北大西洋涛动变率研究进展

介绍了近年来北大西洋涛动研究的最新进展。 NAO指数序列的建立取得了很多成果 ,包括一些观测气象记录的序列以及利用树木年轮、冰芯等代用资料建立的近 30 0多年的序列 ,这些长的序列显示 NAO不仅有突出的年际变率 ,也有显著的年代际变率。总结了 NAO对地面温度、降水、北大西洋飓风和北半球臭氧等影响的一些研究成果。NAO的低频变率可能与气候系统内部的相互作用以及外部强迫有关。许多模拟研究发现 NAO与温盐环流有密切的联系 ,但是这种关系还有待观测资料的证实。全球气候变暖也可能是影响 NAO变率的一个不可忽视的因素。     

1951—2016年中亚努尔苏丹与乌鲁木齐寒潮过程频数变化及其主要影响因子对比分析

利用1951—2016年努尔苏丹和乌鲁木齐的逐日最低气温资料,以当年7月到翌年6月为统计年,对比分析了中亚地区的努尔苏丹与乌鲁木齐的寒潮、强寒潮和超强寒潮过程频数气候变化特征,并初步分析了冬季北极涛动(AO)、北大西洋涛动(NAO)与中亚两个城市同期寒潮活动关系.结果显示:努尔苏丹的年平均寒潮过程频数(15.7次·a-...     

基于LMR的中国石笋氧同位素记录在过去千年气候同化中的应用初探

本研究利用中国石笋氧同位素记录填补了LMR(Last Millennium Reanalysis)的代用资料数据库在中国东部的空白,并分析了代用资料库优化后LMR对中国降水的同化能力。结果表明,中国石笋氧同位素记录的添加提升了LMR对中国东部36°N以南和西北地区降水的同化能力,能较好再现过去530年两个地区发生的旱涝事件。同化数据表明过去530年中国东部发生了干旱和雨涝事件各5次,西北地区发生了5次干旱事件和4次雨涝事件。其中中国东部1470~1526年、1918~1940年干旱事件和1877~1889年、1896~1914年雨涝事件可能主要受北极涛动(AO)、北大西洋涛动(NAO)和大西洋多年代际振荡(AMO)共同作用,当AO、NAO和AMO处于显著正位相则中国东部易发生干旱事件,负位相则易发生雨涝事件;1808~1826年干旱事件和1827~1837年、1941~1950年和1977~2000年雨涝事件则主要受太平洋年代际振荡(PDO)影响,当PDO处于显著负位相则中国东部易发生干旱事件,正位相则易发生雨涝事件;1689~1781年干旱事件主要受PDO负位相、AO和NAO正位相影响;而1579~1607年干旱事件与大气涛动间的联系并不密切。在中国西北地区,18世纪末期之后接连发生的降水异常事件可能与AO、NAO和AMO的位相转变存在联系。

     

Wavelet-based variability of Yellow River discharge at 500-, 100-, and 50-year timescales

Water scarcity in the Yellow River, China, has become increasingly severe over the past half century. In this paper, wavelet transform analysis was used to detect the variability of natural, observed, and reconstructed streamflow in the Yellow River at 500-, 100-, and 50-year timescales. The periodicity of the streamflow series and the co-varying relationships between streamflow and atmospheric circulation indices/sunspot number were assessed by means of continuous wavelet transform (CWT) and wavelet transform coherence (WTC) analyses. The CWT results showed intermittent oscillations in streamflow with increasing periodicities of 1–6 years at all timescales. Significant multidecadal and century-scale periodicities were identified in the 500-year streamflow series. The WTC results showed intermittent interannual covariance of streamflow with atmospheric circulation indices and sunspots. At the 50-year timescale, there were significant decadal oscillations between streamflow and the Arctic Oscillation (AO) and the Pacific Decadal Oscillation (PDO), and bidecadal oscillations with the PDO. At the 100-year timescale, there were significant decadal oscillations between streamflow and Niño 3.4, the AO, and sunspots. At the 500-year timescale, streamflow in the middle reaches of the Yellow River showed prominent covariance with the AO with an approximately 32-year periodicity, and with sunspots with an approximately 80-year periodicity. Atmospheric circulation indices modulate streamflow by affecting temperature and precipitation. Sunspots impact streamflow variability by influencing atmospheric circulation, resulting in abundant precipitation. In general, for both the CWT and the WTC results, the periodicities were spatially continuous, with a few gradual changes from upstream to downstream resulting from the varied topography and runoff. At the temporal scale, the periodicities were generally continuous over short timescales and discontinuous over longer timescales.     

