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51.
全球变暖背景下, 2015/2016年超强厄尔尼诺(El Ni?o)事件倍受关注, 此次事件是中部型和东部型El Ni?o的混合。研究发现, 西风爆发和北太平洋经向模态对触发此次事件均有所贡献。通过对比2015/2016年、1997/1998年与中部型事件可知, 2015/2016年事件在暖背景中产生, 其发展形态与中部型事件较为相似, 后期海表面温度异常迅速衰退主要与赤道东太平洋海域持续的东风异常以及纬向平流较弱有关。较之1997/1998年事件, 2015/2016年事件的海洋动力调整较弱, 表现为较弱的温跃层反馈和海洋波动, 纬向平流反馈的贡献大于温跃层反馈, 大气强迫影响显著, 中部海域相关要素异常值较大。在2015/2016年事件期间, 赤道海域以及近赤道海域海洋上层热含量的变化基本呈负相关, 且变化较为同步; 衰退阶段热含量的流失主要集中在5°S—5°N海域, 向两极的热输送明显。 相似文献
52.
Temporal variations of the subsurface meridional flow with the solar cycle have been reported by several authors. The measurements
are typically averaged over periods of time during which surface magnetic activity existed in the regions where the velocities
are calculated. The present work examines the possible contamination of these measurements due to the extra velocity fields
associated with active regions plus the uncertainties in the data obtained where strong magnetic fields are present. We perform
a systematic analysis of more than five years of GONG data and compare meridional flows obtained by ring-diagram analysis
before and after removing the areas of strong magnetic field. The overall trend of increased amplitude of the meridional flow
towards solar minimum remains after removal of large areas associated with surface activity. We also find residual circulation
toward the active belts that persists even after the removal of the surface magnetic activity, suggesting the existence of
a global pattern or longitudinally-located organized flows. 相似文献
53.
Based on high-resolution,Array for Real-time Geostrophic Oceanography(Argo)profiles and Sea Level Anomaly(SLA)data,this study statistically analyzes and compares turbulent diapycnal mixing profiles inside and outside mesoscale eddies in the Gulf Stream region.The result indicates that average diapycnal diffusivity at 300–540 m depths in anticyclonic eddies reaches4.0×10-5 m2 s-1.This is significantly higher than the 1.6×10-5 m2 s-1 outside eddies and 0.8×10-5 m2 s-1 in cyclonic eddies.Probabilities of diapycnal diffusivity greater than 10-4 m2 s-1 within anticyclonic and cyclonic eddies and outside eddies are29%,5%and 12%,respectively.However,magnitudes of average diapycnal diffusivity at 540–900 m depths in these three cases are of the same order,10-5 m2 s-1.Twenty-four of a total 38 anticyclonic eddies had enhanced mixing in the ocean interior,and 22 were observed during or shortly after strong winds.The coincidence between enhanced mixing and strong wind stress indicates that more wind-induced,near-inertial wave energy propagates downward in anticyclonic eddies.The deeper part of 12 profiles(below 540 m)in anticyclonic eddies had vertical overturns with Thorpe scale exceeding 5 m,among which three profiles had overturns reaching 20 m.Enhanced mixing may have occurred in deep layers of some profiles,although it was not evident in average conditions. 相似文献
54.
The effect of fluctuating daily surface fluxes on the time-mean oceanic circulation is studied using an empirical flux model.
The model produces fluctuating fluxes resulting from atmospheric variability and includes oceanic feedbacks on the fluxes.
Numerical experiments were carried out by driving an ocean general circulation model with three different versions of the
empirical model. It is found that fluctuating daily fluxes lead to an increase in the meridional overturning circulation (MOC)
of the Atlantic of about 1 Sv and a decrease in the Antarctic circumpolar current (ACC) of about 32 Sv. The changes are approximately
7% of the MOC and 16% of the ACC obtained without fluctuating daily fluxes. The fluctuating fluxes change the intensity and
the depth of vertical mixing. This, in turn, changes the density field and thus the circulation. Fluctuating buoyancy fluxes
change the vertical mixing in a non-linear way: they tend to increase the convective mixing in mostly stable regions and to
decrease the convective mixing in mostly unstable regions. The ACC changes are related to the enhanced mixing in the subtropical
and the mid-latitude Southern Ocean and reduced mixing in the high-latitude Southern Ocean. The enhanced mixing is related
to an increase in the frequency and the depth of convective events. As these events bring more dense water downward, the mixing
changes lead to a reduction in meridional gradient of the depth-integrated density in the Southern Ocean and hence the strength
of the ACC. The MOC changes are related to more subtle density changes. It is found that the vertical mixing in a latitudinal
strip in the northern North Atlantic is more strongly enhanced due to fluctuating fluxes than the mixing in a latitudinal
strip in the South Atlantic. This leads to an increase in the density difference between the two strips, which can be responsible
for the increase in the Atlantic MOC. 相似文献
55.
