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1.
南海夏季风爆发前后扰动演变及其数值研究 总被引：2，自引：0，他引：2
以球面正压涡度方程为数学模型,建立了线性和非线性的数值积分模式,通过在模式中设置不同的基本流场和初始扰动场,研究基流和初始场对扰动发展的作用,揭示在球面正压大气中扰动发展的动力学机制。数值试验结果表明:在线性模式中,扰动的移动和发展与基流的分布有着很密切的关系,基流影响着扰动纬向传播的速度和方向; 在非线性模式中,当基流稳定时,扰动的移动以及传播与线性模式的结果相同,但与线性情况的最大区别在于,此时扰动能量的增长存在上限。同时发现,扰动的发展既依赖于基本气流的分布,也依赖初始扰动的结构;南海夏季风爆发前后的基本流场是正压不稳定的,且这种不稳定在季风爆发时达到最强,这可以成为季风爆发的动力学解释。 相似文献
2.
利用高分辨率的区域气候模式 (RegCM_NCC) 对南海夏季风爆发进行模拟研究。研究表明:该模式对积云对流参数化方案的选择十分敏感, 其中以Kuo积云参数化方案为最好, 可以比较成功地模拟出南海夏季风的爆发时间、爆发前后高、低层风场的剧烈变化以及季风与季风雨带的向北推进。然而该方案对于雨量和副热带高压位置的模拟, 与观测相比尚存在一定的偏差, 主要表现为副热带高压位置模拟偏北、偏东; 南海地区的降水量模拟偏少、降水范围偏小。此外, 采用4种参数化方案 (Kuo, Grell, MFS, Betts-Miller) 集成的结果在某种程度上要优于单个方案的结果, 这种改善主要体现在对南海地区季风爆发后降水的模拟上。 相似文献
3.
使用1998年南海季风试验期问高质量资料和NCEP／NCAR40年再分析资料分析了南海季风建立前后的大尺度环流特征和要素的突变及爆发过程。发现南亚高压迅速从菲律宾以东移到中南半岛北部，孟加拉湾槽加深加强，赤道印度洋西风加强并向东向北迅速扩展和传播，以及伴随的中低纬相互作用和西太平洋副高连续东撤是南海夏季风建立的大尺度特征。与此同时，亚洲低纬地区的南北温差和纬向风切变也发生相应的突变。数值试验结果表明，印度半岛地形的陆面加热作用在其东侧激发的气旋性环流对于孟加拉湾槽的加强有重要作用，并进而有利于南海夏季风先于印度夏季风爆发。 相似文献
4.
By use of the concept of wave packet and WKB method,the all-round characteristics of the Rossby wavepacket under the background of the basic current and the topography are obtained,and the equation andcondition for the development of the wave packet are gained as well.Applying the condition obtained tothe background basic current of southwest and southeast jet,we propose the concept on the wave packetsplitting and the wave passage branching,i.e.according to the disposition of the wave packet with respect tothe jet and the condition satisfied by the stationary wave packet,its trough(ridge)line must be deformed,bent,splitted and bifurcated,the wave passage hence bifurcates accordingly.Under the SW jet,one bifur-cated wave packet propagates toward high latitudes and penetrates upward into the stratosphere,and theother propagates toward low latitudes,but it propagates a far less distance than the former,and only reachesthe tropopause in the vertical.By means of the feature of the wave passage bifurcation of the Rossby wavepacket in the SW jet,the PNA and EU patterns of teleconnections suggested by Wallace and Gutzler(1981)are investigated. 相似文献
5.
Emmanouil Flaounas Serge Janicot Sophie Bastin Rémy Roca Elsa Mohino 《Climate Dynamics》2012,38(5-6):965-983
In spring the inland penetration of the West African Monsoon (WAM) is weak and the associated rainband is located over the Guinean coast. Then within a few days deep convection weakens considerably and the rainband reappears about 20?days after over the Sahel, where it remains until late September signalling the summer rainy season. Over the period 1989–2008 a teleconnection induced by the Indian monsoon onset is shown to have a significant impact on the WAM onset, by performing composite analyses on both observational data sets and atmospheric general circulation model simulations ensembles where the model is nudged to observations over the Indian monsoon sector. The initiation of convective activity over the Indian subcontinent north of 15°N at the time of the Indian monsoon onset results in a westward propagating Rossby wave establishing over North Africa 7–15?days after. A back-trajectory analysis shows that during this period, dry air originating from the westerly subtropical jet entrance is driven to subside and move southward over West Africa inhibiting convection there. At the same time the low-level pressure field over West Africa reinforces the moisture transport inland. After the passage of the wave, the dry air intrusions weaken drastically. Hence 20?days after the Indian monsoon onset, convection is released over the Sahel where thermodynamic conditions are more favourable. This scenario is very similar in the observations and in the nudged simulations, meaning that the Indian monsoon onset is instrumental in the WAM onset and its predictability at intraseasonal scale. 相似文献
6.
