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1.
利用河南119站的降水观测资料以及NCEP/NCAR各层高度场、风场和垂直速度场的再分析资料,研究2011年9月在河南发生的一次持续的区域性连阴雨过程。对降水进行的墨西哥帽小波分析发现,降水存在着低频特征。通过对造成低频降水的高度场和风场资料滤波计算,分析了造成降水的低频环流特征,结果表明：2011年9月河南秋季持续性降水低频振荡最主要的周期是32 d左右;低频降水的周期分为4个位相,降水从低频谷值和峰值之间的过渡位相开始,在峰值位相达到最大。低频环流场的配置在低频降水的谷值位相和峰值位相有着显著的差异,环流场的高低层配置从不利于对流发展转为有利于对流发展;同时低层水汽输送在过渡位相开始逐渐加强。降水的发生在850 hPa上主要是与低频正涡度的分布相一致,低频正涡度有着明显的波列变化及北跳;500 hPa、200 hPa上的低频负涡度变化和降水变化相一致。降水的峰值(谷值)位相散度场的高低空配置主要为低层辐合(辐散)、中高层辐散(辐合),有利于(不利于)对流的发展。 相似文献
2.
利用1985—2015年6—8月登陆中国东南部(福建和浙江)的35个西北行热带气旋(TC)和站点观测的日降水量,根据区域TC过程降水量,分为强降水、适量降水和弱降水TC,分析影响各级TC降水的环境场异常特征及其季节内振荡(ISO)的调制作用。(1)对流层低层850 hPa表现为中心位于福建东部强的气旋异常,来自孟加拉湾和南海强水汽输送在中国东南部产生强的水汽辐合促使TC强降水的发生,其中10~20天和30~60天ISO的环流和水汽输送都有贡献,但东南部的水汽辐合主要受10~20天ISO的影响;与TC强降水相比,TC弱降水对应的异常气旋和水汽辐合明显减弱。(2)影响TC强降水的10~20天ISO环流异常在TC登陆过程,自菲律宾群岛附近向西北方向传播至中国东南部,30~60天ISO环流异常自南海向东北偏北方向传播至台湾西南部,且环流异常强度不断加强。(3)影响TC弱降水的10~20天ISO环流异常自菲律宾西部向北传播,30~60天ISO环流异常自南海南部向东北方向传播。 相似文献
3.
为了研究青藏高原夏季降水的低频振荡特征,利用1978-2017年高原地区62个气象站日降水资料和ERA5高分辨率逐日再分析资料,采用集合经验模态分解（EEMD）、 Lanczos滤波以及合成分析方法,对青藏高原夏季旱涝年降水的低频振荡特征、气象要素场变化及环流特征进行了深入分析,揭示了高原地区旱涝年降水低频振荡周期特征、环流特征以及低频风场、涡度场等传播特点。结果表明：（1）高原夏季降水存在10～20天的振荡周期;旱涝年的周期频率不同,涝年振荡频率明显高于旱年;涝年显著的振荡为10～20天和30天以上的振荡,而旱年主要以10～20天的振荡为主。（2）涝年在低频降水强位相,高空低频气旋控制高原主体,高空辐散,低空辐合,来自孟加拉湾偏南风的水汽供应充足,低频扰动强,利于降水发生,自西向东存在低频反气旋-低频气旋-低频反气旋的异常环流分布;反之在低频降水弱位相,高空低频反气旋控制高原主体,高空辐合,低空辐散,暖湿的偏南气流较弱,低频扰动偏弱,不利于降水发生。旱年配置有相似的特征,但低频反气旋-低频气旋-低频反气旋的环流形势不明显,整体上振荡强度较涝年偏弱,低频要素场强度也偏弱。（3）低频波动... 相似文献
4.
利用上海台风所组织整编的《台风年鉴》(1949—2005年)、NCEP逐日再分析资料和中国逐日降水资料,分析南海-西太平洋热带气旋形成个数多年(以下简称多年)、形成个数少年(以下简称少年)对广东30～60天振荡降水的影响。考虑到其周期振荡的非规则性,相应降水9个位相(即第1、3、5、7和9位相分别对应降水的最低值、正转折点(由负转为正)、最高值、负转折点(由正转负)和最低值)分别对850 hPa、200 hPa风场和850 hPa的动能、涡度、水汽通量输送以及Hadley环流和Walker环流场进行合成分析。结果表明,在多年,具有较大动能的阿拉伯海-孟加拉湾地区环流东移与南海-西太平洋的西北-东南走向的异常气旋-反气旋对西移的交汇,通过在北半球上升、南半球下沉的异常闭合经圈环流和水汽输送,把西边和南边海洋暖湿气流源源不断输送到广东,使其30～60天振荡降水增加;而在少年,广东地区30～60天振荡降水与阿拉伯海-孟加拉湾地区环流联系不强,主要受南海-西太平洋的东北-西南走向的异常气旋反气旋对的影响,通过北半球低纬增强的异常上升支的局地作用和水汽输送,把南边海洋暖湿气流源源不断输送到广东,使其30～60天振荡降水增加。由于109～119°E,10～20°N区域异常的动能、西风、东风切变、垂直速度和水汽输送均比少年强,从而使得广东30～60天振荡降水在多年比少年强。 相似文献
5.
