我国东部夏季降水异常主模态的年代际变化及其与东亚水汽输送的关系

本文利用1958～2000年ERA-40再分析每日资料和我国516台站降水资料以及EOF方法,分析了我国东部季风区夏季降水异常主模态的年代际变化特征及其与东亚上空水汽输送通量时空变化的关系.分析结果表明了我国东部季风区夏季降水的时空变化存在两种主模态:第1主模态不仅显示出明显的准两年周期振荡的年际变化特征且也有明显的年...     

东亚季风区大气季节内振荡经向与纬向传播特征分析

将NECP/NCAR资料中850 hPa纬向风分量进行30～60天带通滤波, 研究东亚季风区大气季节内振荡的传播特征。分析表明, 夏季东亚季风区大气季节内振荡(ISO)的传播分为经向传播和纬向传播, 其中经向传播主要为热带地区ISO的向北传播, 纬向传播则是分别起源于印度季风区的ISO东传和起源于西太平洋海域的ISO西传。东传和西传的ISO在120°E附近汇合后增强自热带地区北传到此的ISO, 使得ISO在经向上可以继续向北传播, 其最北界可达35°N以北, 并对我国长江中下游地区夏季降水产生一定的影响。     

准40天振荡的基本特征及其研究进展

本文主要介绍准40天周期振荡的基本特征及其有关的观测研究结果。重点讨论了与准40天振荡的纬向和经向传播相联系的研究进展。提出了准40天振荡在季风区经向传播的可能的天气学过程.     

亚洲季风区ITCZ对华北雨季异常的可能影响

分析了冬、春季亚洲季风区ITCZ活动对华北夏季降水的影响。用OLR资料定义了ITCZ综合指数，分析表明该指数能比较清晰、客观地综合反映出亚洲季风区深对流活动的强度和位置。用该指数分析了华北多雨年和少雨年前期热带大范围对流活动的变化特征。印度和东亚季风区的ITCZ活动在多雨和少雨年显示出明显不同。华北夏季降水与2-4月ITCZ综合指数的时滞相关性最明显。这种时滞相关可能与球面Rossby波的频散相联系，并可以为华北夏季降水的长期预报提供新的参考依据。低频振荡分析表明，多雨年南北两个半球的低频振荡强度较强，范围较大，并不断由南向北传播，这种传播很可能与副热带高压的北跳有关。而少雨年低频振荡在南半球或热带地区呈准静止状态。     

IOD对北半球夏季季节内振荡强度的可能影响

利用1979-1998年NCEP/NCAR再分析资料和GISST逐月海温资料,分析了印度洋偶极子(IOD)对季节内振荡强度的影响.结果表明:在非洲地区,IOD对季节内振荡强度存在显著影响,其对SLP季节内振荡强度的影响主要集中在非洲中部、西部和南部地区.在亚洲地区,IOD对季节内振荡强度也存在显著影响.在亚洲季风区的大部分地区,IOD与200hPa纬向风(U)、高度场(H)和经向风(V)的季节内振荡强度都存在显著关联.IOD和ENSO对季节内振荡强度的作用差别显著,在有些地区甚至相反.进一步分析了1994年200hPa上U、V的季节内振荡强度分布,并给出了1994年低频风场的传播特征.     

多要素表征的东亚季风区准双周振荡特征

为评估不同要素对东亚季风区准双周振荡的表征能力,对大气向外长波辐射（OLR）、500 hPa位势涡度、850 hPa相对涡度、850 hPa风场和750 hPa比湿等要素的准双周振荡特征进行对比,发现各要素均能很好反映东亚季风区明显的准双周振荡时空特征。OLR及500 hPa位势涡度、850 hPa相对涡度、850 hPa纬向风表征的准双周振荡呈明显的西北向传播特征,500 hPa位势涡度、850 hPa相对涡度、850 hPa纬向风北传更强,北传速度更快。850 hPa经向风的准双周振荡呈明显西移特征,北传弱,北传速度最慢。而750 hPa比湿准双周振荡呈东南向传播。不同要素准双周振荡的强度略有差异,其中750 hPa比湿与其他要素的差异大。总体而言,750 hPa比湿不能较好地表现出东亚季风区准双周振荡活动特征,而其余要素能很好地表征东亚季风区大气准双周振荡,其中500 hPa位势涡度和850 hPa相对涡度准双周振荡特征一致性高。     

