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1.
利用NCEP/NCAR再分析资料研究了季节转换期间副热带高压结构的气候特征。在亚、非季风区 ,冬季副热带高压带是相对对称的 ,具有脊线连续的带状结构 ,脊面随高度增加向南倾斜 ;夏季副热带高压带中低层是间断的 ,高层是连续的 ,脊面随高度增加向北倾斜。副热带高压脊面倾斜受热成风关系的制约 ,总是倾向暖区。 5月份副热带高压形态变异最显著 ,不同地域副热带高压的结构、性质存在较大差异。夏季型副热带高压于 5月初首先出现在孟加拉湾东部 ,5月第 3候稳定建立在孟加拉湾东部、中南半岛及南海西部地区 ;5月第 4~ 5候在南海建立 ;6月第 1~ 2候在印度中部建立。夏季型副热带高压建立的 3个阶段与亚洲夏季风爆发的 3个阶段存在着较好的对应关系。孟加拉湾夏季风的建立在很大程度上取决于高空副热带高压脊面附近经向温度梯度的反转。对流层中上层副热带高压脊面附近经向温度梯度可以作为表征亚洲夏季风爆发的指标  相似文献   

2.
利用NCEP/NCAR再分析资料从能量收支的角度探讨了气候平均状态下副热带高压形态变异和季节转换的物理机制。在考察温度场和加热场季节变化的基础上 ,发现中国江南地区春季降水所形成的非绝热加热源非常显著 ,该热源对后期亚洲季节转换有影响。副热带高压脊面附近经向温度梯度反转取决于温度脊所在纬度位置的变化。温度脊北移是由脊轴北侧的增温率大于脊轴附近的增温率而造成的。热力学方程诊断结果表明 ,亚洲各季风区 (孟加拉湾、南海和南亚 )季节转换的热力机制不同。导致孟加拉湾温度脊显著北跳的主要因素在季风爆发初期是经向暖平流 ,爆发以后是下沉运动 ;引起南海地区经向温度梯度反转的因素有经向暖平流、纬向暖平流和江南地区的非绝热加热 ,特别是经向暖平流的贡献更大 ;造成南亚季风区经向温度梯度逆转的原因是下沉增温。  相似文献   

3.
利用NCEP/NCAR再分析资料研究东亚高空温带急流的位置、强度、结构和季节转换特征及其与亚洲季风的关系,发现温带急流在300 hPa高度上最为明显,在风场分布上表现为全风速大值脊线延伸区和流线密集区,冬季主要活动于120°E以西的45°-60°N地区,在逐日风场上对应着急流发生频数的高值区域,并与副热带急流有清晰的分界.对比温带急流和副热带急流中的经向风强度发现,温带急流区的北风分量明显强于副热带急流中的南风分量,在温带急流的形成和季节变化过程中经向风分量起着重要作用.温带急流所在区域为对流层纬向温度梯度大值区,同时经向温度梯度也比较大,因而温带急流位于具有最大纬向温度梯度同时又有南北方向温度梯度这样一个特定的区域,从而形成了温带急流与副热带急流不同的结构特征和季节变化,而东亚地区海陆热力差异引起的温度梯度及其季节转换是引起温带急流季节变化的主要原因.此外,温带急流的强度与副热带急流位置之间具有协同变化关系,温带急流区经向风强度的季节转换时间与东亚大气环流的季节转换、亚洲夏季风爆发和江淮流域梅雨开始也有着密切关系,与中国东部地区冬季和夏季的降水之间具有显著的相关关系.从气候平均的角度来看,温带急流强度变化早于亚洲季风爆发和梅雨开始时间,因而对亚洲季风爆发和梅雨开始有预示作用.  相似文献   

