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1.
By the use of space-time spectral analysis and band-pass filter, some of the features of the medium-range Oscillations in the summer tropical easterlies (10oS-20o) at 200 hPa are investigated based on a two-year (1980 and 1982) wind (u, v) data set for the period from May to September. Space-time power spectral analysis shows that the total energy of the westward moving waves was the largest and that of the standing waves and eastward moving waves was relatively small in the 200 hPa easterlies; the total energy of the eastward moving waves was at minimum at 10oN. Three kind of the medium-range oscillations with about 50 day, 25 day and quasi-biweekly periods were found in the easterlies, which all show a remarkable interannual variation and latitudinal differences in these two years. The wave energy of zonal wind is mainly associated with the planetary waves (1-3), which all may make important contributions to the 50 day and 25 day oscillations in different years or different latitudes. The quasi-biweekly oscillation is mainly related to the synoptic waves (4-6). In equatorial region, the 50 day oscillation was dominant with a eastward phase propagation in 1982 while the dominant oscillation in 1980 was of 25day period with a westward phase propagations in 1980. Both of them are of the mode of zonal wavenumber 1. Strong westward 50 day oscillation was found in 10oN-20oN in these two years. Regular propagations of the meridional wind 50 day oscillation were also found in the easterlies.The 50 day and 25 day oscillation of zonal wind all demonstrate southward phase propagation over the region of the South Asia monsoon and northward phase propagation near interational date line, where are the climatic mean position of the tropical upper-tropospheric easterly jet and the tropical upper tropospheric trough (TUTT), respectively. 相似文献
2.
江南南部初夏雨季的降水和环流气候特征 总被引：3，自引：0，他引：3
基于1961～2010年气象台站逐日降水资料、同期美国NCEP/NCAR的逐日再分析格点资料,通过气候平均、REOF分析、聚类分析等方法,分析了江南地区初夏降水的地域性和时段性特征,及西太平洋副高和高、低空急流等大气环流的相应演变过程。结果发现:（1）江南南部27.5°～29.5°N存在一个独立于华南前汛期和江淮梅雨的初夏雨季,该雨季平均发生时间为6月11～30日,比江淮梅雨早约8天左右。（2）西太平洋副高的西伸东退是江南南部初夏雨季发生发展的重要环流背景,6月第2候副高发生突变性加速西伸之后雨季开始,雨季期间850 hPa副高西伸脊点基本稳定在最西位置即133°E附近,6月第6候副高东退北抬后雨季结束。（3）低层急流大风带的形成和位置是江南南部初夏雨季阶段的重要动力条件,印度洋和孟加拉湾向东北延伸的低层急流与西太平洋副高西北侧的气流连通形成低层急流大风带,并与北侧上空的高空急流耦合,降水集中区位于低层急流大风带左侧、高空急流入口区右侧。 相似文献
3.
In this paper, the tropical air-sea interaction is discussed by using a simple air-sea coupled model, in which the inertia-gravity waves are filtered off and only the equatorial Rossby waves are reserved in both the atmosphere and the ocean. There exist two kinds of air-sea interaction waves in the coupled model, that is, the high-frequency fast waves and the low-frequency slow waves. The phase speed of the fast waves is westward and the frequencies are close to those of the equatorial Rossby waves in the atmosphere. The slow waves propagate westward in the part of short wavelengths and eastward in that of long wavelengths. There exist instabilities for both the westward and eastward propagating slow waves. If the fast waves are filtered off, there is little effect on the slow waves which have great in-fluence on the long range process in the tropical air-sea coupled system. According to the tropical air-sea interaction waves we obtain here, a possible explanation to the propagating process of ENSO events is given. 相似文献
4.
利用卫星云图及柳州Doppler雷达等资料,对2010年6月17—18日发生在桂西北局地性的一次强降雨天气过程进行分析,结果表明：（1）高原有小槽不断东移、超低空西南急流的建立为此次暴雨发生提供了有利的大尺度背景。（2）地面静止锋附近有明显的上升运动区存在,非常有利于中尺度对流的发生发展。（3）高水汽、高对流不稳定能量... 相似文献
5.
