共查询到20条相似文献，搜索用时 671 毫秒
1.
Mark R. Jury 《Theoretical and Applied Climatology》2010,101(1-2):29-40
Ethiopian decadal climate variability is characterized by application of singular value decomposition to gridded rainfall data over the period 1901–2007. Two distinct modes are revealed with different annual cycles and opposing responses to regional and global forcing. The northern zone that impacts the Nile River and underlies the tropical easterly jet has a unimodal rainy season that is enhanced by Atlantic Multidecadal Oscillation warm phase. This rainfall mode is linked with the Atlantic zonal overturning circulation and exhibits 10–12-year cycles through much of the twentieth century. The southern zone has a bimodal rainy season that is enhanced by Pacific Decadal Oscillation cool phase and the southern meridional overturning circulation. Multiyear wet and dry spells are characterized by sympathetic responses in the near-equatorial trough extending from Central America across the African Sahel to Southeast Asia. The interaction of Walker and Hadley cells over Africa appears to be a key feature that modulates Ethiopian climate at decadal frequency through anomalous north–south displacement of the near-equatorial trough. 相似文献
2.
Phase transition of the Pacific decadal oscillation and decadal variation of the East Asian summer monsoon in the 20th century 总被引：1，自引：0，他引：1
This paper focuses on the relationship between the phase transition of the Pacific decadal oscillation (PDO) and decadal variation of the East Asian summer monsoon (EASM) in the twentieth century. The first transition occurred in the 1940s, with an enhanced SST in the North Pacific and reduced SST in the tropical eastern Pacific and South Indian Ocean. In agreement with these SST changes, a higher SLP was found in most parts of the Pacific, while a lower SLP was found in the North Pacific and most parts of the Indian Ocean. In this case, the EASM was largely enhanced with a southerly anomaly in the lower troposphere along the east coast of China. Correspondingly, there was less rainfall in the Yangtze River valley and more rainfall in northern and southern China. An opposite change was found when the PDO reversed its phase in the late 1970s. In the tropical Indian Ocean and western Pacific, however, the SST was enhanced in both the 1940s and 1970s. As a result, the western Pacific subtropical high (WPSH) tended to extend westward with a larger magnitude in the 1970s. The major features were reasonably reproduced by an atmospheric general circulation model (IAP AGCM4.0) prescribed with observed SST and sea ice. On the other hand, the westward extension of the WPSH was exaggerated in the 1970s, while it was underestimated in the 1940s. Besides, the spatial pattern of the simulated summer rainfall in eastern China tended to shift southward compared with the observation. 相似文献
3.
Real-time multi-model decadal climate predictions 总被引：1，自引：1，他引：0
Doug M. Smith Adam A. Scaife George J. Boer Mihaela Caian Francisco J. Doblas-Reyes Virginie Guemas Ed Hawkins Wilco Hazeleger Leon Hermanson Chun Kit Ho Masayoshi Ishii Viatcheslav Kharin Masahide Kimoto Ben Kirtman Judith Lean Daniela Matei William J. Merryfield Wolfgang A. Müller Holger Pohlmann Anthony Rosati Bert Wouters Klaus Wyser 《Climate Dynamics》2013,41(11-12):2875-2888
We present the first climate prediction of the coming decade made with multiple models, initialized with prior observations. This prediction accrues from an international activity to exchange decadal predictions in near real-time, in order to assess differences and similarities, provide a consensus view to prevent over-confidence in forecasts from any single model, and establish current collective capability. We stress that the forecast is experimental, since the skill of the multi-model system is as yet unknown. Nevertheless, the forecast systems used here are based on models that have undergone rigorous evaluation and individually have been evaluated for forecast skill. Moreover, it is important to publish forecasts to enable open evaluation, and to provide a focus on climate change in the coming decade. Initialized forecasts of the year 2011 agree well with observations, with a pattern correlation of 0.62 compared to 0.31 for uninitialized projections. In particular, the forecast correctly predicted La Niña in the Pacific, and warm conditions in the north Atlantic and USA. A similar pattern is predicted for 2012 but with a weaker La Niña. Indices of Atlantic multi-decadal variability and Pacific decadal variability show no signal beyond climatology after 2015, while temperature in the Niño3 region is predicted to warm slightly by about 0.5 °C over the coming decade. However, uncertainties are large for individual years and initialization has little impact beyond the first 4 years in most regions. Relative to uninitialized forecasts, initialized forecasts are significantly warmer in the north Atlantic sub-polar gyre and cooler in the north Pacific throughout the decade. They are also significantly cooler in the global average and over most land and ocean regions out to several years ahead. However, in the absence of volcanic eruptions, global temperature is predicted to continue to rise, with each year from 2013 onwards having a 50 % chance of exceeding the current observed record. Verification of these forecasts will provide an important opportunity to test the performance of models and our understanding and knowledge of the drivers of climate change. 相似文献
4.
