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Investigating the ocean’s role in the Atlantic multidecadal variability
来源:LASG    访问次数:    报告时间:2017-8-11
【报告人】        Dr. Laifang Li
【报告人单位】Duke University, USA
【报告时间】    2017年8月11日(星期五)15:00
【报告地点】    科研楼303会议室
【报告简介】    The Atlantic multidecadal variability (AMV) has a significant impact on global and regional climate. However, the role of the ocean, if any, in driving the AMV remains a matter of debate. Based on historical sea surface temperature (SST) records and atmospheric reanalysis datasets, we provide evidence that atmospheric forcing alone is insufficient to explain the AMV SSTA. First, from an investigation of SST patterns, we show that the low-frequency decadal variability of the AMV SSTA is largely attributable to the long persistence of extratropical SSTA. The SSTA associated with NAO does not show the same persistence, suggesting that the AMV SSTA, especially its extratropical branch, is not solely a response to atmospheric forcing. Secondly, we evaluate the sufficiency of atmospheric forcing in driving AMV SSTA by constructing an idealized red-noise model which mimics the mixed layer heat balance in the North Atlantic. In the model, the oceanic contribution is neglected in order to isolate the effects of atmospheric forcing. Model parameters, including system decay time scale and atmospheric forcing, are derived from EN4.2.0 and 20th century reanalysis datasets. The model is run for many simulations using parameters for either the extratropical or tropical North Atlantic. These simulations reveal that the long persistence of extratropical SSTA is tied to a weak system decay, a result of both deep mixed layers and cold mean SSTs in the region. Importantly, the modeled extratropical SSTA underestimate the observed SSTA variability: none of the simulations produces an SSTA standard deviation higher than that observed. In contrast, the variability of observed tropical SSTA is within the 95% confidence interval quantified from the idealized model simulations, indicating that tropical SSTA can be explained by atmospheric forcing. Our study is consistent with previous studies that emphasize the importance of atmospheric circulation in creating the spatial coherence of AMV SSTA. However, in terms of extratropical SSTA, our work suggests that atmospheric forcing alone is insufficient to explain the AMV.
 
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