INFLUENCE OF THE SURFACE AIR TEMPERATURE OVER ASIAN-PACIFIC REGION ON THE SUMMERTIME NORTHEASTERN ASIAN BLOCKING HIGH^*          下载免费PDF全文

CAO Jie  DONG Huilin  YAO Ping 《Acta Meteorologica Sinica》2004,18(4):455-466

Synthesis analysis and singular value decomposition (SVD) methods were used to study the impact of surface air temperature (SAT) over Asian-Pacific region on the summertime northeastern Asian blocking high (NABH) with NCEP/NCAR Reanalysis Data.The results showed that 500 hPa geopotential height and SAT fields over Asian-Pacific region shared the similar pattern of East Asian Pacific (EAP) wave train;there was steady remote response relationship between the EAP wave train in summer and the "+-+" pattern of tropical SAT in zonal direction from former winter to summer;there were two relative negative(positive) Walker circulations over the tropical Indian Ocean and Pacific when being more(less) summertime NABH. The influence of sea surface temperature anomaly (SSTA) on the summertime NABH was possibly as follows.The special distribution of SSTA in tropical zonal direction continuously forced the tropical convection and zonal circulation from former winter to summer,and led them to act anomaly.Finally the abnormal conditions were transported to middle-high latitudes through EAP wave train and yielded the advantageous or disadvantageous atmospheric circulation background for the summertime NABH.  相似文献   

Spectra of poorly resolved ocean data     

Hans?van HarenEmail author 《Ocean Dynamics》2004,54(1):49-53

Standard temperature and pressure sensors on Aanderaa RCM8 current meters have a resolution of 0.024 °C and 0.6 bar, each equal to 1 digital number (value) over a range of 1024. It is shown that an 11-month deep-ocean temperature record using only four values can contain useful spectral information on internal wave motions. This is partially due to the modulation of high-frequency data by non-zero low-frequency (subinertial) variations. This result follows from the comparison of this record with artificial three- and four-value data constructed from temperature records observed in stronger stratified waters nearby. These artificial records show main features of the internal wave band similar to those observed in the original data spectra. Peaks at tidal harmonic frequencies and enhancements at sum-tidal-inertial interaction frequencies are preserved in the artificial data, but overall noise level (and thus the continuum spectral slope) is enhanced with respect to the properly resolved records (using 15 and 100 values). As a demonstration of the stable accuracy of the temperature sensors, the poorly resolved records provided an estimate of mean stratification to within 5% of the estimate using Seabird CTD data.Responsible Editor: Hans Burchard  相似文献   

Probing the history of the Mathematician paleoplate using surface waves     

Yu J. Gu   《Tectonophysics》2006,424(1-2):41-51

This paper investigates the shear velocity structure under the northern East Pacific Rise at the latitude range of 9–18°N, using intermediate-period Rayleigh and Love waves. The selected ocean-bottom seismic records provide source–receiver paths that ideally constrain the lithospheric mantle structure beneath the southern Rivera plate and the Mathematician paleoplate. The Rayleigh wave data infer a relatively thin ( 30 km) lithosphere under the eastern side of the present-day East Pacific Rise. The associated shear velocities are consistent with existing models of oceanic mantle beneath this region, and the estimated plate age of 2–3 million years agrees with results from magnetic dating. The west of the rise axis is characterized by a thicker and faster lithosphere than the eastern flank, and such structural differences suggest the presence of a relatively old Mathematician paleoplate. The discontinuous change in mantle structure across the East Pacific Rise spreading center are observed in both isotropic and anisotropic velocities. The young oceanic lithosphere east of the rise axis shows strong polarization anisotropy, where the dominant orientation of crystallographic axes roughly parallels the spreading direction. However, the western flank of the rise axis is approximately isotropic, and the lack of anisotropy suggests complex deformation mechanisms associated with earlier episodes of ridge segmentation, propagation and dual-spreading on and around the Mathematician paleoplate.  相似文献   

Observations and modelling of the travel time delay and leading negative phase of the 16 September 2015 Illapel,Chile tsunami     

Peitao Wang  Zhiyuan Ren  Lining Sun  Jingming Hou  Zongchen Wang  Ye Yuan  Fujiang Yu 《海洋学报(英文版)》2021,40(11):11-30

