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A Possible Feedback Mechanism Involving the Arctic Freshwater,the Arctic Sea Ice,and the North Atlantic Drift

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Advances in Atmospheric Sciences 2004年第5期21卷 784-801页

作者： Odd helge OTTER helge drange Nansen Environmental and Remote Sensing Center Edv. Griegsvei 3A5059 Bergen Bjerknes Centre for Climate Research Allégt. 55 5007 BergenNansen Environmental and Remote Sensing Center Edv. Griegsvei 3A5059 Bergen Bjerknes Centre for Climate Research Allégt. 55 5007 BergenGeophysical Institute University of Bergen Allégt. 70 5007 Bergen Nansen-Zhu International Research Centre Beijing 100029

Model studies point to enhanced warming and to increased freshwater ?uxes to high northern latitudes in response to global warming. In order to address possible feedbacks in the ice-ocean system in response to such changes, the combined e?ect of increased freshwater input to the Arctic Ocean and Arctic warming—the latter manifested as a gradual melting of the Arctic sea ice—is examined using a 3-D isopycnic coordinate ocean general circulation model. A suite of three idealized experiments is carried out: one control integration, one integration with a doubling of the modern Arctic river runo?, and a third more extreme case, where the river runo? is ?ve times the modern value. In the two freshwater cases, the sea ice thickness is reduced by 1.5–2 m in the central Arctic Ocean over a 50-year period. The modelled ocean response is qualitatively the same for both perturbation experiments: freshwater propagates into the Atlantic Ocean and the Nordic Seas, leading to an initial weakening of the North Atlantic Drift. Furthermore, changes in the geostrophic currents in the central Arctic and melting of the Arctic sea ice lead to an intensi?ed Beaufort Gyre, which in turn increases the southward volume transport through the Canadian Archipelago. To compensate for this southward transport of mass, more warm and saline Atlantic water is carried northward with the North Atlantic Drift. It is found that the increased transport of salt into the northern North Atlantic and the Nordic Seas tends to counteract the impact of the increased freshwater originating from the Arctic, leading to a stabilization of the North Atlantic Drift.

关键词： Arctic Ocean freshwater seaice North Atlantic Drift

A Preliminary Study on the Relationship Between Arctic Oscillation and Daily SLP Variance in the Northern Hemisphere During Wintertime

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Advances in Atmospheric Sciences 2005年第3期22卷 313-327页

作者：龚道溢 helge drange Key Laboratory of Environmental Change and Natural DisasterCollege of Resources Science and Technology Beijing Normal University Beijing 100875 Bjerknes Centre for Climate Research/Nansen Environmental and Remote Sensing CenterUniversity of Bergen Norway

In the present study, the authors investigated the relationship between the Arctic Oscillation (AO) and the high-frequency variability of daily sea level pressures in the Northern Hemisphere in winter (November through March), using NCEP/NCAR reanalysis datasets for the time period of 1948/49-2000/01. High-frequency signals are defined as those with timescales shorter than three weeks and measured in terms of variance, for each winter for each grid. The correlations between monthly mean AO index and high-frequency variance are conducted. A predominant feature is that several regional centers with high correlation show up in the middle to high latitudes. Significant areas include mid- to high-latitude Asia centered at Siberia, northern Europe and the middle-latitude North Atlantic east of northern Africa. Their strong correlations can also be confirmed by the singular value decomposition analysis of covariance between mean SLP and high-frequency variance. This indicates that the relationship of AO with daily Sea Level Pressure (SLP) is confined to some specific regions in association with the inherent atmospheric dynamics. In middle-latitude Asia, there is a significant (at the 95% level) trend of variance of-2.26% (10 yr)-1. Another region that displays a strong trend is the northwestern Pacific with a significant rate of change of 0.80% (10 yr)-1. If the winter of 1948/49, an apparent outlier, is excluded, a steady linear trend of +1.51% (10 yr)-1 shows up in northern Europe. The variance probability density functions (PDFs) are found to change in association with different AO phases. The changes corresponding to high and low AO phases, however, are asymmetric in these regions. Some regions such as northern Europe display much stronger changes in high AO years, whereas some other regions such as Siberia show a stronger connection to low AO conditions. These features are supported by ECMWF reanalysis data. However, the dynamical mechanisms involved in the AO-high fr