夏季东亚高空急流与太平洋-日本遥相关型的关系 总被引：1，自引：1，他引：1
利用NCEP/NCAR和NOAA月平均资料,采用奇异值分解方法分析了夏季东亚高空纬向风场和西北太平洋海表温度(SST)的耦合关系,并据此研究了东亚副热带高空急流和太平洋-日本(Pacific-Japan,PJ)遥相关型的可能联系。合成分析结果表明,东亚副热带高空急流正模态年,急流偏南偏强,对流层上层南亚高压增强东进,中层西太平洋副热带高压加强西伸,菲律宾周边海域SST升高,中纬度黑潮延伸体区SST降低,菲律宾海和热带西太平洋地区对流活动偏弱,日本海和黑潮延伸体海区对流活动增强,对应PJ遥相关型的负位相;而东亚副热带高空急流负模态年,急流偏北偏弱,对流层上层南亚高压减弱西退,中层西太平洋副热带高压减弱东撤,菲律宾周边SST降低,中纬度黑潮延伸体区SST升高,菲律宾海和热带西太平洋地区对流活动强盛,日本海和黑潮延伸体海区对流活动减弱,对应PJ遥相关型的正位相。由于夏季东亚副热带高空急流活动与PJ遥相关型存在关联,PJ遥相关型可能是东亚副热带高空急流响应太平洋海温异常的纽带。 相似文献
6.
采用动态合成分析方法,对1970-2006年登陆后北上类TC（tropicalcyclone）和西行类TC各7个样本做动态合成分析和诊断,结果表明：（1）北上类TC在背景场长波槽前北移靠近中纬度斜压锋区,通过吸附运动使TC低压并入西风槽,而西行类TC背景场没有长波槽,离中纬度斜压锋区较远;（2）北上类TC登陆时存在西南低空急流水汽输送带,当其强度减弱后,TC东南侧存在东南暖湿气流作为补充,而西行类TC减弱后逐渐与之分离,且不存在东南暖湿气流作为补充;（3）北上类TC高层辐散区与高空急流边界靠近,因此增强了其向东北方向的辐散,低层由于高层动量下传,加强了低空西风,从而使TC低压环流维持,而西行类TC离高空急流边界较远;（4）北上类TC从中纬度斜压锋区获取斜压能量,其环流垂直切变增强,相对涡度差负值增大,在高空TC中心散度由大变小后又由小变大的过程中,TC发生了变性,而西行类TC没有环境能量补给,逐渐填塞消亡。因此,当一个TC登陆后,其预报移动方向、水汽输送状况、与斜压锋区的关系以及高空辐散气流等特征,可以作为初步判定登陆TC将减弱消亡还是将变性加强的可能原因。 相似文献
7.
利用NCEP1°×1°再分析资料、常规高空及地面资料,对2010年8月12~14日川西高原北部阿坝州东南部的漩映地区出现的连续性暴雨形成机制进行了探讨。结果表明:此次过程发生在副热带高压加强西伸至青藏高原形成一个强大的高压带,此高压带断裂后,在两高之间形成长时间切变,缓慢东移触发不稳定能量的释放;700hPa上西南低空急流为暴雨区输送了源源不断的水汽;地面冷锋受副高阻塞缓慢东移;地形摩擦抬升在盆地西部不断形成气流辐合都是造成此次连续性降水的直接原因。 相似文献
8.
9.
北半球冬季非定常扰动的气候分析 总被引：1，自引：1，他引：1
本文利用Hoskins提出的E向量和曾庆存提出的波包理论对北半球冬季非定常扰动的强度及其性质进行了气候分析。结果表明，非定常扰动的强度和高空急流及大地形有密切关系。非定常扰动的形状和传播揭示出:低频扰动大多是西退的，并且在急流出口区是正压衰减的；高频扰动大多是东进的，并且在急流入口区是正压发展的。高频扰动的分布和传播反映了Rossby波的波导及地面气旋、反气旋的路径。非定常扰动的气候分析为气候和大气环流的诊断提供了有用的背景材料。 相似文献
10.
北大西洋涛动对新疆夏季降水异常的影响 总被引：19，自引：3，他引：16
利用1961~2003年NCEP/NCAR再分析和新疆75个气象站月降水资料,分析新疆夏季降水与沿西亚副热带西风急流Rossby波和北大西洋涛动（NAO）的关系,研究表明,夏季斯堪的纳维亚半岛-中欧—西亚和中亚的准静止波传播是联系NAO与沿西亚副热带西风急流波活动和新疆夏季降水变化的纽带。通过波作用量的动力学诊断分析,讨论了夏季NAO正、负位相异常年准静止波传播特征和差异,夏季NAO强弱活动影响斯堪的纳维亚半岛EP通量散度强度和位置异常,该区EP通量散度强度和位置异常导致强辐散中心在中高纬向东传播的准静止波和沿副热带西风急流准静止波活动变化,从而影响新疆夏季降水。 相似文献
11.