4.
孟加拉湾季风爆发可预测性的分析和初步应用   总被引:4,自引:0,他引:4  
基于季风区对流层中高层副高脊附近的经向温度梯度能表征季节转换和季风爆发的物理本质这一事实,使用1980—1999年过渡季节期间(3~5月)逐日和月平均的NCEP/NCAR高空温度场再分析资料,对该温度梯度潜在的预报季风爆发进行了分析。结果表明:在已知初始时刻孟加拉湾季风区对流层中高层经向温度梯度的前提下,依据初始时刻的经向温度梯度和气候平均的经向增温率梯度,可以对孟加拉湾季风爆发的迟早做出定性预测。另外,由于孟加拉湾地区季风爆发日期与3月份青藏高原上空对流层中高层气温有显著相关,故前期高原上空对流层中高层的气温高低也是判断孟加拉湾季风爆发迟早的重要因子。对2000年和2001年孟加拉湾季风爆发迟早定性预测的结果表明,这两种预报方法具有潜在的应用价值。  相似文献   

5.
6月初,亚洲中高纬地区的气温迅速增暖后趋于稳定,大气环流由冬季环流转变为夏季环流。根据1951~2017年间各年亚洲中高纬地区春夏季节转换(以下简称季节转换)的时间,基于NCEP再分析资料和中国地区的观测资料,研究了季节转换发生早晚对梅雨期中国地区降水及环流的影响。在季节转换偏早(晚)年的梅雨期,对流层中层(500 hPa)高度距平场从东北亚中高纬、中国东北和日本以南地区出现“+ ? +”(“? + ?”)的经向波状结构。在850 hPa距平风场上,也有相近的波状结构。当东北亚脊偏强(弱)时,东北地区为气旋式(反气旋式)环流距平,西太平洋副热带为反气旋式(气旋式)距平。环流异常导致东北地区降水异常偏多(少),长江流域降水偏少(多)。本文还初步探讨了亚洲中高纬地区入夏时间的早晚如何影响梅雨期大气环流和中国东部降水异常的途径。在季节转换偏早(晚)年,东北亚高压脊建立较早(晚),强度偏强(弱),而且对应的东北亚脊异常往往可持续到梅雨期结束,从而有利于东亚沿岸 “+ ? +”(“? + ?”)经向波状环流及相应雨带的形成。  相似文献   

6.
青藏高原冬春积雪影响南海季风爆发的数值研究   总被引:1,自引:0,他引:1  
采用NCAR CAM3.0大气环流模式,研究了冬春季青藏高原积雪异常对南海夏季风爆发的可能影响机制.通过比较多雪年与少雪年试验中的热力场、环流场季节演变的差异得出,多雪年青藏高原感热加热偏弱、高原纬度的中上层大气温度偏低,导致大尺度经向温度梯度反转时间偏晚;同时,青藏高原感热加热偏弱将不利于Hadley环流的季节转换,使得中南半岛上空的下沉异常气流维持时间较长、副高在孟加拉湾断裂的时间偏晚、中南半岛对流爆发偏晚、中南半岛地表温度下降时间偏晚,从而造成中南半岛与南海局地纬向温度梯度反转时间也偏晚.在上述大尺度经向温度梯度以及中南半岛与南海局地纬向温度梯度的共同作用下,多雪年南海季风爆发偏晚.  相似文献   

7.
利用美国NCEP/NCAR再分析资料(1980~1999年)探讨了东亚夏季风活动的两个重要事件,即南海夏季风爆发和江淮流域梅雨起始,与东亚高空西风急流位置北跳的关系.系统的分析研究表明,东亚高空西风急流在由冬向夏的转变过程中一般存在着两次向北突跳现象,并与东亚夏季风活动有密切关系.第一次东亚高空急流的北跳(由25~28°N跳到30°N以北)平均发生在5月8日左右,比南海夏季风爆发日期(平均为5月15日)早7天左右;高空急流位置的北跳是中高纬度大气环流系统减弱北退的表现,它为热带环流和系统的向北推进提供了条件,从而有利于南海夏季风的爆发.第二次东亚高空急流的北跳(由32°N左右北跳到35°N以北)平均发生在6月7日左右,先于江淮流域梅雨起始时间(平均在6月18日左右)10天左右,它是梅雨起始的前期征兆.高空西风急流的两次北跳分别与亚洲大陆南部地区对流层中上层(500~200 hPa)经向温度梯度的两次逆转(反向)有关,在由冬到夏的季节转换中,由于大陆加热较快,导致对流层中上层大气在5~25°N间的经向温度梯度发生反向(逆转),通过地转适应使流场向气压场(温度场)调整,从而高空急流位置北跳.数据分析还发现,东亚高空急流位置的第一次北跳有时也受到南半球副热带高空急流位置北移和加强的影响.  相似文献   

