气候平均状况下亚洲夏季风的季节内演变过程

根据1979—1995年美国NOAA的向外长波辐射逐日资料,用功率谱分析和带通滤波方法,对气候平均状况下亚洲夏季风的季节内演变过程进行分析,归纳得到亚洲季风区各个子系统季节内变化的8个关键阶段。利用1979—1999年NCEP/NCAR的大气环流再分析资料及中国气象局降水资料CMAP,对每个关键阶段亚洲夏季风的环流和降水的时空演变特征进行分析,得到亚洲季风区环流和降水季节内变化的物理图像。研究表明,在不同的季节内演变阶段,亚洲夏季风各个子系统成员的环流系统的变化特征可以将亚洲夏季风系统的季节内演变过程较好地描述出来。     

南亚地区黑碳气溶胶对亚洲夏季风的影响

利用NCAR的全球大气模式CAM3,模拟了南亚地区黑碳气溶胶对亚洲夏季风的影响.结果表明:晚春时期,南亚地区黑碳气溶胶强烈吸收太阳辐射,加热低层大气,造成孟加拉湾及沿岸地区雨季的提前,可能导致南亚夏季风提前爆发.夏季,被加热的大气沿青藏高原南坡爬升,在高空形成一个稳定的加热层.高空的持续加热,引起局地的深对流活动,使得印度洋和南亚大陆之间产生一个北升南降的经圈环流,导致印度洋洋面上的向北运动加强,从而使南亚夏季风的强度增大.但是,南亚地区黑碳气溶胶通过影响表面气压、垂直运动、降水和850 hPa风场等减弱了东亚夏季风,且导致西太平洋副热带高压北移西伸,使我国梅雨带位置向东北方向移动.     

亚洲夏季风爆发的基本气候特征分析

利用统一的亚洲热带夏季风爆发指标,重新制作了季风爆发日期的推进图,确证了亚洲热带夏季风最早在热带东印度洋与中印半岛中南部爆发的观点,这发生在26候(5月10日前后),28候(5月20日前后)在南海地区相继爆发,这两个地区的爆发是属同一季风系的不同爆发阶段.以后通过对海陆热力对比、季节内振荡等多方面的分析,对夏季风的爆发机制问题进行了深入的研究,提出了气候学意义下影响亚洲热带夏季风爆发的关键影响因子.在此基础上,给出了夏季风最早在热带东印度洋-中印半岛-南海地区爆发机理的一种概念模式图,即大气环流的季节进程是季风爆发的背景条件;而中印半岛及其邻近地区对流活动和感热与潜热加热的迅速增强与北推、印缅槽的强烈加深,以及高原东部地区的西风暖平流作用是夏季风爆发的主要驱动力,其结果是使经向温度梯度首先在这个地区反向并建立强的上升运动区,使热带季风和降水迅速发展和加强;来自不同源地的低频30-60 d和10-20 d季节内振荡的锁相则是夏季风爆发的一种触发因子,正是这些因子的共同作用导致了亚洲热带夏季风在这个地区的最早爆发.     

热带太平洋印度洋海温异常对亚洲夏季风影响的数值研究

利用L9R15气候谱模式，就热带太平洋－印度洋夏季海温异常对亚洲夏季风的影响进行了数值研究。结果表明，夏季热带太平洋和印度洋海温正异常时，不仅能造成热带地区大气环流和降水的同时性响应，还能导致东亚夏季风和南亚夏季风的一致减弱，两者的影响是同号的，但并不是两者单独影响的线性叠加，由此给出了亚洲夏季风与热带太平洋－印度洋海气系统的同期关系。     

亚洲夏季风对强外辐射强迫变化的响应

该文通过改变太阳常数,利用NCAR气候系统模式CSM1.4研究了亚洲夏季风对强外辐射强迫变化的响应。结果表明:随太阳常数增加,局地增温幅度变化很大,中高纬地区比低纬地区增暖幅度强,这在太阳常数增加较大的试验中表现尤为明显;随太阳常数增大越大,大气温度升高越高,对流层有强烈增温,对流层高层更为显著;随太阳常数增大,亚洲夏季风系统的响应越强,太平洋副热带高压和南亚高压强度增强明显,并且太阳常数增加越大,高压强度越强,但形式有所不同,500 hPa太阳常数增加2.5%高压强度随纬度增高增强幅度变小,太阳常数增加10%和25%高压强度随纬度增高增强幅度变大。100 hPa太阳常数增加2.5%和10%高压强度随纬度增高增强幅度变小,太阳常数增加25%高压强度随纬度增高增强幅度变大。     

