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1.
任意正交曲线坐标系下的海洋模式动力框架的发展与评估 总被引：1，自引：1，他引：0
本文发展了一个可以适用于任意水平正交曲线坐标系的海洋模式动力框架,并将其应用于中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室发展的气候系统海洋模式LICOM2.0（LASG/IAP Climate system Ocean Model,version2.0）。在经纬网格坐标系下,新的动力框架与LICOM2.0原有的动力框架模拟结果完全一致。基于新的动力框架,海洋模式可采用能够准确描述北冰洋地形的三极网格,克服了LICOM2.0经纬网格版本必须将北极点处理为孤岛的缺陷,从而显著改进了模式对于北冰洋环流和北大西洋经圈翻转流函数（AMOC）的模拟能力。此外,引进三极网格还可以避免模式网格距随纬度增加而急剧减小带来的计算不稳定,在LICOM2.0的三极网格版本中,模式不需要采用任何空间滤波方案仍然能够保证计算的稳定性,从而与LICOM2.0的经纬网格版本相比,极大地提高了模式的并行效率,这一点在当水平分辨率提高到0.1度时表现得尤为明显,海洋模式的并行加速比可以从经纬网格版本的5.8左右提高到三极网格版本的15.0左右。 相似文献
2.
Seawater property changes in the North Atlantic Ocean affect the Atlantic meridional overturning circulation (AMOC), which transports warm water northward from the upper ocean and contributes to the temperate climate of Europe, as well as influences climate globally. Previous observational studies have focused on salinity and freshwater variability in the sinking region of the North Atlantic, since it is believed that a freshening North Atlantic basin can slow down or halt the flow of the AMOC. Here we use available data to show the importance of how density patterns over the upper ocean of the North Atlantic affect the strength of the AMOC. For the long-term trend, the upper ocean of the subpolar North Atlantic is becoming cooler and fresher, whereas the subtropical North Atlantic is becoming warmer and saltier. On a multidecadal timescale, the upper ocean of the North Atlantic has generally been warmer and saltier since 1995. The heat and salt content in the subpolar North Atlantic lags that in the subtropical North Atlantic by about 8–9 years, suggesting a lower latitude origin for the temperature and salinity anomalies. Because of the opposite effects of temperature and salinity on density for both long-term trend and multidecadal timescales, these variations do not result in a density reduction in the subpolar North Atlantic for slowing down the AMOC. Indeed, the variations in the meridional density gradient between the subpolar and subtropical North Atlantic Ocean suggest that the AMOC has become stronger over the past five decades. These observed results are supported by and consistent with some oceanic reanalysis products. 相似文献
3.
利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室（LASG/IAP）发展的耦合的气候系统模式FGOALS-s2工业革命前控制试验结果研究了大西洋经向翻转流（Atlantic Meridional Overturning Circulation,AMOC）的年代际变率及其物理机制。传统AMOC是利用深度坐标下的质量流函数来表征,本文通过对密度坐标下49.5°N的AMOC指数与其余纬度的AMOC指数作相关分析,发现AMOC的变化有从深水形成区向南传播的过程,且密度坐标下的AMOC变率在北大西洋高纬度明显大于低纬度。分析进一步表明,模式模拟的AMOC具有年代际振荡,周期约为70年。这个低频振荡主要是由与AMOC变化相关的温度和盐度的变化与海表风场之间的相互作用引起,具体机制如下:格陵兰-冰岛-挪威海有异常强的海表风场,导致蒸发增强,继而使海表盐度增加,深水形成增多,从而使AMOC增强。AMOC加强后,会使得向北的热量和盐度输送增加,减弱此处的经向温度梯度,风场随之减弱,从而完成位相的反转。 相似文献
4.
