Extinction of the northern oceanic deep convection in an ensemble of climate model simulations of the 20th and 21st centuries
Extinction of the northern oceanic deep convection in an ensemble of climate model simulations of the 20th and 21st centuries
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DOI：
10.1007/s00382-015-2736-5
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发表时间：
2016-05-01
期刊：
影响因子：
4.6
通讯作者：
Koenigk, Torben
中科院分区：
文献类型：
--
作者：
Brodeau, Laurent;Koenigk, Torben
我们利用EC-Earth的12个气候模式模拟，研究了1850-2100年北大西洋北部和北欧海域海洋深对流的变率和演变。在历史时期，该模式显示了深对流的主要地点的真实局部化，其中拉布拉多海占了北半球深对流混合的大部分。拉布拉多对流部分由NAO驱动(相关系数为0.6)，并在年代际尺度上控制部分AMOC的变化(当对流提前3-4年时，相关系数为0.6)。20世纪初，拉布拉多海的深层对流活动开始减少，并变得更浅。这一下降主要是由于冬季大气条件变暖导致大气的显热损失减少所致。它是逐步发生的，主要是20世纪20年代和90年代深部对流活动两次严重下降的结果。这两个事件都可以与NAO的低频变化联系在一起。对流混合减少导致次表层变暖，再加上来自北欧海洋的淡水流入增加，迅速加强了表层分层，防止了2020年代后拉布拉多海可能出现的深对流死灰复燃。格陵兰海的深对流在本世纪20年代开始下降，直到2100年完全消失。作为对拉布拉多海和格陵兰海深对流消退的响应，AMOC在21世纪经历了大约每十年-0.3 Sv的线性下降。
We study the variability and the evolution of oceanic deep convection in the northern North Atlantic and the Nordic Seas from 1850 to 2100 using an ensemble of 12 climate model simulations with EC-Earth. During the historical period, the model shows a realistic localization of the main sites of deep convection, with the Labrador Sea accounting for most of the deep convective mixing in the northern hemisphere. Labrador convection is partly driven by the NAO (correlation of 0.6) and controls part of the variability of the AMOC at the decadal time scale (correlation of 0.6 when convection leads by 3-4 years). Deep convective activity in the Labrador Sea starts to decline and to become shallower in the beginning of the twentieth century. The decline is primarily caused by a decrease of the sensible heat loss to the atmosphere in winter resulting from increasingly warm atmospheric conditions. It occurs stepwise and is mainly the consequence of two severe drops in deep convective activity during the 1920s and the 1990s. These two events can both be linked to the low-frequency variability of the NAO. A warming of the sub-surface, resulting from reduced convective mixing, combines with an increasing influx of freshwater from the Nordic Seas to rapidly strengthen the surface stratification and prevent any possible resurgence of deep convection in the Labrador Sea after the 2020s. Deep convection in the Greenland Sea starts to decline in the 2020s, until complete extinction in 2100. As a response to the extinction of deep convection in the Labrador and Greenland Seas, the AMOC undergoes a linear decline at a rate of about -0.3 Sv per decade during the twenty-first century.