that: (1) the transformed potential energy and shear stress would increase by approximately 4.89 J s^?1 and 26.4 Pa on average when the step height increased 0.25 m; (2) the mean depth and width of the plunge pool exhibited obvious growth, and the morphology of the cross-section developed from approximately V-shaped to U-shaped; and (3) soil loss volume increased logarithmically, with total soil loss volumes of 0.076, 0.105 and 0.116 m³, respectively. Although the significant effects of the initial step height on headcut erosion were verified, further quantitative studies are required to quantify the mechanism of headcut erosion, especially for plunge pool erosion.  相似文献   

西太平洋暖池海温和山西盛夏降水关系研究     

张冬峰  王永光  张国宏 《气象与环境学报》2019,35(3):60-67

利用1961—2016年山西盛夏(7—8月)平均降水和同期NOAA重构海温资料,分析了山西盛夏降水分别与赤道中东太平洋海温和西太平洋暖池海温相关性的变化。结果表明:山西盛夏降水和赤道中东太平洋海温之间呈现稳定的显著负相关;和西太平洋暖池海温呈现正相关,并在20世纪70年代末到80年代初之后相关性加强,通过了0.05显著性检验。进一步分析表明,这种西太平洋暖池海温对20世纪80年代以来山西盛夏降水指示意义加强的事实,主要体现在赤道中东太平洋海温偏冷的背景下。西太平洋暖池海温异常通过影响与山西盛夏降水密切相关的大气环流、季风槽位置和东亚夏季风,导致山西盛夏降水异常。盛夏赤道中东太平洋海温偏冷时,西太平洋暖池海温偏暖(冷),通过遥相关引起中高纬度大气欧亚—太平洋型遥相关(EUP)和负太平洋—日本(PJ)波列,通过影响季风槽位置偏西偏北(偏东偏南),引起西太平洋副热带高压偏北(南)和季风指数偏小(大),导致山西盛夏降水偏多(少)。  相似文献   

一次强飑线过程极端大风的中尺度分析     

沈杭锋  方桃妮  蓝俊倩  翟国庆  苏涛 《气象学报》2019,77(5):806-822

利用常规气象观测资料、区域自动气象站加密观测资料和GFS 0.25°×0.25°逐6 h的分析场数据以及多普勒雷达、风廓线等资料,通过背景形势场分析、物理量诊断分析和中尺度分析,对2018年3月4日发生在华东地区的强飑线天气过程进行了诊断分析。结果表明,这次过程具有发生时间(季节)早、移速快、范围广、致灾强等特点,是一次比较少见的早春(冬末)十分强烈的飑线天气过程,是在高空急流辐散区、低空西南急流轴前端、低涡南侧的暖区中发展起来的。飑线过程的地面要素变化十分剧烈,地面有强冷池,与飑线前暖空气之间构成了强的水平温度梯度,致使飑线强度更强;飑线经过时气压涌升所形成的雷暴高压、强气压梯度以及飑线的快速移动均有利于地面极端大风的出现。飑线发展过程中观测到弓形回波、超级单体等强天气系统。中高层动量下传和光滑湖面、喇叭口、狭管效应等特殊地形对于大风的增强效应比较显著,这些因素也加剧了地面极端大风的形成。   相似文献   

热带西太平洋海温距平与Rossby波传播对1993和1994年东亚夏季风异常影响的差异   总被引：12，自引：4，他引：8  

吕俊梅  琚建华  张庆云  陶诗言 《大气科学》2006,30(5):977-987

利用NCEP/NCAR再分析资料、Hadley中心海温资料与降水资料,分析了1993和1994年东亚夏季风异常的天气气候特征以及大气环流的差异.分析结果表明: 1993年东亚夏季风弱,副热带西风急流和副热带高压位置偏南,来自于孟加拉湾和南海的水汽仅输送到35°N以南地区.东亚地区出现低温凉夏天气.1994年东亚夏季风强,副热带西风急流和副热带高压位置偏北,7～8月副高持续偏强并控制日本,水汽可以输送到45°N以北的较高纬度,东亚发生破纪录的热浪干旱.对1993和1994年东亚夏季风异常物理过程差异的研究发现,副热带西风急流中静止Rossby波的传播和热带西太平洋暖池海温距平激发出来的PJ型遥相关波列作用的叠加引起1994和1993年东亚夏季风异常差异.  相似文献   