亚洲—太平洋夏季风系统的基本模态特征分析

亚洲—太平洋季风区各季风子系统间的相互作用对季风区甚至全球的气候变化都有着显著的影响.整个亚洲—太平洋夏季风系统都处于高层辐散、低层辐合的庞大辐散环流中,从高层辐散中心流出的三支气流分别对推动印度夏季风、东亚副热带夏季风和南海夏季风起着重要的作用,很好地表现了亚洲—太平洋夏季风系统的整体性特征.季风区多种气象要素的基本模态在年代际和年际尺度上都表现出较为一致的变化特征:年代际尺度上亚洲—太平洋夏季风系统整体呈现减弱趋势;年际尺度上存在准2年和准4年的两个周期,其中准2年振荡特征表现为若印度西南季风偏强,则印度季风雨带偏强偏北,导致印度大陆中北部地区降水偏多;同时,由于西太平洋副热带高压的北移和偏强的印度西南季风显著向东延伸,10°N~30°N范围内的西北太平洋地区则表现为异常的气旋性环流,而30°N~50°N之间为反气旋性环流异常,对应东亚夏季风偏强,季风雨带能够北推至我国华北地区.也就是说,当亚洲夏季风中某一季风子系统表现为异常偏强时,另一季风子系统在这一年中也将表现为异常偏强,反之亦然.准2年的振荡周期可能是亚洲—太平洋夏季风系统的一种固有振荡,它从年际尺度上反映了亚洲—太平洋夏季风受热带太平洋—印度洋海温的强迫表现出明显的整体一致特征.     

亚洲夏季风建立前后全球环流调整的气候风场变差度分析

利用变差度诊断分析,分析讨论了亚洲夏季风建立及前后(4月1日至6月30日)气候风场变差度的时空特征,发现北半球在4月10日和21日、5月15日和31日、6月11日和28日分别有6次大气环流大调整;变差度的大值区则均位于广义季风区;变差度确实是诊断大气环流调整和研究广义季风的客观定量工具.得到的主要结论如下:该6次环流大...     

亚洲沙尘与污染物对云、天气与气候的影响

美国科研人员本月将利用最先进的环境研究飞机开展一项大规模野外试验PACDEX(Pacific Dust Ex-peri ment),研究起源于亚洲经过太平洋飘到北美的沙尘与污染物烟羽。科研人员认为这些大范围的烟羽会影响数千公里外的云和天气,在全球气候中发挥作用。PACDEX计划由NCAR和斯克里普斯     

青藏高原积雪对亚洲夏季风影响的诊断及数值研究

通过对青藏高原多、少雪年的合成分析及数值试验，研究了青藏高原积雪对亚洲 夏季风和我国东部气候异常的影响。结果表明:青藏高原积雪造成亚洲大气环流较大的年际变化。高原积雪改变了高原陆面春、夏季的热状况，使亚洲夏季风爆发推迟20天左右。高原积雪通过以下物理过程影响亚洲夏季风和我国东部气候:高原积雪多(少)→高原春、夏季的感热弱(强)→感热加热引起的上升运动弱(强)，高原强(弱)环境风场→不利(有利)于高原感热通量向上输送→高原上空对流层加热弱(强)→高原对流层温度低(高)→高原南侧温度对比弱(强)→造成亚洲夏季风弱(强)→我国长江流域易涝(旱)。     