大气环流模式IAP AGCM4.0对东亚高空副热带西风急流的模拟及偏差原因分析 总被引:1,自引:1,他引:0
基于中国科学院大气物理所大气环流模式IAP AGCM4.0总共30年(1979~2008年)的AMIP(大气环流模式比较计划)数值模拟试验结果,评估了模式对东亚高空副热带西风急流的模拟能力,分析了模式模拟偏差的可能原因,以及不同对流参数化方案对模拟结果的影响。结果表明,IAP AGCM4.0可以较好地模拟出东亚高空副热带西风急流冬季和夏季的空间结构及其季节变化特征;与JRA-25再分析资料相比,模式模拟的急流强度总体偏弱;就急流位置而言,模式模拟的急流位置冬季略偏南,夏季则相对偏北;模式可以较好地模拟出夏季西风急流的季节内演变特征,包括夏季西风急流位置逐月北跳的特征,只是模式模拟的逐月西风急流位置仍偏北。夏季200 h Pa纬向风EOF分解结果表明,模式模拟和再分析资料的EOF第一模态空间型态较为接近,均反映了西风急流的年际变化特征,但两者的时间系数相关较小,表明模式对西风急流南北位置年际变化的模拟偏差较大。针对模式模拟的地表感热通量及对流层中上层经向温度差(MTD)的分析结果表明,模式对阿拉伯半岛东南部、阿拉伯海西北部及印度北部的地表感热通量的模拟存在偏差,影响到对流层中高层温度场、高度场的模拟,使得IAP AGCM4.0模拟的MTD强度较再分析资料相对偏弱,MTD变化最大的区域位置相对偏北,且模式模拟的MTD年际变化与再分析资料相比也有较大偏差,从而造成模式对西风急流模拟的偏差。此外,不同积云对流参数化方案也可影响对流层中上层经向温度差的模拟,进而影响模式对东亚高空副热带西风急流的模拟。 相似文献
56.
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
57.
The response of the internal variability of the Atlantic Meridional Overturning Circulation (MOC) to enhanced atmospheric
greenhouse gas concentrations has been estimated from an ensemble of climate change scenario runs. In the model, enhanced
greenhouse forcing results in a weaker and shallower MOC with reduced internal variability. At the same time at 55°N between
0 and 1,000 m the overturning increases as a result of a change in the area of convection. In a warmer world, new regions
of deepwater formation form further north due to the poleward retreat of the sea-ice boundary. The dominant pattern of internal
MOC-variability consists of a monopole centered around 35°N. Due to anthropogenic warming this monopole shifts poleward. The
shift is associated with a stronger relation between MOC-variations and heat flux variations over the subpolar gyre. In old
convective sites (Labrador Sea) convection becomes more irregular which leads to enhanced heat flux variability. In new convective
sites heat flux variations initially are related to sea-ice variations. When the sea-ice coverage further decreases they become
associated with (irregular) deepwater formation. Both processes act to tighten the relation between subpolar surface heat
flux variability and MOC-variability, resulting in a poleward shift of the latter. 相似文献
58.
Interdecadal variability of the meridional overturning circulation as an ocean internal mode 总被引:1,自引:1,他引:0
The meridional overturning circulation (MOC) in the coupled ECHAM5/MPIOM exhibits variability at periods of near 30 years
and near 60 years. The 30-year variability, referred to as interdecadal variability (IDV), exist in an ocean model driven
by climatological atmospheric forcing, suggesting that it is maintained by ocean dynamics; the 60-year variability, the multidecadal
variability (MDV), is only observed in the fully coupled model and therefore is interpreted as an atmosphere–ocean coupled
mode. The coexistence of the 30-year IDV and the 60-year MDV provides a possible explanation for the widespread time scales
observed in climate variables. Further analyses of the climatologically forced ocean model shows that, the IDV is related
to the interplay between the horizontal temperature-dominated density gradients and the ocean circulation: temperature anomalies
move along the cyclonic subpolar gyre leading to fluctuations in horizontal density gradients and the subsequent weakening
and strengthening of the MOC. This result is consistent with that from less complex models, indicating the robustness of the
IDV. We further show that, along the North Atlantic Current path, the sea surface temperature anomalies are determined by
the slow LSW advection at the intermediate depth. 相似文献
59.
ENSO事件对东亚副热带西风急流影响的诊断分析 总被引:14,自引:10,他引:4
本文利用NCEP/NCAR月平均再分析资料,用合成分析和相关分析方法就ENSO事件对东亚副热带西风急流的影响进行诊断分析.主要结论为:El Nino年冬季200 hPa东亚副热带西风急流主要在急流出口区纬向风有正距平,急流增强东扩.而La Nina年冬季急流在急流出口区纬向风有负距平,急流减弱西移.El Nino年夏季急流增强,主要在急流区内的偏南部纬向风有正距平.La Nina年夏季急流减弱,主要在急流区内的偏南部纬向风有负距平;相关分析表明东亚副热带西风急流冬、夏季纬向风与热带中东太平洋冬、夏季海表温度有显著的相关.研究表明,ENSO年冬、夏季对流层中上层有较大的气温异常,并由此产生大的经向温度梯度的异常,这可能是ENSO事件影响东亚副热带西风急流的原因之一. 相似文献
60.
The Bhuj earthquake (26 January 2001) in India and the Ghori earthquake (8 October 2005) in Pakistan, both occurred close
to the Indian-Iranian plate boundary related to the activity along the intercontinental Chaman transform fault. It is suggested
that the seismic activity along NNW — NNE trending weak zones or faults is more intense in the sub-continent than along the
WNW trending zones. Since the stress along the former is less compressive but more of the shear or translational type. The
devastative Koyna (1967) and Latur (1993) earthquakes both occurred along faults or weak zones that were close to the meridional
rather than the equatorial trend. The Indian plate is moving to the north or NNE or NNW, along a rotational trajectory and
hence the force tends to be more compressive along the equatorial weak zones. In contrast, it tends to be less compressive
and more of the shear or translational along the weak zones that are close to meridional trend. The seismic activity is therefore
more intense along the weak zones with NNW to NNE trend than along the ENE to EW trending zones. 相似文献