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1.
The problem of the optimal sampling strategy for moored current velocity observations in the Northern Bering Sea is addressed. We analyze dynamically induced correlations in the North Bering Sea currents and conduct their sensitivity analysis to optimize positions of a limited number of moorings. Optimization of the sampling strategy is performed with respect to robustness of the reconstruction of the North Bering Sea circulation with a particular emphasis on the accurate monitoring of the mean Bering Strait transport. Computations reveal four major regions in the North Bering Sea basin that are highly correlated with the Bering Strait transport. Apart from the regions within the Bering Strait itself, they include the Anadyr Strait and a region 100 km south of the Cape of Prince of Wales. Results of the sensitivity analysis are tested in the framework of twin data experiments with the quasi-stationary and oscillatory background circulations.  相似文献   

2.
 To understand the influence of the Bering Strait on the World Ocean’s circulation, a model sensitivity analysis is conducted. The numerical experiments are carried out with a global, coupled ice–ocean model. The water transport through the Bering Strait is parametrized according to the geostrophic control theory. The model is driven by surface fluxes derived from bulk formulae assuming a prescribed atmospheric seasonal cycle. In addition, a weak restoring to observed surface salinities is applied to compensate for the global imbalance of the imposed surface freshwater fluxes. The freshwater flux from the North Pacific to the North Atlantic associated with the Bering Strait throughflow seems to be an important element in the freshwater budget of the Greenland and Norwegian seas and of the Atlantic. This flux induces a freshening of the North Atlantic surface waters, which reduces the convective activity and leads to a noticeable (6%) weakening of the thermohaline conveyor belt. It is argued that the contrasting results obtained by Reason and Power are due to the type of surface boundary conditions they used. Received: 27 October 1995/Accepted: 20 November 1996  相似文献   

3.
北极海冰变化的时间和空间型   总被引：14，自引：0，他引：14  
汪代维  杨修群 《气象学报》2002,60(2):129-138
利用 4 4a(195 1～ 1994年 )北极海冰密度逐月资料 ,分析提出了一种与北极冰自然季节变化相吻合的分季法 ,并根据这种分季法 ,使用EOF分解 ,揭示了北极各季海冰面积异常的特征空间型及其对应的时间变化尺度。结果表明 :(1)北极冰面积异常变化的关键区 ,冬季 (2～ 4月 )主要位于北大西洋一侧的格陵兰海、巴伦支海和戴维斯海峡以及北太平洋一侧的鄂霍次克海和白令海 ,夏季 (8～ 10月 )则主要限于从喀拉海、东西伯利亚海、楚科奇海到波佛特海的纬向带状区域内 ,格陵兰海和巴伦支海是北极海冰面积异常变化的最重要区域 ;(2 )春 (5～ 7月 )、秋 (11月～次年 1月 )季各主要海区海冰面积异常基本呈同相变化 ,夏季东西伯利亚海、楚科奇海、波佛特海一带海冰面积异常和喀拉海呈反相变化 ,而冬季巴伦支海、格陵兰海海冰面积异常和戴维斯海峡、拉布拉多海、白令海、鄂霍次克海的海冰变化呈反相变化 ;(3)北极冰总面积过去 4 4a来确实经历了一种趋势性的减少 ,并且叠加在这种趋势变化之上的是年代尺度变化 ,其中春季 (5～ 7月 )海冰面积异常变化对年平均北极冰总面积异常变化作出了主要贡献 ;(4)位于北太平洋一侧极冰面积异常型基本具有半年的持续性 ,而位于北大西洋一侧极冰面积异常型具有半年至一年的持续性  相似文献   

4.
Tom Agnew 《大气与海洋》2013,51(2):259-280
Abstract

This study looks at simultaneous changes in atmospheric circulation and extremes in sea‐ice cover during winter. Thirty‐six years of ice‐cover data and 100‐kPa height and 50–100‐kPa thickness data are used. For the entire Arctic, the study found a general weakening of the Aleutian and Icelandic lows for heavy (i.e. severe) compared with light sea‐ice conditions suggesting reduced surface heating as a possible cause. The weakening of the two lows would also reduce meridional atmospheric circulation and poleward heat transport into the Arctic. The study also looks at three regions of high sea ice and atmospheric variability: the Bering Sea, the Davis Strait/Labrador Sea and the Greenland Sea. For the Bering Sea, heavy sea‐ice conditions were accompanied by weakening and westward displacement of the Aleutian Low again suggesting reduced surface heating and the formation of a secondary low in the Gulf of Alaska. This change in circulation is consistent with increased cold air advection over the Bering Sea and changes in storm tracks and meridional heat transport found in other studies. For the Davis Strait/Labrador Sea, heavy ice‐cover winters were accompanied by intensification of the Icelandic Low suggesting atmospheric temperature and wind advection and associated changes in ocean currents as the main cause of heavy ice. For the Greenland Sea no statistically significant difference was found. It is felt that this may be due to the important role that ice export through Fram Strait and ocean currents play in determining ice extent in this region.  相似文献   