5.
A regional climate model is used to investigate the mechanism of interdecadal rainfall variability, specifically the drought
of the 1970s and 1980s, in the Sahel region of Africa. The model is the National Center for Environmental Prediction’s (NCEPs)
Regional Spectral Model (RSM97), with a horizontal resolution of approximately equivalent to a grid spacing of 50 km, nested
within the ECHAM4.5 atmospheric general circulation model (AGCM), which in turn was forced by observed sea surface temperature
(SST). Simulations for the July–September season of the individual years 1955 and 1986 produced wet conditions in 1955 and
dry conditions in 1986 in the Sahel, as observed. Additional July–September simulations were run forced by SSTs averaged for
each month over the periods 1950–1959 and the 1978–1987. These simulations yielded wet conditions in the 1950–1959 case and
dry conditions in the 1978–1987 case, confirming the role of SST forcing in decadal variability in particular. To test the
hypothesis that the SST influences Sahel rainfall via stabilization of the tropospheric sounding, simulations were performed
in which the temperature field from the AGCM was artificially modified before it was used to force the regional model. We
modified the original 1955 ECHAM4.5 temperature profiles by adding a horizontally uniform, vertically varying temperature
increase, taken from the 1986–1955 tropical mean warming in either the AGCM or the NCEP/National Center for Atmospheric Research
Reanalysis. When compared to the 1955 simulations without the added tropospheric warming, these simulations show a drying
in the Sahel similar to that in the 1986–1955 difference and to the decadal difference between the 1980s and 1950s. This suggests
that the tropospheric warming may have been, at least in part, the agent by which the SST increases led to the Sahel drought
of the 1970s and 1980s. 相似文献
6.
S. Kravtsov 《Climate Dynamics》2012,39(9-10):2377-2391
This paper assesses potential predictability of decadal variations in the El Ni?o/Southern Oscillation (ENSO) characteristics by constructing and performing simulations using an empirical nonlinear stochastic model of an ENSO index. The model employs decomposition of global sea-surface temperature (SST) anomalies into the modes that maximize the ratio of interdecadal-to-subdecadal SST variance to define low-frequency predictors called the canonical variates (CVs). When the whole available SST time series is so processed, the leading canonical variate (CV-1) is found to be well correlated with the area-averaged SST time series which exhibits a non-uniform warming trend, while the next two (CV-2 and CV-3) describe secular variability arguably associated with a combination of Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO) signals. The corresponding ENSO model that uses either all three (CVs 1–3) or only AMO/PDO-related (CVs 2 and 3) predictors captures well the observed autocorrelation function, probability density function, seasonal dependence of ENSO, and, most importantly, the observed interdecadal modulation of ENSO variance. The latter modulation, and its dependence on CVs, is shown to be inconsistent with the null hypothesis of random decadal ENSO variations simulated by multivariate linear inverse models. Cross-validated hindcasts of ENSO variance suggest a potential useful skill at decadal lead times. These findings thus argue that decadal modulations of ENSO variability may be predictable subject to our ability to forecast AMO/PDO-type climate modes; the latter forecasts may need to be based on simulations of dynamical models, rather than on a purely statistical scheme as in the present paper. 相似文献
7.
