热带季节内振荡研究新进展

季节内振荡既是热带大气活动的强信号，也是热带海洋中较为普遍的现象。本文叙述了热带大气和热带海洋季节内振荡研究的进展，包括热带大气季节内振荡的观测研究、机制研究以及热带海洋季节内振荡方面的研究；讨论了海气相互作用、不同尺度间相互作用对季节内振荡的影响；在总结上述研究成果的基础上提出了热带季节内振荡研究进一步的发展方向。     

热带大气季节内振荡的一个数值模拟研究

文中分析了中国科学院大气物理研究所全球气候谱模式ALGCM (R4 2L9) 12a(1978～ 1989年 )积分的逐日输出结果 ,并与 1978～ 1989年的逐日NCEP资料对照 ,以此对热带季节内振荡 (30～ 6 0d振荡 )进行数值模拟研究。分析表明 ,该模式在热带地区可以模拟出明显的季节内振荡 (ISO)的准周期信号 ,并抓住了热带ISO的基本传播特征 ,能较好地再现东、西半球传播速度的差异 ,同时模式模拟存在东传要好于西传 ,冬、春季的模拟要好于夏、秋季的现象。该模式模拟的热带ISO的强度较许多大气模式明显提高 ,尤其是对 2 0 0hPa上ISO动能强度的模拟。模式基本模拟出了ISO低层辐合、高层辐散的水平风场特征。模式较好地再现了热带ISO纬向风的垂直结构。此外 ,观测资料表明热带ISO在冬、春强 ,而夏、秋弱的季节性倾向与ISO的年际变化相联系 ,模拟的ISO在季节性倾向偏差上表现为冬、夏相对强 ,而春、秋相对弱。垂直速度、散度、水汽等物理量的配置同NCEP资料的结构特征仍有明显差异 ,模拟的ISO空间分布也不太理想 ,表明要很好模拟ISO结构和空间分布特征 ,还须做不少工作。     

外强迫对热带季节内振荡影响的模拟研究

应用经过修改的NCAR CCM3模式和CAM2模式进行的数值实验结果以及NCEP的GFS模式的输出结果讨论了海温等外强迫作用对热带季节内振荡的影响.结果表明,热带季节内振荡是热带大气固有的内部变率.它是由大气内部过程的相互作用决定的.但外强迫对热带季节内振荡的强度、传播方向等有明显的影响.当外强迫没有变化时,模式可以模拟出与观测近似的低频振荡.当作为外强迫的海温和太阳辐射有年内季节变化时,模式模拟的季节内振荡则明显减弱.当海温与辐射不仅有季节变化而且有年际变化时,模式模拟的季节内振荡会进一步减弱.具有长周期的外强迫还会削弱季节内振荡中东移波动的能量而增加静止波的强度.在与海洋模式耦合的状态下,模式不受来自海洋的外强迫影响,而是与海洋构成一个耦合系统,可以产生最强的季节内振荡.     

北京气候中心大气模式对季节内振荡的模拟

对北京气候中心大气模式(BCC AGCM2.0.1)模拟热带季节内振荡的能力进行了检验.北京气候中心新一代气候模式(BCC AGCM2.0.1)是在原中国国家气候中心模式的基础上参考NCAR CAM3改进形成的.新模式中引进了一个新的参考大气和参考面气压.因此原模式的预报量中的气温(T)和地面气压(p_s)则变为它们对参考大气气温的偏差和对参考面气压的偏差.模式还加入了新的Zhang-Mcfarlane对流参数化方案,并对其参数计算方法进行调整和改进.此外还对模式边界层处理、雪盖计算等进行了改进.上述模式在实测的月海温作为下边界条件的情况下运行52年(1949年9月-2001年10月).然后对运行结果中的季节内振荡的状况进行分析,主要结果如下:NCAR CAM3模式模拟热带季节内振荡的能力很差,主要表现在模拟的热带季节内振荡强度很弱;东移波与西移波的强度很接近,而实际观测中是东移波的能量要远大于西移波;季节内振荡的季节变化及空间分布与观测相差很远.北京气候中心大气模式(BCC AGCM2.0.1)模拟热带季节内振荡的能力有显著的提高.模拟的热带季节内振荡很明显,强度接近于观测结果;模拟东移波的能量要大于西移波,这与观测较为一致;季节内振荡的季节变化和空间分布与观测相差不大.总的来看,BCC AGCM2.0.1模式在模拟热带季节内振荡方面比CAM3模式有明显的改进.     

