Millennial and orbital variations of El Niño/Southern Oscillation and high-latitude climate in the last glacial period

The El Ni?o/Southern Oscillation (ENSO) phenomenon is believed to have operated continuously over the last glacial-interglacial cycle. ENSO variability has been suggested to be linked to millennial-scale oscillations in North Atlantic climate during that time, but the proposals disagree on whether increased frequency of El Ni?o events, the warm phase of ENSO, was linked to North Atlantic warm or cold periods. Here we present a high-resolution record of surface moisture, based on the degree of peat humification and the ratio of sedges to grass, from northern Queensland, Australia, covering the past 45,000 yr. We observe millennial-scale dry periods, indicating periods of frequent El Ni?o events (summer precipitation declines in El Ni?o years in northeastern Australia). We find that these dry periods are correlated to the Dansgaard-Oeschger events--millennial-scale warm events in the North Atlantic climate record--although no direct atmospheric connection from the North Atlantic to our site can be invoked. Additionally, we find climatic cycles at a semiprecessional timescale (approximately 11,900 yr). We suggest that climate variations in the tropical Pacific Ocean on millennial as well as orbital timescales, which determined precipitation in northeastern Australia, also exerted an influence on North Atlantic climate through atmospheric and oceanic teleconnections.     

Variation of the NAO and NPO associated with climate jump in the 1960s

The interannual variation of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO) and its relationship with the climate jump in the Northern Hemisphere in the 1960s, are discussed using the data analyses. It is clearly shown that the amplitudes of the NAO and NPO were all increased obviously in the 1960s and the main period of the oscillations changed from 3–4 years before the 1960s to 8–15 years after the 1960s. Therefore, the climate jump in the 1960s is closely related to the anomalies of the NAO and NPO.     

Interannual and interdecadal variations in the North Atlantic Oscillation spatial shift

The spatial shift of the North Atlantic Oscillation (NAO) is analyzed by using the Twentieth Century Reanalysis version 2 dataset and identifying NAO action centers directly on winter mean sealevel pressure (SLP) anomaly maps. The spatial shift of the NAO is characterized by four NAO spatial shift indices: the zonal and meridional shifts of the NAO southern and northern action centers. It is found that the zonal and meridional shift trends of the NAO action centers move along a path of southwest-northwest direction. Spectral analysis shows that the four NAO spatial shift indices have periodicity of 2-6 years and the NAO index has periodicity of 2-3 years in terms of high-frequency variations. On a decadal time scale, the NAO spatial shift indices are closely (positively) related to the NAO index, which is in agreement with previous studies of the relationship between the NAO index and the spatial shift of the NAO pattern. However, there is no relationship between the NAO index and the meridional shift of the northern action center on an interannual time scale. The significant relationship between the NAO index and the interannual variability of NAO spatial shift indices is very likely to be associated with synopticscale Rossby wave breaking, which generates surface pressure anomalies and thus affects the phase and pattern of the NAO. The correlations of winter westerly winds over 90°W-0° and the NAO index and the NAO spatial shift indices have a ’+ - + -’ structure from the Equator to the North Pole. Although there is close correlation between the NAO spatial shift indices and the strength of the zonal winds in the North Atlantic region, the effect of the zonal winds on the NAO spatial shift differs at different latitudes. Hence, the role of the zonal winds is probably a result of the NAO spatial shifts.     

Forced response of atmospheric oscillations during the last millennium simulated by a climate system model

Variations in global atmospheric oscillations during the last millennium are simulated using the climate system model FGOALS_gl. The model was driven by reconstructions of both natural forcing (solar variability and volcanic aerosol) and anthropogenic forcing (greenhouse gases and sulfate aerosol). The model results are compared against proxy reconstruction data. The reconstructed North Atlantic Oscillation (NAO) was out of phase with the Pacific Decadal Oscillation (PDO) in the last millennium. During the ...     

