Impacts of the stratospheric quasi-biennial oscillation on the tropospheric circulation and climate in the Northeast Asia-North Pacific region in early summer

本文研究了平流层准两年振荡(QBO)对东北亚-北太平洋地区初夏对流层环流和地表气温的影响.在QBO西风位相年,东北亚至北太平洋地区存在一支由QBO引发的平均经向环流异常,该经向环流异常可在东北亚至北太平洋地区激发正涡度,并形成异常气旋式环流.气旋左侧出现的异常偏北风导致6月东北亚地表气温下降.QBO东风位相年的结果与西风位相年大致相反.这些结果为QBO对热带外地区天气,气候的影响提供了新的证据,并为东北亚初夏地表气温的预测提供了新的线索。

Effects of South China Sea/western North Pacific summer monsoon on tropospheric biennial oscillation （TBO）

Several theories have been developed to explain tropical biennial oscillation （TBO）, as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including airsea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon （SCS/WNPSM）, a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γand wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS /WNPSM.

Spatial Patterns of Tropospheric Biennial Oscillation and Its Numerical Simulation

In order to investigate the spatial patterns of the Tropospheric Biennial Oscillation （TBO） on the global scale, the Climate Prediction Center （CPC） Merged Analysis of Precipitation （CMAP） monthly averaged precipitation and the Climate Diagnostics Center （CDC） monthly outgoing long-wave radiation （OLR） and SST are used in conjunction with TBO bandpass-filtering. The results indicate active biennial variability in the tropical eastern-central Pacific regions. It is evident that observations reflect the biennial component of the ENSO rather than the TBO itself. Since some studies have pointed out that the TBO is a broad-scale phenomenon differing from the ENSO, to investigate the pure TBO the ENSO signal must be excluded. The Scale Interaction Experiment-FRCGC （SINTEX-F） coupled general circulation model （CGCM） developed at Japan Frontier Research Center for Global Change （FRCGC） can capture both the ENSO and the biennial signals. Air-sea interactions in the tropical eastern-central Pacific are decoupled to eliminate the effects of ENSO in a experiment by SINTEX-F and the results show that biennial variability still exists even without ENSO. It seems to mean that the TBO and ENSO are independent from each other. Furthermore, the model results indicate that the two key regions are southwest Sumatra and the tropical western Pacific for the TBO cycle.

Interdecadal variability of the tropospheric biennial oscillation in the western North Pacific

The observed tropospheric biennial oscillation （TBO） in the western North Pacific （WNP） monsoon region has an interdecadal variability with a period of 40-50 yr. That suggests a weaker effect of the TBO on the East Asia followed by a stronger one. A simple analytic model was designed to investigate the mechanism of the interdecadal variability of the TBO. The results indicated that a local TBO air-sea system not only supports the TBO variability in the WNP monsoon region but also produces an interdecadal variability of the TBO.

Air-sea interactions associated with tropospheric biennial oscillation in South China Sea summer monsoon and their effects on El Nio-Southern Oscillation

The South China Sea summer monsoon （SCSSM） behaves with prominent climate variability from the in- traseasonal to interdecadal time scales. On the interannual time scale, the biennial variability （so-called tropospheric biennial oscillation, TBO） is as important as the E1 Nifio-Southem Oscillation （ENSO） period. Some observed data sets, including reanalysis data, are used to explore the associated air-sea interactive physical processes and how the SCSSM TBO affects the ENSO. The results show that the shearing vorticity induced by the north Indian Ocean sea surface temperature anomalies （SSTAs） and the anomalous Philip- pine Sea anticyclone both contribute to the TBO in the SCSSM. The results also indicate that the ENSO has a weak effect on the SCSSM TBO, whereas the latter affects the ENSO to some extent.