A. Persechino R. Marsh B. Sinha A. P. Megann A. T. Blaker A. L. New 《Climate Dynamics》2012,39(3-4):1021-1042
A wide range of statistical tools is used to investigate the decadal variability of the Atlantic Meridional Overturning Circulation (AMOC) and associated key variables in a climate model (CHIME, Coupled Hadley-Isopycnic Model Experiment), which features a novel ocean component. CHIME is as similar as possible to the 3rd Hadley Centre Coupled Model (HadCM3) with the important exception that its ocean component is based on a hybrid vertical coordinate. Power spectral analysis reveals enhanced AMOC variability for periods in the range 15–30 years. Strong AMOC conditions are associated with: (1) a Sea Surface Temperature (SST) anomaly pattern reminiscent of the Atlantic Multi-decadal Oscillation (AMO) response, but associated with variations in a northern tropical-subtropical gradient; (2) a Surface Air Temperature anomaly pattern closely linked to SST; (3) a positive North Atlantic Oscillation (NAO)-like pattern; (4) a northward shift of the Intertropical Convergence Zone. The primary mode of AMOC variability is associated with decadal changes in the Labrador Sea and the Greenland Iceland Norwegian (GIN) Seas, in both cases linked to the tropical activity about 15 years earlier. These decadal changes are controlled by the low-frequency NAO that may be associated with a rapid atmospheric teleconnection from the tropics to the extratropics. Poleward advection of salinity anomalies in the mixed layer also leads to AMOC changes that are linked to processes in the Labrador Sea. A secondary mode of AMOC variability is associated with interannual changes in the Labrador and GIN Seas, through the impact of the NAO on local surface density. 相似文献
5.
Ruza F. Ivanovic Paul J. Valdes Lauren Gregoire Rachel Flecker Marcus Gutjahr 《Climate Dynamics》2014,42(3-4):859-877
Mediterranean Outflow Water (MOW) is thought to be a key contributor to the strength and stability of Atlantic Meridional Overturning Circulation (AMOC), but the future of Mediterranean-Atlantic water exchange is uncertain. It is chiefly dependent on the difference between Mediterranean and Atlantic temperature and salinity characteristics, and as a semi-enclosed basin, the Mediterranean is particularly vulnerable to future changes in climate and water usage. Certainly, there is strong geologic evidence that the Mediterranean underwent dramatic salinity and sea-level fluctuations in the past. Here, we use a fully coupled atmosphere–ocean General Circulation Model to examine the impact of changes in Mediterranean-Atlantic exchange on global ocean circulation and climate. Our results suggest that MOW strengthens and possibly stabilises the AMOC not through any contribution towards NADW formation, but by delivering relatively warm, saline water to southbound Atlantic currents below 800 m. However, we find almost no climate signal associated with changes in Mediterranean-Atlantic flow strength. Mediterranean salinity, on the other hand, controls MOW buoyancy in the Atlantic and therefore affects its interaction with the shallow-intermediate circulation patterns that govern surface climate. Changing Mediterranean salinity by a factor of two reorganises shallow North Atlantic circulation, resulting in regional climate anomalies in the North Atlantic, Labrador and Greenland-Iceland-Norwegian Seas of ±4 °C or more. Although such major variations in salinity are believed to have occurred in the past, they are unlikely to occur in the near future. However, our work does suggest that changes in the Mediterranean’s hydrological balance can impact global-scale climate. 相似文献
6.