亚洲热带气候态夏季风涌传播特征及其对中国降水的影响

基于1979—2020年逐日的NOAA向外长波辐射资料、NCEP/NCAR再分析风场资料,以及全球CMAP再分析降水资料,探讨了气候态亚洲热带夏季风涌的传播过程及与我国夏季相应的降水联系。分析结果表明,主汛期亚洲热带气候态夏季风季节内振荡(CISO)活动是亚洲夏季风活动的主要特征,随时间北传的亚洲热带夏季风CISO称为亚洲热带夏季风涌,主要有南亚夏季风涌和南海夏季风涌。亚洲热带夏季风涌的传播可分为四个阶段。在亚洲热带夏季风涌的发展阶段,印度洋区域低频气旋与对流活跃,孟加拉湾和南海热带区域被低频东风控制,我国大部分地区无降水发生,降水中心位于两广地区。当进入亚洲热带夏季风涌活跃阶段,孟加拉湾和南海热带地区低频气旋和对流活跃,东亚低频“PJ”波列显著,我国降水中心北移到长江以南的附近区域。亚洲热带夏季风涌减弱阶段,孟加拉湾与南海低频气旋消亡,对流减弱,低频西风加强,日本南部附近为低频反气旋控制,我国长江中下游低频南风活跃,降水中心也北移到长江中下游地区,而华南地区已基本无降水,此阶段的大气低频环流场与亚洲热带夏季风涌发展阶段基本相反。进入亚洲热带夏季风涌间歇阶段时,孟加拉湾和南海热带地区低...     

On the Temporal and Spatial Structure of Troposphere-to- Stratosphere Transport in the Lowermost Stratosphere over the Asian Monsoon Region during Boreal Summer

This study produced a novel characterization of the troposphere-to-stratosphere transport(TST) over the Asian monsoon region during boreal summer,using a comprehensive analysis of 60-day backward trajectories initialized in the stratosphere.The trajectory datasets were derived from the high-resolution Lagrangian particle dispersion model(FLEXPART) simulation driven by the wind fields acquired from the National Center for Environmental Prediction(NCEP).The results indicate that the distribution of residence time(tTST) of tropopause-crossing trajectories in the lowermost stratosphere represents a horizontal signature of the Asian summer monsoon.Vertically,the distribution of tTST can be roughly separated into two layers:a consistent lower layer with tTST <5 days forming a narrow band,corresponding to a layer～3 km thick following the location of the tropopause,and an upper layer at a larger distance from the local tropopause.The maximum residence time was～20 days,especially within the Asian high anticyclone consistent with its confinement effects.In general,the overall geographical distribution of dehydration points was not coincident with the location of tropopause crossing.TST trajectories,which were initialized in the stratosphere,underwent their Lagrangian cold points mostly in the tropics and subtropics 1-4 days after the TST event;they were characterized by a wide range of temperature differences,with a mean value of 3-12 K.The vertical extent of the influence of tropospheric intrusion on the Asian monsoon region in the stratosphere exhibited a peak at～16.5-18.5 km,and the uppermost height was～21 km.     

亚澳季风各子系统气候学特征的异同研究 II. 夏季风水汽输送

利用1979~2002年的ERA-40和NCEP/NCAR逐日再分析资料以及CMAP降水资料探讨了亚澳季风各夏季风子系统(南亚夏季风、东亚夏季风、北澳夏季风)水汽输送的气候学特征及其与夏季降水的关系。分析表明:各夏季风子系统水汽输送通量主要取决于低层季风气流,南亚夏季风和北澳夏季风以纬向水汽输送为主,而东亚夏季风有很强的经向水汽输送。分析也证实,亚澳季风区的夏季风降水主;要源于水汽输送的辐合,而且ERA-40资料对夏季风水汽输送辐合的描述能力强于NCEP/NCAR资料。此外,受低层季风气流结构的影响,三夏季风子系统水汽输送辐合的动力机理存在明显差异,南亚夏季风和北澳夏季风的水汽输送辐合主要由低层西风气流的风场辐合所造成,而东亚夏季风的水汽输送辐合则由低层南风气流的风场辐合和季风湿平流共同作用造成。因此,东亚夏季风降水有别于南亚夏季风降水和北澳夏季风降水。     