Synchronization of animal population dynamics by large-scale climate

The hypothesis that animal population dynamics may be synchronized by climate is highly relevant in the context of climate change because it suggests that several populations might respond simultaneously to climatic trends if their dynamics are entrained by environmental correlation. The dynamics of many species throughout the Northern Hemisphere are influenced by a single large-scale climate system, the North Atlantic Oscillation (NAO), which exerts highly correlated regional effects on local weather. But efforts to attribute synchronous fluctuations of contiguous populations to large-scale climate are confounded by the synchronizing influences of dispersal or trophic interactions. Here we report that the dynamics of caribou and musk oxen on opposite coasts of Greenland show spatial synchrony among populations of both species that correlates with the NAO index. Our analysis shows that the NAO has an influence in the high degree of cross-species synchrony between pairs of caribou and musk oxen populations separated by a minimum of 1,000 km of inland ice. The vast distances, and complete physical and ecological separation of these species, rule out spatial coupling by dispersal or interaction. These results indicate that animal populations of different species may respond synchronously to global climate change over large regions.     

Atmospheric oscillations over the last millennium

The variations of global atmospheric oscillations over the last millennium, including the North Atlantic Oscillation (NAO), the North Pacific Oscillation (NPO) highly associated with the Pacific Decadal Oscillation (PDO), the Southern Oscillation (SO) and the Antarctic Oscillation (AAO), are studied and compared in this paper based on observations and reconstructed data. The cross correlation analysis of AAO, NAO and NPO shows that there is no significant relationship on interannual variation among them. However, the consistency on decadal variability is prominent. During A.D.1920–1940 and A.D.1980–2000, the positive (strong) phase was dominant and the negative (weak) one noticeable during A.D.1940–1980. In addition, the reconstructed atmospheric oscillations series demonstrate that the positive phase existed in the early of the last millennium for NAO and in the late of the last millennium for AAO, respectively; while it occurred in the mid-late of the last millennium for PDO and ENSO.     

新疆玛纳斯河径流波动与北大西洋涛动的关系

对新疆玛纳斯河流量资料、北疆地区温度、降水资料进行整理,分析了其变化的特征和规律,并将其与北大西洋涛动指数进行了对比分析.研究发现,冬季北大西洋涛动指数与玛纳斯河冬季流量呈现显著的正向变化关系,夏季两者的关系则相反.利用交叉小波变换,分别发现了冬、夏季北大西洋涛动指数与玛纳斯河流量变化关系最密切的振荡周期.文中还发现冬、夏季北大西洋涛动指数与北疆温度、降水的变化也存在显著的相关关系.     

Eastern Pacific cooling and Atlantic overturning circulation during the last deglaciation

Surface ocean conditions in the equatorial Pacific Ocean could hold the clue to whether millennial-scale global climate change during glacial times was initiated through tropical ocean-atmosphere feedbacks or by changes in the Atlantic thermohaline circulation. North Atlantic cold periods during Heinrich events and millennial-scale cold events (stadials) have been linked with climatic changes in the tropical Atlantic Ocean and South America, as well as the Indian and East Asian monsoon systems, but not with tropical Pacific sea surface temperatures. Here we present a high-resolution record of sea surface temperatures in the eastern tropical Pacific derived from alkenone unsaturation measurements. Our data show a temperature drop of approximately 1 degrees C, synchronous (within dating uncertainties) with the shutdown of the Atlantic meridional overturning circulation during Heinrich event 1, and a smaller temperature drop of approximately 0.5 degrees C synchronous with the smaller reduction in the overturning circulation during the Younger Dryas event. Both cold events coincide with maxima in surface ocean productivity as inferred from 230Th-normalized carbon burial fluxes, suggesting increased upwelling at the time. From the concurrence of equatorial Pacific cooling with the two North Atlantic cold periods during deglaciation, we conclude that these millennial-scale climate changes were probably driven by a reorganization of the oceans' thermohaline circulation, although possibly amplified by tropical ocean-atmosphere interaction as suggested before.     