Simulated variability of the Atlantic meridional overturning circulation 总被引：11，自引：3，他引：11
To examine the multi-annual to decadal scale variability of the Atlantic Meridional Overturning Circulation (AMOC) we conducted a four-member ensemble with a daily reanalysis forced, medium-resolution global version of the isopycnic coordinate ocean model MICOM, and a 300-years integration with the fully coupled Bergen Climate Model (BCM). The simulations of the AMOC with both model systems yield a long-term mean value of 18 Sv and decadal variability with an amplitude of 1–3 Sv. The power spectrum of the inter-annual to decadal scale variability of the AMOC in BCM generally follows the theoretical red noise spectrum, with indications of increased power near the 20-years period. Comparison with observational proxy indices for the AMOC, e.g. the thickness of the Labrador Sea Water, the strength of the baroclinic gyre circulation in the North Atlantic Ocean, and the surface temperature anomalies along the mean path of the Gulf Stream, shows similar trends and phasing of the variability, indicating that the simulated AMOC variability is robust and real. Mixing indices have been constructed for the Labrador, the Irminger and the Greenland-Iceland-Norwegian (GIN) seas. While convective mixing in the Labrador and the GIN seas are in opposite phase, and linked to the NAO as observations suggest, the convective mixing in the Irminger Sea is in phase with or leads the Labrador Sea. Newly formed deep water is seen as a slow, anomalous cold and fresh, plume flowing southward along the western continental slope of the Atlantic Ocean, with a return flow of warm and saline water on the surface. In addition, fast-travelling topographically trapped waves propagate southward along the continental slope towards equator, where they go east and continue along the eastern rim of the Atlantic. For both types of experiments, the Northern Hemisphere sea level pressure and 2 m temperature anomaly patterns computed based on the difference between climate states with strong and weak AMOC yields a NAO-like pattern with intensified Icelandic low and Azores high, and a warming of 0.25–0.5 °C of the central North Atlantic sea-surface temperature (SST). The reanalysis forced simulations indicate a coupling between the Labrador Sea Water production rate and an equatorial Atlantic SST index in accordance with observations. This coupling is not identified in the coupled simulation. 相似文献
7.
潮汐混合对大西洋经圈翻转环流(AMOC)模拟影响的数值模拟研究 总被引：1，自引：1，他引：0
海洋中的潮汐混合对大西洋经圈翻转环流AMOC(Atlantic Meridional Overturning Circulation)模拟的影响是海洋环流模式研究的热点问题之一。本文采用IAP/LASG发展的气候系统海洋模式LICOM(LASG/IAP Climate system Ocean Model)及与海冰耦合模式进行了有无潮汐混合方案的试验,重点探讨了潮汐混合对AMOC强度模拟的影响。结果显示,引入潮汐混合后模拟的AMOC强度极大值比对照试验增加约1倍,更接近RAPID(Rapid Climate Change Programme)观测。而且,潮汐混合试验中模拟的AMOC上层环流深度(3200 m)比对照试验加深1000 m左右,同样更接近RAPID观测。海洋底部的垂直混合增强,使海洋层结变得更加不稳定,加强了北大西洋高纬地区,特别是拉布拉多海等地区的深对流,这是AMOC加强的直接原因。同时,潮汐混合试验中上层海洋环流也加强,增加了中低纬副热带高盐海水向高纬输送,使表层增密,海洋层结更加不稳定,也可以进一步增强AMOC。 相似文献
8.
Mechanisms for decadal scale variability in a simulated Atlantic meridional overturning circulation 总被引：1，自引：1，他引：0
Variability in the Atlantic Meridional Overturning Circulation (AMOC) has been analysed using a 600-year pre-industrial control simulation with the Bergen Climate Model. The typical AMOC variability has amplitudes of 1?Sverdrup (1 Sv?=?106?m3?s?1) and time scales of 40–70?years. The model is reproducing the observed dense water formation regions and has very realistic ocean transports and water mass distributions. The dense water produced in the Labrador Sea (1/3) and in the Nordic Seas, including the water entrained into the dense overflows across the Greenland-Scotland Ridge (GSR; 2/3), are the sources of North Atlantic Deep Water (NADW) forming the lower limb of the AMOC’s northern overturning. The variability in the Labrador Sea and the Nordic Seas convection is driven by decadal scale air-sea fluxes in the convective region that can be related to opposite phases of the North Atlantic Oscillation. The Labrador Sea convection is directly linked to the variability in AMOC. Linkages between convection and water mass transformation in the Nordic Seas are more indirect. The Scandinavian Pattern, the third mode of atmospheric variability in the North Atlantic, is a driver of the ocean’s poleward heat transport (PHT), the overall constraint on northern water mass transformation. Increased PHT is both associated with an increased water mass exchange across the GSR, and a stronger AMOC. 相似文献
9.
