破解“厄尔尼诺”之谜——评河海版科普新书《厄尔尼诺》

20世纪80年代以来,在世界范围内,越来越频繁地出现灾害性天气气候。进入2002年,这种世界性的灾害天气气候更加明显。欧洲德国、匈牙利等国的洪水,中南美洲秘鲁等国的暴雨,亚洲中国南方地区及印度北方地区的洪涝。

Subtropical Air-Sea Interaction and Development of Central Pacific El Nio

The standard deviation of the central Pacific sea surface temperature anomaly （SSTA） during the period from October to February shows that the central Pacific SSTA variation is primarily due to the occurrence of the Central Pacific E1 Nifio （CP-E1 Nifio） and has a connection with the subtropical air-sea interaction in the northeastern Pacific. After removing the influence of the Eastern Pacific E1 Nifio, an S-EOF analysis is conducted and the leading mode shows a clear seasonal SSTA evolving from the subtropical northeastern Pacific to the tropical central Pacific with a quasi-biennial period. The initial subtropical SSTA is generated by the wind speed decrease and surface heat flux increase due to a north Pacific anomalous cyclone. Such subtropical SSTA can further influence the establishment of the SSTA in the tropical central Pacific via the wind-evaporation-SST （WES） feedback. After established, the central equatorial Pacific SSTA can be strengthened by the zonal advective feedback and thermocline feedback, and develop into CP-E1 Nifio. However, as the thermocline feedback increases the SSTA cooling after the mature phase, the heat flux loss and the reversed zonal advective feedback can cause the phase transition of CP-EI Nifio. Along with the wind stress variability, the recharge （discharge） process occurs in the central （eastern） equatorial Pacific and such a process causes the phase consistency between the thermocline depth and SST anomalies, which presents a contrast to the original recharge/discharge theory.

ECHAM5-Simulated Impacts of Two Types of El Nio on the Winter Precipitation Anomalies in South China

The authors used an atmospheric general circulation model （AGCM） of European Centre Hamburg Model （ECHAM5.4） and investigated the possible impacts of eastern Pacific （EP） and central Pacific （CP） El Ni（n）o on the winter precipitation anomalies in South China.A composite analysis suggested much more rainfall during the mature phase of EP El Ni（n）o than in the case of CP El Ni（n）o,and their corresponding observed wet centers to be located in the southeast coast and the region to the south of the Yangtze River,respectively.Results obtained on the basis of model-sensitive run imply that the modelsimulated rainfall anomalies agree well with the observation,and the magnitude of simulated rainfall anomalies were found to be reduced when the amplitude of sea surface temperature anomaly （SSTA） forcing of EP and CP El Ni（n）o was cut down.These results imply that the rainfall anomaly in South China is very sensitive not only to the type of El Ni（n）o but also to its intensity.

Impacts of ENSO on wintertime PM_(2.5)pollution over China during 2014-2021

China has implemented a series of emission reduction policies since 2013,and the concentration of air pollutants has consequently decreased significantly.However,PM_(2.5)(particulate matter with an aerodynamic diameter less than_(2.5)μm)pollution still occurs in China in relation to the interannual variations in meteorological conditions.Considering that El Nino-Southern Oscillation(ENSO)is the strongest signalmodulating the interannual variation in the atmosphere-ocean system,in this study the authors investigate the variations in PM_(2.5)concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021.Results show that the wintertime PM_(2.5) concentrations in the Beijing-Tianjin-Hebei and Fenwei Plain regions during El Nino years are higher than those during La Nina years,which can be explained by the anomalous southerly(northerly)winds during El Nino(La Nina) favoring PM_(2.5) accumulation(diffusion).In the Pearl River Delta region,PM_(2.5)concentrations decrease in El Nino relative to La Nina years owing to the enhanced water vapor flux and precipitation,removing more PM_(2.5)from the atmosphere.The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_(2.5)over the Yangtze River Delta region,which should be analyzed case by case.

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.