Arctic sea ice bordering on the North Atlantic and interannual climate variations

Variations of winter Arctic sea ice bordering on the North Atlantic are closely related to climate variations in the same region. When winter North Atlantic Oscillation (NAO) index is positive (negative) anomaly phase, Icelandic Low is obviously deepened and shifts northwards (southwards). Simultaneously, the Subtropical High over the North Atlantic is also intensified, and moves northwards (southwards). Those anomalies strengthen (weaken) westerly between Icelandic Low and the Subtropical High, and further result in positive (negative) sea surface temperature (SST) anomalies in the mid-latitude of the North Atlantic, and increase (decrease) the warm water transportation from the mid-latitude to the Barents Sea, which causes positive (negative) mixed-layer water temperature anomalies in the south part of the Barents Sea. Moreover, the distribution of anomaly air temperature clearly demonstrates warming (cooling) in northern Europe and the subarctic regions (including the Barents Sea) and cooling (warming) in Baffin Bay/Davis Strait. Both of distributions of SST and air temperature anomalies directly result in sea ice decrease (increase) in the Barents/Kara Seas, and sea ice increase (decrease) in Baffin Bay/Davis Strait. :     

不同平均强度热盐环流的年代际波动特征

基于美国国家大气研究中心的CCSM3(community climate system model version 3)模式,对淡水扰动试验下不同平均强度热盐环流(thermohline circulation,THC)的年代际波动特征及北大西洋气候响应特征进行研究。结果表明,百年以上尺度的THC变化对其年代际尺度波动产生显著影响,高平均强度下THC的年代际波动周期更长、更显著。对不同平均强度下北大西洋海、气要素与THC在年代际尺度上的相关分布进行分析,发现在高平均强度下,THC与海表温度(sea surface temperature,SST)的相关呈现为经向三核型分布,与海平面气压(sea lever pressure,SLP)的相关呈现为类NAO(North Atlantic oscillation)分布,而在低平均强度下,则不存在这2种模态分布;同时,在不同平均强度下,THC与各要素间的相关程度也不同,高平均强度下相关程度更高。     

Forced response of atmospheric oscillations during the last millennium simulated by a climate system model

Variations in global atmospheric oscillations during the last millennium are simulated using the climate system model FGOALS_gl. The model was driven by reconstructions of both natural forcing (solar variability and volcanic aerosol) and anthropogenic forcing (greenhouse gases and sulfate aerosol). The model results are compared against proxy reconstruction data. The reconstructed North Atlantic Oscillation (NAO) was out of phase with the Pacific Decadal Oscillation (PDO) in the last millennium. During the Medieval Warm Period (MWP), the NAO was strong while the PDO was weak. During the Little Ice Age (LIA), the NAO was weak while the PDO was strong. A La Niña-like state prevailed in the MWP, while an El Niño-like state dominated in the LIA. This phenomenon is particularly obvious in the 15th, 17th and 19th centuries. Analysis of the model output indicates that the NAO was generally positive during 1000?C1400 AD and negative during 1650?C1900 AD. There is a discrepancy between the simulation and reconstruction during 1400?C1650 AD. The simulated PDO generally varies in parallel with the reconstruction, which has a negative phase during the MWP and a positive phase during the LIA. The correlation coefficient between the reconstruction and simulation is 0.61, and the correlation is statistically significant at the 1% level. Neither the La Niña-like state of the MWP nor the El Niño-like state of the LIA is reproduced in the model. Both the reconstructed and the simulated Antarctic Oscillations had a negative phase in the early period of the last millennium and a positive phase in the late period of the last millennium. The Asian-Pacific Oscillation was generally strong during the WMP and weak during the LIA, and the correlation coefficient between the simulation and reconstruction is 0.50 for the period 1000?C1985 AD. The analysis suggests that the specified external forcings significantly affected the evolution of atmospheric oscillation during the last millennium.     

近40年大尺度气候因子对中国洪涝灾害的可能影响

基于中国1980—2018年0.5°×0.5°逐日降水数据、紧急灾害数据库数据（EM-DAT）,分析了厄尔尼诺-南方涛动（ENSO）和北大西洋涛动（NAO）对中国极端降水频次及强度、洪水发生率及损失的可能影响．结论如下:1)当冬季厄尔尼诺发生后,次年我国东部沿海及黄河、长江下游地区秋季极端降水强度增加26%;当冬季拉尼娜发生后,次年我国东部地区春、夏季极端降水强度分别增加8.8%、5.1%．2)当NAO为正位相时,我国大部分地区春、夏、秋季极端降水频次较高,华东地区夏季极端降水强度增加8.5%．3)与正常年份相比,冬季厄尔尼诺或拉尼娜发生后,次年我国春季洪水损失偏多14.5%,秋季洪水发生率偏低30%;NAO为正位相时,我国春季洪水损失偏少20%,秋季洪水发生率偏高14%．4)当拉尼娜发生后及NAO正位相、负位相时,我国长江、黄河和珠江流域极端降水与洪涝灾害的变化具有一致性．      