Atlantic forcing of Pacific decadal variability 总被引：1，自引：0，他引：1
Fred Kucharski Farah Ikram Franco Molteni Riccardo Farneti In-Sik Kang Hyun-Ho No Martin P. King Graziano Giuliani Kristian Mogensen 《Climate Dynamics》2016,46(7-8):2337-2351
8.
On the predictability of decadal changes in the North Pacific 总被引：2，自引：0，他引：2
The predictability of decadal changes in the North Pacific is investigated with an ocean general circulation model forced
by simplified and realistic atmospheric conditions. First, the model is forced by a spatially fixed wind stress anomaly pattern
characteristic for decadal North Pacific climate variations. The time evolution of the wind stress anomaly is chosen to be
sinusoidal, with a period of 20 years. In this experiment different physical processes are found to be important for the decadal
variations: baroclinic Rossby waves dominate the response. They move westward and lead to an adjustment of the subtropical
and subpolar gyre circulations in such a way that anomalous temperatures in the central North Pacific develop as a delayed
response to the preceding wind stress anomalies. This delayed response provides not only a negative feedback but also bears
the potential for long-term predictions of upper ocean temperature changes in the central North Pacific. It is shown by additional
experiments that once these Rossby waves have been excited, decadal changes of the upper ocean temperatures in the central
North Pacific evolve without any further anomalous atmospheric forcing. In the second part, the model is forced by surface
heat flux and wind stress observations for the period 1949–1993. It is shown that the same physical processes which were found
to be important in the simplified experiments also govern the evolution of the upper ocean in this more realistic simulation.
The 1976/77 cooling can be mainly attributed to anomalously strong horizontal advection due to the delayed response to persistent
wind stress curl anomalies in the early 1970s rather than local anomalous atmospheric forcing. This decadal change could have
been predicted some years in advance. The subsequent warming in the late 1980s, however, cannot be mainly explained by advection.
In this case, local anomalous atmospheric forcing needs to be considered.
Received: 6 July 1998 / Accepted: 16 October 1999 相似文献
9.
ENSO循环年代际变化及其数值模拟 总被引：2，自引：1，他引：1
从20世纪70年代后期的观测资料分析中显示了全球气候的年代际变化, 同时也表现在热带太平洋上最重要的海气耦合现象ENSO的年代际变化上。本文利用中国科学院大气物理研究研究所 (IAP) 大气科学和地球流体力学数值模拟国家重点实验室 (LASG) 的气候系统海洋模式 (简称LICOM), 对ENSO的年际以及年代际变率进行模拟, 结果表明LICOM基本能够模拟出ENSO年际变化的特征, 通过对海洋上层热含量的计算以及对热量和质量输送的变化分析, 能够看到模式中ENSO循环中的反馈机制与理论研究的结论是一致的。同时, 作者还发现模式能够重现ENSO循环的年代际变化特征, 例如周期、 传播方向和冷暖事件不对称性等特征的模拟也基本接近观测事实, 其中重点分析了冷暖事件的不对称性与非线性加热 (NDH) 之间的关系, 进一步分析还发现ENSO的强度、 不对称性与海洋内部的非线性过程之间在年代际尺度上也存在密切的关系。但是, 模式模拟与观测结果之间仍然存在着一定的误差, 模式有待于进一步改进。 相似文献
10.