热带季节内振荡时空特征的诊断研究

文中应用谱分析、小波分析等方法及较长时段的资料进一步总结了热带季节内振荡的一些基本气候特征。热带季节内振荡主要活跃在 3个地区 ,最强的是西太平洋地区 ,其次是印度洋地区 ,第三是东太平洋沿岸的赤道以北地区。热带季节内振荡有明显的季节变化 ,西太平洋地区和印度洋地区的季节内振荡 1a中有两次极大值 ,冬季主要活跃在南半球 (10°S附近 ) ,而夏季则活跃在北半球 (10°N附近 ) ,春、秋季热带季节内振荡则明显减弱。东赤道太平洋北侧的季节内振荡只在夏季活跃 ,而冬季则很弱 ,且不随季节而南北移动。对于大气的大尺度要素 ,例如u风场 ,热带季节内振荡的能量主要集中在 1波。而对于像降水这样尺度较小的要素 ,热带季节内振荡的能量则相对较分散 ,尽管它仍然在 1波有最大的能量 ,但 2～ 4波也具有较接近的能量。热带季节内振荡以东移的波动为主。热带季节内振荡存在着年际甚至更长时间的变化。 2 0世纪 70年代末期季节内振荡的幅度有一明显的突变。     

中国热带大气季节内振荡研究进展

热带大气季节内振荡(包括MJO)是大气环流的重要系统,它的活动及异常既对其他系统有一定的作用,也对长期天气和短期气候有明显影响。因此,热带大气季节内振荡一直是大气科学的前沿研究课题之一。文中对近5—10年中国学者的有关研究工作及其进展做了简要回顾和综合,主要包括:(1)热带大气季节内振荡特别是MJO的动力学机制;(2)热带大气季节内振荡以及MJO的数值模拟问题,特别是大气非绝热加热廓线对模式模拟MJO的重要作用;(3)热带大气季节内振荡和MJO,特别是在赤道西太平洋地区,与ENSO的相互作用关系;(4)热带大气季节内振荡(包括MJO)及其流场形势对西太平洋台风活动的重要影响,即MJO对西北太平洋台风生成数的调制作用,以及热带大气季节内低频气旋性(LFC)和反气旋性(LFAC)流场对西太平洋台风路径的影响;(5)热带大气季节内振荡(包括MJO)的活动及异常对东亚和南亚夏季风建立、活动异常的影响,以及它们与中国降水异常的密切关系。     

层云加热对热带大气季节内振荡的影响

本文研究了层云降水加热对于激发热带大气季节内振荡(Madden-Julian oscillation,简称MJO)所起到的作用.将层云加热作用引入到非线性的CISK (Conditional Instability of Second Kind)-Kelvin波方程组,并分别利用截谱方法和四阶Runge-Kutta方法...     

热带大气季节内振荡对华南前汛期降水的影响

本文基于实时的热带大气季节内振荡(MJO)指数和中国台站降水资料,研究了MJO对中国华南前汛期(4～6月)降水的影响.结果表明,随着MJO的活跃中心从印度洋进入西太平洋,华南地区的降水由偏多转为偏少.最显著的降水正负异常分别位于第4位相和第7位相,其区域平均的最大正负异常值相对于气候平均值的变化约为17%和11%.与降...     

季节内振荡的数值模拟Ⅰ.模拟的自然变率

利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室 (LASG) 发展的耦合气候系统模式FGOALS 1.0_g控制试验 (二氧化碳浓度保持工业革命前的浓度不变, 代表无人类活动影响的自然变率) 模拟结果, 研究了模拟的自然变率下热带季节内振荡 (Intraseasonal Oscillation, 简称ISO) 的基本特征与年际、年代际变化.研究发现, 模拟的自然变率下全球ISO主要活跃区与近六十年的实测结果基本接近; ISO主要活跃区的季节变动特征与实际结果基本一致; 全球ISO强度冬强、夏弱的季节变化也与实际结果一致; 但模拟的ISO强度偏弱与ISO周期不明显.进一步利用控制试验模拟结果研究了模拟的自然变率下热带ISO特征的年际与年代际变化, 得出: 第一, 模拟的自然变率下的热带ISO强度存在明显的年际与年代际变化, 低强度指数阶段, 全球ISO强度减弱, 活跃区范围缩小, 高强度指数阶段则相反; 并存在季节性差异, 冬季不明显, 春秋季明显, 实测结果有类似结论, 但高、低指数似乎与增暖有关.第二, 模拟的自然变率下的热带东传或西传ISO能量比值总体来看基本上维持一种平衡状态, 不存在上升或下降趋势; 与实际状况下的东传相对能量增强、西传相对能量减弱趋势明显不同.     