5.
冬春季节北极海冰的年际和年代际变化   总被引：6，自引：0，他引：6  
利用1953～1990年海冰密集度资料,研究了冬、春季节北极海冰的时空变化特征.结果表明:冬,春季节海冰变率大的海区主要有巴伦支海、格陵兰海、巴芬湾、戴维斯海峡以及白令海;在巴芬湾、戴维斯海峡和白令海海区,冬季海冰变率比春季的大;冬、春季节喀拉海、巴伦支海海冰面积均与春季白令海海冰面积呈反向变化关系,与巴芬湾、戴维斯海峡海冰面积也存在相反的变化趋势.分析还表明:北极海冰面积还表现出年代际时间尺度变化,尤其在冬季.春季格陵兰海海冰明显存在12年变化周期,而在冬、春季节,喀拉海、巴伦支海海冰存在l0年变化周期.  相似文献   

6.
An ocean general circulation model of global domain, full continental geometry and bottom topography, is used to study the influence of the Bering Strait on the general circulation by comparing equilibrium solutions obtained with and without a land-bridge between Siberia and Alaska. The model is integrated with restoring boundary conditions (BC) on temperature and salinity, and later, with mixed BC in which a restoring BC on temperature is maintained but a specified flux condition on salinity is imposed. In both cases, the effect of the Bering Strait is to allow a flow of about 1.25–1.5 Sv from the North Pacific to the Arctic Ocean and, ultimately, back to the North Pacific along the western boundary current regions of the Atlantic and Indian Oceans. When a restoring BC on salinity is used, the overturning associated with North Atlantic Deep Water and Antarctic Intermediate Water formation are increased if the Bering Strait is present in the model geometry. The result of switching to a specified flux BC on salinity is to cause a transition in the THC in which the overturning associated with North Atlantic Deep Water formation increases from about 12 Sv to about 22 Sv. This transition occurs in an essentially smooth fashion with no significant variability and is about 12% smaller in magnitude if the Bering Strait is present in the model geometry. Because the Bering Strait appears to exert some influence on the general circulation and the formation of deep water masses, it is recommended that this Strait be included in the geometry of similar resolution models designed to study the deep ocean and potential changes in climate. Correspondence to: CJC Reason  相似文献   

7.
Hydrological and hydrochemical conditions in the Kamchatka Strait are considered, the computation of geostrophic flows is carried out, and estimations of the water exchange between the Bering Sea and the Pacific Ocean through this strait are made on the basis of the analysis of data obtained during the trip of the research vessel Miraii in August, 2004. According to the results of computations, the volume transport from the Bering Sea to the Pacific Ocean made up 10.2 Sv; mass transport, 10.4 × 109 kg/s; salt transport, 0.35 × 106 kg/s. The estimated value of heat transport through the strait is 11.4 × 1015 W. The Eastern Kamchatka Current carries oxygen and biogenic elements through the strait: 1222, 28, 380, and 1036 kmol/s for oxygen, phosphates, nitrates, and silicon, respectively. In total, the Bering Sea is the source of oxygen and biogenic elements for the northern part of the Pacific Ocean in the upper 500-m layer.  相似文献   

8.
Carried out is analysis of variations of temperature, salinity, and currents in the Bering Strait area based on the data of American and Russian-American studies of the Bering Strait during the period from 1992 to 2010. Major attention is paid to the analysis of the long-term variability of water dynamics using the data of observations at the autonomous buoy stations in the Russian and American parts of the Bering Strait. Revealed are the trends towards the increase in the velocity of the Pacific water transport to the Chukchi Sea and Arctic Ocean, as well as the absence of the significant trend towards the changes in the temperature and salinity of deep waters in the Bering Strait. Estimated is the seasonal variability of hydrophysical conditions.  相似文献   