高纬度淡水强迫增强背景下大西洋经向翻转环流的响应及其机制 总被引：1，自引：0，他引：1
利用卑尔根海洋－大气－海冰耦合气候模式(Bergen Climate Model, 简称BCM), 研究在北冰洋及北欧海淡水强迫增强的背景下, 大西洋经向翻转环流(Atlantic Meridional Overturning Circulation, 简称AMOC)的响应及其机制, 着重讨论了海表热力性质、北大西洋深层水 (North Atlantic Deep Water, 简称NADW) 的生成率、 海洋内部等密度层间的垂直混合 (Diapycnal Mixing, 简称DM) 以及大气风场等物理过程随AMOC的响应所发生的时间演变特征。结果显示, 在持续150年增强 (强度为0.4 Sv) 的淡水强迫下 (淡水试验, FW1), AMOC的强度表现为前50年的快速减弱和在接下来100年中的逐渐恢复。同时, 在淡水试验的前50年北大西洋高纬度海表盐度 (Sea Surface Salinity, 简称SSS) 减小, 海水密度降低, 冬季对流混合减弱, 导致NADW生成率快速减弱; 在接下来的100年中, 尽管增强的淡水强迫依然维持, 由于海洋内部自身的调节和海气相互作用, 导致了AMOC的逐渐恢复。恢复机制可以概括为: (1) 随着向南的NADW的减少, 大西洋中低纬度海水垂直层结逐渐减弱, DM随之逐渐增强, 有利于中低纬度海盆内深层水的上升; (2) 南半球西风应力增强与东风应力的减弱及北半球东风的增强使得大西洋向北的埃克曼体积通量净传输恢复; (3) 大西洋向北的盐度传输逐渐恢复及次极地回旋区降水的减弱, 导致SSS和NADW生成率的恢复, 与之对应, AMOC逐渐恢复。研究还发现, 淡水试验中, NADW的恢复主要以厄尔明格海 (Irminger Sea) 为主, 冬季北大西洋海平面气压场 (SLP) 呈现类似正北大西洋涛动 (NAO+) 的模态, 热带降水中心移到赤道以南, 大西洋热带SSS增强。 相似文献
10.
Andrea A. Cimatoribus Sybren S. Drijfhout Matthijs den Toom Henk A. Dijkstra 《Climate Dynamics》2012,39(9-10):2291-2306
The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to changes in basin integrated net evaporation is highly dependent on the zonal salinity contrast at the southern border of the Atlantic. Biases in the freshwater budget strongly affect the stability of the AMOC in numerical models. The impact of these biases is investigated, by adding local anomaly patterns in the South Atlantic to the freshwater fluxes at the surface. These anomalies impact the freshwater and salt transport by the different components of the ocean circulation, in particular the basin-scale salt-advection feedback, completely changing the response of the AMOC to arbitrary perturbations. It is found that an appropriate dipole anomaly pattern at the southern border of the Atlantic Ocean can collapse the AMOC entirely even without a further hosing. The results suggest a new view on the stability of the AMOC, controlled by processes in the South Atlantic. 相似文献
11.
We study the impact of horizontal resolution in setting the North Atlantic gyre circulation and representing the ocean–atmosphere interactions that modulate the low-frequency variability in the region. Simulations from five state-of-the-art climate models performed at standard and high-resolution as part of the High-Resolution Model Inter-comparison Project (HighResMIP) were analysed. In some models, the resolution is enhanced in the atmospheric and oceanic components whereas, in some other models, the resolution is increased only in the atmosphere. Enhancing the horizontal resolution from non-eddy to eddy-permitting ocean produces stronger barotropic mass transports inside the subpolar and subtropical gyres. The first mode of inter-annual variability is associated with the North Atlantic Oscillation (NAO) in all the cases. The rapid ocean response to it consists of a shift in the position of the inter-gyre zone and it is better captured by the non-eddy models. The delayed ocean response consists of an intensification of the subpolar gyre (SPG) after around 3 years of a positive phase of NAO and it is better represented by the eddy-permitting oceans. A lagged relationship between the intensity of the SPG and the Atlantic Meridional Overturning Circulation (AMOC) is stronger in the cases of the non-eddy ocean. Then, the SPG is more tightly coupled to the AMOC in low-resolution models.
相似文献12.