夏季低纬地区散度风分量准40天振荡的观测研究

本文用ECMWF逐日资料分析了1982年夏季30°S—30°N纬带散度风分量Vx准40天振荡的空间分布和传播特点。结果表明:整个纬带振荡周期长度比较一致;高低层间反位相,辐散与辐合相反配置;强度分布有明显地域性,季风区最强,850和200hPa上振幅分别是1和2m/s左右,亦道附近110°W两侧(?)x有分别向东西两个方向传播的现象。     

西北太平洋夏季风的气候学研究

西北太平洋季风区(5°~25°N,120°~160°E)是亚洲-太平洋季风区与亚洲-澳大利亚季风区的一个重要部分,也是一个独立的季风区。文中对西北太平洋夏季风进行了气候学研究,发现西北太平洋夏季风的爆发发生在31候(6月上旬)前后。爆发后,夏季风经历了3次活跃-中断循环,每个循环都相应于独立的干期和湿期。第1个循环是从6月初到7月中旬,降水与低层西风的中心主要位于5°~10°N。第2个循环是7月下旬至9月下旬,降水与低层西风明显向东北方向移动,位于10°~20°N。这个循环是西北太平洋夏季风最强盛的时期。第3个循环是从9月末到10月末,降水与低层西风又向南退回到5°~10°N,达到了西北太平洋夏季风最弱的阶段。这个循环的结束也就预示着西北太平洋夏季风的结束。西北太平洋季风区有明显的季节内振荡(ISO),这种气候的季节内振荡(CISO)主要由30~60 d与10~20 d两种周期组成,但是主要以30~60 d的低频振荡为主。根据西北太平洋的对流和低层西风在不同位相分布的分析,可以看出西北太平洋的低频对流和西风是向西向北传播的。西北太平洋的季风降水、对流与西风的活跃-中断循环在很大程度上受30~60和10~20 d低频振荡的调制。     

北太平洋海温变化的年代际模及其演变特征

用近百年的海温(SST)资料,分析研究了北太平洋海温的年代际变化特征及其基本形势(模态).结果表明,它主要存在准7～10年周期和准25～35年周期两类年代际变化;这两类年代际变化又都有类似的形势(模态),但却与所谓"类ENSO模"明显不同.同时,两个年代际模都有呈西北一东南向振荡和沿海盆作顺时针旋转的共存活动(演变)特征.     

秋季中低纬低频振荡传播与长江中下游的连晴、连阴雨

对1983年～1985年9月～11月份850hpa的经纬向风场进行了15d～25d的带通滤波分析。结果表明,110°E经向风低频振荡波存在阶段性地从南半球(北半球)越过赤道向北(南)传播,低频越赤道气流存在阶段性地明显向东、向西传播,它们在5天平均低频风场中表现为低频气旋、反气旋环流的周期性振荡变化,并都与长江中下游地区的连晴、连阴雨天气的时间分布相联系。     

IMPACTS OF MONTHLY ANOMALIES OF INTRASEASONAL OSCILLATION OVER SOUTH CHINA SEA AND SOUTH ASIA ON THE ACTIVITY OF SUMMER MONSOON AND RAINFALL IN EASTERN CHINA