The North Atlantic Oscillation (NAO) and Europe Blocking and Their Impacts on Extreme Snowstorms: A Review

Large-scale, low frequency modes such as the North Atlantic Oscillation(NAO)and blocking, have an important modulation on the northern hemisphere weather and climate. In this paper, the physical mechanism studies on inter-decadal and decadal variability of NAO and blocking were summarized. The relationship between NAO regime transitions and the interannual variability of NAO in winter during was examined by using a statistical approach. The time-space relationship between NAO and European blocking were discussed. Based on two extreme cold and snowstorm events, the impacts on local weather especially the extreme events within the life cycle (two weeks) of the NAO and blocking were further examined. It was found that the frequently occurrence of the Eurasian extreme snowstorm was closely related to the special combination of NAO and blocking regime. In addition, the development of theoretical modes for NAO and blocking was discussed and issues that remain to be solved were proposed.     

Influence of Icelandic Low pressure on winter precipitation variability over northern part of Indo-Pak Region

Several studies demonstrate that North Atlantic Oscillation (NAO) has dominant influence on the variability of climate over Southwest Asia. We deconstruct the NAO into its two components, the Azores High and the Icelandic Low. Regional circulations are influenced by changes not only in the pressure but also the positions of the Azores High and the Icelandic Low. The results presented in this paper exhibit that significantly great portions of interannual variance of winter precipitation over Indo-Pak Region (consists of Northeast Pakistan and Northwest India) can be explained by including the contributions of the Icelandic Low pressure in addition to ENSO and AO. This contribution also explains the physical mechanisms to establish the relationships between the COA and regional climate by examining composite maps of large-scale circulation fields using NCEP/NCAR reanalysis data.     

<Emphasis>H</Emphasis>ydrological variability of the <Emphasis>S</Emphasis>oummam watershed <Emphasis>(N</Emphasis>ortheastern <Emphasis>A</Emphasis>lgeria<Emphasis>)</Emphasis> and the possible links to climate fluctuations

The long-term variability of rainfall in the Soummam watershed (NE Algeria) has been analysed over the past 108 years using continuous wavelet method in order to identify the interannual modes controlling the rainfall variability. Statistical analyses of rainfall timeseries have shown its distribution following five periods of time, limited by a series of discontinuities around 1935, 1950, 1970 and 1990. The continuous wavelet transform have demonstrated different low frequency modes: 2–4, 4–8, 8–16 and 16–32 years.The annual band is expanded during the full study period with some pics around 1905, 1920–1935 and 1960; it shows a negative long-term trend, in particular since the period 1970–1990 when a major change has been identified. Then, the relationships between climate patterns of North Atlantic Oscillation (NAO) and Southern Oscillation Index (SOI) and the hydrological variability in the frequency domain have been investigated; they have shown a mean explained variance of 40 and 24 %, respectively. Such variances are less obvious for the annual mode and increase for the interannual frequencies. The coherence suffer from high perturbations since the period 1970–1990 when the NAO (SOI) shifts from negative (positive) phases to positive (negative) ones. Such anomalies are responsible for significant changes of rainfall variability, emphasising the global warming effects.     

过去2000年温度集成重建研究:进展与展望

过去2000年气候变化研究是全球气候变化研究的核心内容,不仅可以提供20世纪气候增暖的自然背景,也是最终揭示20世纪气候变暖机理并预估未来气候变化趋势的关键途径,是国际大型计划（如PAGES,过去全球变化研究计划）的优先研究时段。近20多年来,特别是近几年,随着代用资料的不断积累和气候重建方法的改进和发展,过去2000年大尺度气候重建研究取得了长足发展,在区域和北半球气候集成重建方法,年际、年代、百年乃至千年时间尺度上的气候时空变化特征和机制,及最近几十年气候增暖的历史地位等方面的研究均取得了重要科学认识,形成了现代气候增暖机理和未来气候趋势预估的科学基础。本文主要从方法学、研究历史回顾和现阶段形成的科学认识等3个方面论述过去2000年气候变化研究取得的成就,并对未来的研究方向进行了展望。

