Interannual Climate Variability Change during the Medieval Climate Anomaly and Little Ice Age in PMIP3 Last Millennium Simulations

In this study, we analyzed numerical experiments undertaken by 10 climate models participating in PMIP3(Paleoclimate Modelling Intercomparison Project Phase 3) to examine the changes in interannual temperature variability and coefficient of variation(CV) of interannual precipitation in the warm period of the Medieval Climate Anomaly(MCA) and the cold period of the Little Ice Age(LIA). With respect to the past millennium period, the MCA temperature variability decreases by 2.0% on average over the globe, and most of the decreases occur in low latitudes. In the LIA, temperature variability increases by a global average of 0.6%, which occurs primarily in the high latitudes of Eurasia and the western Pacific. For the CV of interannual precipitation, regional-scale changes are more significant than changes at the global scale, with a pattern of increased(decreased) CV in the midlatitudes of Eurasia and the northwestern Pacific in the MCA(LIA). The CV change ranges from-7.0% to 4.3%(from -6.3% to 5.4%), with a global average of -0.5%(-0.07%) in the MCA(LIA).Also, the variability changes are considerably larger in December–January–February with respect to both temperature and precipitation.     

几年来我国气候年际变异和短期气候预测研究的一些新成果

为了热烈庆祝中国科学院大气物理研究所成立80周年(1928～2008年),作者谨就五年来中国科学院大气物理研究所的科学家们完成的关于我国气候变异和气候预测方面的研究工作若干新成果作一些非常概要性的介绍,个中也包含一点所外科学家的工作。不周和不当之处只有请读者海涵和批评指正了。本文介绍的主要进展有三个方面:关于我国气候年际变异的研究、ENSO预测研究和数值气候预测研究。     

年际气候变率的数值模拟

本文利用IAP GCM 20年的模式输出结果，计算了海平面气压、表面气温和降水的年际气候变率，并与观测资料作了对比分析，以考察模式模拟年际变率的能力。结果表明，模式成功地再现了观测变率地理分布的基本特征，这说明大气内部动力-物理相互作用过程对年际变率有重要影响，而模拟值的偏低则显示了模式中未包括的某些外界强迫因子如海温和海冰年际变化的潜在作用。     

Interannual Salinity Variability in the Tropical Pacific in CMIP5 Simulations

Salinity variability and its causes in the tropical Pacific are analyzed using observations, reanalysis products and model simulations. The mixed-layer salinity(MLS) budget analyses from observations and reanalysis products indicate that its interannual evolution is closely related to ENSO and is predominantly governed by surface forcing and surface advection in the western-central equatorial Pacific. It is found that the observed MLS tendency leads Nin?o3.4 by about 12 months due to the effect of negative freshwater flux(evaporation minus precipitation). These observation-based analyses are used to evaluate the corresponding simulation using GFDL-ESM2 M. It is evident that the model can simulate the spatiotemporal variations of MLS with some discrepancies compared to observations. In the warm pool of the equatorial Pacific the MLS tendency in the model is sensitive to ocean dynamics, however model biases cause the tendency to be underestimated. In particular, the freshwater flux is overestimated while the ocean surface zonal current and vertical velocity at the base of the mixed layer are underestimated. Due to model biases in representing the related physics, the effects of surface forcing on the simulated MLS budget are overestimated and those of subsurface and surface advection are relatively weak. Due to weaker surface advection and subsurface forcing than observed, the simulated compensations for surface forcing are suppressed, and the simulated MLS tendency that leads Nin?o3.4 by 8–10 months, which is shorter than the observed lead time. These results are useful for the interpretation of observational analyses and other model simulations in the tropical Pacific.     

Comparison of the Influence of Interannual Vegetation Variability between Offline and Online Simulations

This study investigates the influence of interannual vegetation variability. Two sets of offline and online simulations were performed using the Community Earth System Model. The interannual Global LAnd Surface Satellite （GLASS） leaf area index （LAI） dataset from 1985 to 2000 and its associated climatological LAI were used to replace the default climatological LAI data in version 4 of the Community Land Model （CLM4）. The re- sults showed that on a global scale, canopy transpiration and evaporation, as well as total evapotranspiration in offline simulations were significantly positively corre- lated with LAI, whereas ground evaporation and ground temperature showed significant negative correlation with LAI. However, the correlations in online simulations were reduced markedly because of interactive feedbacks between albedo, changed climatic factors and atmospheric variability. In the offline simulations, the fluctuations of differences in interannual variability of evapotranspiration and ground temperature focused on vegetation growing regions and the magnitudes were smaller. Those in online simulations spread over more regions and the magnitudes were larger. These results highlight the influence of interannual vegetation variability, particularly in online simulations, an effect that deserves consideration and attention when investigating the uncertainty of climate change.     

