The Atlantic Multidedal Oscillation(AMO) is a prominent mode of sea surface temperature variability in the Atlantic and incurs significant global influence. Most coupled models failed to reproduce the observed 50–80-...The Atlantic Multidedal Oscillation(AMO) is a prominent mode of sea surface temperature variability in the Atlantic and incurs significant global influence. Most coupled models failed to reproduce the observed 50–80-year AMO, but were overwhelmed by a 10–30-year AMO. Here we show that the 50–80-year AMO and 10–30-year AMO represent two different AMO regimes. The key differences are:(1) the 50–80-year AMO involves transport of warm and saline Atlantic water into the Greenland-Iceland-Norwegian(GIN)Seas prior to reaching its maximum positive phase, while such a transport is weak for the 10–30-year AMO;(2) the zonality of atmospheric variability associated with the 50–80 year AMO favors the transport of warm and saline water into the GIN Seas;(3) the disappearance of Pacific variability weakens the zonality of atmospheric variability and the transport of warm and saline water into the GIN Seas, leading to the weakening of the 50–80-year AMO. In contrast, the 10–30-year AMO does not show dependence on the variability in Pacific and in the GIN Seas and may be an Atlantic-intrinsic mode. Our results suggest that differentiating these AMO regimes and a better understanding of the cross-basin connections are essential to reconcile the current debate on the nature of AMO and hence to its reliable prediction, which is still lacking in most of coupled models.展开更多
This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation （AMO） as a mode of internal vari- ability. Given the difficulties involved in excluding the effects of external forcing from intern...This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation （AMO） as a mode of internal vari- ability. Given the difficulties involved in excluding the effects of external forcing from internal variation, i.e., owing to the short record length of instrumental observations and historical simulations, we assess and compare the AMO and its related climatic impacts both in observations and in the ＂Pre-industrial＂ experiments of models participating in CMIP5. First, we evaluate the skill of the 25 CMIP5 models＇ ＂Historical＂ simulations in simulating the observational AMO, and find there is generally a considerable range of skill among them in this regard. Six of the models with higher skill relative to the other models are selected to investigate the AMO-related climate impacts, and it is found that their ＂Pre-industrial＂ simulations capture the essential features of the AMO. A positive AMO favors warmer surface temperature around the North Atlantic, and the Atlantic ITCZ shifts northward leading to more rainfall in the Sahel and less rainfall in Brazil. Furthermore, the results confirm the existence of a teleconnection between the AMO and East Asian surface temperature, as well as the late withdrawal of the Indian summer monsoon, during positive AMO phases. These connections could be mainly caused by internal climate variability. Opposite patterns are true for the negative phase of the AMO.展开更多
基金supported by the National Key R&D Program for Developing Basic Sciences (2016YFC1401401, 2016YFC1401601, Y83A01c801)Sun Yat-Sen University’s ‘‘Hundred Talents" Program, the National Natural Science Foundation of China (41576026 and 41576025)the Regional and Global Model Analysis (RGMA) under the Earth and Environmental System Modeling Program of the U.S. Department of Energy’s Office of Biological & Environmental Research (BER) Cooperative Agreement (DE-FC0297ER62402)
文摘The Atlantic Multidedal Oscillation(AMO) is a prominent mode of sea surface temperature variability in the Atlantic and incurs significant global influence. Most coupled models failed to reproduce the observed 50–80-year AMO, but were overwhelmed by a 10–30-year AMO. Here we show that the 50–80-year AMO and 10–30-year AMO represent two different AMO regimes. The key differences are:(1) the 50–80-year AMO involves transport of warm and saline Atlantic water into the Greenland-Iceland-Norwegian(GIN)Seas prior to reaching its maximum positive phase, while such a transport is weak for the 10–30-year AMO;(2) the zonality of atmospheric variability associated with the 50–80 year AMO favors the transport of warm and saline water into the GIN Seas;(3) the disappearance of Pacific variability weakens the zonality of atmospheric variability and the transport of warm and saline water into the GIN Seas, leading to the weakening of the 50–80-year AMO. In contrast, the 10–30-year AMO does not show dependence on the variability in Pacific and in the GIN Seas and may be an Atlantic-intrinsic mode. Our results suggest that differentiating these AMO regimes and a better understanding of the cross-basin connections are essential to reconcile the current debate on the nature of AMO and hence to its reliable prediction, which is still lacking in most of coupled models.
基金jointly supported by the National Natural Science Foundation of China(Grant No.41421004)the National Key Basic Research Development Program of China(Grant No.2016YFA0601802 and 2015CB453202)the National Natural Science Foundation of China(Grant Nos.41375085)
文摘This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation （AMO） as a mode of internal vari- ability. Given the difficulties involved in excluding the effects of external forcing from internal variation, i.e., owing to the short record length of instrumental observations and historical simulations, we assess and compare the AMO and its related climatic impacts both in observations and in the ＂Pre-industrial＂ experiments of models participating in CMIP5. First, we evaluate the skill of the 25 CMIP5 models＇ ＂Historical＂ simulations in simulating the observational AMO, and find there is generally a considerable range of skill among them in this regard. Six of the models with higher skill relative to the other models are selected to investigate the AMO-related climate impacts, and it is found that their ＂Pre-industrial＂ simulations capture the essential features of the AMO. A positive AMO favors warmer surface temperature around the North Atlantic, and the Atlantic ITCZ shifts northward leading to more rainfall in the Sahel and less rainfall in Brazil. Furthermore, the results confirm the existence of a teleconnection between the AMO and East Asian surface temperature, as well as the late withdrawal of the Indian summer monsoon, during positive AMO phases. These connections could be mainly caused by internal climate variability. Opposite patterns are true for the negative phase of the AMO.