Molecular phylogenetic analysis of sulfate-reducing bacteria from deep sediment layers of the tropical West Pacific warm pool     

LUO Zhuhu  YE Dezan  HUANG Xiangling 《海洋学报(英文版)》2006,25(3):98-107

1IntroductionThe tropical West Pacific warm pool(TWP-WP),which spans an area roughly between10°Nto10°S of the equator from Indonesia to the dateline,has the world’s warmest sea surface temperature ofbeing greater than29℃.With the increase of recog-niz…  相似文献   

太平洋东边界波浪输运   总被引：4，自引：0，他引：4  

邓增安  吴克俭  于婷 《海洋学报》2007,29(6):1-9

通过计算2000年涌浪指标(swell index)的全球分布,发现太平洋东边界赤道附近区域存在涌浪池.利用ECMWF再分析波浪资料,计算出2000年全球月平均波浪体积输运.比较2000年全球月平均波浪体积输运和2000年QUICKSCAT月平均风场,发现在赤道太平洋东边界涌浪池区域内的波浪输运方向和风向存在很大的差别,两者方向相差大约90°.这进一步验证了该地区涌浪池存在的真实性.研究发现,赤道太平洋东边界涌浪主要来源于北太平洋和南太平洋的西风带对应的海区.在涌浪池区域内分别在2.5°S和2.5°N取两条边界(边界起点为125°W,终点为美洲大陆西边界),计算通过这两条边界进入赤道区域涌浪的Stokes体积净输运量.结果表明,不同月份通过南、北两条边界波浪的净输运量与当月南、北太平洋西风带的风浪强度密切相关.同时指出了,涌浪的体积输运将会对大洋环流系统产生潜在的重要影响.  相似文献   

Effects of wind waves of the Pacific westerly on the eastern Pacific wave transport   总被引：1，自引：1，他引：0  

DENG Zeng''an  WU Kejian  ZHAO Dongliang  YU Ting 《海洋学报(英文版)》2009,28(1):83-88

There exists a tongueshaped swelldominance pool known as Swell Pool (SP) in the Eastern Pacific region. The monthlymean wave transports (WT) for each month of 2000 is computed using the wave products of ECMWF reanalysis data. By comparing the 2000 monthlymean WT and monthlymean wind field from QUICKSCAT, large differences are found between the wave transport direction and the wind direction over the Eastern Pacific. This may serve as an evidence for the existence of the SP in this region. The work done in this study indicates that the sources of swell in the Tropical Eastern Pacific (TEP) are in the westerly regions of the Southern and Northern Pacific.  相似文献   

Distinct activity phases during the recent geologic history of a Gulf of Mexico mud volcano     

I.R. MacDonald  M.B. Peccini 《Marine and Petroleum Geology》2009

Laser line scan imaging and chirp sub-bottom profiling were used to detail the morphology of a submarine mud volcano and brine-filled crater at 652 m water depth in the northern Gulf of Mexico. The mud volcano has a relief of 6 m and a basal diameter of about 80 m. The feature comprises a central, brine-filled crater (253 m²) surrounded by a continuous bed of methanotrophic mussels (Bathymodiolus childressi) covering 434 m² and a patchy bed covering an additional 214 m² of the periphery. The brine pool was mostly <2 m deep, but there were two holes of >28 m and 12 m deep, respectively at the northern end of the pool which emitted continual streams of small clear bubbles. Sub-bottom profiles indicated three distinct strata beneath the present surface of the mud volcano. Integration of 17 profiles shows that the mud volcano has been built in at least three successive stages: the lowest stage deposited 35,400 m³, while the middle and upper stages deposited 7700 and 20,400 m³, respectively. Piston cores were taken at the northern edge of the mussel bed and a site ∼100 m southwest of the pool. Mussel and lucinid shells were recovered from the closer core, lucinid shells from the distant core. A mussel shell from 3.4 m sub-bottom had a Δ¹⁴C age of 16.2 ka. Mixture of modern carbon with “carbon dead” reservoir material would produce actual ages ∼2 ka less than the radiocarbon ages.  相似文献