2020—2022年与2010—2012年两个“二次变冷”La Nina事件的特征与机制对比

厄尔尼诺-南方涛动(EI Nino-Southern Oscillation, ENSO)是由热带太平洋海-气相互作用产生的显著年际变率,其负位相的拉尼娜(La Nina)事件对中国极端天气有巨大影响。本文利用海洋、大气观测、再分析资料集,对比研究了2010—2012年和2020—2022年两个“二次变冷”La Nina事件演变过程中各阶段的物理过程和机制。结果表明,2010—2012年La Nina事件第一个峰值强于2020—2022年La Nina事件,但第二个峰值较后者弱,且其海表温度异常(Sea surface temperature anomaly, SSTA)偏西,该SSTA的强度和位置特征可从次表层海温异常得到进一步验证。另外,赤道太平洋的东风异常也在2010年夏秋季明显比2020年偏强、偏西;而偏东且增强的东风异常使2020—2022年La Nina事件的第二个冬季峰值强于2010—2012事件。通过海洋混合层热收支诊断分析,纬向平流反馈(海表面热通量异常)是引起La Nina事件发展(衰减)的主要因素。在发展阶段,东风异常引起的纬向海流异常将冷水向西输运,成为赤道中-东太平洋冷SSTA发展的主导因子,垂直方向温跃层反馈过程的贡献也不可忽略。本研究以近十年来的两个“二次变冷”La Nina事件为例进行定性和定量的对比分析,明晰了二者生命演变史过程中的物理机制,为探究La Nina事件生消机理和ENSO不对称性在全球变暖下的可能变化提供了一定的参考。

南方极端雨雪冰冻过程东亚冬季风环流特征及与EINino/La Nina事件的关系

根据南方极端雨雪冰冻过程的定义,确定1964、1969、1977、1984、2008年的强降水、降温过程为南方极端雨雪冰冻过程。对发生在EINino/LaNina事件之后的南方极端雨雪冰冻过程的分析表明:EINino/LaNina是造成中国东部1月降水异常的一个主要原因,但不能解释气温异常。前一年秋季热带中东太平洋发生暖事件时,利于1月降水黄河流域偏少,长江以南偏多,而发生冷事件时,则利于1月降水黄河流域偏多,长江以南偏少。南方极端雨雪冰冻过程期间对流层低层和高层矢量风距平场表明:发生月对流层低层在1977、1984年南方极端雨雪冰冻过程中,北太平洋出现大范围气旋环流异常,中国长江中下游及以南至菲律宾出现气旋环流异常,长江中下游及以南为东风距平控制。1964、1969、2008年北太平洋出现大范围反气旋环流异常,中国长江中下游及以南出现大片偏南风距平。其共同点是均存在洋面上空暖湿空气向长江中下游及以南地区的输送。南方极端雨雪冰冻过程的前一年11月北太平洋无一例外地出现大范围气旋环流异常,发生月对流层高层副热带西风急流在中国黄海至日本一带较常年都有不同程度的偏强。

近40年秦岭南北地区气候变化及与El Nino/La Nina事件相关性分析

通过对近 40年来秦岭南北地区气候变化及与ElNino/LaNina事件相关性研究发现 ,秦岭南北地区气温与降水同步波动 ,但波动幅度有差别。二者都有暖干化趋势 ,秦岭以北变暖程度超过秦岭以南 ,而秦岭以南年降水量的绝对减少量大于秦岭以北 ,两地年平均气温和年降水量差值有缩小趋势。LaNina事件对秦岭南北地区的影响大于ElNino事件 ,LaNina年年平均气温明显下降 ,超过极显著相关水平 ,而降水增多。ElNino年气温略有升高趋势 ,降水略有减少趋势 。