Research on the Relationship of ENSO and the Frequency of Extreme Precipitation Events in China

Based on a daily precipitation observation dataset of 743 stations in China from 1951 2004, the F distribution function is used to calculate the probability distribution of daily precipitation and to define extreme precipitation events. Based on this, the relationship of ENSO and the frequency of extreme precipitation events is studied. Results reveal that ENSO events have impact on extreme precipitation events, with different magnitudes at different regions and seasons. In general, during winter and spring, extreme precipitation events occur more often during E1 Nino events than during La Nina events. While during summer and autumn, the opposite is found. The relationship of a two season-lag ENSO and extreme precipitation frequency shows different pattern. Extreme precipitation events occur more often in several regions if an ENSO warm phase happened in the central-eastern tropical Pacific two seasons before. No similar impacts of El Nino and La Nina on the frequency of extreme precipitation events are found.

Impacts of the Two Types of El Ni?o on Pacific Tropical Cyclone Activity

It is well known that Tropical cyclone （TC） activities over the Pacific are affected by E1 Nino events. In most studies El Nifio phenomena have been separated into east Pacific warming （EPW） and central Pacific wanning （CPW） based on the location of maximum SST anomaly. Since these two kinds of El Nino have different impacts on Pacific tropical cyclone activities, this study investigates different features of TC activities and the genesis potential index （GPI） during EPW years and CPW years. Four eontrib- nting factors, i.e., the low-level absolute vorticity, the relative humidity, the potential intensity and the vertical wind shear, are exam- ined to determine which factors are most important in causing the anomalous TC activities. Our results show that during EPW years in July-August （JA-0）, TC activities are more frequent with stronger intensity over the Western North Pacific （WNP） and Eastern North Pacific （ENP）. The maximum anomaly center of TC activities then drifts eastward siguifieantly in September-October （SO-0）. However, centers of anomalous TC activity barely change from JA-0 to SO-0 during CPW years. In January-February-March （JFM-1） of the decaying years of warming events, TC frequency and intensity both have positive anomaly over the South Pacific, The anoma- lies in EPW years have larger amplitude and wider spatial distribution than those in CPW years. These anomalous activities of TC are associated with GPI anomaly and the key factors affecting GPI anomaly for each ocean basin are quite different.

Traditional El Nio and El Ni o Modoki Revisited:Is El Nio Modoki Linearly Independent of Traditional El Nio?

The present study revisited the first two leading modes of tropical Pacific sea surface temperature anomalies （SSTA） during the period of 1979-2008. It is suggested that the so-called El Nino Modoki, which is captured by the second mode, exists objectively and exhibits obvious differences from traditional El Nifio, which is captured by the first mode, in terms of its spatial characteristics. Furthermore, the authors found that El Nino Modoki is linearly independent of traditional El Nino; hence, it cannot be described as part of the traditional El Nino evolution, and vice versa.

Asymmetric Response of the South China Sea SST to El Nio and La Nia

The interannual variability of the sea surface temperature （SST） in the South China Sea （SCS） is investigated according to its relationship with E1 Nifio/La Nifia （EN/LN） using monthly products from ICOADS. The SCS SST bears two peaks associated with EN/LN and shows the asymmetric features. Coinciding with the mature phase of EN/LN, the first SST warming/cooling peaks in December（0）-February（1） （DJF（1）） and centers in the southern part. The major difference is in the amplitude associated with the strength of EN/LN. However, the SCS SST anomaly shows distinct difference after the mature phase of EN/LN. The EN SST warm- ing develops a mid-summer peak in June-August（1） （JJA（1）） and persists up to September-October（l）, with the same amplitude of the first warming peak. Whereas the LN SST cooling peaks in May（l）, it decays slowly until the end of the year, with amplitude much weaker. Comparing with SST and atmospheric circulations, the weak response and early termination of the second cooling is due to the failure of the cyclonic wind anomalies to develop in the northwest Pacific during JJA（1）.

Super Typhoon Activity over the Western North Pacific and Its Relationship with ENSO

This paper analyzes the characteristics of super typhoons （STYs） over the western North Pacific （WNP） from 1965 to 2005 and describes the seasonal variability of STY activity. The relation between STY activity and the E1 Nifio-Southern Oscillation （ENSO） as well as the possible reason for the influence of the ENSO on STY activity are also investigated. The results showed that about one fifth of the tropical cyclones （TCs） over the WNP could reach the rank of STY. Most STYs appeared from July to November while there was a highest ratio between number of STYs and total number of TCs in November. Most STYs appeared east of the Philippine Sea. In E1 Nino years, affected by sea surface temperature （SST）, monsoon trough and weak vertical wind shear, TC formation locations shifted eastward and there were more STYs than in La Nifia years when the affecting factors changed.