卑尔根气候模式中大西洋热盐环流年代际与年际变率的气候影响

利用一个全球海气耦合模式--卑尔根气候模式的积分结果,揭示了与大西洋热盐环流(THC)年代际和年际振荡相对应的气候异常型.年代际振荡发生在全海盆尺度,伴有亚速尔高压的增强、冰岛低压的加深;年际振荡发生在局地尺度,伴有亚速尔高压的减弱.这两种海平面气压异常型都反映了北大西洋涛动(NAO)活动中心的强度变化,两种变率型对应的拉布拉多海对流活动都加剧.但伴随局地尺度的THC调整,伊尔明格海的对流活动减弱.蒸发异常对拉布拉多海表层盐度异常的影响较为显著.分析表明,局地尺度的THC振荡主要是对大气强迫的被动响应,而海盆尺度THC振荡的实质是反映整个输送带的强度变化,其气候意义要大于THC的局地振荡.     

Influences of Climate Change and Its Interannual Variability on Surface Energy Fluxes from 1948 to 2000

Understanding changes in land surface processes over the past several decades requires knowledge of trends and interannual variability in surface energy fluxes in response to climate change. In our study, the Community Land Model version 3.5 (CLM3.5), driven by the latest updated hybrid reanalysis-observational surface climate data from Princeton University, is used to obtain global distributions of surface energy fluxes during 1948 to 2000. Based on the climate data and simulation results, long-term trends and interannual variability (IAV) of both climatic variables and surface energy fluxes for this span of 50+ years are derived and analyzed. Regions with strong long-term trends and large IAV for both climatic variables and surface energy fluxes are identified. These analyses reveal seasonal variations in the spatial patterns of climate and surface fluxes; however, spatial patterns in trends and IAV for surface energy fluxes over the past ～50 years do not fully correspond to those for climatic variables, indicating complex responses of land surfaces to changes in the climatic forcings.     

The Impacts of the Interannual Variability of Vegetation on the Interannual Variability of Global Evapotranspiration: A Modeling Study

The impact of the interannual variability (IAV) of vegetation on the IAV of evapotranspiration is investigated with the Community Land Model (CLM3.0) and modified Dynamic Global Vegetation Model (DGVM). Two sets of 50-year off-line simulations are used in this study. The simulations begin with the same initial surface-water and heat states and are driven by the same atmospheric forcing data. The vegetation exhibits interannual variability in one simulation but not in the other simulation. However, the climatological means for the vegetation are the same. The IAV of the 50-year annual total evapotranspiration and its three partitions (ground evaporation, canopy evaporation, and transpiration) are analyzed. The global distribution of the evapotranspiration IAV and the statistics of evapotranspiration and its components in different ecosystems show that the IAV of ground evaporation is generally large in areas dominated by grass and deciduous trees, whereas the IAV of canopy evaporation and transpiration is large in areas dominated by bare soil and shrubs. For ground evaporation, canopy evaporation, and transpiration, the changes in IAV are larger than the mean state over most grasslands and shrublands. The study of two sites with the same IAV in the leaf area index (LAI) shows that the component with the smaller contribution to the total evapotranspiration is more sensitive to the IAV of vegetation. The IAV of the three components of evapotranspiration increases with the IAV of the fractional coverage (FC) and the LAI. The ground evaporation IAV shows the greatest increase, whereas the canopy evaporation shows the smallest increase.     

Seasonality of Interannual Inter-hemispheric Oscillations over the Past Five Decades

Air mass is inter-hemispherically redistributed, leading to an interesting phenomenon known as the Inter-Hemispheric Oscillation (IHO). In the present article, the seasonality of the interannual IHO has been examined by employing monthly mean reanalyses from NCEP/NCAR, EAR40, and JRA25 for the period of 1958-2006. It is found that the IHO indices as calculated from different reanalyses are generally consistent with each other. A distinct seesaw structure in all four seasons between the northern and southern...     