A Data Analysis Study on the Evolution of the EI Nino/ La Nina Cycle

The curved surface of the maximum sea temperature anomaly (MSTA) was created from the JEDAC subsurface sea temperature anomaly data at the tropical Pacific between 1955 and 2000. It is quite similar to the depth distribution of the 20℃ isotherm, which is usually the replacement of thermocline. From the distribution and moving trajectory of positive or negative sea temperature anomalies (STA) on the curved surface we analyzed all the El Nino and La Nina events since the later 1960s. Based on the analyses we found that, using the subsurface warm pool as the beginning point, the warm or cold signal propagates initially eastward and upward along the equatorial curved surface of MSTA to the eastern Pacific and stays there several months and then to (urn north, usually moving westward near 10°N to western Pacific and finally propagates southward to return to warm pool to form an off-equator closed circuit. It takes about 2 to 4 years for the temperature anomaly to move around the cycle. If the STA of warm (cold) water is strong enough, there will be two successive El Nino (La Nina) events during the period of 2 to 4 years. Sometime, it becomes weak in motion due to the unsuitable oceanic or atmospheric condition. This kind process may not be considered as an El Nino ( La Nina) event, but the moving trajectory of warm (cold) water can still be recognized. Because of the alternate between warm and cold water around the circuits, the positive (negative) anomaly signal in equatorial western Pacific coexists with negative (positive) anomaly signal near 10°N in eastern Pacific before the outbreak of El Nino (La Nina) event. The signals move in the opposite directions. So it appears as El Nino (La Nina) in equator at 2-4 years intervals. The paper also analyzed several exceptional cases and discussed the effect and importance of oceanic circulation in the evolution of El Nino/ La Nina event.

Another Record: Ocean Warming Continues through 2021 despite La Nina Conditions

The increased concentration of greenhouse gases in the atmosphere from human activities traps heat within the climate system and increases ocean heat content(OHC). Here, we provide the first analysis of recent OHC changes through 2021 from two international groups. The world ocean, in 2021, was the hottest ever recorded by humans, and the 2021 annual OHC value is even higher than last year’s record value by 14 ± 11 ZJ(1 zetta J = 1021 J) using the IAP/CAS dataset and by16 ± 10 ZJ using NCEI/NOAA dataset. The long-term ocean warming is larger in the Atlantic and Southern Oceans than in other regions and is mainly attributed, via climate model simulations, to an increase in anthropogenic greenhouse gas concentrations. The year-to-year variation of OHC is primarily tied to the El Nino-Southern Oscillation(ENSO). In the seven maritime domains of the Indian, Tropical Atlantic, North Atlantic, Northwest Pacific, North Pacific, Southern oceans,and the Mediterranean Sea, robust warming is observed but with distinct inter-annual to decadal variability. Four out of seven domains showed record-high heat content in 2021. The anomalous global and regional ocean warming established in this study should be incorporated into climate risk assessments, adaptation, and mitigation.

Roles of Wind Stress and Subsurface Cold Water in the Second-Year Cooling of the 2017/18 La Nina Event

After the strong 2015/16 El Nino event,cold conditions prevailed in the tropical Pacific with the second-year cooling of the 2017/18 La Ni?a event.Many coupled models failed to predict the cold SST anomalies(SSTAs)in 2017.By using the ERA5 and GODAS(Global Ocean Data Assimilation System)products,atmospheric and oceanic factors were examined that could have been responsible for the second-year cooling,including surface wind and the subsurface thermal state.A time sequence is described to demonstrate how the cold SSTAs were produced in the central-eastern equatorial Pacific in late 2017.Since July 2017,easterly anomalies strengthened in the central Pacific;in the meantime,wind stress divergence anomalies emerged in the far eastern region,which strengthened during the following months and propagated westward,contributing to the development of the second-year cooling in 2017.At the subsurface,weak negative temperature anomalies were accompanied by upwelling in the eastern equatorial Pacific,which provided the cold water source for the sea surface.Thereafter,both the cold anomalies and upwelling were enhanced and extended westward in the centraleastern equatorial Pacific.These changes were associated with the seasonally weakened EUC(the Equatorial Undercurrent)and strengthened SEC(the South Equatorial Current),which favored more cold waters being accumulated in the central-equatorial Pacific.Then,the subsurface cold waters stretched upward with the convergence of the horizontal currents and eventually outcropped to the surface.The subsurface-induced SSTAs acted to induce local coupled air–sea interactions,which generated atmospheric–oceanic anomalies developing and evolving into the second-year cooling in the fall of 2017.