The systematic discrepancies in both tsunami arrival time and leading negative phase (LNP) were identified for the recent transoceanic tsunami on 16 September 2015 in Illapel, Chile by examining the wave characteristics from the tsunami records at 21 Deep-ocean Assessment and Reporting of Tsunami (DART) sites and 29 coastal tide gauge stations. The results revealed systematic travel time delay of as much as 22 min (approximately 1.7％ of the total travel time) relative to the simulated long waves from the 2015 Chilean tsunami. The delay discrepancy was found to increase with travel time. It was difficult to identify the LNP from the near-shore observation system due to the strong background noise, but the initial negative phase feature became more obvious as the tsunami propagated away from the source area in the deep ocean. We determined that the LNP for the Chilean tsunami had an average duration of 33 min, which was close to the dominant period of the tsunami source. Most of the amplitude ratios to the first elevation phase were approximately 40％, with the largest equivalent to the first positive phase amplitude. We performed numerical analyses by applying the corrected long wave model, which accounted for the effects of seawater density stratification due to compressibility, self-attraction and loading (SAL) of the earth, and wave dispersion compared with observed tsunami waveforms. We attempted to accurately calculate the arrival time and LNP, and to understand how much of a role the physical mechanism played in the discrepancies for the moderate transoceanic tsunami event. The mainly focus of the study is to quantitatively evaluate the contribution of each secondary physical effect to the systematic discrepancies using the corrected shallow water model. Taking all of these effects into consideration, our results demonstrated good agreement between the observed and simulated waveforms. We can conclude that the corrected shallow water model can reduce the tsunami propagation speed and reproduce the LNP, which is observed for tsunamis that have propagated over long distances frequently. The travel time delay between the observed and corrected simulated waveforms is reduced to <8 min and the amplitude discrepancy between them was also markedly diminished. The incorporated effects amounted to approximately 78％ of the travel time delay correction, with seawater density stratification, SAL, and Boussinesq dispersion contributing approximately 39％, 21％, and 18％, respectively. The simulated results showed that the elastic loading and Boussinesq dispersion not only affected travel time but also changed the simulated waveforms for this event. In contrast, the seawater stratification only reduced the tsunami speed, whereas the earth's elasticity loading was responsible for LNP due to the depression of the seafloor surrounding additional tsunami loading at far-field stations. This study revealed that the traditional shallow water model has inherent defects in estimating tsunami arrival, and the leading negative phase of a tsunami is a typical recognizable feature of a moderately strong transoceanic tsunami. These results also support previous theory and can help to explain the observed discrepancies.  相似文献   

Acoustic experimental study of two types of rock from the Tibetan Plateau under the condition of freeze-thaw cycles     

Hua Liu  FuJun Niu  ZhiYing Xu  ZhanJu Lin  Jian Xu 《寒旱区科学》2012,4(1):0021-0027

Under the condition of freeze-thaw cycles, two types of rocks (granite and andesite), used as slope protection for the Qinghai-Tibet Railway, were tested according to the special climatic conditions in the Tibetan Plateau, and their various damage processes in appearance were carefully observed. Observation results show that damage of andesite was more serious than that of granite. Using an acoustic instrument, ultrasonic velocity was tested. The changing trends of velocity with the number of freeze-thaw cycles were analyzed, and the freeze-thaw cycle damaging the physical and mechanical properties of rocks can be seen. According to the changing trends of ultrasonic velocity with the number of freeze-thaw cycles, mechanical parameters of rocks, such as dynamic elasticity modulus, Poisson’s ratio, and dynamic bulk modulus were analyzed. It is found that they all have declining trends as the number of freeze-thaw cycles increases, and in particular, when the cycle number reaches a certain extent, the Poisson’s ratio of rocks begins to become negative.  相似文献   

2009年“莫拉克”台风登陆过程阵风特征分析   总被引：3，自引：2，他引：1  

李永平  郑运霞  方平治 《气象学报》2012,70(6):1188-1199

利用上海台风研究所移动观测车获取的“莫拉克”台风登陆过程中超声风、温等观测资料对地面阵风特性进行了诊断分析.结果表明,在风速时间序列中叠加有周期为3-7 min的阵风扰动,显现出明显的相干结构,即沿顺风方向阵风风速峰期有下沉运动,谷期有上升运动;阵风扰动的各向异性特征明显,沿顺风方向的阵风扰动能量最大,其次是沿侧向和垂直方向的扰动能量;沿顺风方向的阵风垂直动量通量向下传播,而沿侧风方向阵风扰动动量垂直通量总体贡献接近于0.阵风扰动沿顺风方向的积分空间尺度和时间尺度最大,沿侧风方向和垂直方向其次,均明显大于湍流的积分空间和时间尺度.此外,阵风扰动的其他特征还包括:感热垂直通量极小;当平均风速较大时阵风风向变化幅度较小,而风速较小时阵风风向变化幅度则较大;动力学分析表明,阵风扰动主要表现出重力内波的一些特性.  相似文献   

