A predictability study of simulated North Atlantic multidecadal variability
A predictability study of simulated North Atlantic multidecadal variability
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DOI：
10.1007/s003820050177
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发表时间：
1997-08
期刊：
影响因子：
4.6
通讯作者：
S. Griffies;Kirk Bryan
中科院分区：
文献类型：
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作者：
S. Griffies;Kirk Bryan
北大西洋是地球上少数几个通过海气相互作用将大气与深海联系在一起的地方之一。虽然大气本身的内部变化只能在一到两周的时间内预测，但由于与海洋的耦合，气候变化有可能在几个月甚至几年的更长时间内是可以预测的。这项工作提供了第一项研究的细节，该研究旨在量化模拟的北大西洋数十年气候变率的可预测性。为此目的使用的模式是GFDL海洋-大气耦合气候模式，广泛用于研究全球变暖和自然气候变异性。该模式包含北大西洋和高纬度海洋环流的波动，变率集中在40-60年的范围内。通过分析经向流函数、动态地形、170 m温度、表面温度和表面盐度的大尺度经验正交函数模式的时间依赖行为，量化了海洋的可预报性。结果表明，北大西洋的可预报性取决于三个主要的物理机制。第一个涉及亚极区的海洋深对流，其作用是对大气波动进行积分，从而提供哈塞尔曼所阐述的红色噪声海洋反应。第二种是热盐环流的大尺度动力学，它可以导致海洋变化在几十年的时间尺度上具有振荡特征。第三种是东格陵兰海流中从极地向南平流的周期性异常淡水输送对北大西洋的非局地影响。当热盐环流的年代际振荡变化活跃时，北大西洋动力地形的第一和第二EOF型具有10-20 y的可预报性时间尺度，而海温EOF-1的可预报性时间尺度为5-7 y，当热盐环流具有较弱的年代际变化能力时，Hasselmann机制占主导地位，可预报性至少降低1倍。当第三种机制处于极端阶段时，北大西洋动态地形型实现了10-20年的可预报时间尺度。对格陵兰海与向南传播的淡水异常相关的区域的SST的补充分析表明，该高纬度区域也具有年代际尺度可预报性的潜力。模式计算还可以洞察区域可预测性的变化，这可能是设计北大西洋监测系统的有用信息。可预报性似乎在北大西洋高纬度地区的对流活跃地区破坏得最快。
The North Atlantic is one of the few places on the globe where the atmosphere is linked to the deep ocean through air–sea interaction. While the internal variability of the atmosphere by itself is only predictable over a period of one to two weeks, climate variations are potentially predictable for much longer periods of months or even years because of coupling with the ocean. This work presents details from the first study to quantify the predictability for simulated multidecadal climate variability over the North Atlantic. The model used for this purpose is the GFDL coupled ocean-atmosphere climate model used extensively for studies of global warming and natural climate variability. This model contains fluctuations of the North Atlantic and high-latitude oceanic circulation with variability concentrated in the 40–60 year range. Oceanic predictability is quantified through analysis of the time-dependent behavior of large-scale empirical orthogonal function (EOF) patterns for the meridional stream function, dynamic topography, 170 m temperature, surface temperature and surface salinity. The results indicate that predictability in the North Atlantic depends on three main physical mechanisms. The first involves the oceanic deep convection in the subpolar region which acts to integrate atmospheric fluctuations, thus providing for a red noise oceanic response as elaborated by Hasselmann. The second involves the large-scale dynamics of the thermohaline circulation, which can cause the oceanic variations to have an oscillatory character on the multidecadal time scale. The third involves nonlocal effects on the North Atlantic arising from periodic anomalous fresh water transport advecting southward from the polar regions in the East Greenland Current. When the multidecadal oscillatory variations of the thermohaline circulation are active, the first and second EOF patterns for the North Atlantic dynamic topography have predictability time scales on the order of 10–20 y, whereas EOF-1 of SST has predictability time scales of 5–7 y. When the thermohaline variability has weak multidecadal power, the Hasselmann mechanism is dominant and the predictability is reduced by at least a factor of two. When the third mechanism is in an extreme phase, the North Atlantic dynamic topography patterns realize a 10–20 year predictability time scale. Additional analysis of SST in the Greenland Sea, in a region associated with the southward propagating fresh water anomalies, indicates the potential for decadal scale predictability for this high latitude region as well. The model calculations also allow insight into regional variations of predictability, which might be useful information for the design of a monitoring system for the North Atlantic. Predictability appears to break down most rapidly in regions of active convection in the high-latitude regions of the North Atlantic.