关键词： Arctic Oscillation sea level pressure (SLP) Northern Hemisphere synoptic variance

Sensitivity of East Asian Climate to the Progressive Uplift and Expansion of the Tibetan Plateau Under the Mid-Pliocene Boundary Conditions

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Advances in Atmospheric Sciences 2008年第5期25卷 709-722页

作者：姜大膀丁仲礼 helge drange 郜永祺 Nansen-Zhu International Research Centre Institute of Atmospheric PhysicsChinese Academy of Sciences Institute of Geology and Geophysics Chinese Academy of Sciences Nansen Environmental and Remote Sensing Centre Bergen N-5006 Norway

A global atmospheric general circulation model has been used to perform eleven idealized numerical experiments, i.e., TP10, TP10, .., TP100, corresponding to different percentages of the Tibetan Plateau altitude. The aim is to explore the sensitivity of East Asian climate to the uplift and expansion of the Tibetan Plateau under the reconstructed boundary conditions for the mid-Pliocene about 3 Ma ago. When the plateau is progressively uplifted, global annual surface temperature is gradually declined and statistically significant cooling signals emerge only in the Northern Hemisphere, especially over and around the Tibetan Plateau, with larger magnitudes over land than over the oceans. On the contrary, annual surface temperature rises notably over Central Asia and most parts of Africa, as well as over northeasternmost Eurasia in the experiments TP60 to TP100. Meanwhile, the plateau uplift also leads to annual precipitation augmentation over the Tibetan Plateau but a reduction in northern Asia, the Indian Peninsula, much of Central Asia, parts of western Asia and the southern portions of northeastern Europe. Additionally, it is found that an East Asian summer monsoon system similar to that of the present initially exists in the TP60 and is gradually intensified with the continued plateau uplift. At 850 hPa the plateau uplift induces an anomalous cyclonic circulation around the Tibetan Plateau in summertime and two anomalous westerly currents respectively located to the south and north of the Tibetan Plateau in wintertime. In the mid-troposphere, similarto-modern spatial pattern of summertime western North Pacific subtropical high is only exhibited in the experiments TP60 to TP100, and the East Asian trough is steadily deepened in response to the progressive uplift and expansion of the Tibetan Plateau.

关键词： Tibetan Plateau uplift East Asian climate mid-Pliocene model

Revisiting Effect of Ocean Diapycnal Mixing on Atlantic Meridional Overturning Circulation Recovery in a Freshwater Perturbation Simulation

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Advances in Atmospheric Sciences 2008年第4期25卷 597-609页

作者：于雷郜永祺王会军 helge drange Nansen-Zhu International Research Center Institute of Atmospheric PhysicsChinese Academy of Sciences

The effects of ocean density vertical stratification and related ocean mixing on the transient response of the Atlantic meridional overturning circulation （AMOC） are examined in a freshwater perturbation simulation using the Bergen Climate Model （BCM）. The results presented here are based on the model outputs of a previous freshwater experiment： a 300-year control integration （CTRL）, a freshwater integration （FW1） which started after 100 years of running the CTRL with an artificially and continuously threefold increase in the freshwater flux to the Greenland-Iceland-Norwegian （GIN） Seas and the Arctic Ocean throughout the following 150-year simulation. In FW1, the transient response of the AMOC exhibits an initial decreasing of about 6 Sv （1 Sv=106 m3 s^-1） over the first 50-year integration and followed a gradual recovery during the last 100-year integration. Our results show that the vertical density stratification as the crucial property of the interior ocean plays an important role for the transient responses of AMOC by regulating the convective and diapycnal mixings under the enhanced freshwater input to northern high latitudes in BCM in which the ocean diapycnal mixing is stratification-dependent. The possible mechanism is also investigated in this paper.