太平洋年代际振荡（PDO）是北太平洋海表温度年代际变率的主模态。由于太平洋年代际振荡对区域乃至全球气候的显著影响,其合理的预测结果可以带来多方面收益。然而,针对太平洋年代际振荡及其有关的海表温度的年代际预测,目前气候模式的预测水平还十分有限,因此,提出了一个新的增量方法。一系列的验证结果表明,增量方法可以有效预测太平洋年代际振荡,其中包括成功预测出其振荡的年代际转折。增量方法的预测过程主要包括3个步骤:（1）采用5 a滑动平均得到太平洋年代际振荡的年代际变率;（2）利用3 a增量形式的预测因子构建预测模型,预测3 a增量的太平洋年代际振荡（DI_PDO）;（3）将预测得到的DI_PDO加上3 a前的观测PDO,得到最后预测的PDO。增量方法亦可以应用到气候系统年代际内部变率的其他模态（如:北大西洋年代际振荡）和其他气候变量的年代际预测（如:海表温度）。 相似文献
11.
Tree-ring estimates of Pacific decadal climate variability 总被引：10，自引：0，他引：10
Decadal-scale oscillatory modes of atmosphere-ocean variability have recently been identified in instrumental studies of
the Pacific sector. The regime shift around 1976 is one example of such a fluctuation, which has been shown to have significantly
impacted climate and the environment along the coastline of the western N and S Americas. The length of meteorological data
for the Pacific and western Americas critically limits analyses of such decadal-scale climate variability. Here we present
reconstructions of the annual Pacific Decadal Oscillation (PDO) index based on western North American tree-ring records which
account for up to 53% of the instrumental variance and extend as far back as AD 1700. The PDO reconstructions indicate that
decadal-scale climatic shifts have occurred prior to the period of instrumental record. Evaluation of temperature and precipitation-sensitive
tree-ring series from the northeast Pacific as well as these reconstructions reveals evidence for a shift towards less pronounced
interdecadal variability after about the middle 1800s. Our analyses also suggest that sites from both the northeast Pacific
coast as well as the subtropical Americas need to be included in proxy data sets used to reconstruct the PDO.
Received: 15 September 2000 / Accepted: 30 March 2001 相似文献
12.
丝绸之路遥相关是夏季对流层高层沿亚洲急流波导东传的准定常波列,它能显著影响欧亚大陆的气候异常。最近的研究表明丝绸之路遥相关具有明显的年际和年代际变化分量。本文比较了这两种时间尺度的异同。结果表明:丝绸之路遥相关在年际时间尺度上对应横跨欧亚大陆上空清晰的波列状环流异常,并导致下垫面类似的波列状冷暖温度异常;而其年代际变化对应的环流异常在欧洲到中亚与年际相似,但在东亚明显减弱,而且对应的温度异常也北移到俄罗斯远东地区。我们认为年代际的这些特点可能受到其他气候要素的影响,并认为去除年代际可以更加突出丝绸之路遥相关的物理本质及其气候影响。 相似文献
13.
Recent studies have furnished evidence for interdecadal variability in the tropical Pacific Ocean. The importance of this phenomenon in causing persistent anomalies over different regions of the globe has drawn considerable attention in view of its relevance in climate assessment. Here, we examine multi-source climate records in order to identify possible signatures of this longer time scale variability on the Indian summer monsoon. The findings indicate a coherent inverse relationship between the inter-decadal fluctuations of Pacific Ocean sea surface temperature (SST) and the Indian monsoon rainfall during the last century. A warm (cold) phase of the Pacific interdecadal variability is characterized by a decrease (increase) in the monsoon rainfall and a corresponding increase (decrease) in the surface air temperature over the Indian subcontinent. This interdecadal relationship can also be confirmed from the teleconnection patterns evident from long-period sea level pressure (SLP) dataset. The SLP anomalies over South and Southeast Asia and the equatorial west Pacific are dynamically consistent in showing an out-of-phase pattern with the SLP anomalies over the tropical central-eastern Pacific. The remote influence of the Pacific interdecadal variability on the monsoon is shown to be associated with prominent signals in the tropical and southern Indian Ocean indicative of coherent inter-basin variability on decadal time scales. If indeed, the atmosphere–ocean coupling associated with the Pacific interdecadal variability is independent from that of the interannual El Niño-Southern Oscillation (ENSO), then the climate response should depend on the evolutionary characteristics of both the time scales. It is seen from our analysis that the Indian monsoon is more vulnerable to drought situations, when El Niño events occur during warm phases of the Pacific interdecadal variability. Conversely, wet monsoons are more likely to prevail, when La Niña events coincide during cold phases of the Pacific interdecadal variability. 相似文献
14.