Applications of nonlinear optimization methods to quantifying the predictability of a numerical model for El Nino-Southern Oscillation

The nonlinear optimization methods are applied to quantify the predictability of a numerical model for El Nino-Southern Oscillation (ENSO). We establish a lower bound of maximum predictability time for the model ENSO events (i.e. ENSO events in the numerical model), an upper bound of maximum prediction error, and a lower bound of maximum allowable initial error, all of which potentially quantify the predictability of model ENSO. Numerical results reveal the phenomenon of “spring predictability barrier” (SPB) for ENSO event and support the previous views on SPB. Additionally, we also explore the differences between the linear evolution of prediction error and its nonlinear counterpart. The results demonstrate the limitation of linear estimation of prediction error. All these above results suggest that the nonlinear optimization method is one of the useful tools of quantifying the predictability of the numerical model for ENSO.     

Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean

Climate variability in the tropical Atlantic Ocean is determined by large-scale ocean-atmosphere interactions, which particularly affect deep atmospheric convection over the ocean and surrounding continents. Apart from influences from the Pacific El Ni?o/Southern Oscillation and the North Atlantic Oscillation, the tropical Atlantic variability is thought to be dominated by two distinct ocean-atmosphere coupled modes of variability that are characterized by meridional and zonal sea-surface-temperature gradients and are mainly active on decadal and interannual timescales, respectively. Here we report evidence that the intrinsic ocean dynamics of the deep equatorial Atlantic can also affect sea surface temperature, wind and rainfall in the tropical Atlantic region and constitutes a 4.5-yr climate cycle. Specifically, vertically alternating deep zonal jets of short vertical wavelength with a period of about 4.5?yr and amplitudes of more than 10?cm?s(-1) are observed, in the deep Atlantic, to propagate their energy upwards, towards the surface. They are linked, at the sea surface, to equatorial zonal current anomalies and eastern Atlantic temperature anomalies that have amplitudes of about 6?cm?s(-1) and 0.4?°C, respectively, and are associated with distinct wind and rainfall patterns. Although deep jets are also observed in the Pacific and Indian oceans, only the Atlantic deep jets seem to oscillate on interannual timescales. Our knowledge of the persistence and regularity of these jets is limited by the availability of high-quality data. Despite this caveat, the oscillatory behaviour can still be used to improve predictions of sea surface temperature in the tropical Atlantic. Deep-jet generation and upward energy transmission through the Equatorial Undercurrent warrant further theoretical study.     

The relationship between the thermohaline circulation and climate variability

The long-term integration with the Global Ocean-Atmosphere-Land System model of the State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics(IAP), Chinese Academy of Sciences has been used in the investigations on the relationship between the thermohaline circulation and climate variability. The results show that the strength of the North Atlantic Thermohaline circulation (THC) is negatively correlated with the North Atlantic Oscillation (NAO). Based on this kind of relationship, and also the instrument-measured climate record such as air pressure and sea surface temperature, the activity of the thermohaline circulation during the 20th century has been evaluated. The inferred variations of the strength of the THC is that, during two multi-decadal periods of 1867–1903 and 1934–1972, the THC is estimated to have been running stronger, whereas during the two periods of 1904–1933 and 1973–1994, it appears to have been weaker.     

Tropical climate changes at millennial and orbital timescales on the Bolivian Altiplano

Tropical South America is one of the three main centres of the global, zonal overturning circulation of the equatorial atmosphere (generally termed the 'Walker' circulation). Although this area plays a key role in global climate cycles, little is known about South American climate history. Here we describe sediment cores and down-hole logging results of deep drilling in the Salar de Uyuni, on the Bolivian Altiplano, located in the tropical Andes. We demonstrate that during the past 50,000 years the Altiplano underwent important changes in effective moisture at both orbital (20,000-year) and millennial timescales. Long-duration wet periods, such as the Last Glacial Maximum--marked in the drill core by continuous deposition of lacustrine sediments--appear to have occurred in phase with summer insolation maxima produced by the Earth's precessional cycle. Short-duration, millennial events correlate well with North Atlantic cold events, including Heinrich events 1 and 2, as well as the Younger Dryas episode. At both millennial and orbital timescales, cold sea surface temperatures in the high-latitude North Atlantic were coeval with wet conditions in tropical South America, suggesting a common forcing.     