关键词： North Atlantic meridional overturning circulation enhanced freshwater forcing, diapycnal mixing

Changes in the Tropical Cyclone Genesis Potential Index over the Western North Pacific in the SRES A2 Scenario

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Advances in Atmospheric Sciences 2010年第6期27卷 1246-1258页

作者：张颖王会军孙建奇 helge drange Nansen-Zhu International Research Centre Institute of Atmospheric PhysicsChinese Academy of Sciences Climate Change Research Center Chinese Academy of Sciences Graduate University of Chinese Academy of Science Department of Geophysics University of Bergen

The Tropical Cyclone Genesis Potential Index （GPI） was employed to investigate possible impacts of global warming on tropical cyclone genesis over the western North Pacific （WNP）. The outputs of 20th century climate simulation by eighteen GCMs were used to evaluate the models＇ ability to reproduce tropical cyclone genesis via the GPI. The GCMs were found in general to reasonably reproduce the observed spatial distribution of genesis. Some of the models also showed ability in capturing observed temporal variation. Based on the evaluation, the models （CGCM3.1-T47 and IPSL-CM4） found to perform best when reproducing both spatial and temporal features were chosen to project future GPI. Results show that both of these models project an upward trend of the GPI under the SRES A2 scenario, however the rate of increase differs between them.

关键词： Genesis Potential Index tropical cyclone western North Pacific global warming SRES A2

Diagnosing Ocean Tracer Transport from Sellafield and Dounreay by Equivalent Diffusion and Age

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Advances in Atmospheric Sciences 2008年第5期25卷 805-814页

作者： Steinar ORRE Yongqi GAO helge drange Eric DELEERSNIJDER Nansen Environmental and Remote Sensing Center Bergen Norway Bjerknes Centre for Climate Research Bergen Norway Nansen-Zhu International Research Centre Institute of Atmospheric Physics （ IAP） Chinese Academy of Sciences （ CAS） Beijing 100029 Geophysical Institute University of Bergen Bergen Norway Centre for Systems Engineering and Applied Mechanics （CESAME） Louvain School of Engineering Universite catholique de Louvain Louvain-la-Neuve Belgium

A simple approach for estimating the equivalent diffusion for diagnosing tracer transport is proposed. Two different expressions are derived; one is based directly on an analytical solution of the two-dimensional advection-diffusion equation, the other uses the variance of the tracer distribution. To illustrate some features of the equivalent diffusion and possible applications thereof, idealized releases of passive tracers from the nuclear fuel reprocessing plants at Sellafield in the Irish Sea and Dounreay on the northern coast of Scotland have been simulated with a regional isopycnic co-ordinate Ocean General Circulation Model. Both continuous and pulse releases are considered; the former being representative of the actual historical discharges from the reprocessing plants, the latter resembling an accidental scenario. Age tracers are included to calculate the mean time elapsed since the tracers left their source regions. It is found that in the Nordic Seas the age of tracers from Dounreay is approximately 2 years younger than the age from Sellafield. Although tracers from both sources eventually end up along the same transport routes, significant qualitative differences regarding the dispersion properties are found. It is argued that one single parameter, the equivalent horizontal diffusion, which is estimated to be in the range of 20 56 m^2 s^-1 from Sellafield and 170-485 m^2 s^-1 from Dounreay, determines these differences.

关键词： equivalent diffusion passive tracers age tracers sellafield dounreay

Diapycnal Mixing in Transient Responses of the Atlantic Meridional Overturning Circulation in an Enhanced Freshwater Perturbation Experiment

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Atmospheric and Oceanic Science Letters 2010年第4期3卷 201-206页

作者： helge drange Odd helge OTTER Nansen-Zhu International Research Centre Institute of Atmospheric PhysicsChinese Academy of Sciences Nansen Environmental and Remote Sensing Center/Bjerknes Centre for Climate Research

It has been reported recently that the simulated Atlantic meridional overturning circulation(AMOC) using the coupled Bergen climate model(BCM) showed initial intensity declines followed by gradual recoveries over a 150-year enhanced freshwater input ***-dependent oceanic diapycnal mixing has been hypothesized as a reason for the simulated recovery of the *** study investigated the role of diapycnal mixing in transient responses of simulated *** results showed that stratification-dependent diapycnal mixing can cause stronger upwelling of deep water in the tropical Atlantic than that produced under conditions of fixed diapycnal ***,simulated AMOCs were more sensitive to active stratification-dependent diapycnal mixing than fixed ***,stratification-dependent diapycnal mixing cannot be conclusively singled out as the critical cause of the recoveries of simulated AMOCs under enhanced-freshwater inputs.