A statistical test has revealed that abrupt regional climate changes are produced in a coupled atmosphere-ocean general circulation
model. Abrupt changes are detected over much of the globe although the occurrence frequency is small over the continents.
Over the tropical Pacific Ocean and northern Pacific Ocean, surface air temperature (SAT) and sea level pressure (SLP) shift
rapidly on decadal time scales. The regional climate changes presented here have been classified into three types. The first
type consists of statistically significant shifts in SLP and statistically significant shifts in SAT which are of opposite
sign, and which are reinforced through a positive feedback between the atmosphere and the ocean. The second type is for those
occurrences where changes are of the same sign. The third type includes those with a significant shift in only one meteorological
element. The second and third types are generally generated by changes in air pressure and wind fields induced by changes
of the first type. For example, when SLP increases and sea surface temperature (SST) decreases abruptly in the tropical Pacific
Ocean, it triggers abrupt regional changes in middle and high latitudes. The abrupt changes in the model climate have characteristics
which are very similar to those of observed rapid shifts. Thus, it is concluded that abrupt changes are a predominant part
of regional climate change on decadal time scales.
Received: 11 February 1999 / Accepted: 18 May 2000 相似文献
15.
We study the impact of three ocean state estimates (GECCO, SODA, [ECMWF]-ORA-S3) on decadal predictability in one particular forecast system, the Earth system model from the Max Planck Institute for Meteorology in Hamburg. The forecast procedure follows two steps. First, anomalies of temperature and salinity of the observational estimates are assimilated into our coupled model. Second, the assimilation runs are then used to initialize 10-year-long hindcasts/forecasts starting from each year between 1960 and 2001. The impact of the individual ocean state estimates is evaluated both by the extent to which climate variations from the ocean state estimates are adopted by the forecast system (‘fidelity’) and by the prediction skill of the corresponding hindcast experiments. The evaluation focuses on North Atlantic (NA) sea surface temperature (SST), upper-level (0–700?m) NA ocean heat content (OHC) and the Atlantic meridional overturning circulation (MOC). Regarding fidelity, correlations between observations and the assimilation runs are generally high for NA SST and NA OHC, except for NA OHC in the GECCO assimilation. MOC variations experience strong modifications when GECCO and SODA are assimilated, much less so when assimilating ORA-S3. Regarding prediction skill, when initializing with ORA-S3 and SODA, correlations with observations are high for NA OHC and moderate for NA SST. Correlations in case of GECCO, on the other hand, are high for NA SST and moderate for NA OHC. Relatively high MOC correlations between hindcasts and respective assimilation run appear in the first five years in GECCO in the tropics and subtropics and in ORA-S3 north of 50N. Correlations are largely reduced when the MOC signals are detrended. The trends in the assimilation runs are to some extent artifacts of the assimilation procedure. Hence, our potential predictabilities of the MOC are optimistic estimates of the upper limits of predictability. However, the ORA-S3 reanalysis gives the best results for our forecast system as measured by both overall fidelity of the assimilation procedure and predictions of upper-level OHC in the North Atlantic. 相似文献
16.