9.
The ocean heat transport into the Arctic and the heat budget of the Barents Sea are analyzed in an ensemble of historical and future climate simulations performed with the global coupled climate model EC-Earth. The zonally integrated northward heat flux in the ocean at 70°N is strongly enhanced and compensates for a reduction of its atmospheric counterpart in the twenty first century. Although an increase in the northward heat transport occurs through all of Fram Strait, Canadian Archipelago, Bering Strait and Barents Sea Opening, it is the latter which dominates the increase in ocean heat transport into the Arctic. Increased temperature of the northward transported Atlantic water masses are the main reason for the enhancement of the ocean heat transport. The natural variability in the heat transport into the Barents Sea is caused to the same extent by variations in temperature and volume transport. Large ocean heat transports lead to reduced ice and higher atmospheric temperature in the Barents Sea area and are related to the positive phase of the North Atlantic Oscillation. The net ocean heat transport into the Barents Sea grows until about year 2050. Thereafter, both heat and volume fluxes out of the Barents Sea through the section between Franz Josef Land and Novaya Zemlya are strongly enhanced and compensate for all further increase in the inflow through the Barents Sea Opening. Most of the heat transported by the ocean into the Barents Sea is passed to the atmosphere and contributes to warming of the atmosphere and Arctic temperature amplification. Latent and sensible heat fluxes are enhanced. Net surface long-wave and solar radiation are enhanced upward and downward, respectively and are almost compensating each other. We find that the changes in the surface heat fluxes are mainly caused by the vanishing sea ice in the twenty first century. The increasing ocean heat transport leads to enhanced bottom ice melt and to an extension of the area with bottom ice melt further northward. However, no indication for a substantial impact of the increased heat transport on ice melt in the Central Arctic is found. Most of the heat that is not passed to the atmosphere in the Barents Sea is stored in the Arctic intermediate layer of Atlantic water, which is increasingly pronounced in the twenty first century.  相似文献   

10.
We investigate some aspects of the variability of the Arctic freshwater content during the 1965–2002 period using the DRAKKAR eddy admitting global ocean/sea-ice model (12 km resolution in the Arctic). A comparison with recent mooring sections shows that the model realistically represents the major advective exchanges with the Arctic basin, through Bering, Fram and Davis Straits, and the Barents Sea. This allows the separate contributions of the inflows and outflows across each section to be quantified. In the model, the Arctic freshwater content variability is explained by the sea-ice flux at Fram and the combined variations of ocean freshwater inflow (at Bering) and outflow (at Fram and Davis). At all routes, except trough Fram Strait, the freshwater transport variability is mainly accounted for by the liquid component, with small contributions from the sea-ice flux. The ocean freshwater transport variability through both Davis and Fram is controlled by the variability of the export branch (Baffin Island Current and East Greenland Current, respectively), the variability of the inflow branches playing a minor role. We examine the respective role of velocity and salinity fluctuations in the variability of the ocean freshwater transport. Fram and Davis Straits offer a striking contrast in this regard. Freshwater transport variations across Davis Strait are completely determined by the variations of the total volume flux (0.91 correlation). On the other hand, the freshwater transport through Fram Strait depends both on variations of volume transport and salinity. As a result, there is no significant correlation between the variability of freshwater flux at Fram and Davis, although the volume transports on each side of Greenland are strongly anti-correlated (−0.84). Contrary to Davis Strait, the salinity of water carried by the East Greenland Current through Fram Strait varies strongly due to the ice-ocean flux north of Greenland.  相似文献   

11.
The thermal state of the Bering Sea exhibits interdecadal variations, with distinct changes occurred in 1997–1998. After the unusual thermal condition of the Bering Sea in 1997–1998, we found that the recent climate variability (1999–2010) in the Bering Sea is closely related to Pacific basin-scale atmospheric and oceanic circulation patterns. Specifically, warming in the Bering and Chukchi Seas in this period involves sea ice reduction and stronger oceanic heat flux to the atmosphere in winter. The atmospheric response to the recent warming in the Bering and Chukchi Seas resembles the North Pacific Oscillation (NPO) pattern. Further analysis reveals that the recent climate variability in the Bering and Chukchi Seas has strong covariability with large-scale climate modes in the Pacific, that is, the North Pacific Gyre Oscillation and the central Pacific El Niño. In this study, physical connections among the recent climate variations in the Bering and Chukchi Seas, the NPO pattern and the Pacific large-scale climate patterns are investigated via cyclostationary empirical orthogonal function analysis. An additional model experiment using the National Center for Atmospheric Research Community Atmospheric Model, version 3, is conducted to support the robustness of the results.  相似文献   