亚洲季风建立及其中期振荡的高空环流特征 总被引：14，自引：1，他引：13
本文主要通过对100毫巴散度场、高度场和垂直积分的水汽输送场的分析,着重讨论了1979年整个亚洲季风区季风建立及其振荡中的高空环流特征。发现南亚高压周围不同部位的高空辐散场的建立导致了这些地区夏季风的建立,且南亚高压脊线中部和东部散度场具有不同的分布特点。从而使得印度季风有与长江流域梅雨同时开始而与华南雨季降水反位相的特点.在东亚,南亚高压外围东风对于夏季风的向北推进具有很好的指示性。在印度,伊朗高压(南亚高压环流的一部分)外围的东北气流对于印度季风的爆发具有指示性。100毫巴若干地区高度场和亚洲季风区域大范围水汽输送场的40—50天振荡清楚地显示出向东向北移动,而20—30天的散度场的振荡在印度季风爆发后则有系统地向西移动. 相似文献
6.
东移西南低涡空间结构的气候学特征 总被引：4，自引：1，他引：3
对1991～2004年夏季（6～8月）西南四川盆地的低涡活动进行统计分类,比较分析了移出型和停滞型两类西南低涡生成初期的合成环流场,总结出影响低涡东移的三维环流结构的气候学特征：东亚中纬度地区对流层中高层的冷空气入侵造成中高层气温偏低,位势高度降低,伴随冷偏差中心南侧20°N～30°N由对流层顶至850 hPa都出现偏强西风,最大的西风偏差位于长江下游地区上空200 hPa。一方面,高层风速差异的纬向梯度加强了长江中游地区的高空辐散,在西南低涡东部形成有利于降水和气旋性环流发展的动力抬升机制。另一方面,对流层低层的西风偏差在青藏高原南麓至我国东部长江以南形成一条异常的水汽输送带,加强了低涡南侧的偏西风水汽输送作用,为低涡东部的降水潜热反馈作用提供了充足的水汽。西南低涡在这样有利的环流形势和水汽条件下更容易移出盆地。 相似文献
7.
本文讨论分析了１９９４年盛夏东亚季风区垂直积分的平均水汽通量及水汽通量散度场，揭示出该时期东亚季风区存在四个强水汽泊；西太平洋、东涨、苏禄海、安达曼海和三个水汽汇：华北、长江中游南岸、南海南部。山西位于华北汇区中，盛夏降水的水汽是由安达曼海和莎经取西南气流，东南气流输送而来。 相似文献
8.
《高原气象》2016,(6)
热带大气季节内振荡(MJO)对中国的降水具有明显的调节作用,研究MJO对华西秋雨的影响对于提高华西秋雨的季节内预测能力具有重要的意义。利用1979 2012年9 10月澳大利亚气象局提供的实时多变量MJO指数、中国台站逐日降水资料以及NCEP再分析资料,通过异常合成分析的方法研究了MJO对华西秋雨的影响以及相应环流背景场的变化。研究表明,在MJO对流主体自西向东传播的过程中,华西地区的秋季降水量呈先增加后减少的趋势。当MJO对流主体位于印度洋中西部(1~2位相)时,华西秋雨偏多,当MJO对流主体位于印度洋东部至太平洋中西部(3~8位相)时,华西秋雨偏少。其中MJO对流主体位于中东印度洋(第2位相)和西太平洋(第7位相)时,华西地区秋季有降水最大正异常和最大负异常。与此同时,对应分析MJO不同位相上的高空形势场和中低空流场、水汽输送、垂直运动的异常变化发现:第1、2位相时,我国上空出现两槽一脊、西低东高的环流形势,此时华西地区冷空气活动频繁,且孟加拉湾、南海和西太平洋对华西地区的水汽输送较强,有利于干冷与暖湿气流在华西地区交汇,水汽辐合、上升运动亦显著,从而造成降水偏多;第7位相时,我国上空受较强的西风带长波脊控制,并且三个海区对华西地区的水汽输送较弱,水汽辐散、下沉运动亦较强,造成降水偏少。 相似文献
9.