A long-term simulation performed with a coarse-resolution, global, atmosphere-ocean-sea-ice model displays strong decadal variability of the sea-ice volume in the Northern Hemisphere with a significant peak at about 15-18 years. This model results from the coupling of ECBILT, a spectral T21, 3-level quasi-geostrophic atmospheric model, and CLIO, a sea-ice-ocean general circulation model. First, the mechanism underlying the variability of ice volume in the model was studied by performing correlation analyses between the simulated variables. In a second step, a series of additional sensitivity experiments was performed in order to illustrate the role of specific physical processes. This has allowed us to identify a feedback loop in the ice-ocean system, which proceeds as follows: an increase in Arctic sea-ice volume induces an increase in the salinity there. This salinity anomaly is transported to the Greenland Sea where it promotes convective activity. This warms up the surface oceanic layer and the atmosphere in winter and induces a decrease of the ice volume, completing half a cycle. The changes in ice volume are driven by a geopotential height pattern characterised by centres of action of opposite signs over Greenland and the Barents-Kara-Central Arctic area. Thermodynamic feedback between the ice and the atmosphere appear also to be very important for the persistence of the oscillation. The dynamical response of the atmosphere to sea-ice and temperature anomalies at surface plays a smaller role. 相似文献
17.
Preliminary evaluations of FGOALS-g2 for decadal predictions 总被引：3，自引：0，他引：3
王斌 刘咪咪 俞永强 李立娟 林鹏飞 董理 刘利 刘骥平 黄文誉 徐世明 申思 普业 薛巍 夏坤 王勇 孙文奇 胡宁 黄小猛 刘海龙 郑伟鹏 吴波 周天军 杨广文 《大气科学进展》2013,30(3):674-683
The Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2) for decadal predictions, is evaluated preliminarily, based on sets of ensemble 10-year hindcasts that it has produced. The results show that the hindcasts were more accurate in decadal variability of SST and surface air temperature (SAT), particularly in that of Nin o3.4 SST and China regional SAT, than the second sample of the historical runs for 20th-century climate (the control) by the same model. Both the control and the hindcasts represented the global warming well using the same external forcings, but the control overestimated the warming. The hindcasts produced the warming closer to the observations. Performance of FGOALS-g2 in hindcasts benefits from more realistic initial conditions provided by the initialization run and a smaller model bias resulting from the use of a dynamic bias correction scheme newly developed in this study. The initialization consists of a 61-year nudging-based assimilation cycle, which follows on the control run on 01 January 1945 with the incorporation of observation data of upper-ocean temperature and salinity at each integration step in the ocean component model, the LASG IAP Climate System Ocean Model, Version 2 (LICOM2). The dynamic bias correction is implemented at each step of LICOM2 during the hindcasts to reduce the systematic biases existing in upper-ocean temperature and salinity by incorporating multi-year monthly mean increments produced in the assimilation cycle. The effectiveness of the assimilation cycle and the role of the correction scheme were assessed prior to the hindcasts. 相似文献
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20.
The pacific decadal oscillation (PDO) is a mode of natural decadal climate variability, typically defined as the principal component of North Pacific sea surface temperature (SST) anomalies. To remove any global warming signal present in the data, the traditional definition specifies that monthly-mean, global-average SST anomalies are subtracted from the local anomalies. Differences in the warming rates over the globe and the PDO region may therefore be aliased into the PDO index. Here, we examine the possibility of a human component in the PDO, considering three different definitions. The implications of these definitions are explored using SSTs from both observations and simulations of historical and future climate, all projected onto (definition-dependent) observed PDO patterns. In the twenty first century scenarios, a systematic anthropogenic component is found in all three PDO indices. Under the first definition??in which no warming signal is removed??this component is so large that it is also statistically detectable in the observed PDO. Using the second/traditional definition, this component is also large, and arises primarily from the differential warming rates predicted in the North Pacific and over global oceans. Removing the spatial average SST signal in the PDO region (in the third definition) partially solves this problem, but a human signal persists because the predicted pattern of SST response to human forcing projects strongly onto the PDO pattern. This illustrates the importance of separating internally-generated and externally-forced components in the PDO, and suggests that caution should be exercised in using PDO indices for statistical removal of ??natural variability?? effects from observational datasets. 相似文献