     

NAO在末次冰盛期和全新世对AMOC影响的对比研究

大西洋经向翻转环流(AMOC)的年代际变率对气候变化起着重要的调制作用。在现代气候背景下, 北大西洋涛动(NAO)加强能使AMOC增强, 但这种关系在更长时间尺度上是否成立尚不清楚。本研究利用TraCE-21ka模拟资料, 对比分析末次冰盛期(LGM)和全新世时期NAO对AMOC影响的异同。结果表明, LGM时期较全新世时期经向温度梯度偏强, NAO位置偏南, 这导致NAO与AMOC关系的不同: NAO的增强在LGM时期可以使AMOC增强, 而在全新世使AMOC减弱。具体地, 在LGM时期NAO的加强使北大西洋副极地气旋性环流增强, 其南支导致向北的高盐海水输送增加, 从而使北大西洋副极地区域密度升高, AMOC增强。与此同时, NAO正位相还能在中纬度激发异常的Ekman下沉流使AMOC加强。相反, 在全新世时期, NAO正位相导致北大西洋副极地地区气旋性环流减弱, 这导致中纬度向高纬度输送的高盐度海水减少, AMOC减弱。本研究表明NAO与AMOC的关系在很大程度上取决于不同气候背景下NAO的位置。

     

北大西洋涛动和北极涛动与新疆河川径流变化

分析了冬季北大西洋涛动(NAO)和北极涛动(AO)与新疆天山南北不同流域河川径流变化的关系.结果表明:影响北半球气温、降水等气候驱动因子的NAO和AO同样与新疆河川径流的变化具有显著的遥相关.在年际变化上,NAO和AO的强弱分别与径流变化的相关性具有明显的区域性差异;在年代际尺度上,NAO和AO有超前于新疆河流年径流5 a的显著相关,相关关系分别超过了95%和99%置信水平.NAO和AO变化对预测新疆河川径流的变化有很好的实际意义.     

Investigating possible links between the North Atlantic Oscillation and rainfall variability in Marrakech (Morocco)

Eighty-two-year rainfall time series have been studied together with climatic patterns of NAO using classical statistical methods. Then, the wavelet approach has been applied to show annual (1 year (1y)) and inter-annual (2–4 years (2-4y), 5–8 years (5-8y), and 8–16 years (8-16y)) modes distributed following four major discontinuities: 1945, 1960, 1975, and 1995. The 1y, 2-4y, and 5-8y powers show high energy during the wet period 1922–1930 and a low one in 1928–1938. After 1945, the annual mode highlights a high energy while the inter-annual modes present low energy. Between 1975 and 1995, powerful modes of 1 and 2–4 years are identified with low power of 5-8y and 8-16y modes. Since 1995, the low power of 5–8y decreases, while the 8-16y mode emphasizes a high variability. The coherence between NAO and Marrakech precipitation is strongly defined for low frequencies with a total contribution of 75 %. This coherence is in phase in the beginning and presents out phase signs since 1945. The change of phase can be associated to a decreasing of coherence especially around 1990. This finding is useful to understand the relationship between the hydrological variability and NAO climate patterns in the southern side of the Mediterranean Sea.     

Seasonal-Scale and Decadal-Scale Sediment-Vegetation Interactions on the Subaqueous Susquehanna River Delta,Upper Chesapeake Bay

Submersed aquatic vegetation (SAV) have been a prominent feature on the Susquehanna Flats, the shallow, subaqueous delta of the Susquehanna River, Maryland. SAV were absent from the Flats between 1972 and 2000, but have since recovered. While it is well established that SAV can improve water quality by promoting sediment and nutrient retention, it is not well understood how SAV on the Flats modulate sediment input from the Susquehanna River into the Upper Chesapeake Bay over different timescales. This study evaluates sedimentation on the Flats over seasonal to decadal timescales, using naturally occurring radioisotopes (⁷Be, ²¹⁰Pb) within the context of SAV biomass and Flats geomorphology. Results indicate that sedimentation on the Flats is both spatially and temporally variable. Although this variability cannot be explained by relationships with grain size and SAV biomass, river discharge, sediment supply, and geometry over the SAV bed likely control sedimentation in this system. Decadal-scale sedimentation is influenced by both flood events and changes in SAV biomass abundance. Average annual sediment accumulation was higher when SAV were present than when SAV were absent. SAV bed area was strongly correlated with average annual accumulation rate. These results suggest that a positive feedback between SAV abundance and accumulation rate exists; however, sediment supply and transport pathways are also important factors.     

