共查询到20条相似文献，搜索用时 157 毫秒
1.
Global North Atlantic Oscillation (NAO) oceanic precipitation features in the latter half of the twentieth century are documented based on the intercomparison of multiple state-of-the-art precipitation datasets and the analysis of the NAO atmospheric circulation and SST anomalies. Most prominent precipitation anomalies occur over the ocean in the North Atlantic, where in winter a “quadrupole-like” pattern is found with centers in the western tropical Atlantic, sub-tropical Atlantic, high-latitude eastern Atlantic and over the Labrador Sea. The extent of the sub-tropical and high-latitude center and the amount of explained variance (over 50%) are quite remarkable. However, the tropical Atlantic center is probably the most intriguing feature of this pattern apparently linking the NAO with ITCZ variability. In summer, the pattern is “tripole-like” with centers in the eastern Mediterranean Sea, the North Sea/Baltic Sea and in the sub-polar Atlantic. In the eastern Indian Ocean, the correlation is positive in winter and negative in summer, with some link to ENSO variability. The sensitivity of these patterns to the choice of the NAO index is minor in winter while quite important in summer. Interannual NAO precipitation anomalies have driven similar fresh water variations in these “key” regions. In the sub-tropical and high-latitude Atlantic in winter precipitation anomalies have been roughly 15 and 10% of climatology per unit change of the NAO, respectively. Decadal changes of the NAO during the last 50 years have also influenced precipitation and fresh water flux at these time-scales, with values lower (higher) than usual in the high-latitude eastern North Atlantic (Labrador Sea) in the 1960s and the late 1970s, and an opposite situation since the early 1980s; in summer the North Sea/Baltic region has been drier than usual during the period 1965–1975 when the NAO was generally positive. 相似文献
2.
In this study, we investigate the influence of low-frequency solar forcing on the East Asian winter monsoon(EAWM)by analyzing a four-member ensemble of 600-year simulations performed with Had CM3(Hadley Centre Coupled Model,version 3). We find that the EAWM is strengthened when total solar irradiance(TSI) increases on the multidecadal time scale. The model results indicate that positive TSI anomalies can result in the weakening of Atlantic meridional overturning circulation, causing negative sea surface temperature(SST) anomalies in the North Atlantic. Especially for the subtropical North Atlantic, the negative SST anomalies can excite an anomalous Rossby wave train that moves from the subtropical North Atlantic to the Greenland Sea and finally to Siberia. In this process, the positive sea-ice feedback over the Greenland Sea further enhances the Rossby wave. The wave train can reach the Siberian region, and strengthen the Siberian high. As a result, low-level East Asian winter circulation is strengthened and the surface air temperature in East Asia decreases. Overall,when solar forcing is stronger on the multidecadal time scale, the EAWM is typically stronger than normal. Finally, a similar linkage can be observed between the EAWM and solar forcing during the period 1850–1970. 相似文献
3.
山西春季降水与500hPa环流场及太平洋海温场异常的关系 总被引：1，自引：0，他引：1
利用1961—2008年春季山西省62个气象站的逐月降水资料、NCEP/NCAR再分析资料、NOAA太平洋海温资料等,应用SVD、Monte Carlo统计检验和合成分析等方法,探讨了山西春季降水与500hPa环流场及太平洋海温场的异常关系。结果表明,当春季500hPa平均高度场上,欧洲北部、日本海和北太平洋东部出现正异常,而极地、西西伯利亚出现负异常时,山西春季降水易偏多;反之,则易偏少。当春季赤道中东太平洋海温异常偏高,北太平洋东南部海温异常偏低,且前期冬季也有相似的海温距平分布时,山西春季降水易偏多;反之,则易偏少。春季,850hPa我国东部地区110°～120°E范围偏南风减弱是导致山西春季降水偏少的重要因素。 相似文献
4.
