NCEP/CFSR再分析耦合资料中MJO对ENSO的影响研究

基于1979—2008年NCEP/CFSR再分析耦合数据集,研究了冬季MJO对ENSO事件的影响。结果表明,在年际时间尺度以及长期的年代际时间尺度上,热带印度洋MJO活动的强弱性都可以影响热带中东太平洋ENSO事件的发生和发展。在年际时间尺度上,ENSO发生前期征兆的赤道中东太平洋的西风爆发事件(Westerly Wind Burst,WWB),作为MJO影响ENSO的主要途径,存在着显著的次季节时间尺度的变化。相对于气候平均的赤道太平洋西部暖池区上升而东部下沉的Walker环流,MJO正位相东传后的西风异常,减弱了低层东风和赤道东太平洋海水上翻。这一上升海流的减弱导致了中东赤道太平洋的海温升高,从而有利于ENSO暖海温事件的发生。而在年代际时间尺度上,MJO范围和强度在1998年前后出现了明显的转变,1998年之前MJO的东移范围更东,强度更强,从而导致了西太平洋西风爆发区的次季节西风异常事件更加显著,在Bjeknes正反馈机制下对应了年代际时间尺度下的强尼诺事件出现,1998年之后则与之相反。冬季MJO对ENSO影响的这一年代际特征主要体现在晚冬季节,而在早冬伴随着印度洋的增暖,MJO强度一直在逐年增加。

MJO持续异常对ENSO的影响

MJO在夏季会出现在太平洋持续异常活跃和在印度洋持续异常活跃两种形式,用指数定义了这种异常的强度,并发现这种异常表现与秋冬季节ENSO的出现之间有很高的相关性。当夏季MJO在太平洋持续异常活跃时,经常激发当年秋冬季节发生El Nino事件;当夏季MJO在印度洋持续异常活跃时,经常激发当年秋冬季节发生La Nina事件。对大气环流的分析表明,MJO的持续异常活跃会对整个赤道太平洋上空的环流造成影响,引起风应力的异常。异常风应力激发次表层冷/暖海水向东输送。冬季冷/暖海水在东太平洋次表层堆积,最终导致ENSO的形成。

热带MJO和ENSO对西北太平洋热带气旋影响研究综述

对西北太平洋热带气旋的活动规律作了综合评述,简单回顾了热带季节内振荡(MJO)特征和厄尔尼诺/南方涛动(ENSO)特征以及两者间关系,较系统地总结了近年来国内外学者关于MJO和ENSO对西北太平洋海域热带气旋活动影响和机理等方面的研究成果。讨论的热带气旋活动特征包括源地、频数、路径、强度、生命期和登陆等几个方面,并简单讨论了目前该领域存在的科学问题和未来可能的研究方向。

赤道高频纬向风强迫对ENSO事件强度的影响

ENSO强度的影响因子是一个具有争议性的问题。作者探讨了一种理想的赤道高频纬向风强迫对ENSO强度的影响。将该问题转化为一类关于模式参数扰动的非线性最优化问题;基于所用的理论ENSO模式,研究了赤道高频纬向风强迫在调制ENSO强度中的角色。结果表明,对于El Nio和La Nia事件,存在两类外强迫,一类促进El Nio事件的发展却抑制La Nia事件的发展,另一类则抑制El Nio而促进La Nia事件的发展。这两类外强迫的主要区别在于初始相位的不同。相位决定了外强迫对ENSO事件是促进的还是抑制的,而外强迫的振幅和周期则决定了外强迫影响ENSO强度的大小。这些外强迫主要是通过海洋波动对斜温层深度的调节来影响ENSO事件的强度的。

MJO与ENSO关系的研究进展

MJO是热带大气的强信号,ENSO是热带太平洋海气相互作用的最强信号,两者的时间空间尺度不同,但都对全球范围的大气活动有显著的影响,且两者之间也有着密切的关系。总结了近年来MJO和ENSO相互关系方面的研究,并在此基础上提出需要进一步研究的问题。

Effect of Stochastic MJO Forcing on ENSO Predictability

Within the frame of the Zebiak-Cane model,the impact of the uncertainties of the Madden-Julian Oscillation（MJO） on ENSO predictability was studied using a parameterized stochastic representation of intraseasonal forcing.The results show that the uncertainties of MJO have little effect on the maximum prediction error for ENSO events caused by conditional nonlinear optimal perturbation（CNOP）;compared to CNOP-type initial error,the model error caused by the uncertainties of MJO led to a smaller prediction uncertainty of ENSO,and its influence over the ENSO predictability was not significant.This result suggests that the initial error might be the main error source that produces uncertainty in ENSO prediction,which could provide a theoretical foundation for the data assimilation of the ENSO forecast.