Storm climate on the Danube delta coast: evidence of recent storminess change and links with large-scale teleconnection patterns

This paper presents an overview of storminess along the Danube delta coast since 1949 by analysing wind and wave data and discusses the influences of teleconnections on climate variability. To this end, a five-category storm classification is proposed based on wind speed intensity and storm duration. On average, this coast experiences 30 storms/year occurring predominantly in winter, three of them considered severe (categories III–IV). The extreme storms (cat. V) endanger most the coastal settlements and the back-beach ecosystems (sand dunes, wetlands, lagoons) and have a mean recurrence rate of 7 years, but occur with a large inter-annual variability more frequent during the late 1960s, the 1970s and the 1990s. The prevalence of northern storms, in particular for the severe ones (>90% frequency for wind speeds >20 m/s) is responsible for the vigorous southward longshore sediment transport, which shaped the Danube delta physiognomy over the last millennia. The application of the newly developed energetic (Storm Severity Index—SSI) and morphologic (Storm Impact Potential—SIP) proxies allowed the better assessment of both the storm strength and the temporal variation in storm energy. It appears that storm climate follows a cyclic pattern with successive periods of 7–9 years of high, moderate and low storminess in accordance with the main teleconnections patterns (North Atlantic Oscillation—NAO, East Atlantic oscillation—EA, East Atlantic/Western Russia—EAWR, Scandinavian oscillation—SCAND). If NAO succeeded to explain best most of the storminess evolution (r = ?0.76 for 1962–2005), it failed during the latest decade (since 2006) when an unprecedented low in storminess occurred. There is also evidence of increased southern circulation during the latter period, associated with a reversal of correlation with NAO (from negative to positive). Significant correlations were also found for the EA, EAWR and SCAND (r = ?0.55, 0.56, 0.55, respectively, significant at p < 0.01) for all the study period suggesting that besides NAO, the north-western Black Sea coast storminess is considerably influenced by several modes of climate variability, most notable the EA and the EAWR, which succeed to address the recent decrease in storminess.     

Spectral analysis of climate cycles to predict rainfall induced landslides in the western Mediterranean (Majorca,Spain)

In the present work, spectral analysis has been applied to determine the presence and statistical significance of climate cycles in long-term data series from different rainfall and gauging stations located in the Tramuntana Range, in the north-western sector of the island of Majorca. Climate signals recorded previously in the Mediterranean region have been identified: the ENSO, NAO, HALE, QBO and Sun Spot cycles as well as others related to solar activity; the most powerful signals correspond to the annual cycle, followed by the 6-month and NAO cycles. The incorporation of data derived from gauging stations contributes to better climate signal detection as local and exceptional influences are eliminated. Simulations have been performed for each rainfall/gauging station, using the most significant climate cycles obtained by means of the power spectrum. A good correlation between rainfall/flow values and simulated cycles has been obtained. The NAO and ENSO cycles are the most influential in the rainy periods, and specifically the NAO cycle, where a good correlation between episodes of high rainfall/flow and high values of ANAOI can be observed. At a second stage, landslides dated and recorded in the Tramuntana Range since 1954 (174 events) have been correlated with the simulated cycles obtaining good results, as the landslide events match rainfall peaks well. The correlation for the past decade (since 2005), when a detailed landslide inventory is available, also reveals a coincidence between landslide events and climate cycles, and specifically NAO and ENSO cycles. That is the case of the period 2008–2010, when numerous mass movements took place, and when the largest movement of the inventory was recorded. Results show a potential rainy period in the Tramuntana Range for the coming years (with maximum values around year 2021), when conditions similar to those related to the 2008–2010 event could take place again. The methodology presented in this work can contribute to the prediction of temporal, extreme hydrological events in order to design short-/medium-term mitigation strategies on a regional scale.     