对2004年夏季安徽省降水以及850 hPa涡度、水汽通量散度场进行Morlet小波分析，结果发现:6月中下旬，三者都存在着2~6 d，7~15 d以及18~30 d的振荡周期，并且三者的各频带的低频分量与实际降水距平的对应关系较好。其中18~30 d低频涡旋系统和水汽通量散度具有源自孟加拉湾和中南半岛自西南向安徽省传播特征；7~15 d低频涡旋系统主要是沿着中纬度地区自西向东传入安徽省，低频水汽通量散度则由低纬度地区自南向北传入安徽省。6月中下旬赤道西太平洋地区沿东南-西北向移动的7~15 d低频气旋和反气旋波列，以及安徽省附近低层流场的2~6 d高频变化，为其6月中下旬的三次强降水过程提供了有利条件。 相似文献
10.
基于台站降水观测数据和MERRA-2再分析资料,分析了2014年夏季我国长江流域降水的季节内振荡特征,并从位涡角度重点研究了与之相关的环流演变。结果表明:2014年夏季长江流域降水季节内变率以10~20d的准双周振荡为主。在降水准双周振荡的极端湿位相,受对流层高层随中纬度波列东传的正异常位涡和南亚高压东侧西南向传播的正异常位涡的共同影响,南亚高压呈“马鞍型”分布,在长江流域形成高空辐散环流;在对流层中低层,当中纬度波列的异常气旋向东南传播至长江流域以北时,西太平洋异常反气旋延伸至中国东南沿海,二者共同导致长江流域低空水汽辐合加强;在高、低层环流的共同作用下,长江流域持续性降水显著偏多,形成准双周振荡的极端湿位相;同时,长江以北高空位涡正异常导致其下方冷空气下沉,触发长江流域异常上升运动和南海地区异常下沉运动,该经向垂直环流圈的形成有利于长江流域正异常降水的维持。反之则形成极端干相位。 相似文献
11.
利用1951—2004年我国740站逐日降水资料对夏季长江中下游典型旱涝年季节内振荡周期、强度和位相等特征进行合成对比分析发现:长江中下游涝年降水季节内振荡周期较旱年长, 涝年以30~60 d周期为主, 而旱年以10~30 d周期为主。旱涝年长江中下游地区夏季降水的10~30 d振荡整体上均强于30~60 d振荡; 10~30 d及30~60 d振荡, 涝年的强度都大于旱年。季节内振荡在旱年的北传较涝年强, 能达到50°N附近; 而涝年不仅有明显的季节内振荡从低纬度地区向北传播, 同时还有弱的振荡从中高纬度地区向南传播, 两者汇合于长江流域形成强的振荡中心。影响我国低频降水的低频异常环流分布模态在旱涝年是一致的, 但涝年的低频环流强于旱年, 而这种低频环流场的差异正是造成涝年的低频降水强于旱年的原因之一。 相似文献
12.
Effects of intraseasonal oscillation on the anomalous East Asian summer monsoon during 1999 总被引：2，自引：0，他引：2
The 1999 East Asian summer monsoon was very unusual for its weak northward advance and remarkably anomalous climate conditions. The monsoonal southwesterly airflow and related rain belt in East Asia were blocked south of the Yangtze River Valley. The monsoonal airflow and major moisture transport conduct shifted eastward and turned northward to Japan from the tropical western Pacific rather than to East China from the South China Sea （SCS） as in normal years. Severe and prolonged drought occurred over extensive areas of North China and heavy precipitation in South China and Japan. The investigation on the possible intrinsic mechanisms related to such an anomalous monsoon year has shown that the unique behavior of intraseasonal oscillation may play an essential role during this process. During this year, the northward propagation of 30-60-day anomalous low-level cyclone/anticyclone collapsed in the region around 20°N and did not extend beyond the latitudes of the Yangtze River basin due to the barrier of strong cold air intrusion from the mid-latitudes. The southwesterly moisture flux on the northwestern flank of the anticyclonic moisture transport system in the western North Pacific, which was regulated by the northward shift of 30-60-day cyclonic/anticyclonic moisture transport, also did not reach the region north of 30°N as well. Under this circumstance, the weak northward advance of the monsoon westerlies and associated northward moisture transport could not arrive in North China and led to the severe droughts there in 1999. The SCS and South China were mostly affected by the airflow in the southern and northern flanks of the same 30-60-day cyclones or anticyclones, respectively, and thus controlled by the nearly reverse zonal wind and moisture convergent/divergent conditions. The rainfall in the SCS and South China showed out-of-phase oscillation through the transient local Hadley circulation, with the rainfall maximum occurring in the SCS （South China） when the 30-60-day anticyclone （cyclone） r 相似文献
13.