利用第五次耦合模式比较计划(Coupled Model Intercomparison Project Phase 5,简称CMIP5)月平均资料,从季节变化角度,对热带太平洋、印度洋海温变化与降水变化的关系及其成因进行了初步分析。20个模式集合平均结果表明:在全球增暖背景下,热带太平洋年平均的海温变化与降水变化符合"warmer-get-wetter"型特征,而季节平均与年平均存在明显的差异;冬季和春季,海温增暖最大区和降水增加区之间存在东西向和南北向的位置偏差;夏季和秋季,二者只存在明显的南北位置偏差,且与冬季和春季的情况相反。热带印度洋的冬季和春季海温变化与降水变化也存在位置偏差。两个热带大洋季节平均的降水变化均是"warmer-get-wetter"和"wet-get-wetter"两个机制共同作用的结果。 相似文献
5.
根据观测资料的研究指出春季北极涛动(Arctic Oscillation, AO)对随后冬季厄尔尼诺-南方涛动(El Nino–Southern Oscillation, ENSO)的影响具有明显不对称性。春季AO处于正位相时,它对随后冬季厄尔尼诺(El Nino)事件的影响显著,然而春季AO负位相对随后冬季拉尼娜(La Nina)的影响不明显。本研究分析了30个来自CMIP5的耦合模式对春季AO与随后冬季ENSO不对称性关系的模拟能力。30个CMIP5耦合模式中,只有CNRM-CM5和GISS-E2-H-CC模式能较好地抓住春季AO与冬季ENSO的联系。进一步分析这两个模式中春季AO与冬季ENSO的不对称性关系,发现CNRM-CM5模式能较好地再现春季AO与冬季ENSO的非对称关系,即春季AO正(负)位相会导致赤道中东太平洋出现El Nino(La Nina)型海表温度增暖(冷却)。然而,GISS-E2-H-CC模式的模拟结果显示,春季AO对随后冬季ENSO的影响是对称的。本文随后解释了CNRM-CM5(GISS-E2-H-CC)模式能(不能)模拟出春季AO与冬季ENSO不对称关系的原因。对于CNRMCM5模式,在春季AO正位相年,副热带西北太平洋上空存在明显的异常气旋和正降水异常,正降水异常通过Gill型大气响应对赤道西太平洋异常西风的形成和维持起着重要作用,异常西风通过激发向东传播的暖赤道Kelvin波对随后冬季El Nino事件的发生产生显著的影响;然而,在春季AO负位相年,副热带北太平洋的异常反气旋和负降水异常较弱,导致赤道西太平洋的异常东风不明显,因此,春季AO负异常对随后冬季La Nina的影响不显著。所以,CNRM-CM5模式能够较好地抓住春季AO对随后冬季ENSO事件的非对称性影响。相比之下,对于GISS-E2-H-CC模式,春季AO正(负)位相年副热带西北太平洋上存在显著的正(负)降水异常,通过Gill型大气响应在赤道西太平洋激发出明显的异常西(东)风从而影响随后冬季的El Nino(La Nina)事件。因此,在GISS-E2-H-CC模式中,春季AO对随后冬季ENSO具有对称性影响。另外,模式捕捉春季AO对随后冬季ENSO非对称性影响的能力与模式对春季AO空间结构的模拟能力有一定的联系。 相似文献
6.