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7.
1990s年代际转型前后南海季风系统的气候季节内振荡(CISO)特征 总被引：1，自引：0，他引：1
利用多变量经验正交分解(MV-EOF)等方法,研究了在季节内振荡尺度上南海季风系统的时空分布特征。结果表明:南海夏季风的爆发时间在1993/1994年前后存在显著的年代际转型,由爆发偏晚转变成爆发偏早。第一模态反映了南海夏季风爆发时季风系统的时空特征,转型前后特征类似,降水场自赤道向北依次呈现干-湿-干交替分布的特征,南海中心为异常气旋。相应的大范围环流场主要反映了转型前的偏晚年,南海夏季风槽位置偏南,转型后的偏早年,南海夏季风槽位置偏北。第二模态体现了南海季风系统夏季的时空特征,转型前后共同特征表现为南海地区夏季北湿南干的南北偶极子降水分布及南海中心区的异常西风。相应的大范围环流场主要反映了南海季风活动与东亚季风呈现反位相的特点,且对流信号向北传播。转型前的偏晚年,季风活动受准双周振荡控制,对流信号由西北方向传入南海;转型后的偏早年,季风活动以30～60天振荡为主,对流信号由东南方向传播至南海。 相似文献
8.
Global gridded daily mean data from the NCEP/NCAR Reanalysis(1948-2012) are used to obtain the onset date,retreat date and duration time series of the South China Sea summer monsoon(SCSSM) for the past 65 years.The summer monsoon onset(retreat) date is defined as the time when the mean zonal wind at 850 hPa shifts steadily from easterly(westerly) to westerly(easterly) and the pseudo-equivalent potential temperature at the same level remains steady at greater than 335 K(less than 335 K) in the South China Sea area[110-120°E(10-20°N)].The clockwise vortex of the equatorial Indian Ocean region,together with the cross-equatorial flow and the subtropical high,plays a decisive role in the burst of the SCSSM.The onset date of the SCSSM is closely related to its intensity.With late(early) onset of the summer monsoon,its intensity is relatively strong(weak),and the zonal wind undergoes an early(late) abrupt change in the upper troposphere.Climate warming significantly affects the onset and retreat dates of the SCSSM and its intensity.With climate warming,the number of early-onset(-retreat) years of the SCSSM is clearly greater(less),and the SCSSM is clearly weakened. 相似文献
9.
Observations of the South China Sea summer monsoon （SCSSM） demonstrate the different features between the early and late onsets of the monsoon. The determining factor related to the onset and the resultant monsoon rainfall might be the off-equatorial ITCZ besides the land-sea thermal contrast. The northward-propagating cumulus convection over the northern Indian Ocean could enhance the monsoon trough so that the effect of the horizontal advection of moisture and heat is substantially increased, thus westerlies can eventually penetrate and prevail over the South China Sea （SCS） region. 相似文献
10.
利用NCEP/NCAR再分析资料, 分析了2003年6—7月亚洲中高纬地区阻塞形势对淮河暴雨的作用。结果表明:亚洲北部阻塞高压的建立和维持, 使得500 hPa高度上西风锋区南压, 引导冷空气南下, 造成中纬度地区冷暖空气和能量交换频繁。尤其在2003年6月20日后, 阻塞高压活动加强, 淮河流域北部维持为大气能量锋区, 低层850 hPa副热带锋区也长期停滞在35°N附近。阻塞高压的异常活动通过对大气动量和热量的一次次向南频散, 造成淮河流域连续发生暴雨天气过程。阻塞高压的强度及位置变化与前部低涡的活动密切相关, 并通过西风带基本气流及长波系统的螺旋结构的变化, 激发Rossby波的经向传播来影响副热带高压的南北进退, 从而决定了雨带的位置。 相似文献
11.
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
12.
早期的理论分析认为大气中临界纬度的存在使得热带-热带外的大气活动互不影响。然而,大量的观测事实表明中低纬度大气运动存在着明显的动力联系。为了帮助人们更好地理解大气中的遥相关现象,在大量文献的基础上,综述了几种波能量传播理论:(1) 大圆理论指出了罗斯贝波在球形大气中的传播特征;(2) 西风通道理论发现了中纬度瞬变扰动越赤道传播的“走廊”;(3) 能量堆积-波列发射理论揭示了热带扰动影响到更高纬度大气活动的可能过程;(4) 赤道波侧向膨胀理论则利用转折纬度的概念更进一步解释了这种中低纬度大气相互作用的物理机制;(5) 经向基本流理论则认为在一定的条件下定常波可以穿过热带东风带传播到另一半球。此外,文中还回顾了在波-流相互作用诊断方面的研究进展,尤其是关于罗斯贝波、惯性重力波和赤道开尔文波。大气能量的经向传播具有显著的年变化和年际变化,这与ENSO、西风急流、大洋中部槽等的变化密切相关。 相似文献
13.