An enhanced influence of sea surface temperature in the tropical northern Atlantic on the following winter ENSO since the early 1980s

Previous studies have revealed a connection between springtime sea surface temperature （SST） in the tropical northern Atlantic （TNA） and the succeeding wintertime El Nino-Southern Oscillation （ENSO）. The present analysis demonstrates that the linkage between springtime TNA SST and the following ENSO experiences an obvious interdecadal change around the early 1980s, with the connection being weak before but significant after. After the early 1980s, springtime positive TNA SST anomalies induce an anomalous cyclone over the northeastern subtropical Pacific and an anomalous Walker circulation with a descending branch over the tropical central-eastern Pacific. This leads to anomalous cold SST in the northeastern Pacific and an anomalous anticyclone over the western-central tropical Pacific, with anomalous easterlies to the equatorward side. As such, springtime TNA SST anomalies are followed by wintertime ENSO after the early 1980s. In contrast, before the early 1980s, anomalous cold SST in the northeastern Pacific and related anomalous easterlies over the western-central tropical Pacific are weak, corresponding to springtime positive TNA SST anomalies and resulting in a weak linkage between springtimeTNA SST and the succeeding wintertime ENSO. Further investigation implies that the change in the TNA SST-ENSO relationship is probably due to a change in springtime mean precipitation over the tropical Atlantic and South America.

Contrasting the Indian and western North Pacific summer monsoons in terms of their intensity of interannual variability and biennial relationship with ENSO

The intensity of interannual variability(IIV)of the monsoon and monsoon–ENSO biennial relationship(MEBR)were examined and compared for both the Indian summer monsoon(ISM)and western North Pacific summer monsoon(WNPSM)during 1958–2018.Covariability of the IIV and MEBR were identified for the two monsoons.When the MEBR was strong(weak),the IIV of the monsoon was observed to be large(small).This rule applied to both the ISM and WNPSM.Out-ofphase relationships were found between the ISM and the WNPSM.When the IIV and MEBR of the ISM were strong(weak),those of the WNPSM tended to be weak(strong).During the period with a stronger(weaker)ENSO–Atlantic coupling after(before)the mid-1980 s,the IIV and MEBR of the WNPSM(ISM)were observed to be stronger.The increasing influences from the tropical Atlantic sea surface temperature(SST)may trigger the observed seesaw pattern of the ISM and WNPSM in terms of the IIV and MEBR multidecadal variability.The results imply that tropical Atlantic SST may need to be given more attention and consideration when predicting future monsoon variability of the ISM and WNPSM.

Environmental anomalies in the northeastern East China Sea during the last 3 000 years:implications for El Nio activity in the Holocene

To reconstruct the productivity changes for the last 10 500 a in the northeastern East China Sea （ECS）, biogenic compounds （such as carbonate, organic carbon and opal）, marine micropaleontological fossils （planktonic foraminifera, benthic foraminifera, radiolarian and silicoflagellate） and the compositional characters of benthic foraminifera fauna analyses were carried out on a sediment core DOC082 obtained from the western slope of Okinawa Trough （29°13.93′N, 128°08.53′E; 1 128 m water depth）. The long-term changes of biogenic and micropaleontological proxies display some similarities through the last 10 500 a, which show three different phases： lower values are recorded during the early and middle ttolocene （before about 4 000 a BP）, followed by an abrupt and remarkable increase at about 4 000 a BP, the late Holocene （after about 3 000 a BP） is characterized by continuously high values. The multi-proxy data of paleoproductivity and percents of benthic foraminifera genera （Uvigerina and Bulimina） show that during the early and middle Holocene （10 500-4 000 a BP） productivity was relatively low with a sudden and distinct increase at about 4 000 a BP, and the late Holocene （3 400-0 a BP） is marked by significantly higher productivity. Also, the radiolarian-based sea surface temperature （SST） records reveal a distinct decline in SST in the late Holocene after 3 200 a BP, very different from the early and middle Holocene. For the last 3 000 a, the enhanced biological productivity and distinctly lower SST indicate a major change of oceanographic conditions in the northeastern ECS. These marine environmental anomalies are consistent with other paleoclimatic records for the late Holocene in the Chinese continent and its surrounding regions. After analyzing the mechanisms of modern productivity and SST changes in the northeastern ECS, and based on the climatic anomalies in the Chinese continent and variations in the Kuroshio Current during modern El Nino periods, we suggest that the anomalous environmental conditions in the northeastern ECS may imply intensified El Nino activity during the late Holocene.