ADVANCE IN STUDIES OF TROPOSPHERIC BIENNIAL OSCILLATION

There are obvious biennial phenomena of circulation, meteorological and climatic elements in the troposphere, named as Tropospheric (Quasi-) Biennial Oscillation (TBO). Many phenomena of TBO are discovered, such as variations of TBO in tropospheric temperature, pressure, winds field, monsoon and subtropical high etc. The mechanism of TBO is explored and the results demonstrate that tropical ocean (the Indian Ocean and the Pacific Ocean, mainly) and Stratospheric QBO play important roles in the TBO. In addition, Eurasian snow cover and solar activity of 11yr period can affect TBO very possibly.

南亚季风区TBO机制的进一步研究

1961—2000年的ECMWF逐日格点资料和印度降水量资料,分析研究表明南亚地区的气候,特别是印度的夏季降水存在明显的准两年振荡(TBO)特征。为了研究南亚地区TBO的机理,定义了一个统一的南亚季风指数来描述南亚冬季风和南亚夏季风以及两者之间的转换特征。通过研究南亚季风指数的异常变化特征,发现南亚冬季风和南亚夏季风存在相互影响和相互作用的关系。通常来说,强(弱)的南亚冬季风后南亚夏季风活动一般偏弱(强);另外,偏强(弱)的南亚冬季风一般发生在强(弱)南亚夏季风活动后。南亚夏季风和南亚冬季风的这种循环演变特征可能是南亚地区出现TBO的重要机制之一。

FURTHER RESEARCH ON MECHANISM OF TBO IN SOUTH ASIAN MONSOON REGION

The results of this study prove that there is significant troposphere biennial oscillation(TBO) in the South Asian climate, especially with the Indian summer monsoon rainfall. In order to explore the mechanism of TBO in the South Asian region, we defined a unified South Asian monsoon index to depict South Asian summer monsoon(SASM) and South Asian winter monsoon(SAWM) and the transition features between SASM and SAWM. Through further analysis, the connection between the abnormity of SASM and SAWM was discovered. Normally, a strong SAWM is beneficial for a weak SASM later, while a weak SAWM favors a strong SASM. Meanwhile, a strong SASM is favorable for a weak SAWM and a weak SAWM always happens after a weak SASM. Such results suggest the evolution of the South Asian monsoon, which may be an important mechanism to excite TBO in South Asia.

Origin of the TBO-Interaction between Anomalous East-Asian Winter Monsoon and ENSO Cycle

Based on the data analyses by using NCEP/ NCAR reanalysis data and other data (OLR, precipitation and temperature), it is shown that the tropospheric circulation and climate in East Asia and the northwestern Pacific region have the evident quasi-biennial oscillation (TBO) feature. It is also shown that anomalous East Asian winter monsoon can impact the atmospheric circulation and climate variations in the following summer, particularly in East Asian region; there is clear interaction between anomalous East Asian winter monsoon and ENSO cycle. The continuous strong (weak) East Asian winter monsoon can excite El Ni o (La Ni a) through the air-sea interaction, the El Ni o (La Ni a) event can lead the East Asian winter monsoon to be weak (strong) through the teleconnections or remote responses. The strong or weak winter monsoon and ENSO cycle are linked each other. It can be suggested that interaction between anomalous East Asian winter monsoon and ENSO cycle is a fundamental origin of the TBO.

Variation of the East Asian Monsoon and the tropospheric biennial oscillation

Study of the tropospheric biennial oscillation (TBO) has attracted significant interest since the 1980s.However,the mechanism that drives this process is still unclear.In the present study,ECMWF daily data were applied to evaluate variation of the East Asian monsoon and its relationship to the TBO.First,the general East Asian monsoon index (EAMI) was delineated on the basis of a selected area using the 850 hPa u and v components.This new index may describe not only the characteristics of summer monsoons,but also the features of winter monsoons,which is crucial to understand the transition process between summer and winter monsoons.The following analysis of EAMI shows that there is a close relationship between summer and winter monsoons.In general,strong East Asian winter monsoons are followed by strong East Asian summer monsoons,and weak winter monsoons lead to weak summer monsoons.While strong (weak) summer monsoons followed by weak (strong) winter monsoons form a kind of 2-year cycle,which may be the possible mechanism leading to the TBO over the East Asian region.