12.
Independent datasets consistently indicate a significant correlation between the sea ice variability in the Bering Sea during melt season and the summer rainfall variability in the Lake Baikal area and Northeastern China. In this study, four sea ice datasets(Had ISST1, Had ISST2.2, ERA-Interim and NOAA/NSIDC) and two global precipitation datasets(CRU V4.01 and GPCP V2.3) are used to investigate co-variations between melt season(March-April-May-June, MAMJ)Bering Sea ice cover(BSIC) and summer(June-July-August, JJA) East Asian precipitation. All datasets demonstrate a significant correlation between the MAMJ BSIC and the JJA rainfall in Lake Baikal-Northeastern China(Baikal-NEC).Based on the reanalysis datasets and the numerical sensitivity experiments performed in this study using Community Atmospheric Model version 5(CAM5), a mechanism to understand how the MAMJ BSIC influences the JJA Baikal-NEC rainfall is suggested. More MAMJ BSIC triggers a wave train and causes a positive sea level pressure(SLP) anomaly over the North Atlantic during MAMJ. The high SLP anomaly, associated with an anti-cyclonic wind stress circulation anomaly,favors the appearance of sea surface temperature(SST) anomalies in a zonal dipole-pattern in the North Atlantic during summer. The dipole SST anomaly drives a zonally orientated wave train, which causes a high anomaly geopotential height at 500 h Pa over the Sea of Japan. As a result, the mean East Asian trough moves westward and a low geopotential height anomaly occurs over Baikal-NEC. This prevailing regional low pressure anomaly together with enhanced moisture transport from the western North Pacific and convergence over Baikal-NEC, positively influences the increased rainfall in summer.  相似文献   

13.
Most state-of-the art global coupled models simulate a weakening of the Atlantic meridional overturning circulation (MOC) in climate change scenarios but the mechanisms leading to this weakening are still being debated. The third version of the CNRM (Centre National de Recherches Météorologiques) global atmosphere-ocean-sea ice coupled model (CNRM-CM3) was used to conduct climate change experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). The analysis of the A1B scenario experiment shows that global warming leads to a slowdown of North Atlantic deep ocean convection and thermohaline circulation south of Iceland. This slowdown is triggered by a freshening of the Arctic Ocean and an increase in freshwater outflow through Fram Strait. Sea ice melting in the Barents Sea induces a local amplification of the surface warming, which enhances the cyclonic atmospheric circulation around Spitzberg. This anti-clockwise circulation forces an increase in Fram Strait outflow and a simultaneous increase in ocean transport of warm waters toward the Barents Sea, favouring further sea ice melting and surface warming in the Barents Sea. Additionally, the retreat of sea ice allows more deep water formation north of Iceland and the thermohaline circulation strengthens there. The transport of warm and saline waters toward the Barents Sea is further enhanced, which constitutes a second positive feedback.  相似文献   

14.
Abstract

Monthly mean sea‐level pressure (SLP) data from the Northern Hemisphere for the period January 1952‐December 1987 are analysed. Fluctuations in this field over the Arctic on interannual time‐scales and their statistical association with fluctuations farther south are determined. The standard deviation of the interannual variability is largest compared with that of the annual cycle along the seaboards of the major land masses. The SLP anomalies are generally in phase over the entire Arctic Basin and extend south over the northern Russia and Canada, but tend to be out of phase with fluctuations at mid‐latitudes. The anomalies are most closely associated with fluctuations over the North Atlantic and Europe except near the Chukchi Sea to the north of Bering Strait. The associations with the North Pacific fluctuations become increasingly more prominent at most Arctic sites (e.g. the Canadian Arctic Archipelago) as the time‐scale increases.

Associations between the SLP fluctuations and atmospheric indices that represent processes affecting sea‐ice drift (wind stress and wind stress curl) are determined. In every case local associations dominate, but some remote ones are also evident. For example, changes in the magnitude of the wind stress curl over the Beaufort Sea are increased if the atmospheric circulation over the North Pacific is intensified; wind stress over the region where sea ice is exchanged between the Beaufort Gyre and the Transpolar Drift Stream is modulated by both the Southern and North Atlantic Oscillations.

Severe sea‐ice conditions in the Greenland Sea (as measured by the Koch Ice Index) coincide with a weakened atmospheric circulation over the North Atlantic.  相似文献   

15.
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   

16.
Interdecadal climate variability in the subpolar North Atlantic   总被引：1，自引：0，他引：1  
The statistical relationships between various components of the subpolar North Atlantic air-sea-ice climate system are reexamined in order to investigate potential processes involved in interdecadal climate variability. It is found that sea surface temperature anomalies concentrated in the Labrador Sea region have a strong impact upon atmospheric sea level pressure anomalies over Greenland, which in turn influence the transport of freshwater and ice anomalies out of the Arctic Ocean, via Fram Strait. These freshwater and ice anomalies are advected around the subpolar gyre into the Labrador Sea affecting convection and the formation of Labrador Sea Water. This has an impact upon the transport of North Atlantic Current water into the subpolar gyre and thus, also upon sea surface temperatures in the region. An interdecadal negative feedback loop is therefore proposed as an internal source of climate variability within the subpolar North Atlantic. Through the lags associated with the correlations between different climatic components, observed horizontal advection time scales, and the use of Boolean delay equation models, the time scale for one cycle of this feedback loop is determined to have a period of about 21 years.  相似文献   