Cross-season relation of the South China Sea precipitation variability between winter and summer 总被引：3，自引：1，他引：2
The present study reveals cross-season connections of rainfall variability in the South China Sea (SCS) region between winter and summer. Rainfall anomalies over northern South China Sea in boreal summer tend to be preceded by the same sign rainfall anomalies over southern South China Sea in boreal winter (denoted as in-phase relation) and succeeded by opposite sign rainfall anomalies over southern South China Sea in the following winter (denoted as out-of-phase relation). Analysis shows that the in-phase relation from winter to summer occurs more often in El Niño/La Niña decaying years and the out-of-phase relation from summer to winter appears more frequently in El Niño/La Niña developing years. In the summer during the El Niño/La Niña decaying years, cold/warm and warm/cold sea surface temperature (SST) anomalies develop in tropical central North Pacific and the North Indian Ocean, respectively, forming an east–west contrast pattern. The in-phase relation is associated with the influence of anomalous heating/cooling over the equatorial central Pacific during the mature phase of El Niño/La Niña events that suppresses/enhances precipitation over southern South China Sea and the impact of the above east–west SST anomaly pattern that reduces/increases precipitation over northern South China Sea during the following summer. The impact of the east–west contrast SST anomaly pattern is confirmed by numerical experiments with specified SST anomalies. In the El Niño/La Niña developing years, regional air-sea interactions induce cold/warm SST anomalies in the equatorial western North Pacific. The out-of-phase relation is associated with a Rossby wave type response to anomalous heating/cooling over the equatorial central Pacific during summer and the combined effect of warm/cold SST anomalies in the equatorial central Pacific and cold/warm SST anomalies in the western North Pacific during the mature phase of El Niño/La Niña events. 相似文献
7.
The South Atlantic dipole and variations in the characteristics of the South American Monsoon in the WCRP-CMIP3 multi-model simulations 总被引：1，自引：1，他引：0
This study investigates relationships between Atlantic sea surface temperature (SST) and the variability of the characteristics of the South American Monsoon System (SAMS), such as the onset dates and total precipitation over central eastern Brazil. The observed onset and total summer monsoon precipitation are estimated for the period 1979?C2007. SST patterns are obtained from the Empirical Orthogonal Function. It is shown that variations in SST on interannual timescales over the South Atlantic Ocean play an important role in the total summer monsoon precipitation. Negative (positive) SST anomalies over the topical South Atlantic along with positive (negative) SST anomalies over the extratropical South Atlantic are associated with early (late) onsets and wet (dry) summers over southeastern Brazil and late (early) onset and dry (wet) summers over northeastern Brazil. Simulations from Phase 3 of the World Climate Research Programme Coupled Model Intercomparison Project (CMIP-3) are assessed for the 20th century climate scenario (1971?C2000). Most CMIP3 coupled models reproduce the main modes of variability of the South Atlantic Ocean. GFDL2.0 and MIROC-M are the models that best represent the SST variability over the South Atlantic. On the other hand, these models do not succeed in representing the relationship between SST and SAMS variability. 相似文献
8.
The present paper selects the northern winter of December 1995–February 1996 for a case study on the impact of sea surface temperature (SST) anomalies on the atmospheric circulation over the North Atlantic and Western Europe. In the Atlantic, the selected winter was characterized by positive SST anomalies over the northern subtropics and east of Newfoundland, and negative anomalies along the US coast. A weak La Niña event developed in the Pacific. The North Atlantic Oscillation (NAO) index was low, precipitation over the Iberian Peninsula and northern Africa was anomalously high, and precipitation over northern Europe was anomalously low. The method of study consists of assessing the sensitivity of ensemble simulations by the UCLA atmospheric general circulation model (UCLA AGCM) to SST anomalies from the observation, which are prescribed either in the World Oceans, the Atlantic Ocean only, or the subtropical North Atlantic only. The results obtained are compared with a control run that uses global, time-varying climatological SST. The ensemble simulations with global and Atlantic-only SST anomalies both produce results that resemble the observations over the North Atlantic and Western Europe. It is suggested that the anomalous behavior of the atmosphere in the selected winter over those regions, therefore, was primarily determined by conditions within the Atlantic basin. The simulated fields in the tropical North Atlantic show anomalous upward motion and lower (upper) level convergence (divergence) in the atmosphere overlying the positive SST anomalies. Consistently, the subtropical jet intensifies and its core moves equatorward, and precipitation increases over northern Africa and southern Europe. The results also suggest that the SST anomalies in the tropical North Atlantic only do not suffice to produce the atmospheric anomalies observed in the basin during the selected winter. The extratropical SST anomalies would provide a key contribution through increased transient eddy activity, which causes an extension of the subtropical jet eastward from the coast of North America. 相似文献
9.