Tropospheric biennial oscillation of the western Pacific subtropical high and its relationships with the tropical SST and atmospheric circulation anomalies

There is the significant period of tropospheric biennial Oscillation(TBO)over East Asian monsoon region at the interannual timescales,which has the important influences on East China climate.Based on a set of reconstructed indices which describes the western Pacific subtropical high(WPSH)objectively,this paper focuses on the TBO component of WPSH,one of the key members of the East Asian Monsoon system,and its relationships with the tropical SST and atmospheric circulation anomalies.It is found that(1)As an important interannual component of WPSH,the time series of TBO has the obvious transition in the late1970s,and the variability of the WPSH’s TBO component is more significant after the late 1970s.(2)The time-lag correlations between the WPSH’s TBO and the tropical sea surface temperature(SST)anomalies in several key ocean regions are more significant and have longer correlation duration than the raw data.The response of the western boundary index to ENSO is earlier than the intensity index,and the time-lag correlations of them are up to maximum when lagging ENSO by 3–5 months and 5–6months,respectively.(3)In the course of the WPSH’s TBO cycle,the occurrence of the El Ni o-like anomaly in the tropical central-eastern Pacific in winter is always coupled with the weak East Asian winter monsoon,with the most significant enhancing phase of the WPSH’TBO.In contrast,the La Ni a-like anomaly in the central-eastern Pacific in winter is coupled with the strong East Asian winter monsoon,with the most weakening phase of the WPSH’s TBO.(4)The distribution of the tropical SST and atmospheric circulations anomalies are asymmetric in the TBO cycle.The WPSH’s TBO is more significant in the period of the developing El Ni o-like anomaly in central-eastern Pacific than in the period of the developing La Ni a-like anomaly.Therefore,during the period of developing El Ni o-like anomaly,more attention should be paid to the interannual component of TBO signal in the short-term climate prediction.

Dynamical mechanism of the stratospheric quasibiennial oscillation impact on the South China Sea Summer Monsoon

The National Center for the Atmospheric Research(NCAR)middle atmospheric model is used to study the effects of the quasi-biennial oscillation in the stratosphere(QBO)on the tropopause and uppe troposphere,and the relationship between the QBO and South China Sea Summer Monsoon SCSSM is explored through NCEP(the National Centers for Environmental Prediction)/NCAR,ECMWF(Euro pean Centre for Medium-Range Weather Forecasts)monthly mean wind data and in situ sounding data The simulations show that the QBO-induced residual circulations propagate downwards,and affect the tropopause and upper troposphere during the periods of mid-late QBO phase and phase transition Meanwhile,diagnostic analyses indicate that anomalous circulation similar to SCSSM circulation is generated to strengthen the SCSSM during the easterly phase and anomalous Hadley-like circulation weakens the SCSSM during the westerly.Though the QBO has effects on the SCSSM by meridiona circulation,it is not a sole mechanism on the SCSSM TBO mode.