ENSO对MJO传播特征演变的影响

利用TRMM降水和ERA-Interim温度、比湿、环流场等再分析资料,探讨了在1998—2018年冬季年际尺度海温变化对MJO的强度、结构和传播特征的影响。主要结论如下:通过一种追踪MJO的方法在研究时间范围内共可挑选出50个MJO事件,其中有14个MJO事件发生在El Ni?o期间,25个发生在La Ni?a期间,11个发生在ENSO正常年。El Ni?o年MJO会传播至更远的中东太平洋附近,而La Ni?a年MJO事件趋于在西太平洋地区消亡,这主要与东太平洋地区持续的季节内尺度的经向水汽输送有关。此外,在印度洋和太平洋地区,El Ni?o年的MJO活动更强,而在海洋性大陆附近,La Ni?a年的MJO活动略强一些。ENSO对MJO强度的影响主要通过影响MJO对流中心东侧水汽的输送,水汽在异常东风气流的输送下穿过对流中心东边界进入对流中心,进而造成MJO活动强度的差异。

从Nio-3指数看MJO不确定性对ENSO可预报性的影响

通过在Zebiak Cane数值模式中引入参数化MJO随机外强迫,着重从Nio 3指数的演变发展探讨了MJO不确定性对ENSO可预报性的影响。结果表明,对Zebiak Cane模式而言,MJO不确定性对由条件非线性最优扰动(CNOP)导致的ENSO事件最大预报误差影响较小;与初始误差相比,由MJO不确定性产生的模式误差在ENSO预报不确定性的产生中具有较小作用,对ENSO可预报性的影响不显著。该结果强调了初始误差在ENSO预报不确定性中的主要作用,从而为ENSO预测的资料同化提供了理论基础。

THE INFLUENCE OF PERSISTENT ANOMALY OF MJO ON ENSO

In this study,two possible persistent anomalies of the Madden-Julian Oscillation mode(MJO) are found in the summer season(persistently Pacific active and Indian Ocean active),and an index is set to define the intensity of the two modes.They are proved to have high statistical correlations to the later ENSO events in the autumn and winter seasons:When persistent anomaly of MJO happens in the Pacific Ocean in summer,El Nino events are often induced during the autumn and winter seasons of that year.However,during the other MJO mode when the summer persistent anomaly of MJO occurs in the Indian Ocean,La Nina events often follow instead.The analysis of the atmospheric circulation field indicates that persistent anomaly of MJO can probably affect the entire Equatorial Pacific circulation,and results in wind stress anomalies.The wind stress anomalies could excite warm or cold water masses which propagate eastwards at the subsurface ocean.The accumulation of warm or cold subsurface water in the Equatorial Eastern Pacific Ocean may eventually lead to the formation of an ENSO.

Combined effect of the QBO and ENSO on the MJO

This study investigates the combined effect of the El Nino–Southern Oscillation(ENSO) and stratospheric quasi-biennial oscillation(QBO) on the Madden Julian Oscillation(MJO). The results show that the western Pacific MJO originating from the Indian Ocean during La Nina/QBO easterly years is stronger than that during El Nino years. This relation, however, disappears during La Nina/QBO westerly years. The reason is that ENSO and the QBO have different effects on each MJO event. For an El Nino year, there is only about one MJO event, and the QBO effect is small. During a La Nina/QBO easterly year, there are 1.7 MJO events, while during a La Nina/QBO westerly year, there are only 0.6 MJO events. El Nino can reinforce the MJO over the western Pacific because of the positive moisture advection of the El Nino mean state by MJO easterly wind anomalies. The QBO mainly affects the MJO over the Maritime Continent region by changing the high-cloud-controlled diurnal cycle;and the Maritime Continent barrier effect is enhanced during the QBO westerly phase because of the strong diurnal cycle. During El Nino years, even the MJO over the Maritime Continent is suppressed by the QBO westerly phase;the MJO can be reinforced over the western Pacific. During La Nina/QBO westerly years,the MJO over the Maritime Continent is suppressed because of the strong Maritime Continent diurnal cycle, and it is further suppressed over the western Pacific because of the lack of a reinforcement process.