利用常规观测资料、区域自动站雨量资料、NCEP 1°×1°再分析资料以及国家气候中心的副高指数资料,分析2017年8月9~15日柳州北部的持续性大暴雨到特大暴雨天气过程。结果表明:这次连续降雨过程可分为副高稳定且高原小波动东移、副高西进且切变线北抬、华北槽南压且副高东退三个阶段。第一阶段,波动引导干冷空气侵入,低层暖湿空气加大,θse锋区增强,边界层辐合抬升触发暴雨,低层风速辐合为增强机制;强降水发生在锋区南侧西南气流加强过程中,落区稳定,集中在柳州北三县,局地性强,傍晚加强,白天减弱,与高原波动频率一致。第二阶段,副高加强西伸,广西整层转为西南急流,桂北处于急流轴附近,垂直运动存在高低两个中心;桂北处于高温高湿的不稳定层结中,中层受副高下沉气流影响,低层暖湿不稳定能量集聚,当近地层超低空急流加强,急流轴北推时,其左侧的气旋性切变和风速辐合抬升触发暴雨,不稳定能量释放过程中使得高低层两个垂直运动中心打通,上升运动进一步加强;其强降雨落区南界北收到三江融水交界,雨强更大,暴雨成片,无时间间歇。第三阶段,前期副高控制让桂北集聚了大量的暖湿不稳定能量,随着华北槽的东移,中高层干冷空气叠加在高温高湿的不稳定气流之上,随低层切变线南压进入广西,低层强烈的辐合抬升触发强降雨,中高层干侵入对降雨有增强作用,强降雨落区随着副高东退从桂北逐渐南压到桂南,其强度、范围和累计雨量均为最大。 相似文献
12.
Interaction of a zonal jet and small-amplitude Rossby-wave turbulence is studied within the framework of the barotropic β-plane model. It is demonstrated that turbulent-laminar interaction in this case transfers energy from the wave turbulence to the laminar flow (the effect of negative friction). We derive a conclusion that, as the geophysical turbulence is determined partly by wave turbulence and none of the traditional heuristic models can adequately describe the effect of negative friction associated with wave turbulence, the application of these models to the ‘real’ ocean and atmosphere is unreliable.It is also demonstrated that, as they are affected by the turbulence, all westward jets slowly expand without strengthening. Each jet has a core, within the limits of which the velocity of the fluid is constant. In some cases, the core expands faster than the jet periphery, resulting in jumps on the profile of the flow. All eastward jets are steady irrespective of their profiles. 相似文献
13.
2014年7月19日夜间黑龙江克山出现雨强超过90 mm的短时强降水,利用常规观测资料、区域站资料、NCEP/NCAR再分析资料等对此次冷锋前部的暖区强降水成因进行分析。结果表明:(1)此次强降水出现在580 dagpm线附近,副高诱发的超低空急流为强降水提供了充沛的水汽和不稳定能量。(2)地面辐合线和地形抬升触发对流。高空急流东移,高空急流出口区左侧和辐散区与低层辐合相耦合促使对流快速发展增强。耦合消失,强降水则快速减弱。(3)低层暖平流明显,尤其地面具有暖锋锋生特征。强降水出现在不稳定层结和上升运动快速增强的阶段。(4)地面～200 hPa辐合层形成深厚的上升运动区,促使对流快速发展。(5)中尺度对流雨带沿地面辐合线生消。降水先出现在暖湿舌前部。随后,强降水产生的冷空气抬升暖湿空气形成冷锋特征的降水,由于强降水和冷空气的正反馈作用,降水持续时间长。冷空气势力最强时,伴随中尺度气旋性环流及0～1 km强垂直风切变有利于龙卷产生。(6)开口状地形的辐合作用、抬升及局地地形导致的中尺度环流风场对暖区降水的形成和维持作用显著。 相似文献
14.
对流层上层东半球副热带西风急流与副热带(南亚)高压的关系 总被引：7，自引：4，他引：3
用NCEP/NCAR月平均再分析资料对南亚高压和对流层上层西风急流的季节变化及盛夏两类型态进行对比。结果表明,南亚高压和西风急流中心都有从冬到夏的西移北进和从夏到冬的东退南撤,急流中心位于南亚高压中心北侧。东亚夏季风盛行期间南亚高压中心的北移提前于西风急流中心的北移,二者的强度呈反相的季节变化。一般情况下,伊朗高压对应西部急流型,青藏高压对应东部急流型。典型东、西部急流年份中高纬气温及高度场的差异表明气压梯度力强弱对比是急流东西型变化的主要原因,南亚高压的位置基本上决定了急流中心的型态,但由于南亚高压具有"趋热性",而急流的移动符合热成风的规律,因而二者的热力影响机制有所不同。 相似文献
15.