亚洲夏季风的年际和年代际变化及其未来预测

本文是对我们近五年在亚洲夏季风年代际与年际变率及其未来预测方面研究的一个综述。主要包括下列三个问题:(1)根据123年中国夏季降水资料和印度学者的分析,检测出亚洲夏季风具有明显的年代际尺度减弱,这种年代际变化使中国东部(包括东亚)和南亚夏季降水的格局在过去60年中发生了明显变化。在东亚,从1970年代后期开始,主要异常雨带有不断南移的趋势,结果造成了南涝北旱的降水分布,这主要受到60～80年年代际振荡的影响。青藏高原前冬和春季积雪的年代际减少与热带中东太平洋海表温度的年代际增加是东亚降水型改变的主要原因,这是通过减弱亚洲地区夏季海陆温差与夏季风强度而实现的。未来亚洲夏季风的预测表明,东亚夏季风和南亚夏季风对气候变暖有十分不同的响应。东亚夏季风在本世纪将增强,雨带北推,尤其在2040年代之后;而南亚夏季风环流将继续减弱。这种不同的变化是由于两者对高低层海陆热力差异的不同响应造成。(2)年际尺度的变率在亚洲夏季风区主要表现为2年与4～7年的振荡。本文着重分析了2年振荡(TBO)形成的过程、机理及其对东亚降水的影响。对TBO—海洋机理进行了具体的改进,说明了东亚夏季风降水深受TBO影响的原因,尤其是阐明了长江型(YRV)TBO和淮河型(HRV)TBO的特征及其形成的循环过程。(3)在总结亚洲夏季风时期遥相关型的基础上,本文提出了季节内和年际尺度的低空遥相关型:即西北太平洋季风的遥相关型与印度"南支"和"北支"遥相关型。它们基本上反映了沿低空夏季风强风速带Rossby波群速度传播的结果。据此可以根据西北太平洋和印度夏季风的变化分别预测中国梅雨和华北雨季来临和降水异常。最后研究还表明,在本世纪亚洲夏季风可能更显著地受到人类活动造成的全球变暖的影响,未来的亚洲夏季风活动是人类排放的CO2引起的全球变暖与自然变化(海洋和陆面过程(积雪))共同作用的结果。

中国东部夏季降水准两年振荡空间分布及背景场特征

本文采用经验正交函数展开(EOF)及相关分析等方法,使用中国气象局整编的160站1 951～2005年月平均降水资料和NCEP/NCAR再分析资料研究了中国东部夏季降水准两年周期振荡的空间模态及其大气环流背景场.结果表明:(1)中国地区降水季节性差异明显,夏季是主要的降水期并具有明显的准两年周期振荡(TBO)特征,中国东部地区是降水TBO方差变化最大的区域.(2)中国东部夏季降水TBO存在两个主要的空间模态,第1模态以27°N为界南北成反位相的变化关系,降水振幅较大;第2模态降水振幅相对较小,大值中心位于河套华北地区.(3)形成中国东部夏季降水TBO的两个主要空间模态环流背景场明显不同.第1模态与西太平洋海温成正相关,与东太平洋海温成负相关.第2模态则主要与日本海附近的海温成正相关.当夏季降水TBO以江淮偏多时(第1模态),西太平洋海温偏高,东太平洋海温偏低,中国东部及沿海上空850 hPa有异常反气旋,500 hPa高度相关场东亚上空呈"正负正"波列特征,200 hPa南亚高压加强,西风急流位置偏南.当夏季降水TBO降水位置偏北时(第2模态),中国东部及沿海上空有异常气旋,200 hPa南亚高压偏弱,西风急流位置偏北.

对流层准两年振荡最新研究进展

为了更好地了解对流层准两年振荡(Tropospheric Biennial Oscillation,TBO)的最新研究概况及目前存在的问题,基于国家自然科学基金项目关于TBO的专门研究和近年来国内外的TBO研究工作,对TBO研究的最新进展作了综述。最新研究指出,热带暖海区的海-气耦合过程可以维持TBO循环而无需热带东太平洋的参与,表明了TBO确实是独立于ENSO而存在的海-气耦合系统,但是对于TBO的本质问题还需要多方面的深入研究。