The impact of strong (weak) intraseasonal oscillation (ISO) over South China Sea (SCS) and South Asia (SA) in summer on the SCS and SA summer monsoon and the summer rainfall in Eastern China are studied by using the NCEP-NCAR analysis data and the rainfall data of 160 stations in China from 1961 to 2010. It is found that the impacts are significantly different in different months of summer. The study shows that in June and July cyclonic (anticyclonic) atmospheric circulation over SCS and SA corresponds to strong (weak) ISO over SCS. In August, however, strong (weak) ISO over SCS still corresponds to cyclonic (anticyclonic) atmospheric circulation over SA. In June and August cyclonic (anticyclonic) atmospheric circulation over South Asia corresponds to strong (weak) ISO over SA while a strong (weak) ISO corresponds to anticyclonic (cyclonic) atmospheric circulation over SA in July. Besides, in June the strong (weak) ISO over SA corresponds to cyclonic (anticyclonic) atmospheric circulation over SCS, while in July and August the atmospheric circulation is in the same phase regardless of whether the ISO over SA is strong or weak. The impacts of the strong（weak）ISO over SCS on the rainfall of eastern China are similar in June and July, which favors less (more) rainfall in Yangtze-Huaihe Rivers basin but sufficient (deficient) rainfall in the south of Yangtze River. However, the impacts are not so apparent in August. In South Asia, the strong (weak) ISO in July results in less (more) rainfall in the south of Yangtze River but sufficient (deficient) rainfall in Yangtze-Huaihe Rivers basin. The influence on the rainfall in eastern China in June and August is not as significant as in July.     

孟加拉湾西南季风与南海热带季风季节内振荡特征的比较

采用美国国家环境预报中心的向外长波辐射和风场资料及日本气象厅的降水资料,用30-60d滤波后的夏季风指数在孟加拉湾和南海的区域平均值分别代表孟加拉湾西南季风和南海热带季风季节内振荡,对两支季风的季节内振荡特征进行比较分析,发现孟加拉湾西南季风的季节内振荡和南海热带季风的季节内振荡在夏季风期间(5-10月)都有约3次半的波动.夏季风期间,在阿拉伯海-西太平洋纬带上,夏季风的季节内振荡有4次从阿拉伯海的东传和3次从西太平洋的西传,其中7月后东传可直达西太平洋.孟加拉湾和南海在夏季风期间都有4次季节内振荡的经向传播,但孟加拉湾在约15°N以南为季节内振荡从热带东印度洋的北传,在约15°N以北则为副热带季风季节内振荡的南传;而在南海则是4次季节内振荡从热带的北传.在以孟加拉湾西南季风季节内振荡和南海热带季风季节内振荡分别划分的6个位相中,都存在1-3位相和4-6位相中低频对流、环流形势相反的特征,这是由热带东印度洋季节内振荡的东传和北传所致.热带印度洋季节内振荡沿西南-东北向经过约14d传到孟加拉湾,激发了孟加拉湾西南季风季节内振荡的东传,经过约6d到达南海,激发了南海热带季风季节内振荡的北传,经过约25d到达华南,形成热带印度洋季节内振荡向华南的经纬向接力传播(45d).孟加拉湾西南季风季节内振荡所影响的降水主要是在20°N以南的热带雨带随低频对流的东移而东移;而南海热带季风季节内振荡所影响的降水除了这种热带雨带随低频对流的东移外,还有在20°N以北的东亚副热带地区存在雨带随南海低频对流的北移而北移.     

RELATIONSHIP BETWEEN TROPICAL ISO AND TROPICAL CYCLONE ACTIVITY OVER THE SOUTH CHINA SEA

The relationship between the tropical intra-seasonal oscillation (ISO) and tropical cyclones (TCs) activities over the South China Sea (SCS) is investigated by utilizing the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) global reanalysis data and tropical cyclone best-track data from 1949 to 2009. The main conclusions are: (1) A new ISO index is designed to describe the tropical ISO activity over the SCS, which can simply express ISO for SCS. After examining the applicability of the index constructed by the Climate Prediction Center (CPC), we find that the convection spatial scale reflected by this index is too large to characterize the small-scale SCS and fails to divide the TCs activities over the SCS into active and inactive categories. Consequently, the CPC index can’t replace the function of the new ISO index; (2) The eastward spread process of tropical ISO is divided into eight phases using the new ISO index, the phase variation of which corresponds well with the TCs activities over the SCS. TCs generation and landing are significantly reduced during inactive period (phase 4-6) relative to that during active period (phase 7-3); (3) The composite analyses indicate distinct TCs activities over the SCS, which is consistent with the concomitant propagation of the ISO convective activity. During ISO active period, the weather situations are favorable for TCs development over the SCS, e.g., strong convection, cyclonic shear and weak subtropical high, and vice versa; (4) The condensation heating centers, strong convection and water vapor flux divergence are well collocated with each other during ISO active period. In addition, the vertical profile of condensation heat indicates strong ascending motion and middle-level heating over the SCS during active period, and vice versa. Thus, the eastward propagation of tropical ISO is capable to modulate TCs activities by affecting the heating configuration over the SCS.     

