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.

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.

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.

Impacts of Anthropogenic Forcings and El Nio on Chinese Extreme Temperatures

This study investigates the potential influences of anthropogenic forcings and natural variability on the risk of summer extreme temperatures over China. We use three multi-thousand-member ensemble simulations with different forcings （with or without anthropogenic greenhouse gases and aerosol emissions） to evaluate the human impact, and with sea surface temperature patterns from three different years around the E1 Nino-Southern Oscillation （ENSO） 2015/16 event （years 2014, 2015 and 2016） to evaluate the impact of natural variability. A generalized extreme value （GEV） distribution is used to fit the ensemble results. Based on these model results, we find that, during the peak of ENSO （2015）, daytime extreme tem- peratures axe smaller over the central China region compared to a normal year （2014）. During 2016, the risk of nighttime extreme temperatures is largely increased over the eastern coastal region. Both anomalies are of the same magnitude as the anthropogenic influence. Thus, ENSO can amplify or counterbalance （at a regional and annual scale） anthropogenic effects on extreme summer temperatures over China. Changes are mainly due to changes in the GEV location parameter. Thus, anomalies are due to a shift in the distributions and not to a change in temperature variability.

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.

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。

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。

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。

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.

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。

ENSO背景下山西忻州7-8月极端降水对玉米产量的影响

利用忻州各县(市、区)42 a 7-8月的降水数据和23 a的玉米产量数据,分析了极端降水对玉米气候产量的影响。结果表明:在1981-2022年期间,忻州及其各县(市、区)7-8月的极端降水指数均呈上升的变化趋势,上升速率由西部向东部逐渐增加;玉米实际单产及趋势产量均呈显著的上升趋势;玉米气候产量与极端降水指数呈正相关,两者间的相关系数在海拔较高地区明显大于平川地区;正极端降水事件发生在拉尼娜结束年的概率明显高于开始年,负极端降水事件发生在厄尔尼诺开始年(或持续年)的概率明显高于结束年;正、负极端降水事件一般与玉米气候产量的丰、歉相对应;因ENSO而发生的极端降水事件使得忻州的玉米气候产量平均下降了15.3 kg/hm^(2),下降幅度近7%。

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。

关于ENSO事件及其对中国气候影响研究的综述

Nio指数和SOI是表征ENSO事件的两个主要特征值。根据Nio3.4区指数变化,1950年以来共发生15次ElNio事件和11次LaNia事件。ElNio年,热带中、东太平洋上的岛屿及沿岸国家多暴雨洪涝,印度、印度尼西亚、澳大利亚等国家发生持续干旱,中国东北地区夏、秋季降水及年降水都偏少,江南地区降水偏多;太平洋和大西洋地区发生的热带风暴以及登陆中国的台风数都比常年偏少;加拿大西南部和美国北部暖冬,东亚夏季低温,中国常出现暖冬凉夏。LaNia年则基本上相反,赤道太平洋中、东部地区干旱少雨,西太平洋上的台风和大西洋飓风及登陆中国的台风明显增多,中国汛期主要雨带偏北,易出现热夏寒冬。

ENSO事件对中国气候的可能影响

利用 1 95 1 -1 998年的北太平洋海温和中国的温度、降水月平均资料 ,分析了ENSO事件对中国夏季主要雨带、长江中下游梅雨、华北雨季和中国秋冬季降水、温度、台风之间的可能影响 ,结果表明ENSO事件是影响中国气候的重要因素之一。

MJO对我国天气气候影响的新事实

在次季节时间尺度上,热带大气季节内振荡(MJO)是全球气候变率的首要模态。MJO不仅对热带天气气候产生直接影响,还能够通过传播和激发大气遥相关等方式对热带外地区产生重要影响,成为目前次季节—季节气候预测最重要的可预报性来源。MJO对于我国天气气候影响的探索由来已久,在很多方面有了显著进展,但仍需深入研究。首先对MJO影响我国天气气候的过往研究进行了回顾,并进一步利用新的观测资料诊断分析,发现了MJO对我国气候影响的一些新事实。初步结论包括:MJO对我国冬季降水的影响主要局限在江南—华南区域,而夏季扩展到南方和青藏高原地区;对冬季气温的影响较大,其范围覆盖了东北、华北以及西部广大区域,而夏季解释方差有所减小,其区域位于除了黄河流域以外的广大地区;在去掉高频噪音后,纯粹MJO信号对我国主要区域气温和降水低频变化的解释方差可接近30%;MJO对我国冬夏季温度降水的影响存在明显滞后效应,应在使用MJO信号进行我国气象要素预报时加以考虑。

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.

中部型ENSO和平流层准两年振荡对冬季北半球平流层臭氧的联合调制作用

利用观测和再分析资料通过合成分析方法,研究了中部型ENSO和平流层准两年振荡(QBO)对冬季北半球平流层臭氧的独立影响和联合调制作用。研究表明,北半球平流层臭氧在中部型厄尔尼诺年增加,而在中部型拉尼娜年减少;准两年振荡东风位相年份,北半球平流层臭氧增加,准两年振荡西风位相结果则相反。相比之下,北半球中、高纬度平流层臭氧异常对准两年振荡活动的响应明显小于其对ENSO活动的响应。进一步研究发现,准两年振荡东风位相会加强中部型厄尔尼诺事件引起的北半球平流层臭氧的增加,而减弱中部型拉尼娜事件造成的平流层臭氧的减少。在准两年振荡西风位相下,中部型厄尔尼诺事件仅导致北半球平流层臭氧含量少量升高,而中部型拉尼娜事件期间臭氧会大幅度减少。因此,准两年振荡东风位相会加强中部型厄尔尼诺事件对北半球平流层臭氧的影响,而减弱中部型拉尼娜事件对北半球平流层臭氧的影响。准两年振荡西风位相会减弱中部型厄尔尼诺而加强中部型拉尼娜事件对北半球平流层臭氧的影响。