东亚夏季风的季节内振荡研究 总被引：44，自引：10，他引：34
利用动力学因子和热力学因子结合的方法,将东亚夏季风区的西南风与OLR进行了综合处理,构造成东亚季风指数(IM).研究结果表明,该指数既可很好地反映东亚季风区的风场、高度场的环流特征,又能较好地描述我国长江中下游地区夏季降水和气温的变化.通过功率谱和带通滤波结合的方法研究东亚夏季风中的季节内振荡,东亚夏季风区内低频振荡在夏季主要是以30～60天周期的振荡为主;东亚夏季风的季节内振荡在东亚沿海呈波列的形式,并表现为随时间向北传播的季风涌;由于该季节内振荡的波动,造成了东亚热带夏季风在东亚热带和副热带地区活动的反位相关系. 相似文献
14.
利用中国逐日降水格点资料和NCAR/NCEP再分析资料,对1998年发生在我国东部长江中下游流域的夏季持续性强降水过程中显著的大气季节内振荡(ISO)的三维结构演变等活动特征进行了分析。1998年夏季长江及江南地区的异常强降水对应着该地区强的ISO活动。利用位相合成方法,对长江流域两个典型的季节内循环周期的ISO降水、850 hPa水平风场以及水汽和垂直速度等循环过程的时空分布特征进行了诊断分析。在低频环流场上,对流层低层的低频气旋和反气旋环流表现出交替在热带西北太平洋增强并向西偏北方向移动发展的特征,当异常气旋环流移动到长江流域上空时,长江流域正好位于气旋环流西南侧的东北风异常和西北太平洋上向西移动的反气旋环流西北侧的西南风异常环流汇合处的下方,引起该地区强降水的发生。在强降水阶段的ISO的垂直结构上,上升运动和水汽表现出从华南到长江流域自南向北移动的特征,强烈的垂直上升运动以及来自南方充足的水汽为增强长江流域地区的降水起到了重要作用。 相似文献
15.
利用NCEP/NCAR逐日再分析资料及长江中下游降水资料, 诊断和分析了长江中下游地区旱年1978年、涝年1999年青藏高原东部大气热源与降水季节内振荡的关系, 并着重讨论了青藏高原低频热力过程的经、纬向传播, 结果表明:1978年夏季青藏高原东部大气热源存在10~20 d周期为主的振荡, 交叉谱分析表明:青藏高原东部热源与长江中下游降水在10~20 d频段存在显著相关, 且青藏高原激发的周期为10~20 d的低频振荡热源在纬向上呈现出驻波形式; 1999年夏季青藏高原东部热源存在30~60 d周期为主的振荡, 热源与长江中下游降水在30~60 d频段存在显著相关。 相似文献
16.
The East Asia-western North Pacific boreal summer intraseasonal oscillation simulated in GAMIL 1.1.1 总被引：1，自引：0，他引：1
We evaluate the performance of GAMIL1.1.1 in a 27-year forced simulation of the summer
intraseasonal oscillation (ISO) over East Asia (EA)-western North Pacific (WNP). The assessment
is based on two measures: climatological ISO (CISO) and transient ISO (TISO). CISO is the ISO
component that is phase-locked to the annual cycle and describes seasonal march. TISO is the
ISO component that varies year by year.
The model reasonably captures many observed features of the ISO, including the stepwise northward
advance of the rain belt of CISO, the dominant periodicities of TISO in both the South China
Sea-Philippine Sea (SCS-PS) and the Yangtze River Basin (YRB), the northward propagation of 30--50-day
TISO and the westward propagation of the 12--25-day TISO mode over the SCS-PS, and the zonal propagating
features of three major TISO modes over the YRB. However, the model has notable deficiencies. These
include the early onset of the South China Sea monsoon associated with CISO, too fast northward
propagation of CISO from 20oN to 40oN and the absence of the CISO signal south of 10oN,
the deficient eastward propagation of the 30--50-day TISO mode and the absence of a southward propagation
in the YRB TISO modes.
The authors found that the deficiencies in the ISO simulation are closely related to the model's biases in
the mean states, suggesting that the improvement of the model mean state is crucial for realistic
simulation of the intraseasonal variation. 相似文献
17.