The Earliest Onset Areas and Mechanism of the Tropical Asian Summer Monsoon

The multi-yearly averaged pentad meteorological fields at 850 hPa of the NCEP/NCAR reanalysis dada and the TBB fields of the Japan Meteorological Agency during 1980-1994 are analyzed. It is found that if the pentad is taken as the time unit of the monsoon onset, then the tropical Asian summer monsoon (TASM) onsets earliest, simultaneously and abruptly over the whole area in the Bay of Bengal (BOB), the Indo-China Peninsula (ICP), and the South China Sea (SCS), east of 90°E, in the 27th to 28th pentads of a year (Pentads 3 to 4 in May), while it onsets later in the India Peninsula (IP) and the Arabian Sea (AS), west of 90°E. The TASM bursts first at the south end of the IP in the 30th to 31st pentads near 10°N, and advances gradually northward to the whole area, by the end of June. Analysis of the possible mechanism depicts that the rapid changes of the surface sensible heat flux, air temperature, and pressure in spring and early summer in the middle to high latitudes of the East Asian continent between 100°E and 120癊are crucially responsible for the earliest onset of the TASM in the BOB to the SCS areas. It is their rapid changes that induce a continental depression to form and break through the high system of pressure originally located in the above continental areas. The low depression in turn introduces the southwesterly to come into the BOB to the SCS areas, east of 90°E, and thus makes the SCS summer monsoon (SCSSM) burst out earliest in Asia. In the IP to the AS areas, west of 90°E, the surface sensible heat flux almost does not experience obvious change during April and May, which makes the tropical Indian summer monsoon (TISM) onset later than the SCSSM by about a month. Therefore, it is concluded that the meridian of 90°E is the demarcation line between the South Asian summer monsoon (SASM, i.e., the TISM) and the East Asian summer monsoon (EASM, including the SCSSM). Besides, the temporal relations between the TASM onset and the seasonal variation of the South Asian high (SAH) are discussed, too, and it is found that there are good relations between the monsoon onset time and the SAH center positions. When the SAH center advances to north of 20°N, the SCSSM onsets, and to north of 25°N, the TISM onsets at its south end. Comparison between the onset time such determined and that with other methodologies shows fair consistency in the SCS area and some differences in the IP area.     

Moisture Transport in the Asian Summer Monsoon Region and Its Relationship with Summer Precipitation in China

The characteristics of moisture transport over the Asian summer monsoon region and its relationship with summer precipitation in China are examined by a variety of statistical methods using the NCEP/NC AR reanalysis data for 1948-2005.The results show that:1) The zonal-mean moisture transport in the Asian monsoon region is unique because of monsoon activities.The Asian summer monsoon region is a dominant moisture sink during summer.Both the Indian and East Asian monsoon areas have their convergence cente...     

亚澳季风各子系统气候学特征的异同研究Ⅰ.夏季风流场结构

利用1979～2003年的NCEP/NCAR再分析资料探讨了亚澳季风各夏季风子系统 (南亚夏季风、东亚夏季风、北澳夏季风) 流场结构及其季节演变的气候学特征.结果表明: 南亚夏季风和北澳夏季风纯属热带季风, 盛行纬向气流和纬向风垂直正切变, 即低层西风、高层东风, 但北澳夏季风的强度明显弱于南亚夏季风, 而东亚夏季风由热带季风和副热带季风组成, 盛行经向气流和经向风垂直正切变, 即低层南风、高层北风, 且纬向气流高低层配置相对复杂, 相对北澳夏季风而言, 南亚夏季风的低层西风强而深厚, 而东亚夏季风的低层南风强而深厚.从热带季风区流场结构的季节演变过程看, 这三个夏季风子系统均为垂直斜压结构.三者的共性还表现在热带季风区纬向气流高低层配置的季节性转向, 即夏季风爆发时从低层东风、高层西风转换为低层西风、高层东风, 夏季风撤退时从低层西风、高层东风转换为低层东风、高层西风.此外, 南亚夏季风的季内变化平稳, 而东亚夏季风和北澳夏季风的季内变化剧烈; 东亚夏季风的经向跨度大、维持时间最长, 而北澳夏季风的经向跨度小、维持时间最短.     

Relationship Between East Asian Winter Monsoon and Summer Monsoon

Using National Centers for Environmental Prediction/National Centre for Atmospheric Research(NCEP/NCAR) reanalysis data and monthly Hadley Center sea surface temperature(SST) data,and selecting a representative East Asian winter monsoon(EAWM) index,this study investigated the relationship between EAWM and East Asian summer monsoon(EASM) using statistical analyses and numerical simulations.Some possible mechanisms regarding this relationship were also explored.Results indicate a close relationship between EAWM and EASM:a strong EAWM led to a strong EASM in the following summer,and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in the tropical Indian Ocean and the South China Sea,and on the equatorial atmospheric thermal anomalies at both lower and upper levels.Through these impacts,the EAWM influences the land-sea thermal contrast in summer and the low-level atmospheric divergence and convergence over the Indo-Pacific region.It further affects the meridional monsoon circulation and other features of the EASM.Numerical simulations support the results of diagnostic analysis.The study provides useful information for predicting the EASM by analyzing the variations of preceding EAWM and tropical SST.     