HUANG Wenyu WANG Bin LI Lijuan DONG Li LIN Pengfei YU Yongqiang ZHOU Tianjun LIU Li XU Shiming XIA Kun PU Ye WANG Lu LIU Mimi SHEN Si HU Ning WANG Yong SUN Wenqi DONG Fang 《大气科学进展》2014,31(1):95-109
The variability of Atlantic Meridional Overturning Circulation （AMOC） in the pre-industrial control experiment of the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 （FGOALS-g2） was investigated using the model outputs with the most stable state in a 512-yr time window from the total 1500-yr period of the experiment. The period of AMOC in FGOALS-g2 is double peaked at 20 and 32 years according to the power spectrum, and 22 years according to an auto-correlation analysis, which shows very obvious decadal variability. Like many other coupled climate models, the decadal variability of AMOC in FGOALS-g2 is closely related to the convection that occurs in the Labrador Sea region. Deep convection in the Labrador Sea in FGOALS-g2 leads the AMOC maximum by 3-4 years. The contributions of thermal and haline effects to the variability of the convection in three different regions [the Labrador, Irminger and Greenland-Iceland- Norwegian （GIN） Seas] were analyzed for FGOALS-g2. The variability of convection in the Labrador and Irminger Seas is thermally dominant, while that in the colder GIN Seas can be mainly attributed to salinity changes due to the lower thermal expansion. By comparing the simulation results from FGOALS-g2 and 11 other models, it was found that AMOC variability can be attributed to salinity changes for longer periods （longer than 35 years） and to temperature changes for shorter periods. 相似文献
13.
Interdecadal North-Atlantic meridional overturning circulation variability in EC-EARTH 总被引：2，自引：2，他引：0
The Atlantic meridional overturning circulation (AMOC) in a 600?years pre-industrial run of the newly developed EC-EARTH model features marked interdecadal variability with a dominant time-scale of 50–60?years. An oscillation of approximately 2 Sverdrup (1?Sv?=?106?m3?s?1) is identified, which manifests itself as a monopole causing the overturning to simultaneously strengthen (/weaken) and deepen (/shallow) as a whole. Eight years before the AMOC peaks, density in the Labrador-Irminger Sea region reaches a maximum, triggering deep water formation. This density change is caused by a counterclockwise advection of temperature and salinity anomalies at lower latitudes, which we relate to the north-south excursions of the subpolar-subtropical gyre boundary and variations in strength and position of the subpolar gyre and the North Atlantic Current. The AMOC fluctuations are not directly forced by the atmosphere, but occur in a delayed response of the ocean to forcing by the North Atlantic Oscillation, which initiates “intergyre”-gyre fluctuations. Associated with the AMOC is a 60-year sea surface temperature variability in the Atlantic, with a pattern and timescale showing similarities with the real-world Atlantic Multidecadal Variability. This good agreement with observations lends a certain degree of credibility that the mechanism that is described in this article could be seen as representative of the real climate system. 相似文献
14.
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. 相似文献
15.
Jin Ba Noel S. Keenlyside Wonsun Park Mojib Latif Ed Hawkins Hui Ding 《Climate Dynamics》2013,41(7-8):2133-2144
Atlantic Multidecadal Variability (AMV) is investigated in a millennial control simulation with the Kiel Climate Model (KCM), a coupled atmosphere–ocean–sea ice model. An oscillatory mode with approximately 60 years period and characteristics similar to observations is identified with the aid of three-dimensional temperature and salinity joint empirical orthogonal function analysis. The mode explains 30 % of variability on centennial and shorter timescales in the upper 2,000 m of the North Atlantic. It is associated with changes in the Atlantic Meridional Overturning Circulation (AMOC) of ±1–2 Sv and Atlantic Sea Surface Temperature (SST) of ±0.2 °C. AMV in KCM results from an out-of-phase interaction between horizontal and vertical ocean circulation, coupled through Irminger Sea convection. Wintertime convection in this region is mainly controlled by salinity anomalies transported by the Subpolar Gyre (SPG). Increased (decreased) dense water formation in this region leads to a stronger (weaker) AMOC after 15 years, and this in turn leads to a weaker (stronger) SPG after another 15 years. The key role of salinity variations in the subpolar North Atlantic for AMV is confirmed in a 1,000 year long simulation with salinity restored to model climatology: No low frequency variations in convection are simulated, and the 60 year mode of variability is absent. 相似文献
16.