Decadal Variation of the Impact of La Nina on the Winter Arctic Stratosphere

The impact of La Ni?a on the winter Arctic stratosphere has thus far been an ambiguous topic of research. Contradictory results have been reported depending on the La Ni?a events considered. This study shows that this is mainly due to the decadal variation of La Ni?a’s impact on the winter Arctic stratosphere since the late 1970 s. Specifically,during the period1951–78,the tropospheric La Ni?a teleconnection exhibits a typical negative Pacific–North America pattern,which strongly inhibits the propagation of the planetary waves from the extratropical troposphere to the stratosphere,and leads to a significantly strengthened stratospheric polar vortex. In contrast,during 1979–2015,the La Ni?a teleconnection shifts eastwards,with an anomalous high concentrated in the northeastern Pacific. The destructive interference of the La Ni?a teleconnection with climatological stationary waves seen in the earlier period reduces greatly,which prevents the drastic reduction of planetary wave activities in the extratropical stratosphere. Correspondingly,the stratospheric response shows a less disturbed stratospheric polar vortex in winter.

Can Eurasia Experience a Cold Winter under a Third-Year La Nina in 2022/23?

The Northern Hemisphere(NH)often experiences frequent cold air outbreaks and heavy snowfalls during La Nina winters.In 2022,a third-year La Nina event has exceeded both the oceanic and atmospheric thresholds since spring and is predicted to reach its mature phase in December 2022.Under such a significant global climate signal,whether the Eurasian Continent will experience a tough cold winter should not be assumed,despite the direct influence of mid-to high-latitude,large-scale atmospheric circulations upon frequent Eurasian cold extremes,whose teleconnection physically operates by favoring Arctic air invasions into Eurasia as a consequence of the reduction of the meridional background temperature gradient in the NH.In the 2022/23 winter,as indicated by the seasonal predictions from various climate models and statistical approaches developed at the Institute of Atmospheric Physics,abnormal warming will very likely cover most parts of Europe under the control of the North Atlantic Oscillation and the anomalous anticyclone near the Ural Mountains,despite the cooling effects of La Nina.At the same time,the possibility of frequent cold conditions in mid-latitude Asia is also recognized for this upcoming winter,in accordance with the tendency for cold air invasions to be triggered by the synergistic effect of a warm Arctic and a cold tropical Pacific on the hemispheric scale.However,how the future climate will evolve in the 2022/23 winter is still subject to some uncertainty,mostly in terms of unpredictable internal atmospheric variability.Consequently,the status of the mid-to high-latitude atmospheric circulation should be timely updated by medium-term numerical weather forecasts and sub-seasonal-to-seasonal prediction for the necessary date information and early warnings.

TYPHOON ACTIVITY IN NORTHWEST PACIFIC IN RELATION WITH EL NINO AND LA NINA EVENTS

Statistic and typical-year composition methods are used to study the northwest Pacific typhoon activities in relation with the El Nino and La Nifia events. The result indicates that the typhoon tends to be inactive in the El Nifio years and active in the La Nina years and it is also dependent on the onset and ending time and intensity of the events and areas of genesis of typhoons. With statistic features of the frequency of typhoon activity in the El Nifio and La Nina years and the time-lag correlation between the frequency and sea surface temperature (SST). useful information is provided for the prediction of typhoon occurrence. In addition, the singular values disassemble (SVD) method is applied to study the correlation between the geopotential field and SST field. The result shows that the air-sea coupling in the El Nino years is unfavorable for the typhoon to develop, which take place with a smaller number. Opposite situations are found with the La Nina years.