ENSO及其组合模态对中国东部各季节降水的影响 总被引：7，自引：1，他引：6
近期的研究发现,热带太平洋低层大气存在两种主要模态,即经向对称ENSO模态和ENSO与海表温度(SST)年循环相互作用产生的经向反对称组合模态。主要探讨了这两种不同ENSO模态对中国东部各季节降水的影响。结果表明,厄尔尼诺年秋季,中国西南、长江及华南大部分区域呈现显著正降水异常;冬季,正降水异常范围扩大,覆盖华南、华东及华北东南部地区。这两个季节的异常降水都主要受ENSO模态的影响。与ENSO模态相关的正异常海温局地强迫导致120°E以西出现反气旋性环流,其西北侧增强的西南暖湿气流使得中国东部地区降水增多。次年春季,从中国华南延伸到东北出现正的异常降水,主要是ENSO组合模态的贡献。因为次年春季热带太平洋地区ENSO模态信号只局限于赤道地区,并没有对中国东部降水有显著的影响,而ENSO与海温年循环相互作用的组合模态使得与ENSO相关的赤道大气异常可以扩展到赤道以外地区。ENSO组合模态对中国降水异常有重要影响,在今后的研究和短期预测中需引起重视。 相似文献
10.
Influence of North Atlantic sea surface temperature (SST) anomalies on tropical Pacific SST anomalies is examined. Both summer and winter North Atlantic SST anomalies are negatively related to central-eastern tropical Pacific SST anomalies in the subsequent months varying from 5 to 13?months. In particular, when the North Atlantic is colder than normal in the summer, an El Ni?o event is likely to be initiated in the subsequent spring in the tropical Pacific. Associated with summer cold North Atlantic SST anomalies is an anomalous cyclonic circulation at low-level over the North Atlantic from subsequent October to April. Corresponded to this local response, an SST-induced heating over the North Atlantic produces a teleconnected pattern, similar to the East Atlantic/West Russia teleconnection. The pattern features two anticyclonic circulations near England and Lake Baikal, and two cyclonic circulations over the North Atlantic and near the Caspian Sea. The anticyclonic circulation near Lake Baikal enhances the continent northerlies, and strengthens the East-Asian winter monsoon. These are also associated with an off-equatorial cyclonic circulation in the western Pacific during the subsequent winter and spring, which produces equatorial westerly wind anomalies in the western Pacific. The equatorial westerly wind anomalies in the winter and spring can help initiate a Pacific El Ni?o event following a cold North Atlantic in the summer. 相似文献
11.
Yajuan SONG Xinfang LI Ying BAO Zhenya SONG Meng WEI Qi SHU Xiaodan YANG 《大气科学进展》2020,37(10):1045-1056
Three tiers of experiments in the Global Monsoons Model Intercomparison Project(GMMIP), one of the endorsed model intercomparison projects of phase 6 of the Coupled Model Intercomparison Project(CMIP6), are implemented by the First Institute of Oceanography Earth System Model version 2(FIO-ESM v2.0), following the GMMIP protocols.Evaluation of global mean surface air temperature from 1870 to 2014 and climatological precipitation(1979–2014) in tier-1 shows that the atmosphere model of FIO-ESM v2.0 can reproduce the basic observed atmospheric features. In tier-2, the internal variability is captured by the coupled model, with the SST restoring to the model climatology plus the observed anomalies in the tropical Pacific and North Atlantic. Simulation of the Northern Hemisphere summer monsoon circulation is significantly improved by the SST restoration in the North Atlantic. In tier-3, five orographic perturbation experiments are conducted covering the period 1979–2014 by modifying the surface elevation or vertical heating in the prescribed region. In particular, the strength of the South Asian summer monsoon is reduced by removing the topography or thermal forcing above 500 m over the Asian continent. Monthly and daily simulated outputs of FIO-ESM v2.0 are provided through the Earth System Grid Federation(ESGF) node to contribute to a better understanding of the global monsoon system. 相似文献
12.