8.
青藏高原冬春季积雪影响南海季风爆发的机制   总被引:4,自引:0,他引:4  
利用1958-1998年NCEP/NCAR再分析资料、1975-1998年OLR资料和1973-1998年青藏高原月平均积雪日数站点资料,分析了高原冬春季积雪影响南海季风爆发的可能机制。结果表明:多雪年,高原感热加热偏弱,高原地区以及东侧的中上层大气温度偏低,大尺度经向温度梯度逆转时间偏晚;同时高原地区Hadley环流季节转换时间偏晚,中南半岛上空维持下沉异常气流,导致孟加拉湾副高断裂偏晚,中南半岛地区对流爆发偏晚,中南半岛地表温度下降时间偏晚,中南半岛与南海局地纬向温度梯度逆转时间偏晚;上述大尺度经向温度梯度和中南半岛与南海局地纬向温度梯度的共同作用使得南海季风爆发偏晚。  相似文献   

9.
伴随南海夏季风爆发的大尺度大气环流演变   总被引:39,自引:11,他引:39  
李崇银  屈昕 《大气科学》2000,24(1):1-14
主要基于美国NCEP和NCAR的再分析资料(1980~1996年),针对南海夏季风爆发日期进行合成分析,研究了伴随南海夏季风爆发的大尺度大气环流演变。其结果清楚地表明伴随南海夏季风爆发,南亚和东南亚地区的对流层低层风场、对流层高层位势高度场以及大气湿度场和垂直运动场都有极显著的变化。南亚和东南亚850 hPa上涡旋对的发展和活动以及500 hPa副高从南海地区的东撤对南海季风爆发起着重要作用。伴随南海夏季风的爆发,在孟加拉湾到南中国海一带整层湿度和500 hPa垂直上升运动都出现了极明显的增加。对流层高层和对流层低层环流演变的特征也清楚表明,南海夏季风爆发既是全球环流冬夏演变的一个部分,又有显著的区域性特征。本文还指出南海夏季风在北部比中部和南部早建立的结论依据不足,进而补充给出了亚洲季风爆发日期示意图。  相似文献   

10.
使用1979~2005年NCEP/NCAR 再分析数据,分析了北半球平流层中低层(300 hPa至10 hPa)纬向风的季节转换规律,并采用二维空间场相似性方法确定了平流层的季节过渡日期。分析表明,平流层大气环流基本为冬夏二元状态,冬夏转换具有突变性;其季节过渡在纬向是接近同步进行的,而在经向则有时间差异,无论是冬夏转换还是夏冬转换高纬都要早于低纬。在平流层中部(10~70 hPa)季节过渡是自上而向下进行的;而在平流层下部(100~200 hPa)季节过渡的上下传递关系则比较复杂,在不同的纬度带有不同的表现。在北半球热带外地区,平流层中部东风期的起止日期与相似性方法计算得到的平流层季节过渡日期之间具有较好的对应关系,在东风期之前和之后往往各存在持续10天左右的零风—弱风期。  相似文献   