南海及周边地区TBB季节内振荡及其与ENSO的联系

文中利用1980～1997年TBB资料,采用小波变换分析方法,对南海及周边地区季节内振荡(ISOs)进行了诊断分析。结果表明:南海及菲律宾以东洋面TBB具有相似的ISOs特征,其年变化表现为单峰型,夏秋季强,冬春季弱,而孟加拉湾地区的ISOs有所不同,呈双峰型,峰值出现5月和11月。南海地区ISOs的周期结构具有复杂性,主要有两个周期段,即以53.8d为峰值的50～70d振荡(ISO1)和以32d为峰值的13～36d振荡(ISO2)。南海地区ISO1的年际变化与周边地区(孟加拉湾、菲律宾以东洋面以及南半球澳大利亚与印度尼西亚之间洋面)ISO1的年变化有显著的正相关,说明这种ISO1的年变化为较大范围的区域现象;而南海地区ISO2的年际变化与周边地区相关性不显著,为局地现象。影响南海地区ISOs的传播具有多向性,ISO1以东传为主,ISO2以西传为主,它们都具有北传的特征。可见,南海地区ISOs既受到来自赤道地区的影响,也受到来自西太平洋和孟加拉湾的影响,同时南海地区局地也可以生成强烈对流活动,从而使得南海地区对流的ISOs变得复杂化。统计结果发现,ENSO与ISO1有密切的联系,但对ISO2的影响不明显。ENSO对ISO1的影响不但表现在南海地区,对孟加拉湾和菲律宾以东洋面上的ISO1有更加明显影响作用,负相关表明ENSO冷事件发生时上述地区ISO1受到压制。可以推测,ENSO通过对热带大气环流(特别是副热带高压)的影响来对南海及周边地区ISO1进行调制。     

Intraseasonal Oscillation of the South China Sea Summer Monsoon and Its Influence on Regionally Persistent Heavy Rain over Southern China

The intraseasonal oscillation（ISO） in the South China Sea summer monsoon（SCSSM） and its influence on regionally persistent heavy rain（RPHR） over southern China are examined by using satelhte outgoing long wave radiation,NCEP/NCAR reanalysis,and gridded rainfall station data in China from 1981 to 2010.The most important feature of the ISO in SCSSM,contributing to the modulation of RPHR,is found to be the fluctuation in the western Pacific subtropical high（WPSH）,along with a close link to the Madden-Julian oscillation（MJO）.Southern China is divided into three regions by using rotated empirical orthogonal functions（REOFs）for intraseasonal rainfall,where the incidence rate of RPHR is closely linked to the intraseasonal variation in rainfall.It is found that SCSSM ISOs are the key systems controlling the intraseasonal variability in rainfall and can be described by the leading pair of empirical orthogonal functions（EOFs） for the 850-hPa zonal wind over the SCS and southern China.Composite analyses based on the principal components（PCs） of the EOFs indicate that the ISO process in SCSSM exhibits as the east-west oscillation of the WPSH,which is coupled with the northward-propagating MJO,creating alternating dry and wet phases over southern China with a period of 40 days.The wet phases provide stable and lasting circulation conditions that promote RPHR.However,differences in the ISO structures can be found when RPHR occurs in regions where the WPSH assumes different meridional positions.Further examination of the meridional-phase structure suggests an important role of northward-propagating ISO and regional air-sea interaction in the ISO process in SCSSM.     