Both seasonal potential predictability and the impact of SST in the Pacific on the forecast skill over China are investigated by using a 9-level global atmospheric general circulation model developed at the Institute of Atmospheric Physics under the Chinese Academy of Sciences (IAP9L-AGCM). For each year during 1970 to 1999, the ensemble consists of seven integrations started from consecutive observational daily atmospheric fields and forced by observational monthly SST. For boreal winter, spring and summer,the variance ratios of the SST-forced variability to the total variability and the differences in the spatial correlation coefficients of seasonal mean fields in special years versus normal years are computed respectively. It follows that there are slightly inter-seasonal differences in the model potential predictability in the Tropics. At northern middle and high latitudes, prediction skill is generally low in spring and relatively high either in summer for surface air temperature and middle and upper tropospheric geopotential height or in winter for wind and precipitation. In general, prediction skill rises notably in western China, especially in northwestern China, when SST anomalies (SSTA) in the Nino-3 region are significant. Moreover,particular attention should be paid to the SSTA in the North Pacific (NP) if one aims to predict summer climate over the eastern part of China, i.e., northeastern China, North China and southeastern China. 相似文献
13.
Identifying regions sensitive to external radiative changes, including anthropogenic (sulphate aerosols and greenhouse gases) and natural (volcanoes and solar variations) forcings, is important to formulate actionable information at multi-year time-scales. Internally-generated climate variability can overcome this radiative forcing, especially at regional level, so that detecting the areas for this potential dominance is likewise critical for decadal prediction. This work aims to clarify where each contribution has the largest effect on North Atlantic sea surface temperature (SST) predictions in relation to the Atlantic multi-decadal variability (AMV). Initialized decadal hindcasts and radiatively-forced historical simulations from the fifth phase of the Climate Model Intercomparison Project are analysed to assess multi-year skill of the AMV. The initialized hindcasts reproduce better the phase of the AMV index fluctuations. The radiatively-forced component consists of a residual positive trend, although its identification is ambiguous. Initialization reduces the inter-model spread when estimating the level of AMV skill, thus reducing its uncertainty. Our results show a skilful performance of the initialized hindcasts in capturing the AMV-related SST anomalies over the subpolar gyre and Labrador Sea regions, as well as in the eastern subtropical basin, and the inability of the radiatively-forced historical runs to simulate the horseshoe-like AMV signature over the North Atlantic. Initialization outperforms empirical predictions based on persistence beyond 1–4 years ahead, suggesting that ocean dynamics play a role in the AMV predictability beyond the thermal inertia. The initialized hindcasts are also more skilful at reproducing the observed AMV teleconnection to the West African monsoon. The impact of the start date frequency is also described, showing that the standard of 5-year interval between start dates yields the main features of the AMV skill that are robustly detected in hindcasts with yearly start date sampling. This work updates previous studies, complementing them, and concludes that skilful initialized multi-model forecasts of the AMV-related climate variability can be formulated, improving uninitialized projections, until 3–6 years ahead. 相似文献
14.
评估了耦合气候系统模式FGOALS海洋同化试验对西北太平洋夏季降水和SST相关关系的模拟技巧,并对比了相应的观测海温强迫试验（AMIP）和历史气候模拟试验结果。结果显示,FGOALS海洋同化试验对亚洲季风区大部分海域夏季SST年际变化有较高的模拟技巧,但其对菲律宾以东海域模拟技巧较低。在西北太平洋夏季降水-SST相关关系方面,同化试验部分地再现了南海和菲律宾以东海域降水超前SST变化1个月和同时二者的负相关关系,优于AMIP试验但逊于自由耦合模拟试验。同化试验对SST倾向-降水相关关系的模拟技巧亦介于AMIP试验和自由耦合试验之间。观测中,西北太平洋夏季降水与环流异常受日界线附近和赤道东印度洋海洋大陆地区海温异常的遥强迫,并通过改变到达海表的净短波辐射通量影响局地SST异常,导致局地海温-降水和局地海温倾向-降水的负相关关系。在AMIP试验中,遥强迫导致的西北太平洋地区环流异常较之观测偏弱,由于缺少局地海气耦合过程,在西北太平洋多数地区表现为海温对大气的强迫作用,即SST-降水正相关关系。FGOALS同化试验和自由耦合试验考虑了局地海气耦合过程,虽然低估了遥强迫对西北太平洋地区夏季环流异常的影响,依然部分模拟出局地降水-SST负相关关系但较之观测偏弱。同时,自由耦合试验高估了西北太平洋20°N以南地区海温异常对大气环流异常的强迫,使得其对中国南海和日本岛以南海域SST-降水负相关关系的模拟稍优于同化试验。 相似文献
15.