11.
Climatological characteristics of subtropical anticyclone structure during seasonal transition are investigated based on NCEP/NCAR reanalysis data.The ridge-surface of subtropical anticyclone is defined by the boundary surface between westerly to the north and easterly to the south (WEB in brief).In Afro-Asian monsoon area,the subtropical high in troposphere whose ridgelines are consecutive in wintertime takes on relatively symmetrical and zonal structure,the WEB tilts southward with increasing height.In summer,the subtropical high ridgelines are discontinuous at low levels and continuous at upper levels,the WEB tilts northward from the bottom up.Under the constraint of thermal wind relation,the WEB usually tilts toward warmer zone.May is the period when subtropical high modality most significantly varies.The structure and properties of subtropical high during seasonal transition are different from area to area.A new concept "seasonal transition axis" is proposed based on formation and variation of the vertical ridge axis of subtropical anticyclone.The subtropical high of summer pattern firstly occurs over eastern Bay of Bengal in the beginning of May.then stabilizes over eastern Bay of Bengal,Indo-China,and western South China Sea in the 3rd pentad of May,it exists over the South China Sea in the 4th-5th pentad of May and establishes over central India in the 1st-2nd pentad of June.The three consequential stages when summer modal subtropical high occurs correspond to that of Asian summer monsoon onset,respectively.To a great extent,the summer monsoon onset over the Bay of Bengal depends on the reversal of meridional temperature gradient in vicinity of the WEB in upper troposphere.The meridional temperature gradient at middle-upper levels in troposphere can be used as a good indicator for measuring the seasonal transition and Asian monsoon onset.  相似文献   

12.
The mechanisms for the variation in the configuration of subtropical anticyclone during seasonal transition are explored from energy budget using the NCEP/NCAR reanalysis data.Based on the seasonal variations of temperature and heating fields,it is found that the significant diabatic heating associated with spring precipitation over southern China has impacts on subsequent Asian seasonal transition.The reversal of meridional temperature gradient in the vicinity of the WEB (westerly-easterly boundary) in the middle and upper troposphere also depends on the latitudinal position where temperature ridge locates.The northward shift of the warm temperature ridge results from the fact that the local temperature increase to the north of the WEB is more than that in its vicinity.The diagnostic results through thermodynamic equation show that physical mechanism responsible for seasonal transition is different from area to area over the Asian monsoon region.The dominant factors responsible for northward shift of the Bay of Bengal warm ridge are the meridional temperature in initial stages of the onset and the descending motion after the onset. The factors for causing the northward jump of the South China Sea warm ridge involve the zonal temperature advection,meridional temperature advection,and diabatic heating associated with the southern China spring rainfall.The subsidence is the factor leading to the northward migration of the South Asia warm ridge.  相似文献   

13.
The features of the temperate jet stream including its location, intensity, structure, seasonal evolution and the relationship with the Asian monsoon are examined by using NCEP/NCAR reanalysis data. It is indicated that the temperate jet stream is prominent and active at 300 hPa in winter over the region from 45°-60°N and west of 120°E. The temperate jet stream is represented by a ridge area of high wind speed and dense stream lines in the monthly or seasonal mean wind field, but it .corresponds to an area frequented by a large number of jet cores in the daily wind field and exhibits a distinct boundary that separates itself with the subtropical jet. A comparison of the meridional wind component of the temperate jet stream with that of the subtropical jet shows that the northerly wind in the temperate jet stream is stronger than the southerly component of the subtropical jet, which plays an important role in the temperate jet stream formation and seasonal evolution, and thus the intensity change of the meridional wind component can be used to represent the temperate jet stream's seasonal variation. Analysis of the temperature gradient in the upper troposphere indicates that the temperate jet stream is accompanied by a maximum zonal temperature gradient and a large meridional temperature gradient, leading to a unique jet stream structure and particular seasonal evolution features, which are different from the subtropical jet. The zonal temperature gradient related to the land-sea thermal contrast along the East China coastal lines is responsible for the seasonal evolution of the temperate jet. In addition, there exists a coordinated synchronous change between the movement of the temperate jet and that of the subtropical jet. The seasonal evolution of the meridional wind intensity is closely related to the seasonal shift of the atmospheric circulation in East Asia, the onset of the Asian summer monsoon and the start of Meiyu in the Yangtze and Huaihe River Valleys, and it correlates well with summer and wint  相似文献   