Enhanced correlation between ENSO and western North Pacific monsoon during boreal summer around the 1990s

The correlation between summertime Nino3.4 index and western North Pacific(WNP)summer monsoon index has strikingly enhanced since the early 1990 s,with nonsignificant correlation before the early1990 s but significant correlation afterward.This observed interdecadal change around the 1990 s may be associated with more frequent occurrences of central Pacific(CP)El Nino and the interdecadal changes in ENSO-associated SST anomalies.During the post-1990 s period(the pre-1990 s period),highly noticeable tropical Atlantic(Indian)Ocean SST anomalies tend to co-occur with the summertime Nino3.4 SST anomalies.The concurrent tropical Atlantic(Indian)Ocean SST anomalies could constructively reinforce(destructively mitigate)the WNP monsoon circulation anomalies induced by the summertime Nino3.4 SST,thus boosting(muting)the correlation between summertime Nino3.4 SST and WNP monsoon.In addition,the faster decaying pace of preceding-winter El Nino after the 1990 s,which may have been mainly induced by the influences from the spring tropical North Atlantic SST anomalies,could also have contributed to the enhanced correlation between the summertime Nino3.4 index and WNP monsoon.These results suggest that the enhanced influences from the tropical Atlantic SST may have triggered the intensified correlation between summertime ENSO and WNP monsoon since the early 1990 s.

Movements of the Western Pacific Warm Pool Centroid and Their Relationship to Sea Surface Temperature Changes in Nino Regions

By using monthly historical sea surface temperature (SST) data for the yearsfrom 1950 to 2000, the Western Pacific Warm Pool (WPWP) climatology and anomalies are studied inthis paper. The analysis of WPWP centroid (WPWPC) movement anomalies and the Nino-3 region SSTanomalies(SSTA) seems to reveal a close, linear relation between the zonal WPWPC and Nino-3 regionSSTA, which suggests that a 9° anomaly of the zonal displacement from the climatological positionof the WPWPC corresponds to about a 1℃ anomaly in the Nino-3 region area-mean SST. This studyconnects the WPWPC zonal displacement with the Nino-3 SSTA, and it may be helpful in betterunderstanding the fact that the WPWP eastward extension is conducive to the Nino-3 region SSTincrease during an El Nino-Southern Oscillation (ENSO) event.

Distinguished Effects of Interannual Salinity Variability on the Development of the Central-Pacific El Ni o Events

El Nio events in the central equatorial Pacific (CP) are gaining increased attention,due to their increasing intensity within the global warming context.Various physical processes have been identified in the climate system that can be responsible for the modulation of El Nio,especially the effects of interannual salinity variability.In this work,a comprehensive data analysis is performed to illustrate the effects of interannual salinity variability using surface and subsurface salinity fields from the Met Office ENSEMBLES (EN3) quality controlled ocean dataset.It is demonstrated that during the developing phase of an El Nio event,a negative sea surface salinity (SSS) anomaly in the western-central basin acts to freshen the mixed layer (ML),decrease oceanic density in the upper ocean,and stabilize the upper layers.These related oceanic processes tend to reduce the vertical mixing and entrainment of subsurface water at the base of the ML,which further enhances the warm sea surface temperature (SST) anomalies associated with the El Nio event.However,the effects of interannually variable salinity are much more significant during the CP-El Nio than during the eastern Pacific (EP) El Nio,indicating that the salinity effect might be an important contributor to the development of CP-El Nio events.