中国黄土记录的季风快速变化

中国黄土高分辨率代用指标研究表明东亚季风气候存有亚轨道尺度的快速波动,与北半球高纬气候和大西洋经向环流变化关系密切。本文回顾前人在黄土高原地区多个典型剖面的研究结果,分末次冰期、最后两个冰期旋回及极端冰期（L₉和L₁₅）3个时段,阐述了粒度、元素比值、风化指数等代用指标揭示的冬、夏季风快速变化特征,并与冰芯、石笋和深海记录进行对比,探讨了季风突变事件的区域一致性和遥相关动力过程。结果表明,黄土高原西北部高分辨率黄土剖面代用指标对季风快速变化敏感,而东南缘黄土记录的突变事件不太清晰,这种差异受控于沉积速率和风化成壤的空间变化;在冰期-间冰期不同气候背景下,黄土粒度和元素比值的变化幅度和周期表现出较大差异,冰期幅度大、频率快,间冰期幅度小、频率慢,表明冰量大小对季风快速变化有调制作用;在两个极端寒冷期（氧同位素阶段22~24和38）,黄土粒度同样表现出快速变化特征,但与北大西洋浮冰碎屑记录似乎难以对应,可能与海陆记录的分辨率差异和年代标尺不确定性有关。综上所述,季风快速变化特征在沉积速率相对较高、成壤相对较弱的黄土剖面比较清晰,在冰期-间冰期不同下垫面条件下季风快速变化的特征和机理可能不同。未来的季风快速变化研究,一方面在时间尺度上拓展高分辨率敏感代用指标研究,揭示季风快速变化的起源和演化特征;另一方面加强地质记录和数值模拟结果的对比研究,获得季风快速变化动力机理的全面认识。

     

过去千年中国西北干旱区温度变化特征及成因分析

本研究基于过去千年多成员集合模拟试验(CESM-LME)数据, 在与同化资料(LMR)、参与CMIP6两个模式(MRI-ESM2和MIROC-ES2L)过去千年模拟结果以及观测/再分析资料(CN05.1)进行对比验证模式模拟结果可靠性的基础上, 分析了中国西北干旱区过去千年地表温度变化特征和影响因子。研究表明, CESM-LME全强迫试验能够较好地模拟出中世纪气候异常期、小冰期和现代暖期温度异常特征, 模式模拟的中国西北干旱区中世纪气候异常期温度变化幅度与现代暖期的相当。通过计算不同尺度上各单因子敏感性试验与全强迫试验中地表温度序列相关系数发现, 不仅在年尺度上, 年代际、多年代际、百年尺度上火山活动强迫出的地表温度序列与全强迫试验中的均呈现显著的相关关系, 但二者的关系在过去千年并不稳定; 另外, 1850年后温室气体排放对西北干旱区地表温度升高起到了主导作用。根据火山喷发纬度位置和气溶胶注入量两个标准将过去千年火山活动分为3种类型, 即北半球火山(NHV)、赤道火山(TRV)和南半球火山(SHV)。NHV爆发对西北干旱区降温的影响最强, TRV次之, 但是二者差别不大, 均在爆发10~12个月之内降温至-2.0 ℃以下。与以往研究不同的是, SHV爆发后中国西北干旱区地表温度在10个月后降温幅度能达到-1.7 ℃, 且该冷异常可持续到22个月之后。

     

Correlation between the oxygen isotope record from Dasuopu ice core and the Asian Southwest Monsoon during the last millennium

Long high-resolution proxy records are valuable for understanding Asian Southwest Monsoon (ASM) dynamics on decadal to centennial timescales. A millennium long δ¹⁸O ice core record from the central Himalayas provides an opportunity to study the ASM variability on decadal to centennial timescales. The Dasuopu ice core δ¹⁸O record indicates that a relatively warm period corresponding with the Medieval Warm Period lasted from AD 1140s to 1390s, a notable warming trend is apparent from 1800s to 1990s, and several cool periods occurred between AD 1010–1130s, 1290–1330s, 1400–1460s, 1520s, 1590–1630s, 1740s, and 1770–1790s. Comparisons with other high-resolution monsoon proxy records from the Arabian Sea, south Oman, and southern China reveal a high correspondence between temperature changes in the central Himalayas and the ASM variability during the last 1000 years. A pronounced warming trend since AD 1670 coincides with an abrupt transition from a weak to a strong intensity of the ASM. The thermal conditions in the Himalayas and on the Tibetan Plateau and associated glacial boundary conditions may have been predominantly responsible for variations of the ASM intensity and for a latitudinal movement in the mean position of the ITCZ on decadal to centennial timescales.     