This article deals with the ocean circulation driven by steady zonal winds, and damped by bottom and biharmonic friction, when represented by the simple barotropic vorticity equation. A double gyre antisymmetrical wind stress pattern in a square basin is considered. Wind forcing and dissipation parameters are chosen within the ranges of what has been used in previous studies. The flow characteristics for both steady and unsteady situations are tentatively described as functions of model external parameters through the analysis of a large set of numerical experiments. Functional relations are derived for the mid-latitude jet parameters (length, width and transport) on the basis of scaling arguments. With the diagrams established for these quantities in forcing and dissipation parameter relations allow quantitative predictions of model response to a wide range of parameter choices to be made. The transition to barotropic instability is interpreted by analysing and comparing the spin-up phase of different numerical experiments leading either to stable or unstable solutions. Two major types of destabilization are identified, namely through meandering of the mid-latitude eastward jet and Rossby wave radiation from the westward return flow. The characteristics of the flows are shown to be highly sensitive to the external parameter changes. Competition between eddy kinetic energy level and eastward jet extension appears to consttitute the key point of this class of solutions, controlling in particular the intensity of transport in the inner gyres, driven by the eddy field on the two sides of the mid-basin jet, in a very similar manner to that of the more complex multilayered EGCMs. 相似文献
16.
基于1971—2016年NCEP/NCAR的逐日、逐月再分析资料,研究冬季北半球西伯利亚风暴轴(Siberian Storm Track,SIST)、北太平洋风暴轴(Pacific Storm Track,PST)和北大西洋风暴轴(Atlantic Storm Track,AST)的协同变化特征及其与大气环流的关系。结果表明:(1)三大风暴轴不仅各自的位置与强度变化存在显著相关性,风暴轴之间也存在一定的协同变化且年代际尺度上比年际尺度上更紧密。年际尺度上,SIST与AST的经度变化呈显著负相关,而PST和AST的协同性较差;年代际尺度上,SIST与PST的经、纬度变化均呈弱的负相关,SIST与AST的经度和强度变化均呈显著正相关,PST与AST的经、纬度变化均呈显著负相关。(2)由联合EOF分析得到北半球风暴轴的协同变化时空特征:在年际尺度上,第一模态主要表现为SIST偏弱(强),PST主体偏弱(强)、东南偏强(弱),AST略偏北(南)偏强(弱)但不显著的协同变化。PC1为正位相时,对应的大气环流异常为:500 hPa高度场上为太平洋北美(Pacific North America,PNA)型和欧亚(Eurasian,EU)型的正位相,东亚急流偏强且偏南;第二模态主要表现为SIST偏强(弱)且偏东(西),PST中东部偏南(北)、西部强度偏强(弱),AST偏强(弱)的协同变化。PC2为正位相时,对应的大气环流异常为:500 hPa高度场上为PNA型和大西洋东部(East Atlantic,EA)型的正位相,北美急流减弱;在年代际尺度上,第一模态主要表现为SIST偏西(东)且偏弱(强),PST偏东(西)且偏弱(强),AST偏西(东)且偏弱(强)的协同变化。PC1为正位相时,对应的大气环流异常为:500 hPa高度场上为西大西洋(West Atlantic,WA)型和EU型的正位相。第二模态主要表现为SIST偏强(弱)且偏北(南),PST偏南(北)且偏弱(强),AST北抬(南压)的协同变化。PC2为正位相时,对应的大气环流异常为:500 hPa高度场上为EU型和WA型的正位相,东亚急流强度加强且偏南,北美急流强度减弱。 相似文献
17.
It has been hypothesized (Moore et al., 1978; O'Brien et al., 1978), that equatorial upwelling and subsequent coastal upwelling on the eastern boundary of the Atlantic Ocean are the result of eastward propagating equatorially trapped Kelvin waves in the Atlantic. Concurrent satellite and ship sea surface temperature observations taken during the GATE experiment permit validation of the satellite data as well as relating sea surface temperature (SST) variability to the local current dynamics. A method based on cross-correlations and cross-spectra of the SST field at various locations is utilized to test the Kelvin wave hypothesis. Significant periodic variation of time lags in the SST variability in the eastern Atlantic is observed by the spectral techniques. Satellite data for the 1974 summer show periodic variability which fits either eastward or westward propagating waves with 1 m s-1 phase speed, i.e., SST supports the quasi-continuous presence of Kelvin or Yanai waves. We find no evidence for a seasonally solitary eastward propagating signal in the eastern Atlantic from SST. 相似文献
18.