Seasonal Prediction Assessment of the South Asian Summer Monsoon: ENSEMBLES versus DEMETER

The seasonal forecasting skill with respect to the South Asian summer monsoon(SASM) was compared between the European Commission FP7 project(ENSEMBLES) and the Development of a European Multimodel Ensemble System for Seasonal to Interannual Prediction project(DEMETER). The Webster-Yang index(WYI) was chosen to represent the intensity of the SASM. First, the authors compared the ability to forecast the zonal wind at 850 h Pa(U850) and 200 h Pa(U200) between ENSEMBLES and DEMETER models. The results indicated that the models from the European Centre for Medium-Range Weather Forecasts, International Organization(ECMWF) and UK Met Office(UKMO) in ENSEMBLES possess greater skill in seasonally forecasting the JJA(June, July, and August) U850, U200, and U850 minus U200 than in DEMETER. Compared to in DEMETER, the JJA U200 and U850 minus U200 forecasting skill was greater for the model from MétéoFrance(MF) in ENSEMBLES over most of the SASM region. The three coupled models(ECMWF, MF, and UKMO), especially the UKMO model in ENSEMBLES, all demonstrated improved skill in their seasonal forecasts compared to in DEMETER with respect to the interannual variability of the SASM. The three ENSEMBLES models also showed better ability in forecasting the sea surface temperature anomalies(SSTAs) over the eastern equatorial Pacific and North Indian Ocean, and more accurately reproduced the large-scale atmospheric circulation and precipitation over northern India, which are related to the SASM. It seems that the couple between the atmospheric system and external forcing of ENSMBLES over Indian Ocean and Pacific is better than that of DEMETER.     

南半球环流变化对东亚夏季风的影响

南半球环流是影响东亚夏季风季节内、季节到年际变化的重要因子之一.作者系统综述了南半球环流各系统包括连接两半球的越赤道气流、马斯克林高压和澳大利亚高压、南极涛动和南极海冰等对东亚夏季风环流和中国夏季降水的影响.特别是,近年来的研究揭示了南极涛动是影响东亚夏季风年际变化的强信号.当南极涛动偏强时,马斯克林高压和澳大利亚高压和相关的越赤道气流也趋于偏强.同时,西太平洋副热带高压偏西偏南,强度增强,长江流域降水偏多,其两侧降水偏少.这对中国夏季降水的预测有重要的应用价值.最后提出了一些相关的科学问题以供进一步研究.       

亚澳季风各子系统气候学特征的异同研究 I.夏季风流场结构

利用1979~2003年的NCEP/NCAR再分析资料探讨了亚澳季风各夏季风子系统(南亚夏季风、东亚夏季风、北澳夏季风)流场结构及其季节演变的气候学特征。结果表明:南亚夏季风和北澳夏季风纯属热带季风,盛行纬向气流和纬向风垂直正切变,即低层西风、高层东风,但北澳夏季风的强度明显弱于南亚夏季风,而东亚夏季风由热带季风和副热带季风组成,盛行经向气流和经向风垂直正切变,即低层南风、高层北风,且纬向气流高低层配置相对复杂,相对北澳夏季风而言,南亚夏季风的低层西风强而深厚,而东亚夏季风的低层南风强而深厚。从热带季风区流场结构的季节演变过程看,这三个夏季风子系统均为垂直斜压结构。三者的共性还表现在热带季风区纬向气流高低层配置的季节性转向,即夏季风爆发时从低层东风、高层西风转换为低层西风、高层东风,夏季风撤退时从低层西风、高层东风转换为低层东风、高层西风。此外,南亚夏季风的季内变化平稳,而东亚夏季风和北澳夏季风的季内变化剧烈;东亚夏季风的经向跨度大、维持时间最长,而北澳夏季风的经向跨度小、维持时间最短。     

东亚夏季风的季节内振荡研究

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.