中国东部夏季降水准两年周期振荡的长期演变

采用中国气象局整编的中国160站月降水量资料(1951年1月～2005年12月),研究了中国东部地区夏季降水准两年周期振荡(TBO)的长期演变特征。最大熵谱分析和相对最大熵谱分析表明,中国东部地区夏季降水TBO信号显著,高值区基本呈带状分布,方差最大值中心分布在江淮流域及南部沿海地区。根据中国东部夏季降水TBO分量的旋转经验正交函数展开(REOF),将东部地区划分为东北地区、河套地区、淮河流域、长江流域、华南西部、华南中部及华南东部7个降水区。对各降水区的研究结果表明:(1)东部夏季降水振幅变化TBO信号明显;(2)各降水区夏季降水TBO有着不同的长期演变特征,表现出不同的年代际变化。淮河流域、长江流域和华南中部降水TBO特征较明显;华南西部和东北地区降水TBO特征较弱;河套地区在1990年代以前表现有较显著的TBO特征,但1990年代后,TBO特征趋于不明显;华南东部地区在1970年代中期以前TBO特征明显,以后TBO特征减弱;(3)淮河流域是中国东部地区由南向北的过渡带,是夏季降水TBO的敏感地区。

对流层准两年周期振荡的研究进展

对流层大气环流和气象气候要素具有明显的准两年周期振荡,被称为Tropospheric(Quasi-) Biennial Oscillation(TBO)。综述了各种TBO现象及其机理研究。目前发现对流层中温度、气压、风场、降水以及季风、副高等系统都存在TBO变化;其机理研究表明,热带海洋(主要是印度洋和太平洋)和平流层QBO在TBO的形成中起着重要的作用。此外,欧亚雪盖和太阳活动的11年周期可能也会影响TBO。

江南春季降水的准2a振荡及其与热带海温异常的关系

基于中国160站的逐月降水观测资料及NOAA扩展重建的海表温度资料,从1951~2012年逐月的历史时间序列中提取出准2 a振荡（TBO）分量,对中国江南地区春季（3~5月）降水的TBO特征及其与热带海温的关系进行了分析。结果发现：①TBO为江南春季降水最主要的年际周期,TBO分量的方差贡献占到原始序列的52.2%。②江南春季降水与热带海温异常存在明显的时滞关系,其TBO分量与前期Nino3.4区和印度洋海表面温度距平（SSTa）的相关较原始序列更为显著,且持续时间更长,说明热带海温异常对江南春季降水TBO分量的影响是非常显著的。③江南春季降水TBO与Nino3.4指数的时滞关系还呈现出显著的年代际转折,20世纪80年代中期之前,江南春季降水TBO分量与Nino3.4指数在滞后1~11个月内都表现出明显的正相关关系,但从80年代中期至90年代末期这种时滞关系减弱,直至21世纪以来,江南春季降水TBO与Nino3.4指数的时滞关系又重新建立。④通过对比分析年代际转折前后与江南春季降水TBO循环所对应的热带海温演变特征,发现在20世纪80年代中期之前,TBO分量与超前1个季节的赤道中东太平洋海温异常演变具有同步性,使得两者之间的正相关关系稳定;而1986~1999年期间,无论是赤道中东太平洋地区或者印度洋地区海温的演变,都没有表现出像之前类似的TBO循环特征,从而导致两者的相关关系减弱。也就是说,江南春季降水的TBO与中东太平洋海温时滞关系的年代际转折与赤道中东太平洋海温是否具有显著的TBO周期密切相关。

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。

集成物理统计模型在南海夏季风预测中的应用

利用影响南海夏季风年际变化的主要气候现象厄尔尼诺-南方涛动(El Nino-Southern Oscillation,ENSO)和对流层准两年振荡(Tropospheric Biennial Oscillation,TBO)相关的气候因子,提出了以过程判别函数确定物理过程的持续性,建立年际尺度的集成物理统计预测模型,而非年际尺度变率由经验统计模型预测,二者相结合,发展了集成物理-经验统计预测模型。经验模型在拟合时段的回报结果很好,但在独立样本预测时效果明显降低,其中预测评分(PS)降低了23%,距平相关系数(ACC)降低了63%;相比之下,集成物理-经验统计预测模型在独立样本预测时比经验模型有更好的预测结果(PS评分提高了9.5%,ACC提高了75%),且预测结果相对稳定。此外,集成物理-经验统计预测模型对南海夏季风降水的空间分布也有一定预测能力。