14.
The NCEP/NCAR reanalysis, CMAP rainfall and Hadley Centre sea surface temperature (SST) datasets are used to investigate the relationship between the seasonal transition of East Asian monsoon and Asian-Pacific thermal contrast, together with the possible causes. Based on the 250 hPa air temperature over two selected key areas, the Asian-Pacific thermal difference (APTD) index is calculated. Results show that the APTD index is highly consistent with the Asian-Pacific Oscillation (APO) index defined by Zhao et al., in terms of different key areas in different seasons. Moreover, the time point of the seasonal transition of the Asian-Pacific thermal contrast can be well determined by the APTD index, indicative of seasonal variation in East Asian atmospheric circulation from winter to summer. The transition characteristic of the circulation can be summarized as follows. The continental cold high at lower tropospheric level moves eastward to the East China Sea and decreases rapidly in intensity, while the low-level northerlies turn to southerlies. At middle tropospheric level, the East Asia major trough is reduced and moves eastward. Furthermore, the subtropical high strengthens and appears near Philippines. The South Asia high shifts from the east of Philippines to the west of Indochina Peninsula, and the prevailing southerlies change into northerlies in upper troposphere. Meanwhile, both the westerly and easterly jets both jump to the north. The seasonal transition of atmospheric circulation is closely related to the thermal contrast, and the possible mechanism can be concluded as follows. Under the background of the APTD seasonal transition, the southerly wind appears firstly at lower troposphere, which triggers the ascending motion via changing vertical shear of meridional winds. The resultant latent heating accelerates the transition of heating pattern from winter to summer. The summer heating pattern can further promote the adjustment of circulation, which favors the formation and strengthening of the low-level southerly and upper-level northerly winds. As a result, the meridional circulation of the East Asian subtropical monsoon is established through a positive feedback between the circulation and thermal fields. Moreover, the time point of this seasonal transition has a significant positive correlation with the SST anomalies over the tropical central-eastern Pacific Ocean, providing a basis for the short-term climate prediction.  相似文献   

15.
Summary Climatological characteristics associated with summer monsoon onset over the eastern Bay of Bengal (BOB) are examined in terms of the westerly-easterly boundary surface (WEB). The vertical tilt of the WEB depends on the horizontal meridional temperature gradient (MTG) near the WEB, under the constraint of the thermal wind balance. The switch in the WEB tilt firstly occurs between 90 and 100°E during the first pentad of May. At this time the 850 hPa ridgeline splits over the BOB and heavy rainfall commences over the eastern BOB, indicating the onset of the BOB summer monsoon (BOBSM). The area-averaged MTG (200–500 hPa) is proposed as an index to define the BOBSM onset. A comparison of the onset determined by the MTG, 850 hPa zonal wind, and outgoing longwave radiation (OLR) shows that the MTG index is the most effective in characterizing the interannual variability of the BOBSM onset. Strong precursor signals are found prior to an anomalous BOBSM onset. Composite results show that early (late) BOBSM onset follows excessive (deficient) rainfall over the western Pacific and anomalous lower tropospheric cyclonic circulation which extends zonally from the northern Indian Ocean into the western Pacific, and strong (weak) equatorial westerly anomalies in the preceding winter and spring. Prior to an early (late) BOBSM onset, significant positive (negative) thickness anomalies exist around the Tibetan Plateau, accompanied by anomalous upper tropospheric anticyclonic (cyclonic) circulation. The interannual variations of the BOBSM onset are significantly correlated with anomalous sea surface temperature related to ENSO. These occurs through changes in the Walker circulation and local Hadley circulation, leading to middle and upper tropospheric temperature anomalies over the Asian sector. The strong precursor signals around the Tibetan Plateau may be partly caused by local snow cover anomalies, and an early (late) BOBSM onset is preceded by less (more) snow accumulation over the Tibetan Plateau during the preceding winter.  相似文献   