Asymmetric relationships between El Nino/La Nina and floods/droughts in the following summer over Chongqing,China

This study presents a detailed analysis of the asymmetric relationships between the warm/cold phase of the El Ni?o–Southern Oscillation and the typical flood/drought years in summer over Chongqing.Furthermore,its underpinning mechanisms are also explored.The results show that:(1)El Ni?o and La Ni?a have an asymmetric influence on summer precipitation in the following year over Chongqing.Generally,the composite atmospheric circulation anomalies for El Ni?o years are consistent with the composite results for typical flood years in summer over Chongqing,which indicates a tight link between typical flood years in summer over Chongqing and El Ni?o events.However,the relationship between typical drought years in summer over Chongqing and La Ni?a events is not significant.(2)From winter to the following summer,the extent of positive SST anomalies in the equatorial eastern Pacific associated with typical flood years in summer over Chongqing shrinks,whereas in the tropical Indian Ocean,the extent slightly expands.This trend indicates that the impact of El Ni?o on typical flood years in summer over Chongqing is maintained through the‘relay effect’of SSTs in the tropical Indian Ocean,which is the result of a lagged response of positive SST anomalies in the tropical Indian Ocean to El Ni?o events in winter.

近57年来El Nino/La Nina事件对鄂尔多斯高原东缘气候的影响

根据1955年～2011年期间发生的El Nino／LaNina事件和鄂尔多斯高原东缘3个站点（兴县，绥德和榆林）的气象资料，利用统计分析的方法研究了1955年以来该区的降水量、温度、旱涝灾害与El Nino／LaNina事件之间的关系，揭示了El Nino／LaNina事件对鄂尔多斯高原东缘气候的影响.结果表明，鄂尔多斯高原东缘近57年降水量呈减少趋势而气温呈升高的趋势；厄尔尼诺年降水量比正常年平均降水量少87.6mm，年平均气温比正常年高0.2℃；拉尼娜年降水量比正常年均降水量少22.3mm，年平均气温比正常年低0.1℃，且其年降水量递减率和增温率略高于全国.厄尔尼诺事件对鄂尔多斯高原东缘降水量减少的影响和气温上升的影响要大于拉尼娜事件对鄂尔多斯高原东缘的影响.由小波分析可知，鄂尔多斯高原东缘降水变化在30a尺度内存在2a、8a、20a、27a的变化周期，而气温变化在30a尺度内存在3a、5a,7a、29a的变化周期.El Nino／LaNina事件对该区的旱涝灾害影响显著，旱灾年份出现厄尔尼诺的概率为63％，出现拉尼娜的概率为25％，厄尔尼诺年易于发生旱灾.

Perturbed solution of sea-air oscillator for the El Nino/ La Nina-Southern Oscillation mechanism

A class of coupled system of the E1 Nino/La Nina-Southern Oscillation （ENSO） mechanism is studied. Using the perturbed theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behavior of solution for corresponding problem is considered.

沿22°～18°N航线上CO_2对ENSO和La Nina的响应的季节变化

根据1986年11月～1997年间月期间在114°～130°E，沿22°～18°N航线各航次所测量的大气和表层汽水中的CO2分压和总CO2浓度的变化，分析海气分压差（△PCO2）和溶解的总CO2浓度（TCO2）在不同季节对海气异常事件的响应。结果表明，无论春、夏、秋、冬，在ENSO暴发期和成熟期TCO2为高值，△PCO2为正值；在LaNina时TCO2为低值，△PCO2为负值；在ENSO暴发前、后，海-气C02分压呈近平衡状态；PCO2（air）和PCO2（sw）在各季节对ENSO的响应一致。在ENSO成熟期为高值，在ENSO暴发前和暴发期为低值；海气分压差与PCO2（SW）一致变化，在ENSO期间达最大值。海气CO2输送通量（Flux）以秋季ENSO期间达最大，而在LaNina时减小，在ENSO暴发前和结束后成为相反向，即从大气到海洋的CO2弱输送。本文根据1986年～93年七个航次的平均值讨论了各季节TCO2的距平对ENSO和LaNina的响应特征及最显著变化区段，并依此推断出：1995年10月，显示1991～95年ENSO结束，1996年5月出现ENSO暴发前的信号，在1997年7月是夏季ENSO暴发期特征，在1997年12月呈现强烈的ENSO特征。