MJO随机强迫对CNOP型初始误差演变的影响

用Zebiak-Cane模式和季节内振荡(Madden-Julian Oscillation,MJO)的参数化表述以及条件非线性最优扰动(Conditional Nonlinear Optimal Perturbation,CNOP)方法,分析了以ENSO事件为基态的CNOP型初始误差的空间结构增长规律。结果表明,参数化的MJO对CNOP型初始误差的发展影响较小,其影响主要是使中东太平洋的海表面温度异常增大。CNOP型初始误差比由MJO不确定性产生的模式误差的影响大,前者可能是造成ENSO事件预报不确定性的主要误差来源。由于CNOP型初始误差的局地性,本结论可用来指导ENSO的目标观测和适应性资料同化。

冬季热带西太平洋MJO活动强弱年的环境场特征

利用1948—2011年NCEP等再分析资料,采用合成分析等方法对比分析了冬季(冬半年)热带西太平洋MJO(Madden-Julian Oscillation)活动强、弱年的环境场特征。结果表明,冬季热带西太平洋MJO的活动具有显著的年际和年代际变化。MJO活动强年,对流层低层在菲律宾以东洋面上空有异常气旋式环流,赤道东太平洋上空为较强的东风距平,赤道印度洋到赤道西太平洋上空是异常西风,西太平洋地区有较强辐合,从而导致热带西太平洋地区积云对流活动显著加强;而MJO活动弱年的环流特征相反。热带MJO以东传为主,有少量西传波动。在MJO活动强年,无论东传还是西传其时空谱值都显著大于MJO活动弱年,其中心频率较MJO活动弱年偏高。MJO活动的异常和海温及东亚冬季风紧密相连,在MJO活动强年,海平面气压和500 h Pa位势高度异常场表现为中高纬度的正异常和低纬地区的负异常,东亚冬季风活动偏强,中国大陆中部气温普遍偏低,同时,黄河以南长江以北地区降水偏多,而长江以南地区降水偏少;台湾附近海域受强东亚冬季风影响,海表温度偏低,东太平洋上海温距平呈现La Nia型的异常分布,而在MJO活动弱年上述特征基本相反。

大气模式中季节内振荡特征对不同海温强迫场的响应

利用美国国家大气研究中心 (NCAR)的全球大气模式 (CCM3) ,分别以月平均和周平均海表温度 (SST)为强迫场进行 2个积分试验 (称为 CCMM和 CCMW试验 )。积分结果与观测资料的对比分析发现 ,CCM3模拟大气季节内振荡 (MJO)信号的强度均较观测资料偏弱 ,而其中以CCMW模拟的强度略大而较接近真实。表明 SST强迫场包含更真实的季节内变化信息对提高模拟 MJO强度有作用。 CCMM与 CCMW模拟 MJO活动的时间位相均与观测差别较大 ,直接原因在于 CCM3中降水季节内振荡与 SST变化的相关关系不正确 ,而更根本的问题在于大气模式无法反映资料分析发现的季节内时间尺度的 SST与大气的相互作用。

国际热带大气季节内振荡(MJO)专题讨论会召开

由大气科学和地球流体力学数值模拟国家重点实验室（LASG）和中科院大气物理研究所（IAP）主办的国际热带大气季节内振荡（MJO）专题讨论会于2016年8月6—9日在成都召开,来自美国、加拿大、日本、韩国、欧洲中心等9个国家和地区高校和气象机构的124名学者参加了会议。结合2017—2019年＂海洋大陆年（Years of the Maritime Continent,YMC）＂增强对印度洋到太平洋之间海洋大陆的观测和模拟的倡议.

The Influence of El Ni?o on MJO over the Equatorial Pacific

In this paper, the influence of E1 Nino event on the Madden-Julian Oscillation （MJO） over the equatorial Pacific is stud- ied by using reanalysis data and relevant numerical simulation results. It is clearly shown that E1 Nino can reduce the intensity of MJO. The kinetic energy of MJO over the equatorial Pacific is stronger before the occurrence of the E1 Nino event, but it is reduced rapidly after E1 v event outbreak, and the weakened MJO even can continue to the next summer. The convection over the cen- tral-western Pacific is weakened in E1 Nino winter. The positive anomalous OLR over the central-western Pacific has opposite variation in E1 Nino winter comparing to the non-ENSO cases. The vertical structure of MJO also affected by E1 Nino event, so the opposite direction features of the geopotential height and the zonal wind in upper and lower level troposphere for the MJO are not remarkable in the E1 Nino winter and tend to be barotropic features. El Nino event also has an influence on the eastward propa- gation of the MJO too. During E1 Nino winter, the eastward propagation of the MJO is not so regular and unanimous and there exists some eastward propagation, which is faster than that in non-ENSO case. Dynamic analyses suggest that positive SSTA （El Nino case） affects the atmospheric thickness over the equatorial Pacific and then the excited atmospheric wave-CISK mode is weakened, so that the intensity of MJO is reduced; the combining of the barotropic unstable mode in the atmosphere excited by external forcing （SSTA） and the original MJO may be an important reason for the MJO vertical structure tending to be barotropic during the E1 Nino.