Climate-Vegetation Interannual Variability in a Coupled Atmosphere-Ocean-Land Model

The coupled models of both the Global Ocean-Atmosphere-Land System (GOALS) and the Atmosphere-Vegetation Interaction Model (GOALS-AVIM) are used to study the main characteristics of interannual variations. The simulated results are also used to investigate some significant interannual variability and correlation analysis of the atmospheric circulation and terrestrial ecosystem. By comparing the simulations of the climate model GOALS-AVIM and GOALS, it is known that the simulated results of the interannual variations of the spatial and temporal distributions of the surface air temperatures and precipitation are generally improved by using AVIM in GOALS-AVIM. The interannual variation displays some distinct characteristics of the geographical distribution. Both the Net Primary Production (NPP) and the Leap Area Index (LAI) have quasi 1-2-year cycles. Meanwhile, precipitation and the surface temperatures have 2--4-year cycles. Conditions when the spectrum density values of GOALS are less than those of GOALS-AVIM, tell us that the model coupled with AVIM enhances the simulative capability for interannual variability and makes the annual cycle variability more apparent. Using Singular Value Decomposition (SVD) analysis, the relationship between the ecosystem and the atmospheric circulation in East Asia is explored. The result shows that the strengthening and weakening of the East Asian monsoon, characterized by the geopotential heights at 500 hPa and the wind fields at 850 hPa, correspond to the spatiotemporal pattern of the NPP. The correlation between NPP and the air temperature, precipitation and solar radiation are different in interannual variability because of the variation in vegetation types.     

北太平洋海气界面湍流热通量的年际变化

本文采用美国伍兹霍尔海洋研究所客观分析海气通量项目提供的1958～2006年月平均的湍流热通量及相关气象场数据, 利用EOF分析、小扰动方法、线性回归、相关分析等方法研究了北太平洋海气界面湍流热通量年际变化的时空特征、 影响因子及其与大气环流的关系。结果表明, 北太平洋湍流热通量的年际变化在冬季最为显著。我国东部海域及其向中东太平洋的延伸部分为冬季潜热通量和感热通量年际变化的关键区。冬季潜热通量的年际变化在副热带太平洋和菲律宾海域主要受风速变化影响, 在北太平洋的高纬和低纬海域尤其是赤道中太平洋主要受比湿差变化影响, 而冬季感热通量的年际变化在整个北太平洋都主要受海气温差变化影响。受大尺度环流影响, 异常低压中心的东 (西) 侧海气比湿差和海气温度差偏小 (偏大), 所以异常低压中心的东 (西) 侧潜热输送和感热输送偏弱 (偏强)。     

南极海冰的年际变化对中国东部夏季降水的影响

根据Hadley中心提供的1969—1998年的南极海冰再分析资料和其它多种观测资料，分析了南极海冰的年际和季节变化，指出南极海冰具有显著的年际变化，但与ENSO的关系则较为复杂。南极海冰维持了南半球高纬地区大气环流的季节持续性，因而对短期气候预测有较大帮助。相关分析和时间序列分析均证实中国东部夏季降水与南极海冰的年际变化有关，当北半球春夏季南极海冰增多时，华北降水增多而华南和东北降水减少。研究还表明，此种雨型分布与南极海冰变化引起的东亚夏季风环流变化有关。     

1960—2009年中国年降水量的年际及年代际变化特征

利用1960-2009年中国台站降水量资料,揭示了全国、区域年降水量变化的多时间尺度的复杂结构和地区性差异,并根据年代际周期对未来降水量变化的贡献进行了预估。我国北方年降水量年际变化较强,年际变化对年降水量的贡献较大;南方年降水量年际变化相对较弱,年际变化对降水量的贡献较小,东北和西北地区年降水量的年代际变化较强,年代际变化明显,且同位相;其他地区年降水量年代际变化相对较弱。我国东北、西北、华南、青藏高原、西南地区年降水量的年代际变率对年降水量的贡献目前处于下降阶段,未来5-10年年代际变化的贡献可能继续呈下降趋势;长江中下游地区年降水量的年代际变率对年降水量的贡献目前处于上升阶段,未来5-10年年代际变化的贡献可能继续呈上升趋势。     

Interannual and Interdecadal Variations of the Mid-Atlantic Trough and Associated American-Atlantic-Eurasian Climate Anomalies

The mid-Atlantic trough (MAT) is one of the most prominent circulation systems over the subtropical North Atlantic during the boreal summer, and it can be viewed as a bridge linking the climate in the American-Atlantic-Eurasian region. The upper-tropospheric MAT attains its maximum intensity of 200–150?hPa in June and July. An index measuring the variability of MAT intensity is defined, which reveals significant interannual and interdecadal variations of the trough.

On interannual time scales, the variation of MAT is significantly associated with the North Atlantic Oscillation, a southeastward propagating stationary wave that possibly originates from the northeastern Pacific, and the Atlantic Meridional Mode. A stronger trough is associated with warmer surface temperatures and higher pressure over central-northern North America and the extratropical North Atlantic and with colder surface temperatures and lower pressure over the Arctic, the subtropical North Atlantic, and the northeastern Pacific. In the meantime, significant negative precipitation anomalies occur over the north of the Mediterranean Sea and the Black Sea, as well as the northeastern Atlantic because of the anomalous low-level northeasterly winds over these areas. On an interdecadal time scale, the variation of MAT seems to be related to the Atlantic Multi-decadal Oscillation. Warmer surface temperatures appear over almost the entire North Atlantic, southern Europe, East Asia, and the North Pacific during the weak phase of the trough. A weak trough is also associated with the dipole pattern of anomalous precipitation over the extratropical North Atlantic, Greenland, and northeastern North America, corresponding to a dipole of low-level atmospheric circulation over these regions.     