Simulating the Holocene climate evolution at northern high latitudes using a coupled atmosphere-sea ice-ocean-vegetation model 总被引：1，自引：1，他引：0
Hans Renssen Hugues Goosse Thierry Fichefet Victor Brovkin Emmanuelle Driesschaert Frank Wolk 《Climate Dynamics》2005,24(1):23-43
The response of the climate at high northern latitudes to slowly changing external forcings was studied in a 9,000-year long simulation with the coupled atmosphere-sea ice-ocean-vegetation model ECBilt-CLIO-VECODE. Only long-term changes in insolation and atmospheric CO2
and CH4 content were prescribed. The experiment reveals an early optimum (9–8 kyr BP) in most regions, followed by a 1–3°C decrease in mean annual temperatures, a reduction in summer precipitation and an expansion of sea-ice cover. These results are in general agreement with proxy data. Over the continents, the timing of the largest temperature response in summer coincides with the maximum insolation difference, while over the oceans, the maximum response is delayed by a few months due to the thermal inertia of the oceans, placing the strongest cooling in the winter half year. Sea ice is involved in two positive feedbacks (ice-albedo and sea-ice insulation) that lead regionally to an amplification of the thermal response in our model (7°C cooling in Canadian Arctic). In some areas, the tundra-taiga feedback results in intensified cooling during summer, most notably in northern North America. The simulated sea-ice expansion leads in the Nordic Seas to less deep convection and local weakening of the overturning circulation, producing a maximum winter temperature reduction of 7°C. The enhanced interaction between sea ice and deep convection is accompanied by increasing interannual variability, including two marked decadal-scale cooling events. Deep convection intensifies in the Labrador Sea, keeping the overall strength of the thermohaline circulation stable throughout the experiment. 相似文献
16.
We analyze decadal climate variability in the Mediterranean region using observational datasets over the period 1850–2009 and a regional climate model simulation for the period 1960–2000, focusing in particular on the winter (DJF) and summer (JJA) seasons. Our results show that decadal variability associated with the winter and summer manifestations of the North Atlantic Oscillation (NAO and SNAO respectively) and the Atlantic Multidecadal Oscillation (AMO) significantly contribute to decadal climate anomalies over the Mediterranean region during these seasons. Over 30% of decadal variance in DJF and JJA precipitation in parts of the Mediterranean region can be explained by NAO and SNAO variability respectively. During JJA, the AMO explains over 30% of regional surface air temperature anomalies and Mediterranean Sea surface temperature anomalies, with significant influence also in the transition seasons. In DJF, only Mediterranean SST still significantly correlates with the AMO while regional surface air temperature does not. Also, there is no significant NAO influence on decadal Mediterranean surface air temperature anomalies during this season. A simulation with the PROTHEUS regional ocean–atmosphere coupled model is utilized to investigate processes determining regional decadal changes during the 1960–2000 period, specifically the wetter and cooler 1971–1985 conditions versus the drier and warmer 1986–2000 conditions. The simulation successfully captures the essence of observed decadal changes. Model set-up suggests that AMO variability is transmitted to the Mediterranean/European region and the Mediterranean Sea via atmospheric processes. Regional feedbacks involving cloud cover and soil moisture changes also appear to contribute to observed changes. If confirmed, the linkage between Mediterranean temperatures and the AMO may imply a certain degree of regional decadal climate predictability. The AMO and other decadal influences outlined here should be considered along with those from long-term increases in greenhouse gas forcings when making regional climate out-looks for the Mediterranean 10–20?years out. 相似文献
17.