16.
华西秋雨起止与秋冬季节大气环流转换   总被引:1,自引:0,他引:1       下载免费PDF全文
袁旭  刘宣飞 《气象学报》2013,71(5):913-924
根据1961—2010年平均的逐候NCEP/NCAR再分析资料、1979—2008年平均的逐候CMAP降水资料以及1961—2010年逐候平均的中国553个台站降水资料,讨论了华西秋雨起止日期与秋冬季大气环流转换特征的关系。结果表明,华西地区降水年变化表现为明显的夏、秋双峰特征,8月4—8日(第44候)为双峰间的低谷,10月8—12日(第57候)以后降水降至年平均以下。由此,将华西秋雨建立和结束日期分别确定为8月9—13日(第45候)和10月8—12日(第57候)。华西秋雨的建立对应于东亚夏季风开始向冬季风转变,其标志性环流调整特征是江南地区的西南风转为东南风。东亚经向海平面气压梯度在8月9—13日(第45候)由南高北低转为南低北高,造成850 hPa江南地区的西南风转为东南风,该东南风与来自孟加拉湾的热带西南季风交汇于华西地区,形成风向和水汽的辐合,使得华西地区的降水在夏峰之后再次增强,华西秋雨由此建立。华西秋雨的结束则对应于孟加拉湾热带西南季风结束和东亚冬季风完全建立,其标志性环流调整特征是孟加拉湾地区的西南风转为东北风。随着东亚纬向海平面气压梯度由北向南依次发生东高西低向东低西高的转变,东亚冬季风也逐步向南推进,9月8—12日(第51候)东北冬季风到达江南地区,10月8—12日(第57候)进一步推进到南海地区,此时来自孟加拉湾的热带西南季风消失,造成华西地区完全受大陆冷高压控制,东亚季风经圈环流也转为冬季型哈得来环流,东亚冬季风完全建立,华西秋雨也随之结束。因此,华西秋雨起止可能与东亚夏季风、南亚夏季风向冬季风的转变时间不同步有关,东亚季风与南亚季风的共同作用使得华西秋雨成为亚洲夏季风在中国大陆上的最后一个雨季。  相似文献   

17.
青藏高原加热与亚洲环流季节变化和夏季风爆发   总被引:13,自引:1,他引:13       下载免费PDF全文
刘新  吴国雄  刘屹岷  刘平 《大气科学》2002,26(6):781-793
利用逐日NCEP/NCAR再分析资料分析了春夏过渡季节青减高原非绝热加热和大气环流季节变化以及亚洲季风爆发的关系.结果表明,过渡季节的早期(5月中旬以前)青藏高原总非绝热加热与感热加热的时间演变曲线趋势一致,感热加热在过渡季节早期的环流演变中有很重要的作用.青藏高原非绝热加热的时间演变与北半球环流的季节变化和亚洲夏季风爆发有很好的相关.在过渡季节里,青藏高原非绝热加热的变化引起了海-陆热力差异对比的变化,给亚洲夏季风的爆发建立了有利的背景环境,对亚洲夏季风爆发有明显的影响.结果还表明,用各区域纬向风垂直差异的时空分布能更准确地表示季节变化的区域差异.  相似文献   

18.
The NCEP/NCAR reanalysis datasets and Climate Prediction Center(CPC) Merged Analysis of Precipitation(CMAP) rain data are used to investigate the large scale seasonal transition of East Asian subtropical monsoon(EASM) and its possible mechanism.The key region of EASM is defined according to the seasonal transition feature of meridional wind.By combining the ’thermal wind’ formula and the ’thermal adaptation’ equation,a new ’thermal-wind-precipitation’ relation is deduced.The area mean wind directions and thermal advections in different seasons are analyzed and it is shown that in summer(winter) monsoon period,the averaged wind direction in the EASM region varies clockwise(anticlockwise) with altitude,and the EASM region is dominated by warm(cold) advection.The seasonal transition of the wind direction at different levels and the corresponding meridional circulation consistently indicates that the subtropical summer monsoon is established between the end of March and the beginning of April.Finally,a conceptual schematic explanation for the mechanism of seasonal transition of EASM is proposed.  相似文献   

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