关键词： diapycnal mixing western tropical North Atlantic freshwater experiment

耦合模式长期积分中东亚夏季风与ENSO联系的不稳定性

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地球物理学报 2004年第6期47卷 976-981页

作者：姜大膀王会军 drange helge 郎咸梅中国科学院大气物理研究所竺可桢-南森国际研究中心 Nansen Environmental and Remote Sensing Center

通过对挪威卑尔根全球大气 -海洋 -海冰耦合模式 30 0a控制积分结果进行交叉子波分析 ,揭示了东亚夏季风 (EASM )与同期Ni no3区 (90 °W～ 15 0 °W ,5 °S～ 5 °N)海洋表面温度异常的相关关系在长期变化中是不稳定的 ,呈现出明显的... 详细信息

通过对挪威卑尔根全球大气 -海洋 -海冰耦合模式 30 0a控制积分结果进行交叉子波分析 ,揭示了东亚夏季风 (EASM )与同期Ni no3区 (90 °W～ 15 0 °W ,5 °S～ 5 °N)海洋表面温度异常的相关关系在长期变化中是不稳定的 ,呈现出明显的阶段性特征 .气候要素场在二者联系的紧密 (HCP)和微弱 (LCP)时期差别显著 ,在HCP时期 ,西北太平洋对流层低层出现一对耦合的异常气旋和反气旋性环流系统 ;东南亚地区对流层低层表现为强东风异常 ,风速的年际变率加大 ;热带西太平洋对流层温度和位势高度场的年际变率普遍加强 .此外 ,中国夏季降水与同期Ni

关键词：耦合模式东亚夏季风 ENSO 不稳定性

Relative Impacts of Sea Ice Loss and Atmospheric Internal Variability on the Winter Arctic to East Asian Surface Air Temperature Based on Large-Ensemble Simulations with NorESM2

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Advances in Atmospheric Sciences 2024年第8期41卷 1511-1526页

作者： Shengping HE helge drange Tore FUREVIK Huijun WANG Ke FAN Lise Seland GRAFF Yvan J.ORSOLINI Geophysical Institute University of Bergen and Bjerknes Centre for Climate ResearchBergen 5020Norway Nansen Environmental and Remote Sensing Center Bergen 5007Norway Key Laboratory of Meteorological Disaster Ministry of Education/Joint International Research Laboratory of Climate and Environment Change(ILCEC)/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters(CIC-FEMD)Nanjing University of Information Science&TechnologyNanjing 211544China Nansen-Zhu International Research Center Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai) Zhuhai 511458China School of Atmospheric Science Sun Yat-Sen Universityand Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)Zhuhai 519082China Norwegian Meteorological Institute Oslo 0313Norway Norwegian Institute for Air Research Kjeller 2007Norway

To quantify the relative contributions of Arctic sea ice and unforced atmospheric internal variability to the “warm Arctic, cold East Asia”(WACE) teleconnection, this study analyses three sets of large-ensemble simulations carried out by the Norwegian Earth System Model with a coupled atmosphere–land surface model, forced by seasonal sea ice conditions from preindustrial, present-day, and future periods. Each ensemble member within the same set uses the same forcing but with small perturbations to the atmospheric initial state. Hence, the difference between the present-day(or future) ensemble mean and the preindustrial ensemble mean provides the ice-loss-induced response, while the difference of the individual members within the present-day(or future) set is the effect of atmospheric internal variability. Results indicate that both present-day and future sea ice loss can force a negative phase of the Arctic Oscillation with a WACE pattern in winter. The magnitude of ice-induced Arctic warming is over four(ten) times larger than the ice-induced East Asian cooling in the present-day(future) experiment;the latter having a magnitude that is about 30% of the observed cooling. Sea ice loss contributes about 60%(80%) to the Arctic winter warming in the present-day(future) experiment. Atmospheric internal variability can also induce a WACE pattern with comparable magnitudes between the Arctic and East Asia. Ice-lossinduced East Asian cooling can easily be masked by atmospheric internal variability effects because random atmospheric internal variability may induce a larger magnitude warming. The observed WACE pattern occurs as a result of both Arctic sea ice loss and atmospheric internal variability, with the former dominating Arctic warming and the latter dominating East Asian cooling.

关键词： Arctic sea ice loss warm Arctic–cold East Asia atmospheric internal variability large-ensemble simulation NorESM2 PAMIP