全球地表温度大气遥相关路径研究

基于复杂网络方法,分析不同区域地表温度之间存在的相关关系及其时滞,建立了体现大气遥相关的全球地表温度网络,进而给出地表温度网络遥相关路径．研究表明:网络连接的空间距离在3 500和7 000 km处有1个峰值,这与大气Rossby波的1/2和1倍波长一致．地表温度网络中,影响传播的主导节点在北半球分布在东亚、向西延伸的北太平洋、美国东海岸及邻接的北大西洋地区;在南半球分布在50° S纬度带．遥相关现象在南半球比北半球更显著,典型遥相关路径与不同的环流作用有明确对应:1）北太平洋中部到墨西哥的连接反映了西风带的作用;2）北大西洋传播到非洲北部、格陵兰岛到里海的连接,均属于连接北大西洋到欧亚大陆的跨欧亚波列的一部分;3）俄罗斯喀拉海到北太平洋的连接与北大西洋涛动（NAO）密切关联;4）南半球的连接反映了大气西风带和Rossby波的影响．大气遥相关路径分析有利于深化对地表温度变化的认识,可为减缓气候全球变化提供理论基础．      

Lagged effects of ocean climate change on fulmar population dynamics

Environmental variation reflected by the North Atlantic Oscillation affects breeding and survival in terrestrial vertebrates, and climate change is predicted to have an impact on population dynamics by influencing food quality or availability. The North Atlantic Oscillation also affects the abundance of marine fish and zooplankton, but it is unclear whether this filters up trophic levels to long-lived marine top predators. Here we show by analysis of data from a 50-year study of the fulmar that two different indices of ocean climate variation may have lagged effects on population dynamics in this procellariiform seabird. Annual variability in breeding performance is influenced by the North Atlantic Oscillation, whereas cohort differences in recruitment are related to temperature changes in the summer growing season in the year of birth. Because fulmars exhibit delayed reproduction, there is a 5-year lag in the population's response to these effects of environmental change. These data show how interactions between different climatic factors result in complex dynamics, and that the effects of climate change may take many years to become apparent in long-lived marine top predators.     

Advancing decadal-scale climate prediction in the North Atlantic sector

The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic, and surface-temperature and rainfall variations over North America, Europe and northern Africa. Although these multidecadal variations are potentially predictable if the current state of the ocean is known, the lack of subsurface ocean observations that constrain this state has been a limiting factor for realizing the full skill potential of such predictions. Here we apply a simple approach-that uses only sea surface temperature (SST) observations-to partly overcome this difficulty and perform retrospective decadal predictions with a climate model. Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state, particularly in the North Atlantic and tropical Pacific oceans. Thus these results point towards the possibility of routine decadal climate predictions. Using this method, and by considering both internal natural climate variations and projected future anthropogenic forcing, we make the following forecast: over the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.     

Possible solar origin of the 1,470-year glacial climate cycle demonstrated in a coupled model

Many palaeoclimate records from the North Atlantic region show a pattern of rapid climate oscillations, the so-called Dansgaard-Oeschger events, with a quasi-periodicity of approximately 1,470 years for the late glacial period. Various hypotheses have been suggested to explain these rapid temperature shifts, including internal oscillations in the climate system and external forcing, possibly from the Sun. But whereas pronounced solar cycles of approximately 87 and approximately 210 years are well known, a approximately 1,470-year solar cycle has not been detected. Here we show that an intermediate-complexity climate model with glacial climate conditions simulates rapid climate shifts similar to the Dansgaard-Oeschger events with a spacing of 1,470 years when forced by periodic freshwater input into the North Atlantic Ocean in cycles of approximately 87 and approximately 210 years. We attribute the robust 1,470-year response time to the superposition of the two shorter cycles, together with strongly nonlinear dynamics and the long characteristic timescale of the thermohaline circulation. For Holocene conditions, similar events do not occur. We conclude that the glacial 1,470-year climate cycles could have been triggered by solar forcing despite the absence of a 1,470-year solar cycle.