Alaskan Arctic waters have participated in hemispheric-wide Arctic warming over the last two decades at over two times the rate of global warming. During 2008–13, this relative warming occurred only north of the Bering Strait and the atmospheric Arctic front that forms a north–south thermal barrier. This front separates the southeastern Bering Sea temperatures from Arctic air masses. Model projections show that future temperatures in the Chukchi and Beaufort seas continue to warm at a rate greater than the global rate, reaching a change of +4℃ by 2040 relative to the 1981–2010 mean. Offshore at 74°N, climate models project the open water duration season to increase from a current average of three months to five months by 2040. These rates are occasionally enhanced by midlatitude connections. Beginning in August 2014, additional Arctic warming was initiated due to increased SST anomalies in the North Pacific and associated shifts to southerly winds over Alaska, especially in winter 2015–16. While global warming and equatorial teleconnections are implicated in North Pacific SSTs, the ending of the 2014–16 North Pacific warm event demonstrates the importance of internal, chaotic atmospheric natural variability on weather conditions in any given year. Impacts from global warming on Alaskan Arctic temperature increases and sea-ice and snow loss, with occasional North Pacific support, are projected to continue to propagate through the marine ecosystem in the foreseeable future. The ecological and societal consequences of such changes show a radical departure from the current Arctic environment. 相似文献
18.
Dong Guo Yongqi Gao Ingo Bethke Daoyi Gong Ola M. Johannessen Huijun Wang 《Theoretical and Applied Climatology》2014,115(1-2):107-119
Observational analysis and purposely designed coupled atmosphere–ocean (AOGCM) and atmosphere-only (AGCM) model simulations are used together to investigate a new mechanism describing how spring Arctic sea ice impacts the East Asian summer monsoon (EASM). Consistent with previous studies, analysis of observational data from 1979 to 2009 show that spring Arctic sea ice is significantly linked to the EASM on inter-annual timescales. Results of a multivariate Empirical Orthogonal Function analysis reveal that sea surface temperature (SST) changes in the North Pacific play a mediating role for the inter-seasonal connection between spring Arctic sea ice and the EASM. Large-scale atmospheric circulation and precipitation changes are consistent with the SST changes. The mechanism found in the observational data is confirmed by the numerical experiments and can be described as follows: spring Arctic sea ice anomalies cause atmospheric circulation anomalies, which, in turn, cause SST anomalies in the North Pacific. The SST anomalies can persist into summer and then impact the summer monsoon circulation and precipitation over East Asia. The mediating role of SST changes is highlighted by the result that only the AOGCM, but not the AGCM, reproduces the observed sea ice-EASM linkage. 相似文献
19.
20.
In 2010, the Northern Hemisphere, in particular Russia and Japan, experienced an abnormally hot summer characterized by record-breaking warm temperatures and associated with a strongly positive Arctic Oscillation (AO), that is, low pressure in the Arctic and high pressure in the midlatitudes. In contrast, the AO index the previous winter and spring (2009/2010) was record-breaking negative. The AO polarity reversal that began in summer 2010 can explain the abnormally hot summer. The winter sea surface temperatures (SST) in the North Atlantic Ocean showed a tripolar anomaly pattern—warm SST anomalies over the tropics and high latitudes and cold SST anomalies over the midlatitudes—under the influence of the negative AO. The warm SST anomalies continued into summer 2010 because of the large oceanic heat capacity. A model simulation strongly suggested that the AO-related summertime North Atlantic oceanic warm temperature anomalies remotely caused blocking highs to form over Europe, which amplified the positive summertime AO. Thus, a possible cause of the AO polarity reversal might be the “memory” of the negative winter AO in the North Atlantic Ocean, suggesting an interseasonal linkage of the AO in which the oceanic memory of a wintertime negative AO induces a positive AO in the following summer. Understanding of this interseasonal linkage may aid in the long-term prediction of such abnormal summer events. 相似文献