Seasonal distribution and variability of atmospheric freeze/thaw cycles in Norway over the last six decades (1950–2013)

This study focused on atmospheric freeze/thaw cycles in Norway and presents the results of processing daily thermal data from 20 Norwegian meteorological stations for the period 1950–2013. Its two major aims were: (i) to provide long‐term time series of atmospheric freeze/thaw cycle data for Norway, and (ii) to analyse their trends over the last six decades. The study highlights the spatial and temporal modalities of the distribution of freeze/thaw cycles in Norway. The differences in the seasonal distributions of cycles and their mean annual number are because of the geographical location of the stations (coastal or inland stations, lowland or mountainous stations) and result from the combined effects of oceanity, continentality, latitude and elevation. The annual average number of freeze/thaw cycles is similar in the north (90) and south of Norway (84) but shows notable differences between coastal stations (27) and inland and/or mountainous stations (114). Since the 1950s, prolonged periods of several years characterized by increasing numbers of cycles have given way to periods of decreasing freeze/thaw frequency. This cyclicity is linked with the Northern Atlantic Oscillation (NAO). Strong positive or negative phases of the NAO since the 1950s have induced marked increases (or decreases) in atmospheric freeze/thaw cycle frequency in Norway.     

珠江流域降水干湿时空特征及气候因子影响研究

利用模糊C-均值聚类算法、皮尔逊相关和滑动相关分析等方法,对珠江流域做了气候一致性分析,在此基础上,研究了珠江流域不同分区年降水和干湿季降水变化的时空特征,分析了区域干湿变化与厄尔尼诺-南方涛动(ENSO)、北大西洋涛动(NAO)、印度洋偶极子(IOD)和太平洋10年涛动(PDO)等主要气候因子的遥相关关系,探讨了珠江流域干湿变化的气候成因。在此基础上,进一步研究上述气候指标对不同时间尺度干湿变化影响的平稳性与差异性。除此之外,还研究了气候指标的冷暖期对基于6个月SPI值的珠江流域干湿状态的影响。研究表明:(1)IOD、NAO和ENSO分别是导致珠江流域年降水、湿季降水和干季降水发生变化的主要影响因素,且对当年及下一年降水的影响是相反的。(2)珠江流域不同时间尺度的降水与对其有显著影响的气候指标(年降水与IOD,湿季降水与NAO,干季降水与ENSO),两者之间不同时期的滑动相关往往具有较强的相关性和前后相关一致性。(3)各气候指标对珠江流域不同时间尺度降水的影响在空间分布上不太均匀。(4)不同位相下气候指标对珠江流域干湿状态的影响存在较大差异。总体而言,当处于各气候指标暖期时珠江流域出现湿润期的概率较冷期时更大且在空间分布上更均匀。     

Long-Term Changes in Population Dynamics of the Shrimp Palaemon longirostris in the Gironde Estuary

Spanning 20?years (1979?C2007), this study is the longest time series pertaining to the resident shrimp species Palaemon longirostris in a European estuary. Data from monthly faunal surveys undertaken across the middle part of the Gironde estuary from April 1979 along with data from a statistical analysis of the commercial catches throughout the entire estuary and river were considered in order to explore their inter and intra-annual variability and long-term trends. Long-term densities series as well as environmental series (salinity, discharge, temperature and NAO) were decomposed and the effects of environmental variables were also examined using statistical models (GAMs). This revealed important spatio-temporal variability and a significant overall decrease in abundance of this species in the Gironde estuary since the beginning of the 1980s. This long-term decrease in abundance corresponded significantly to long-term decreases in both discharge and the NAO index, as well a long-term increase in temperature and salinity in the middle part of the estuary. However, models showed that environmental factors explained only a small part of the variability. The upstream shift of the population highlighted in this study, probably due to the intrusion of marine waters into the middle section of the estuary, may also have contributed to its decrease in abundance. Inter-annual variability of densities was also significantly linked with inter-annual fecundity fluctuations, and a significant decrease in both mean female size and fecundity was shown for preserved samples from 1992. Moreover, the breeding period has been temporally stretched out and began earlier in more recent years, potentially due to the increase in spring temperature.