耦合模式ICM模拟的近千年气候特征

利用中国科学院大气物理研究所季风系统研究中心发展的气候模式(Integrated Climate Model,ICM)开展了近千年气候模拟试验,考察了模式对过去千年温度和大气涛动变化的模拟,并分析了全球季风百年到千年尺度的变化。结果表明:模式对百年尺度气候变率有较好的模拟能力,900~1200年北半球平均表面温度偏高,1500~1800年温度偏低,模拟的北半球、南半球平均表面温度都呈现出了19世纪至2000年的快速增暖。模式对大气涛动百年尺度变化的模拟与重建资料存在较大的不同。全球季风在850~1050年、1150~1200年和1300~1420加强,在1210~1300年和1600~1850年减弱。1875~2000年全球季风指数呈直线上升趋势。中世纪气候异常期(MWP)季风强度在全球大部分季风区域增加,小冰期(LIA)则相反。20世纪暖期(PWP)全球季风强度显著增加,其中赤道西太平洋增加超过1 mm/d。     

一个海陆气耦合模式中大气-植被的年际变化及其相互作用

含有动态植被过程的陆面模式Atmosphere-Vegetation Interaction Model(AVIM)与中国科学院大气物理研究所大气科学与地球流体力学数值模拟国家重点实验室(IAP/LASG)的9层大气环流模式AGCM 及20层的海洋环流模式(OGCM)耦合,建立了一个全球模式(GoALS-AVIM)并进行100年的模拟积分.后40年的结果分析表明,该耦合模式能够合理地模拟大气及陆地生态系统显著的年际变化.用奇异值分解(SVD)分析了东亚地区植被生长和气候变化的相互关系,发现在东业区域的植被净初级生产力(NPP)强弱的变化对血着大气环流的变化,特别是NPP分别与850 hPa的风场和500 hPa的高度场表现出很强的时空一致性.在东亚地区,由于植被类型的不同,导致NPP年际变化与降水、表面气温、短波辐射的年际变化的相关性不同,它们的年际变化与相关物理量场的年际变化表现出很强的植物种类的区别.     

近千年中国东部夏季雨带位置的变化

Based on the variations of geographical locations, the summer rain belts over eastern China were classified in this study into eight types: Inner Mongolia, North China, the Yellow River, the Huaihe River, the Yangtze River, the northern and southern parts of Jiangnan ( to the south of the lower Yangtze River valley), and South China. The file of 8-type rain belts was compiled from 1470 to 2005, and in order to extend the file of rain belts, it was further merged into a file of 4-type rain belts and also completed during the last millennium from 1000 to 1999. At last, the two files show that summer rain belts frequently occur in the Yangtze River valley in warm climate periods, but in the Yellow River or the Huaihe River valley in cold periods.     

混合海气耦合模式中与ENSO相关的大气年际变化性

利用混合海气耦合模式45年模拟积分的结果,对模式大气的年际变化性进行了分析。结果表明,在这样的海气耦合系统中,大气分量表现出显著的年际变化,冬、夏季异常环流型的分布与观测资料的分析结果基本相符。因此,该模式不仅能较好地再现热带太平洋的ENSO变化性,而且能较好地再现ENSO引起的全球大气环流的年际变化性。     

春季欧亚大陆地表气温变化特征的气候意义

研究了春季欧亚大陆地表气温的年际变化及其相联系的环流场特征,发现春季欧亚大陆地表气温年际变化呈现为大陆尺度的南北跷跷板式的空间分布特征, 即当中高纬度地表气温为正距平时,副热带地区则为负距平,反之亦然。这种空间分布型代表了欧亚大陆中高纬度地表气温年际变化的主要特征。进一步的研究表明,这种变化与前期冬季北大西洋涛动（NAO）有着显著的正相关,而与同期的NAO无关。同时,欧亚大陆地表气温异常存在着明显的从冬到夏的持续性。与东亚初夏气候变化关系的研究表明,春季欧亚大陆地表气温的变化通过影响鄂霍次克高压的变化进一步影响初夏梅雨的变化。当春季欧亚大陆中高纬度地表气温为正距平时,鄂霍次克高压偏强,初夏梅雨较活跃,反之亦然。