利用1960—2003年NCEP/NCAR再分析和新疆75个气象站月降水资料, 分析了新疆夏季降水与亚洲副热带西风急流的关系, 新疆夏季降水与西亚急流的南北位置和准静止波活动密切联系。通过波作用量的动力学诊断分析, 研究了新疆降水异常年准静止波活动特征, 新疆降水异常年斯堪的纳维亚半岛向东传播的中高纬静止波传播方式的不同, 从而影响沿副热带西亚西风急流传播的静止波活动, 进而影响新疆夏季降水, 并存在沿60°E自南极高纬低层经向上传至低纬对流层顶部, 并在北半球副热带地区转为经向下传至北半球中纬地区的波列, 该波列活动与西亚急流变化联系。 相似文献
19.
The role of spring Wyrtki jets in modulating the equatorial Indian Ocean and the regional climate is an unexplored problem. The source of interannual variability in the spring Wyrtki jets is explored in this study. The relationship between intraseasonal and interannual variability from 1958 to 2008 and its relation with Indian Summer Monsoon is further addressed. Analysis reveals that the interannual variability in spring Wyrtki jets is controlled significantly by their intraseasonal variations. These are mostly defined by a single intraseasonal event of duration 20 days or more which either strengthens or weakens the seasonal mean jet depending on its phase. The strong spring jets are driven by such intraseasonal westerly wind bursts lasting for 20-days or more, whereas the weak jets are driven by weaker intraseasonal westerlies. During the years of strong jets, the conventional westward phase propagation of Wyrtki jets is absent and instead there is an eastward phase propagation indicating the possible role of Madden Julian Oscillation (MJO) in strengthening the spring Wyrtki jets. These strong intraseasonal westerly wind bursts with eastward phase propagation during strong years are observed mainly in late spring and have implications on June precipitation over the Indian and adjoining land mass. Anomalously strong eastward jets accumulate warm water in the eastern equatorial Indian Ocean (EIO), leading to anomalous positive upper ocean heat content and supporting more local convection in the east. This induces subsidence over the Indian landmass and alters monsoon rainfall by modulating monsoon Hadley circulation. In case of weak current years such warm anomalies are absent over the eastern EIO. Variations in the jet strength are found to have strong impact on sea level anomalies, heat content, salinity and sea surface temperature over the equatorial and north Indian Ocean making it a potentially important player in the north Indian Ocean climate variability. 相似文献
20.
Longitudinal Displacement of the Subtropical High in the Western Pacific in Summer and its Influence 总被引：17，自引：0，他引：17
Using the relative vorticity averaged over a certain area, a new index for measuring the longitudinal position of the subtropical high (SH) in the western Pacific is proposed to avoid the increasing trend of heights in the previous indices based on geopotential height. The years of extreme westward and eastward extension of SH using the new index are in good agreement with those defined by height index. There exists a distinct difference in large-scale circulation between the eastward and westward extension of SH under the new definition, which includes not only the circulation in the middle latitudes but also the flow in the lower latitudes. It seems that when the SH extends far to the east (west), the summer monsoon in the South China Sea is stronger (weaker) and established earlier (later). In addition, there exists a good relationship between the longitudinal position of SH and the summer rainfall in China. A remarkable negative correlation area appears in the Changjiang River valley, indicating that when the SH extends westward (eastward), the precipitation in that region increases (decreases). A positive correlation region is found in South China, showing the decrease of rainfall when the SH extends westward. On the other hand, the rainfall is heavier when the SH retreats eastward. However, the anomalous longitudinal position of SH is not significantly related to the precipitation in North China. The calculation of correlation coefficients between the index of longitudinal position of SH and surface temperature in China shows that a large area of positive values, higher than 0.6 in the center, covers the whole of North China, even extending eastward to the Korean Peninsula and Japan Islands when using NCEP/NCAR reanalysis data to do the correlation calculation. This means that when the longitudinal position of the SH withdraws eastward in summer, the temperature over North China is higher. On the other hand, when it moves westward, the temperature there is lower. This could explain the phenomenon of the seriously high temperatures over North China during recent summers, because the longitudinal position of SH in recent summers was located far away from the Asian continent. Another region with large negative correlation coefficients is found in South China. 相似文献