The impact of solar activity on the 2015/16 El Ni?o event

Recent SST and atmospheric circulation anomaly data suggest that the 2015/16 El Nino event is quickly decaying. Some researchers have predicted a forthcoming La Nina event in late summer or early fall 2016. From the perspective of the modulation of tropical SST by solar activity, the authors studied the evolution of the 2015/16 El Nino event, which occurred right after the 2014 solar peak year. Based on statistical and composite analysis, a significant positive correlation was found between sunspot number index and El Ni^o Modoki index, with a lag of two years. A clear evolution of El Nino Modoki events was found within 1-3 years following each solar peak year during the past 126 years, suggesting that anomalously strong solar activity during solar peak periods favors the triggering of an El Nino Modoki event. The patterns of seasonal mean SST and wind anomalies since 2014 are more like a mixture of two types of El Nino （i.e. eastern Pacific El Nino and El Nino Modoki）, which is similar to the pattern modulated by solar activity during the years following a solar peak. Therefore, the El Nino Modoki component in the 2015/16 El Nino event may be a consequence of solar activity, which probably will not decay as quickly as the eastern Pacific El Nino component. The positive SST anomaly will probably sustain in the central equatorial Pacific （around the dateline） and the northeastern Pacific along the coast of North America, with a low-intensity level, during the second half of 2016.

Revisiting Asymmetry for the Decaying Phases of El Ni?o and La Ni?a

This study investigated the relationship be- tween the asymmetry in the duration of El Nifio and La Nina and the length of their decaying phases. The results suggested that the duration asymmetry comes from the long decaying ENSO cases rather than the short decaying ones. The evolutions of short decaying El Nino and La Nina are approximately a mirror image with a rapid decline in the following summer for the warm and cold events. However, a robust asymmetry was found in long decaying cases, with a prolonged and re-intensified La Nina in the following winter. The asymmetry for long decaying cases starts from the westward extension of the zonal wind anomalies in a mature winter, and is further contributed to by the air-sea interaction over the tropical Pacific in the following seasons.

Interannual variations of North Equatorial Current transport in the Pacific Ocean during two types of El Ni?o

Interannual variations of Pacific North Equatorial Current （NEC） transport during eastern- Pacific E1 Nifios （EP-EI Nifios） and central-Pacific E1 Nifios （CP-E1 Nifios） are investigated by composite analysis with European Centre for Medium-Range Weather Forecast Ocean Analysis/Reanalysis System 3. During EP-E1 Nifio, NEC transport shows significant positive anomalies from the developing to decay phases, with the largest anomalies around the mature phase. During CP-EI Nifio, however, the NEC transport only shows positive anomalies before the mature phase, with much weaker anomalies than those during EP-El Nifio. The NEC transport variations are strongly associated with variations of the tropical gyre and wind forcing in the tropical North Pacific. During EP-E1 Nifio, strong westerly wind anomalies and positive wind stress curl anomalies in the tropical North Pacific induce local upward Ekman pumping and westward-propagating upwelling Rossby waves in the ocean, lowering the sea surface height and generating a cyclonic gyre anomaly in the western tropical Pacific. During CP-E1 Nifio, however, strength of the wind and associated Ekman pumping velocity are very weak. Negative sea surface height and cyclonic flow anomalies are slightly north of those during EP El Nino.

Effect of Decadal Changes in Air-Sea Interaction on the Climate Mean State over the Tropical Pacific

Collaboration of interannual variabilities and the climate mean state determines the type of E1 Nifio. Recent studies highlight the impact of a La Nifia-like mean state change, which acts to suppress the convection and low-level convergence over the central Pacific, on the predominance of central Pacific （CP） E1 Nifio in the most recent decade. However, how interannual variabilities affect the climate mean state has been less thoroughly investigated. Using a linear shallow-water model, the ef- fect of decadal changes of air-sea interaction on the two types of El Nifio and the climate mean state over the tropical Pacific is examined. It is demonstrated that the predominance of the eastem Pacific （EP） and CP E1 Nino is dominated mainly by relationships between anomalous wind stresses and sea surface temperature （SST）. Furthermore, changes between air-sea interactions from 1980-98 to 1999-2011 prompted the generation of the La Ninalike pattern, which is similar to the background change in the most recent decade.