The role of meltwater-induced subsurface ocean warming in regulating the Atlantic meridional overturning in glacial climate simulations 总被引：1，自引：1，他引：0
The Community Climate System Model version 3, (CCSM3) is used to investigate the effect of the high latitude North Atlantic subsurface ocean temperature response in idealized freshwater hosing experiments on the strength of the Atlantic meridional overturning circulation (AMOC). The hosing experiments covered a range of input magnitudes at two locations in a glacial background state. Subsurface subpolar ocean warms when freshwater is added to the high latitude North Atlantic (NATL cases) and weakly cools when freshwater is added to the Gulf of Mexico (GOM cases). All cases show subsurface ocean warming in the Southern Hemisphere (SH). The sensitivity of the AMOC response to the location and magnitude of hosing is related to the induced subsurface temperature response, which affects the magnitude of the large-scale meridional pressure gradient at depth through the effect on upper ocean density. The high latitude subsurface warming induced in the NATL cases lowers the upper ocean density in the deepwater formation region enhancing a density reduction by local freshening. In the GOM cases the effect of SH warming partially offsets the effect of the high latitude freshening on the meridional density gradient. Following the end of hosing, a brief convective event occurs in the largest NATL cases which flushes some of the heat stored in the subsurface layers. This fuels a rapid rise in AMOC that lasts less than a couple of decades before subsequent freshening from increases in precipitation and sea ice melt reverses the initial increase in the meridional density gradient. Thereafter AMOC recovery slows to the rate found in comparable GOM cases. The result for these glacial transient hosing experiments is that the pace of the longer recovery is not sensitive to location of the imposed freshwater forcing. 相似文献
17.
利用卑尔根海洋-大气-海冰耦合气候模式 (Bergen Climate Model, 简称BCM), 研究在北冰洋及北欧海淡水强迫增强的背景下, 大西洋经向翻转环流 (Atlantic Meridional Overturning Circulation, 简称AMOC) 的响应及其机制, 着重讨论了海表热力性质、 北大西洋深层水 (North Atlantic Deep Water, 简称NADW) 的生成率、 海洋内部等密度层间的垂直混合 (Diapycnal Mixing, 简称DM) 以及大气风场等物理过程随AMOC的响应所发生的时间演变特征.结果显示, 在持续150年增强 (强度为0.4 Sv) 的淡水强迫下 (淡水试验, FW1), AMOC的强度表现为前50年的快速减弱和在接下来100年中的逐渐恢复.同时, 在淡水试验的前50年北大西洋高纬度海表盐度 (Sea Surface Salinity, 简称SSS) 减小, 海水密度降低, 冬季对流混合减弱, 导致NADW生成率快速减弱; 在接下来的100年中, 尽管增强的淡水强迫依然维持, 由于海洋内部自身的调节和海气相互作用, 导致了AMOC的逐渐恢复.恢复机制可以概括为: (1) 随着向南的NADW的减少, 大西洋中低纬度海水垂直层结逐渐减弱, DM随之逐渐增强, 有利于中低纬度海盆内深层水的上升; (2) 南半球西风应力增强与东风应力的减弱及北半球东风的增强使得大西洋向北的埃克曼体积通量净传输恢复; (3) 大西洋向北的盐度传输逐渐恢复及次极地回旋区降水的减弱, 导致SSS和NADW生成率的恢复, 与之对应, AMOC逐渐恢复.研究还发现, 淡水试验中, NADW的恢复主要以厄尔明格海 (Irminger Sea) 为主, 冬季北大西洋海平面气压场 (SLP) 呈现类似正北大西洋涛动 (NAO+) 的模态, 热带降水中心移到赤道以南, 大西洋热带SSS增强. 相似文献
18.