THE CONTRASTS BETWEEN STRONG AND WEAK MJO ACTIVITY OVER THE EQUATORIAL WESTERN PACIFIC IN WINTER

This paper investigates the contrasts between strong and weak Madden-Julian Oscillation(MJO) activity over the equatorial western Pacific during winter using the NCEP reanalysis data. It is shown that the MJO over the equatorial western Pacific in winter shows significant interannual and interdecadal variabilities. During the winters with strong MJO activity, an anomalous cyclonic circulation lies east of the Philippines, strong anomalous easterlies control the equatorial eastern Pacific, and anomalous westerlies extend from the Indian Ocean to the western Pacific in the lower troposphere, which strengthens the convergence and convection over the equatorial western Pacific. The moisture convergence in the lower troposphere is also enhanced over the western Pacific, which is favorable to the activity of MJO. Eastward propagation is a significant feature of the MJO, though there is some westward propagation. The space-time spectral power and center period of the MJO are higher during strong MJO activity winters. The anomalous activity of MJO is closely related to the sea surface temperature(SST) and East Asian winter monsoon(EAWM).During strong MJO activity winters, there are positive/negative anomalies at high/low latitudes in both sea level pressure and 500 h Pa geopotential height, and the temperature is lower over the central part of the Chinese mainland, which indicates a strong EAWM. China experiences more rainfall between the Yellow and Yangtze Rivers, but less rainfall south of the Yangtze River. The SSTA is negative near the Taiwan Island due to the impact of strong EAWM and shows a La Nina pattern anomaly over the eastern Pacific. During the weak MJO activity winters, the situation is reversed.

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。

热带大西洋暖海温促使拉尼娜事件发生的可能性研究

首先,通过对多年冬、春季节热带大西洋海温、夏季大气季节内振荡(MJO)异常活动特征和冬季太平洋ENSO之间的分析研究,发现三者之间存在显著的相关关系。其次,1951年以来最强的两次厄尔尼诺年(1982和1997年)后都跟随着拉尼娜年。因此对1983、1998和2016年大西洋春季海温及MJO信号进行的分析和比较表明,2016年初大西洋关键区海温异常偏暖,与1998年情况较为类似。2016年夏季,MJO可能出现在印度洋异常活跃的情况,并可能导致热带太平洋秋、冬季节出现中等强度的拉尼娜事件。

使用ECMWF集合预报数据集估计全球季节平均气候异常的潜在可预报性

利用ECMWFPROVOST项目产生的在给定海表温度强迫下的 15a(1979～ 1993)季节集合预报数据集 ,分析揭示了季节平均气候异常潜在可预报性的全球分布。首先 ,利用可再现的强迫模态重建集合资料场 ,在Kolmogorov Smirnov(K S)检验的基础上定义潜在可预报性指数PUK,然后 ,将重建场的PUK 与重建场贡献于集合平均的方差比结合 ,提出了定量估计局地潜在可预报性的指数PI。以全球 85 0hPa温度季节平均异常场为例 ,对PI进行定量计算表明 :不仅大部分热带地区 ,而且热带外一些地区的季节平均气候异常具有潜在可预报性 ,主要分布在北美、南非和亚洲部分季风区 ;全球大部分潜在可预报地区主要受ENSO型强迫控制 ,而部分温带地区如中国华北、中亚、北美南部主要受非ENSO型强迫控制 ;局地潜在可预报性具有季节性 ,夏季可预报性较强 ,冬季较弱。通过与其他几种估计季节潜在可预报性的方法进行比较表明 。

Impact of ENSO on MJO Pattern Evolution over the Maritime Continent

The modulation of Madden–Julian oscillation(MJO)pattern evolution over the Maritime Continent(MC)by El Nino–Southern Oscillation(ENSO)was investigated through a combined observational and modeling study.MJO convective branches shifted south of the equator over the MC during eastern Pacific(EP)El Nino winters,while it became relatively symmetric about the equator during La Ni?a winters.The impact of central Pacific(CP)El Ninos to MJO pattern,on the other hand,is not statistically significant.The cause of the distinctive MJO pattern evolutions is likely attributed to the ENSO-induced changes of the background moisture and vertical shear over the MC.Idealized numerical experiments with a 2.5-layer model were carried out,and the result revealed that the background moisture change played a dominant role.An observational diagnosis of column-integrated moist static energy(MSE)budgets was further conducted.The result indicated that the MJO pattern difference was attributed to the MSE tendency asymmetry in front of MJO convection between EP El Nino and La Ni?a,caused by the advection of the mean MSE by anomalous meridional wind.The difference in the MJO-scale anomalous meridional wind was ultimately controlled by the change of the background meridional moisture gradient associated with EP El Nino and La Ni?a.