Role of the subtropical westerly jet waveguide in a southern China heavy rainstorm in December 2013 总被引：3，自引：0，他引：3
An extreme rainstorm hit southern China during 13–17 December 2013, with a record-breaking daily rainfall rate, large spatial extent, and unusually long persistence. We examined what induced this heavy rainfall process, based on observed rainfall data and NCEP–NCAR reanalysis data through composite and diagnostic methods. The results showed that a Rossby waveguide within the subtropical westerly jet caused the event. The Rossby wave originated from strong cold air intrusion into the subtropical westerly jet over the eastern Mediterranean. With the enhancement and northward shift of the Middle East westerly jet, the Rossby wave propagated slowly eastward and deepened the India–Burma trough, which transported a large amount of moisture from the Bay of Bengal and South China Sea to southern China. Strong divergence in the upper troposphere, caused by the enhancement of the East Asian westerly jet, also favored the heavy rainfall process over Southeast China. In addition, the Rossby wave was associated with a negative-to-positive phase shift and enhancement of the North Atlantic Oscillation, but convergence in the eastern Mediterranean played the key role in the eastward propagation of the Rossby wave within the subtropical westerly jet. 相似文献
14.
利用1948—2005年的10月—次年5月NCEP/NCAR再分析资料对西风急流中Rossby波的传播及其与冬半年副热带南支西风槽形成的关系进行研究, 结果表明:冬半年亚洲副热带西风急流下方存在3个南支波动, 分别位于阿拉伯海、孟加拉湾和我国华南地区, 其中孟加拉湾南支槽变率最小, 是半永久性低压槽; 从北非、阿拉伯海到孟加拉湾的“-+-”遥相关波列表明南支槽与北非槽呈正相关, 与阿拉伯海槽呈反相关。在西风波动从北非东传到孟加拉湾的过程中, 往往会在阿拉伯海有所停顿, 这种由西向东的传播过程约20 d一次, 具有明显的低频振荡特征; 源自北非的定常Rossby波能量沿着急流波导传播到孟加拉湾, 可能是南支槽明显增幅的一个主要机制; 另外, 从青藏高原东西两侧南下的冷空气活动也是南支槽加深发展的一个重要因素。 相似文献
15.
Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes. However, considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes. To better understand such atmospheric teleconnection, several theories of wave energy propagation are reviewed in this paper: (1) great circle theory, which reveals the characteristics of Rossby waves propagating in the spherical atmosphere; (2) westerly duct theory, which suggests a “corridor” through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere; (3) energy accumulation-wave emanation theory, which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes; (4) equatorial wave expansion theory, which further explains the physical mechanisms involved in the interaction between the tropics and extratropics; and (5) meridional basic flow theory, which argues that stationary waves can propagate across the tropical easterlies under certain conditions. In addition, the progress made in diagnosing wave-flow interaction, particularly for Rossby waves, inertial-gravity waves, and Kelvin waves, is also reviewed. The meridional propagation of atmospheric energy exhibits significant annual and interannual variations, closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs, amongst others. 相似文献
16.
Multi-scale contributions are involved in the South China Sea (SCS) summer monsoon (SCSSM) onset process. The relative roles of intraseasonal oscillation and above-seasonal component in the year-to-year variation of the SCSSM onset are evaluated in this study. The 30-90-day and above-90-day components are major contributors to the year-to-year variation of the SCSSM onset, and the former contributes greater portion, while the 8-30-day component has little contribution to the onset. In the early onset cases, the 30-90-day westerly winds move and extend eastward from the tropical Indian Ocean (TIO) to the SCS monsoon region relatively earlier, and replace the easterly winds over the SCS with the cooperation of the 30-90-day cyclone moving southward from northern East Asia. The westerly anomalies of the above-90-day component in spring jointly contribute to the early SCSSM onset. In the late onset cases, the late eastward expansion of 30-90-day westerly wind over the TIO, accompanied by the late occurrence and weakening of the 30-90-day anticyclone over the SCS, and its late withdraw from the SCS, as well as the persistent easterly anomalies of above-90-day component, suppress the SCSSM onset. However, the SCSSM outbreaks in the obvious weakening stage of 30-90-day easterly anomalies. The easterlies-to-westerlies transition of the 30-90-day 850- hPa zonal wind over the SCS in spring is closely associated with sea surface temperature in the tropical western Pacific in preceding winter and spring, while the interannual variation of the above-90-day zonal wind in April-May is closely related to the decaying stage of the El Ni?o-Southern Oscillation events. 相似文献
17.