强弱南海夏季风活动及大气季节内振荡

应用ＮＣＥＰ再分析资料和中国降水资料，分析研究了对应南海强、弱夏季风的环流形势及其与之相应的中国东部的降水异常。其结果表明，由强、弱夏季风所引起的中国气候异常是完全不同（甚至反相）的。分析大气季节内振荡（ＩＳＯ）的活动还表明，对应大气强（弱）南海夏季风，南海地区 ８５０ ｈＰａ也有强（弱）大气 ＩＳＯ；而强、弱南海夏季风环流（２００ ｈＰａ和 ８５０ ｈＰａ）主要由异常的大气ＩＳＯ所激发。本研究还揭示了南海地区大气ＩＳＯ的变化往往与江淮地区大气ＩＳＯ的变化反相，例如南海地区的强（弱）大气ＩＳＯ常与江淮流域的弱（强）大气ＩＳＯ相对应。对于大气ＩＳＯ的强度，一般多表现出局地激发特征，经向传播相对较弱。     

BASIC CLIMATOLOGICAL FEATURES OF AIR-SEA HEAT EXCHANGES IN THE SOUTH CHINA SEA (SCS) REGION AND THEIR RELATIONS WITH THE SCS MONSOONS

By using the NCEP reanalysis data set in 1979-1995, the fluxes of the latent heat, thesensible heat and the net long-wave radiation in the South China Sea (SCS) are expanded by meansof EOF in order to discuss the basic climatological features in the SCS. The detailed analysis showsthat the air-sea heat exchanges in different SCS regions have different seasonal variations. Themiddle and the north of the SCS are the high value regions of the air-sea heat exchanges during thewinter and the summer monsoon periods, respectively, the seasonal variations of air-sea heatexchanges in the south of the SCS are small. In addition, the proportions of different componentsin the total air-sea heat exchanges have different seasonal variations in different regions. Theresults show that the SCS monsoon and the air-sea heat exchanges in the SCS region are theaccompaniments of each other, the great difference of the sensible heat flux between the IndochinaPeninsula and the SCS before the SCS summer monsoon onset may be one of the triggers of thelatter. There maintains a high value center of the sensible heat flux before the 13th dekad, itsdisappearing time consists with that of the summer monsoon onset. It means that as far as the SCSlocal conditions are concerned, the northwest of the Indochina Peninsula is probably a sensitiveregion to the SCS summer monsoon onset and the land may play a leading role in the SCS summermonsoon onset.     

CHARACTERISTICS OF FREQUENCY SPECTRUM VARIATION OF INTRASEASONAL OSCILLATION OF CONVECTION DURING SOUTH CHINA SEA SUMMER MONSOON

Datasets of equivalent temperature of black body (TBB) and sea surface temperature (SST) ranging from 1980 to 1997 are used to diagnose and analyze the characteristics of frequency spectrum and strength of intraseasonal variation of convection. The relationship between the strength of intraseasonal oscillation of convection, strength of convection itself and SST in the South China Sea (SCS) is studied. It is shown that, there are distinguishable annual, interannual and interdecadal variations in both strength and frequency spectrum of intraseasonal variation of convection in SCS. There are connections between strength of convection, strength of ISO1 in the summer half (s.h.) year and SST in ensuing winter half (w.h.) year in SCS. The strong (weak) convection and strong (weak) ISO1 are associated with negative (positive) bias of SST in ensuing w.h. year in SCS.     

CHARACTERISTICS OF FREQUENCY SPECTRUM VARIATION OF INTRASEASONAL OSCILLATION OF CONVECTION DURING SOUTH CHINA SEA SUMMER MONSOON

1 INTRODUCTIONSituated in the region of East Asian Monsoon(EAM), weather and climate in China are deeplyinfluenced by the activities of EAM. Especially inflood seasons, distribution of precipitation, movementof rain-bands and occurrence of droughts and fl…     

The East Asia-western North Pacific boreal summer intraseasonal oscillation simulated in GAMIL 1.1.1

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 20^oN to 40^oN and the absence of the CISO signal south of 10^oN, 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.