The numerical criteria and characteristics of El Nino and La Nina

-By using the sea surface temperature (SST) index of the Equatorial Pacific Ocean provided by Climate Analysis Center of U. S. A. , the numerical criteria of El Nino and La Nina events and their quantitative characteristics were calculated. Results show that the El Nino event was characterized with strong intensity, shorter life cycle and significant mature phase; however, the La Nina event has longer live cycle, weak intensity, insignificant mature phase. Through teleconnection analysis, it is found that the intensity index of SST over the Equatorial Pacific Ocean leads the intensity index of subtropical high by six months or so. During the El Nino years, the tropical cyclone over the northwestern Pacific is fewer than normal but stronger, and its genesis area shifts southeastward apparently; while in the La Nina years the number of tropical cyclones are larger.

The Initial Errors in the Tropical Indian Ocean that Can Induce a Significant “Spring Predictability Barrier” for La Nina Events and Their Implication for Targeted Observations

Initial errors in the tropical Indian Ocean(IO-related initial errors) that are most likely to yield the Spring Prediction Barrier(SPB) for La Ni?a forecasts are explored by using the CESM model.These initial errors can be classified into two types.Type-1 initial error consists of positive sea temperature errors in the western Indian Ocean and negative sea temperature errors in the eastern Indian Ocean,while the spatial structure of Type-2 initial error is nearly opposite.Both kinds of IO-related initial errors induce positive prediction errors of sea temperature in the Pacific Ocean,leading to underprediction of La Nina events.Type-1 initial error in the tropical Indian Ocean mainly influences the SSTA in the tropical Pacific Ocean via atmospheric bridge,leading to the development of localized sea temperature errors in the eastern Pacific Ocean.However,for Type-2 initial error,its positive sea temperature errors in the eastern Indian Ocean can induce downwelling error and influence La Ni?a predictions through an oceanic channel called Indonesian Throughflow.Based on the location of largest SPB-related initial errors,the sensitive area in the tropical Indian Ocean for La Nina predictions is identified.Furthermore,sensitivity experiments show that applying targeted observations in this sensitive area is very useful in decreasing prediction errors of La Nina.Therefore,adopting a targeted observation strategy in the tropical Indian Ocean is a promising approach toward increasing ENSO prediction skill.

Sea level anomalies in the northwestern Pacific during 2011 associated with La Nina and negative Indian Ocean Dipole

The sea level anomalies(SLAs)pattern in the northwestern Pacific delineated significant differences between La Ni?a events occurring with and without negative Indian Ocean Dipole(IOD)events.During the pure La Ni?a events,positive the sea surface level anomalies(SLAs)appear in the northwestern Pacific,but SLAs are weakened and negative SLAs appear in the northwestern Pacific under the contribution of the negative IOD events in 2010/2011.The negative IOD events can trigger significant westerly wind anomalies in the western tropical Pacific,which lead to the breakdown of the pronounced positive SLAs in the northwestern Pacific.Meanwhile,negative SLAs excited by the positive wind stress curl near the dateline propagated westward in the form of Rossby waves until it approached the western Pacific boundary in mid-2011,which maintained and enhanced the negative phase of SLAs in the northwestern Pacific and eventually,it could significantly influence the bifurcation and transport of the North Equatorial Current(NEC).

The responses of CO_2 to El Nino and La Nina in different seasons along 22°-18°N line