台风中涡旋波1波扰动的形成机制及其变化特征     

陶建军  胡向辉  李朝奎 《气象学报》2012,70(6):1200-1206

通常将台风中的螺旋云带看成是一种称为涡旋罗斯贝波的波动,双臂对应的切向波数为2,单臂对应的切向波数为1,目前这种波动发生发展的物理机制仍不很清楚,值得进一步研究.利用柱坐标下的正压流体涡度方程,研究了台风中涡旋罗斯贝波1波扰动的正压不稳定性及发展变化问题.结果表明,当基本流径向涡度梯度小于0时,由于涡度扰动的速度场对于基本涡度场的平流效应,1波(m=1)扰动可从基本流吸取能量而出现不稳定快速增长.但由于扰动旋臂的缠卷作用,径向速度将很快变小,因此,不稳定增长将受到一定的时间限制;波动的发展速度与半径有关,中心附近的波动先发展且向外传播,距中心较远的波动稍后发展.整体上看,波动由中心向外扩展,大尺度台风的螺旋云带比小尺度台风的螺旋云带发展更快.  相似文献   

我国北方500hPa春、夏季平均长波年际异常的EOF分析     

魏红  韦志刚  刘慧  李振朝  王超 《高原气象》2012,31(1):102-112

利用1958—2008年全球逐日2.5°×2.5°NCEP/NCAR再分析资料,采用经验正交函数分解(EOF)和谐波分析方法对我国北方地区春、夏季平均长波进行了分析。结果表明:(1)我国北方春季平均长波主要表现为亚洲北部从咸海到日本存在一个完整的长波:巴尔喀什湖到我国罗布泊地区以长波脊活动为主,我国东北地区以长波槽活动为主,长波槽、脊的强度均呈增强趋势;夏季平均长波主要表现为乌拉尔山、贝加尔湖及鄂霍次克海地区的长波脊、槽、脊分布,蒙古国到我国北部地区多为长波槽活动,近51年来长波槽存在减弱趋势。(2)春季平均长波的距平变化主要表现为我国西北、华北地区与其上游和下游邻近地区存在反相关关系;夏季平均长波距平变化和春季相比有所东移,即我国北方大部分地区距平变化与其上游和下游地区存在反相关关系。  相似文献   

太行山东麓焚风天气的统计特征和机理分析Ⅱ:背风波对焚风产生和传播影响的个例分析   总被引：1，自引：0，他引：1  

王宗敏  丁一汇  张迎新  范军红  张守保  田利庆 《高原气象》2012,31(2):555-561

利用中尺度模式WRF3.3对太行山东麓焚风典型个例进行了数值模拟。结果表明,太行山东麓焚风的发生和移动与山脉背风波密切相关。由此建立了太行山东麓焚风的概念模型:西北或偏西气流途经山西盆地、山西境内的山脉或高原,再越过太行山,在其东麓形成背风波。背风波的下沉气流气温按干绝热方式上升,同时下沉气流也会对低层大气产生压缩增温效应,使得太行山东麓产生焚风。背风波即为重力波,可以伴随着下沉气流向下游移动,正变温区同时也向东移动。变温区移动的速度和重力波的传播速度相同。背风波的产生,需要Scorer数向上足够的减小,而且不连续,即要求大气是稳定的且存在明显的风速切变。  相似文献   

一种对资源不稳定性敏感的EASY-backfill算法   总被引：2，自引：2，他引：0  

王征宇  肖南峰 《南京气象学院学报》2012,4(2):163-169

利用合成技术对1995—2006年冬季（11月—次年2月）生成在西北太平洋上的34个热带气旋（tropicalcyclone,TC）个例进行分析,研究冬季西北太平洋TC生成的大尺度环流特征及其生成机制,结果表明：冬季TC生成的大尺度环流特征型为东风波西传型;北半球冬季对流层低层出现的跨赤道气旋对是冬季北半球TC形成的重要特征;太平洋中部赤道混合Rossby重力波西北传,与强对流中心重合,性质转为＂热带低压型扰动＂,为冬季热带气旋生成提供扰动源。对合成TC初始场的涡动扰动动能的收支分析表明,涡动有效位能和正压不稳定转换为TC形成提供了能量,这两种能量分别与积云对流加热和水平不均匀气流有关。正压不稳定能量转换为动能主要位于对流层中下层,而扰动有效位能的转换主要位于对流层中上层。低层热带东风波动从平均气流中获得正压不稳定能量,并与强积云对流耦合,热力和动力共同作用下形成TC。  相似文献