Research Progress in China on the Tropical Atmospheric Intraseasonal Oscillation

Tropical intraseasonal oscillation (including the Madden-Julian oscillation) is an important element of the atmospheric circulation system. The activities and anomalies of tropical intraseasonal oscillations affect weather and climate both inside and outside the tropical region. The study of these phenomena therefore represents one of the frontiers of atmospheric sciences. This review aims to synthesize and summarize studies of intraseasonal oscillation (ISO) by Chinese scientists within the last 5-10 years. We focus particularly on ISO's mechanisms, its numerical simulations (especially the impacts of diabatic heating profiles), relationships and interactions with ENSO (especially over the western Pacific), impacts on tropical cyclone genesis and tracks over the northwestern Pacific, and influences on the onset and activity of the South and East Asian monsoons (especially rainfall over China). Among these, focuses of ongoing research and unresolved issues related to ISO are also discussed.     

A GCM Study on the Tropical Intraseasonal Oscillation

The ability of AGCM to simulate the tropical intraseasonal oscillation (ISO) has been studied using the output of global spectral model (ALGCM (R42L9)) of the Institute of Atmospheric Physics, Chinese Academy of Sciences, and the outoput is compared with the results from NCEP/NCAR reanalysis for the year 1978-1989. The model displays an evident periodic signal of the tropical ISO. Basic propagating characters of the tropical ISO are captured, and changes in phase speed between Eastern and Western Hemispheres are also well presented, and the simulation of eastward propagation is better than that of westward propagation. This model has increased the ability to simulate the strength of the tropical ISO, especially at 200 hPa, and basically simulates the horizontal structure of wind characterized by the convergence in low-level and divergence in upper-level. The vertical structure of the zonal wind is also well reproduced. Moreover, observed results show that the representing of seasonal preference to form strong ISO in winter and spring is related to ISO's interannual variability, but it is shown in this model with strong ISO in winter and summer and weak ISO in spring and autumn. Structures of some physical elements such as vertical velocity, divergence, specific humidity, etc., and the special distribution of ISO have also differences with these from NCEP reanalysis data, which make it clear to develop this model to simulate the structure and spatial distribution of the ISO.     

热带大气季节内振荡的进一步分析

利用ＥＣＭＷＦ的格点资料对热带大气季节内振荡作了进一步分析研究,表明热带大气季节内振荡既有Ｋｅｌｖｉｎ波型扰动,也有Ｒｏｓｓｂｙ波型扰动;影响热带大气季节内振荡移动的主要因素有扰动波型和积云对流活动的异常;伴随ＥｌＮｉｎｏ事件的发生,热带大气季节内振荡的动能急剧减小,而准定常扰动动能急剧增大,既反映了热带大气季节内振荡对ＥｌＮｉｎｏ的激发作用,也说明了在ＥｌＮｉｎｏ期间热带大气季节内振荡偏弱的原因。     

El Ni?o影响热带大气季节内振荡的动力学研究

根据El Ni?o期间热带大气状态的异常特征，确定了在简单大气动力模式中描写海温异常的参数化方法。然后利用斜压半地转两层模式从动力学上分析研究了El Ni?o对热带大气低频波的影响。理论分析同有关热带大气季节内振荡的资料分析结果完全一致，El Ni?o事件使热带大气季节内振荡减弱。     

有关全球变暖对热带大气季节内振荡特征的影响及其数值模拟的研究

首先用资料诊断分析了全球变暖前后,热带大气低频振荡特征变化。研究发现,全球变暖前后,热带低频振荡的强度、分布、传播及周期等发生了一系列变化:ISO活跃区及强度范围均有不同程度的增大,气候变暖有缩小ISO强度季节差异趋势;气候变暖后,纬向东传波的大气季节内振荡能量增加,而西传波的能量相对减少;偏暖阶段,ISO振荡主周期相对分散,特别是较长周期的小波能量明显增大。然后利用动力学分析及数值模拟进一步探讨了热带低频振荡与海温的联系,对热带ISO的数值模拟进一步发现,大气模式与海洋模式耦合时,所模拟的热带季节内振荡较强;热带低频振荡的变化可能与全球变暖后海温场发生的变化有关。     

Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

The sensitivity of the simulated tropical intraseasonal oscillation or MJO （Madden and Julian oscillation） to different cumulus parameterizations is studied by using an atmospheric general circulation model （GCM）--SAMIL （Spectral Atmospheric Model of IAP LASG）. Results show that performance of the model in simulating the MJO alters widely when using two different cumulus parameterization schemes-the moist convective adjustment scheme （MCA） and the Zhang-McFarlane （ZM） scheme. MJO simulated by the MCA scheme was found to be more realistic than that simulated by the ZM scheme. MJO produced by the ZM scheme is too weak and shows little propagation characteristics. Weak moisture convergence at low levels simulated by the ZM scheme is not enough to maintain the structure and the eastward propagation of the oscillation. These two cumulus schemes produced different vertical structures of the heating profile. The heating profile produced by the ZM scheme is nearly uniform with height and the heating is too weak compared to that produced by the MCA, which maybe contributes greatly to the failure of simulating a reasonable MJO. Comparing the simulated MJO by these two schemes indicate that the MJO simulated by the GCM is highly sensitive to cumulus parameterizations implanted in. The diabatic heating profile plays an important role in the performance of the GCM. Three sensitivity experiments with different heating profiles are designed in which modified heating profiles peak respectively in the upper troposphere （UH）, middle troposphere （MH）, and lower troposphere （LH）. Both the LH run and the MH run produce eastward propagating signals on the intraseasonal timescale, while it is interesting that the intraseasonal timescale signals produced by the UH run propagate westward. It indicates that a realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low levels, especially in the middle levels, while westward propagating disturbances     

Numerical Simulation and Comparison Study of the Atmospheric Intraseasonal Oscillation

Daily mean outputs for 12 yr (1978-1989) from two general circulation models (SAMIL-R42L9 and CAM2.0.2) are analyzed and compared with the corresponding NCEP/NCAR reanalysis dataset, and results in two models show clearly that the root-mean square errors (RMSEs) from the simulation of intraseasonal oscillation can take 30-40 percent of the total RMSE, particularly, the distributions of the RMSE in simulating intraseasonal oscillation are almost identical with that of the total RMSE. The maximum RMSE of intraseasonal oscillation height at 500 hPa is shown in the middle latitude regions, but there are also large RMSEs of intraseasonal oscillation wind over the tropical western Pacific and tropical Indian Oceans. The simulated ISO energy in the tropic has very large difference from the result of the NCEP/NCAR reanalysis dataset which means the simulation of tropical atmospheric ISO still possesses serious insufficiency. Therefore, intraseasonal oscillation in the weather and climate numerical simulation is very important, and thus, how to improve the ability of the GCM to simulate the intraseasonal oscillation becomes very significant.     

Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

The sensitivity of the simulated tropical intraseasonal oscillation or MJO (Madden and Julian oscilla tion)to different cumulus parameterizations is studied by using an atmospheric general circulation model (GCM)-SAMIL(Spectral Atmospheric Model of IAP LASG).Results show that performance of the model in simulating the MJO alters widely when using two different cumulus parameterization schemes-the moist convective adjustment scheme(MCA)and the Zhang-McFarlane(ZM)scheme.MJO simulated by the MCA scheme was found to be more realistic than that simulated by the ZM scheme.MJO produced by the ZM scheme is too weak and shows little propagation characteristics.Weak moisture convergence at low levels simulated by the ZM scheme is not enough to maintain the structure and the eastward propagation of the oscillation.These two cumulus schemes produced different vertical structures of the heating profile.The heating profile produced by the ZM scheme is nearly uniform with height and the heating is too weak compared to that produced by the MCA,which maybe contributes greatly to the failure of simulating a reasonable MJO.Comparing the simulated MJO by these two schemes indicate that the MJO simulated by the GCM is highly sensitive to cumulus parameterizations implanted in.The diabatic heating profile plays an important role in the performance of the GCM.Three sensitivity experiments with different heating profiles are designed in which modified heating profiles peak respectively in the upper troposphere(UH), middle troposphere(MH),and lower troposphere(LH).Both the LH run and the MH run produce eastward propagating signals on the intraseasonal timescale,while it is interesting that the intraseasonal timescale signals produced by the UH run propagate westward.It indicates that a realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low levels,especially in the middle levels,while westward propagating disturbances axe more prone to be produced when the maximum heating appears very high.     

热带大气季节内振荡的传播及影响因子研究

通过观测资料的分析,对热带大气季节内振荡(ISO)的传播(移动)进行了深入系统的研究,揭示了热带大气ISO的纬向和经向移动的特征,以及热带大气低频动能的跨赤道传播特征.同时,通过对比分析还揭示了ENSO和热带对流加热场异常对热带大气ISO移动的影响.