The analyses on the responses of partial pressure difference between sea and air (PCO2), and total dissolved CO2 concentration (TCO2), to abnormal air-sea event in different seasons, were based on observational data measured during cruises from Nov. 1986 to Dec 1997 in area of 22°N - 18°N, 114°E-130°E. The results indicated that in every season, TCO2 was high and PCO2 was positive during onset and mature period of El Nino, but they were low and negative respectively during La Nina. Before and after El Nino, partial pressure of CO2 in the sea and air were in the state of equilibrium. Both PCO2 (air) and PCO2 (air) had same responses to E1 Nino in each season. PCO2 (air) and PCO2 (sw) were high during mature period of El Nino were low before and in onset period of El Nino PCO2 and PCO2 (sw) reached peak value during E1 Nino and variation of PCO2 and PCO2 (sw) were same The mean exchange of CO2 from sea to air (flux) reached peak value during El Nino in autumn, and decreased during La Nina. Before and after El Nino the flux is weak, but in opposite direction from air to sea. According to the 1986-1993 average the characteristics of response of TCO2 anomaly to El Nino and La Nina and the range of outstanding variation in different season were discussed. From above it can be deduced some signals showing ENSO event as follows: in Oct.1995, El Nino of 91/95 was over: In May 1995 it is before a new El Nino: In July 1997 it is in onset of new El Nino; In Dec.1997 it is in the mature stage of E1 Nino event.

Frequent central Pacific La Nina events may accelerate Arctic warming since the 1980s

Including significant warming trend,Arctic climate changes also exhibit strong interannual variations in various fields,which is suggested to be related to El Nino and Southern Oscillation(ENSO)events.Previous studies have demonstrated the different impacts on the Arctic of central Pacific(CP)and eastern Pacific(EP)ENSO events,and suggested these impacts are largely of opposite sign for ENSO warm and cold phases.Our results illustrate asymmetrical changes for the cold and warm ENSO events,especially for the La Nina events.Compared to the past frequent basin-wide cooling La Nina events,since the 1980 s the cooling center for the La Nina event has strengthened and moved westward along with the increasing frequency for the canonical and CP La Nina events.Contrary to the basin-wide cooling and canonical La Nina events,the frequent CP La Nina events induce significant warming from the Beaufort Sea to Greenland via the convection center moving northward over the western Pacific.Observation analysis and numerical experiments both suggest that the changes in La Nina type may also accelerate Arctic warming.

不同PDO位相下El Nino发展年和La Nina年东亚夏季风的季节内变化

基于1957~2017年观测和再分析资料,合成分析了北太平洋年代际振荡(Pacific decadal oscillation,PDO)不同位相下El Ni?o发展年和La Nina年东亚夏季风的环流、降水特征及季节内变化。结果表明,PDO正、负位相作为背景场,分别对El Ni?o发展年、La Nina年东亚夏季风及夏季降水具有加强作用。PDO正位相一方面可增强El Ni?o发展年夏季热带中东太平洋暖海温异常信号,另一方面通过冷海温状态加强中高纬东亚大陆与西北太平洋的环流异常,从而在一定程度上增强了东亚夏季风环流的异常程度;反之,PDO负位相则增强了La Nina年热带海气相互作用以及中高纬环流(如东北亚反气旋)的异常。在季节内变化方面,El Ni?o发展年6月贝湖以东反气旋性环流为东亚地区带来稳定的北风异常,东北亚位势高度减弱;7月开始,环流形势发生调整,日本以东洋面出现气旋性异常,东亚大陆偏北风及位势高度负异常均得到加强;8月,随着东亚夏季风季节进程和El Ni?o发展,西太平洋出现气旋性环流异常,东亚副热带位势高度进一步降低,西北太平洋副热带高压(简称副高)明显东退。La Nina年6月异常较弱,主要环流差异自7月西北太平洋为大范围气旋性异常控制开始,东亚-太平洋遥相关型显著,副高于季节内始终偏弱偏东。上述两种情况下,均造成东亚地区夏季降水总体上偏少,尤其是中国北方降水显著偏少。

近50年来El Nino和La Nina事件对河西走廊东部干旱气候的影响

分析近50多年来ElNino和LaNina事件与河西走廊东部干旱气候变化的关系,总结了近几年干旱气候预测服务及其在决策气象服务中发挥的重要作用,特别是应用ElNino和LaNina事件等引起气候变化的强信号,连续几年准确地预测出与农业生产关系最大的春末夏初干旱,为农业种植结构调整和经济可持续发展等提供了重要的决策气象服务依据和建议。