17.
Anthropogenic aerosols (AA) have significantly caused anomalous winter mean atmospheric circulation over the Northern Hemisphere, but the main daily patterns of winter large-scale circulation change are not well understood. Here a self-organizing map analysis is applied to identify the leading patterns in AA-induced winter daily geopotential height (Z) anomaly fields simulated by three atmospheric general circulation models, with a focus on fast adjustments. Two winter daily circulation response patterns with a synoptic time scale are found: one pattern shows concurring Z anomalies over North America and North Asia with the same sign and the Bering Sea seeing the opposite, resembling the Asia–Bering–North American teleconnection; while the other is the Arctic Oscillation-like pattern with similar Z anomalies over North Pacific and North Atlantic and the opposite over the Arctic region. The AA-induced anomalous precipitation over the tropics and anomalous synoptic eddy activities over the extratropical oceans concur to support and maintain these circulation anomaly patterns. The winter-mean climate responses to AA can be understood as a result of these daily anomaly patterns, especially over the higher latitudes. Specifically, the associated changes in surface air temperature (SAT) over the mid-high latitudes are caused by the AA-driven meridional movements of polar (cold and dry) airmass and midlatitude (warm and moist) airmass in the regions, mainly through the relevant surface downward longwave radiation. This study highlights the role of AA in altering daily weather patterns, which is not sufficiently captured by seasonal mean responses.  相似文献   

18.
ABSTRACT

The nuclear leak in Fukushima, Japan, which occurred on 11 March 2011, had disastrous impacts in many regions of the northern hemisphere. In this study, a highly resolved, one-way nesting model incorporating tides is set up with the Regional Ocean Modeling System (ROMS) to simulate and predict the potential impact of the disaster on the East China Sea (ECS), with the large domain covering the entire North Pacific. Of the four main waterways, namely Taiwan Strait, the waterway east of Taiwan, Tokara Strait, and Tsushima Strait, the first two have net fluxes of radionuclides into the ECS, while the other two have net outward transport during the entire 14-year period of the simulation (2011–2025). Differing from previous studies, we have taken into account background radionuclides in this model; the results agree well with available observations. Based on the simulation, the radioactive material has arrived in the ECS. The amount will reach its peak in 2019 and late in 2021 will return to its original state before the accident. Temporally it has a clear seasonal variability, with peaks usually appearing during winter. Spatially it is not homogeneously distributed, and the concentration has local maxima along the coasts of Jiangsu and Zhejiang, which are the most populous regions of China; a conspicuous feature is the Subei Bank high in summer. This study is expected to help form policy for rapid response to such disasters.  相似文献   

19.
分析了一个1/10°的涡分辨率全球环流模式LICOM(LASG/IAP Climate system Ocean Model)对吕宋海峡附近海洋环流的模拟能力。结果表明,模拟的吕宋海峡附近上层环流及输运具有明显的季节变化特征,除6月是东向净流出外,其余月份均为西向流入,冬季流量最大。年平均流量在-3.76 Sv(1 Sv=106 m3/s),其中上层(600 m以上)流量起主要贡献,为-3.60 Sv,与目前已有的研究结果基本一致。南海通过6个海峡完成与外界的水交换,其中吕宋海峡和巴拉巴克海峡是大洋水进入南海的主要通道,其余海峡均以流出为主,流出量最大的是台湾海峡(1.99 Sv),其次是卡里玛塔海峡(1.03 Sv)。进一步分析表明,由季风引起的埃克曼输送量约占吕宋海峡流量的11%,而由季风引起的吕宋海峡压力梯度形成的西向的地转流对吕宋海峡的输运起支配作用。作为黑潮源头的太平洋北赤道流流量对吕宋海峡输运的季节变化也有一定影响。  相似文献   

20.
During 1996–2009, the number and intensity of cyclones passing over the Pacific Rim in the winter was gradually increasing. Their trajectories were becoming more zonal and, hence, the area of the maximum cyclonic intensity shifted from the Bering Sea to the ocean. It has been revealed that if the cyclonic activity over the region increases, the sea surface temperature in the North Pacific as well as in the Sea of Japan and Sea of Okhotsk was increasing mainly in the summer. In the Bering Sea, the water temperature was decreasing in the spring.  相似文献   

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