The spatio-temporal variability in summer rainfall within eastern China is identified based on empirical orthogonal function
(EOF) analysis of daily rain-gauge precipitation data for the period 1979–2003. Spatial coherence of rainfall is found in
the Yangtze Basin, and a wavelet transform is applied to the corresponding principal component to capture the intraseasonal
oscillation (ISO) of Yangtze rainfall. The ensemble mean wavelet spectrum, representing statistically significant intraseasonal
variability, shows a predominant oscillation in summer Yangtze rainfall with a period of 20–50 days; a 10–20-day oscillation
is pronounced during June and July. This finding suggests that the 20–50-day oscillation is a major agent in regulating summer
Yangtze rainfall. Composite analyses reveal that the 20–50-day oscillation of summer Yangtze rainfall arises in response to
intraseasonal variations in the western North Pacific subtropical high (WNPSH), which in turn is modulated by a Rossby wave-like
coupled circulation–convection system that propagates northward and northwestward from the equatorial western Pacific. When
an anomalous cyclone associated with this Rossby wave-like system reaches the South China Sea (SCS) and Philippine Sea, the
WNPSH retreats northeastward due to a reduction in local pressure. Under these conditions, strong monsoonal southwesterlies
blow mainly toward the SCS–Philippine Sea, while dry conditions form in the Yangtze Basin, with a pronounced divergent flow
pattern. In contrast, the movement of an anomalous anticyclone over the SCS–Philippine Sea results in the southwestward extension
of the WNPSH; consequently, the tropical monsoonal southwesterlies veer to the northeast over the SCS and then converge toward
the Yangtze Basin, producing wet conditions. Therefore, the 20–50-day oscillation of Yangtze rainfall is also manifest as
a seesaw pattern in convective anomalies between the Yangtze Basin and the SCS–Philippine Sea. A considerable zonal shift
in the WNPSH is associated with extreme dry (wet) episodes in the Yangtze Basin, with an abrupt eastward (westward) shift
in the WNPSH generally leading the extreme negative (positive) Yangtze rainfall anomaly by a 3/8-period of the 20–50-day oscillation.
This finding may have implications for improving extended-range weather forecasting in the Yangtze Basin. 相似文献
18.
19.
This study investigates the relationship between summer low-frequency rainfall over southern China and tropical intraseasonal oscillation (ISO) in the atmosphere by examining systematically the propagation features of the tropical ISO in terms of focusing on five large-scale low-frequency rainfall regimes in summer over southern China. It is demonstrated that there is a close linkage between the five rainfall regimes over southern China and the northward propagation of the tropical ISO. The moist ISO signals, which influence the low-frequency rainfall events in different regions of southern China, mainly propagate northwestward from the tropical ocean to the southeast of China. The southeast China rainfall regime is intimately associated with the moist ISO signals propagating northwestward from the equatorial mid-western Pacific Ocean. For both the Yangtze River regime and South of Yangtze River regime, the moist ISO signals over the northern South China Sea show an evident northward propagation towards the Yangtze River region, and then propagate westward. It is further found that the interaction between the northward propagation of low-latitude ISO signals and the southward propagation of high-latitude ISO signals can also make a clear influence on the low-frequency rainfall in southern China. For the Southern China regime, the moist ISO signals show a significant northward propagation from the Philippines. Moreover, for the rainless regime, southern China is under dry ISO signals’ control, and the latter shows no clear propagation to southern China. This study may provide insights for the extended-range forecasting of summer rainfall in southern China. 相似文献
20.
Relationship Between the Eastern Tibetan Plateau Rainfall and Subtropical High Shift in Summer 
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下载免费PDF全文 Based on the routine rainfall data on the Tibetan Plateau and NCEP/NCAR reanalysis data,the rela- tionship between the eastern Tibetan Plateau rainfall and the southward/northward shift of West Pacific subtropical high in summer of 1993/1994 is studied.The results show that:the West Pacific subtropi- cal high is abnormally located to more southern latitude and the high ridge is mainly the quasi-biweekly southward/northward oscillation in its processes of northward shift from May to August in 1993;but it is ab- normally located to more northern latitude and the high ridge is obviously 30-60-day southward/northward oscillation in its processes of northward shift from May to August in 1994.At the same time,it is found that the changes of the eastern Tibetan Plateau rainfall active/break have the similar characteristics of the high ridge southward/northward oscillation.Therefore,the southward/northward shift of the West Pacific subtropical high in summer may be related to the changes of eastern Tibetan Plateau rainfall active/break. 相似文献