In this study, the improved high-resolution regional climate model of the China National Climate Center （RegCM_NCC） is used to examine the sensitivity of the simulated circulation and rainfall during the South China Sea summer monsoon （SCSSM） period during 1998 in an effort to compare to other cumulus param- eterization schemes. The investigation has indicated that the model is capable of simulating the seasonal march of the SCSSM and that the results were very sensitive to the choice of cumulus parameterization schemes. It seems that the Kuo cumulus parameterization scheme simulates the process of the SCSSM onset reasonably well, which can reproduce the onset timing and dramatic changes before and after the onset, especially the upper- and lower-level wind-fields. However, there are still some discrepancies between the simulations and observations. For example, the model can not completely simulate the intensity of the rainfall or the location of the western Pacific subtropical high as well as the feature of the rapid northward propagation of seasonal rain belt. 相似文献
18.
东亚副热带西风急流位置变化与亚洲夏季风爆发的关系 总被引：1，自引：0，他引：1
利用1961～2000年的NCEP/NCAR候平均再分析资料,初步探讨了季节转换期间东亚副热带西风急流南北和东西向位置变化与亚洲季风爆发之间的联系。结果表明,亚洲夏季风爆发伴随着东亚副热带西风急流轴线的北跳和急流中心西移,急流轴北跳至35°N以北的青藏高原上空,南支西风急流消失,亚洲季风环流形势建立。南海季风爆发早年,低纬的东风向北推进的时间早,到达的纬度偏北,中纬的西风急流强度偏弱,季风爆发晚年则相反。同时,南海夏季风爆发早年,青藏高原上空急流核出现较早,西太平洋上空急流核减弱较快,急流中心“西移”较早。而在南海夏季风爆发晚年,西太平洋上空的急流核减弱较迟,青藏高原上空急流核形成偏晚,急流中心“西移”较迟。此外,急流中心东西向位置和强度变化与江淮流域梅雨的开始和结束也有密切关系。 相似文献
19.
盛夏两类东亚高空西风急流北跳的动力过程 总被引：6，自引：2，他引：4
在气候态上,7月底东亚高空西风急流中心突然从40°N北跳到45°N以北.逐年统计分析显示此次急流北跳存在两类典型方式:急流北侧西风强度增强引起的北跳(第一类)和急流中心西风强度的减弱引起的北跳(第二类).本文基于1958年到2002年的NCEP/NCAR再分析资料,采用波活动通量诊断这两类典型北跳相应的动力过程,进一步... 相似文献
20.
A study on the variability of atmospheric and oceanic processes over the Arabian Sea during contrasting monsoons 总被引：1，自引：0，他引：1
J. S. Chowdary C. Gnanaseelan S. K. Sinha B. Thompson 《Meteorology and Atmospheric Physics》2006,94(1-4):65-85
Summary The atmospheric and oceanic conditions associated with the southwest monsoon during the contrasting monsoon years of 2002
and 2003 over the Arabian Sea have been analyzed in the present study. Early onset of southwesterlies and reduced net heat
gain due to low solar radiation were responsible for low sea-surface temperatures (SSTs) over the Arabian Sea during 2002
pre-monsoon (particularly in May). Conversely, light winds and an increased net heat gain set up the pre-monsoon warming in
2003. The development and intensification of deep convection over a large area of the Arabian Sea prior to the onset of the
monsoon was observed during 2003, but was absent in 2002. Weak cross equatorial flow and a weak low level jet over the Arabian
Sea reduced moisture transport towards the Indian subcontinent in July 2002. This scenario helped to contribute to a prolonged
break in monsoon conditions during July. However, no such break in conditions occurred during July 2003. In 2002, the summer
monsoon cooling of the Arabian Sea occurred well before July, whereas in 2003 cooling occurred during July. Estimates of wind
driven Ekman (horizontal) and vertical transports showed maximum values in the month of June (July) in 2002 (2003). These
estimates clearly show the importance of horizontal and vertical advection in the summer cooling of the Arabian Sea.
During the southwest monsoon period, the Arabian Sea was warmer in 2003 than in 2002. Late onset of the southwesterlies in
June, late cooling of the Arabian Sea in July, and downwelling Rossby wave propagation were responsible for the warm SSTs
in 2003. Weak wind stress curl in July dampened the westward propagating sea surface height anomaly signals (Rossby waves)
before they reached the western Arabian Sea in 2002, whereas, in 2003 strong wind stress curl enhanced Rossby wave propagation.
During the summer monsoon period, subsurface temperatures in the south central Arabian Sea were warmer in 2003 than in 2002,
particularly in July and August. Strong Ekman convergence, solar penetration, and downwelling (downward velocities) are responsible
for the enhanced subsurface warming in 2003. 相似文献