Local and remote impacts of a tropical Atlantic salinity anomaly 总被引：1，自引：1，他引：0
The climatic impacts of an enhanced evaporation prescribed during 50 years in the tropical Atlantic are investigated in a coupled ocean–atmosphere general circulation model. Locally, the salinity increase leads to a rapid deepening and cooling of the surface mixed layer. This induces a deepening of the equatorial undercurrent and an intensification of the south equatorial current. A remote atmospheric response to the tropical Atlantic perturbation is detected in the North Atlantic sector after ten years. It has the form of a robust wave-like tropospheric perturbation seemingly excited by the weakening of atmospheric deep convection over the Amazonian basin. Meanwhile, the salt anomaly is carried northward by the mean oceanic circulation. It is traced up to the convection sites and then on its return path at depth towards lower latitudes. Consistent with the density increase, deep convection is enhanced after the arrival of the salt anomaly and the Atlantic meridional overturning circulation (AMOC) intensifies about 20 years after the beginning of the perturbation. The adjustment of the tropical Atlantic to the AMOC intensification then modifies its initial response to the freshwater forcing, leading to a weaker cooling in the northern tropical Atlantic than in the southern tropical Atlantic, a slight northward shift of the tropical Atlantic precipitation pattern and an intensification of the North Brazil current. On the other hand, no significant anomalous precipitations are found in the Pacific. The initial remote atmospheric response is also modulated, by an NAO-like response to the AMOC intensification. 相似文献
19.
Yuyang GUO Yongqiang YU Pengfei LIN Hailong LIU Bian HE Qing BAO Bo AN Shuwen ZHAO Lijuan HUA 《大气科学进展》2020,37(10):1133-1148
This study documents simulated oceanic circulations and sea ice by the coupled climate system model FGOALS-f3-L developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, under historical forcing from phase 6 of the Coupled Model Intercomparison Project (CMIP6). FGOALS-f3-L reproduces the fundamental features of global oceanic circulations, such as sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), vertical temperature and salinity, and meridional overturning circulations. There are notable improvements compared with the previous version, FGOALS-s2, such as a reduction in warm SST biases near the western and eastern boundaries of oceans and salty SSS biases in the tropical western Atlantic and eastern boundaries, and a mitigation of deep MLD biases at high latitudes. However, several obvious biases remain. The most significant biases include cold SST biases in the northwestern Pacific (over 4°C), freshwater SSS biases and deep MLD biases in the subtropics, and temperature and salinity biases in deep ocean at high latitudes. The simulated sea ice shows a reasonable distribution but stronger seasonal cycle than observed. The spatial patterns of sea ice are more realistic in FGOALS-f3-L than its previous version because the latitude–longitude grid is replaced with a tripolar grid in the ocean and sea ice model. The most significant biases are the overestimated sea ice and underestimated SSS in the Labrador Sea and Barents Sea, which are related to the shallower MLD and weaker vertical mixing. 相似文献
20.
Cold-season atmospheric response to the natural variability of the Atlantic meridional overturning circulation 总被引：3，自引：3，他引：0
The influence of the natural variability of the Atlantic meridional overturning circulation (AMOC) on the atmosphere is studied in multi-centennial simulations of six global climate models, using Maximum Covariance Analysis (MCA). In all models, a significant but weak influence of the AMOC changes is found during the Northern Hemisphere cold-season, when the ocean leads the atmosphere by a few years. Although the oceanic pattern slightly varies, an intensification of the AMOC is followed in all models by a weak sea level pressure response that resembles a negative phase of the North Atlantic Oscillation (NAO). The signal amplitude is typically 0.5?hPa and explains about 10% of the yearly variability of the NAO in all models. The atmospheric response seems to be due primarily due to an increase of the heat loss along the North Atlantic Current and the subpolar gyre, associated with an AMOC-driven warming. Sea-ice changes appear to be less important. The stronger heating is associated to a southward shift of the lower-tropospheric baroclinicity and a decrease of the eddy activity in the North Atlantic storm track, which is consistent with the equivalent barotropic perturbation resembling the negative phase of the NAO. This study thus provides some evidence of an atmospheric signature of the AMOC in the cold-season, which may have some implications for the decadal predictability of climate in the North Atlantic region. 相似文献