The Atlantic Multidecadal Oscillation(AMO)is the leading mode of low-frequency variability in sea surface temperatures in the Atlantic,affecting global climate.Higher-resolution models substantially improve AMO simula...The Atlantic Multidecadal Oscillation(AMO)is the leading mode of low-frequency variability in sea surface temperatures in the Atlantic,affecting global climate.Higher-resolution models substantially improve AMO simulations,closely matching observed periods and amplitudes,yet the reason for the improvement remains unclear.Here,using 4 experiments conducted within the Alfred Wegener Institute Climate Model with different atmospheric and oceanic resolutions,we found that models with a high-resolution ocean capture the positive feedback between the AMO and the Fram Strait sea ice export mediated by the Atlantic Meridional Overturning Circulation through a more realistic simulation of North Atlantic currents,extending the AMO period to 40 to 80 years.Further increasing the atmospheric resolution results in an AMO amplitude closer to observations due to stronger coupling between atmospheric blocking and Arctic sea ice.This indicates the importance of higher resolution in models for simulating the interaction between synoptic-scale atmospheric processes and long-term ocean variability,which is crucial for AMO simulations.展开更多
A wide range of evidence reveals that the tropical belt is expanding.Several mechanisms have been proposed to contribute to this expansion,some of which even contradict each other.The study of Yang et al.suggests that...A wide range of evidence reveals that the tropical belt is expanding.Several mechanisms have been proposed to contribute to this expansion,some of which even contradict each other.The study of Yang et al.suggests that the poleward advancing mid-latitude meridional temperature gradient(MTG),originating from enhanced subtropical ocean warming,plays a leading role in driving tropical expansion.However,the abrupt4xCO_(2) experiment indicates that tropical expansion occurs at a faster rate than is indicated by changes related to ocean temperature rise.The idealized amip4K experiment illustrates that without introducing any ocean warming pattern,uniform ocean surface warming also drives tropical expansion.The results based on these idealized experiments seem to contradict the hypothesis proposed by Yang et al.In this study,we revisit these 2 experiments and show that both experiments actually support the hypothesis that MTG migration is driving tropical expansion.More specifically,in the abrupt4xCO_(2) experiment,although the rate of ocean warming is relatively slow,the poleward shift of the MTG is as rapid as tropical expansion.In the amip4K experiment,although ocean surface warming is uniform,the heating effect of the ocean on the atmosphere is nonuniform because of the nonlinear relationship between temperature,evaporation,and thermal radiation.The nonuniform oceanic heating to the atmosphere introduces a poleward shift of the MTG within the upper troposphere and drives a shift in the jet streams.By conducting an additional idealized experiment in which tropical expansion occurs under both a migrating MTG and a cooling climate,we argue that the migration of the MTG,rather than global warming,is the key mechanism in driving tropical expansion.展开更多
基金supported by the Natural Science Foundation of China under grant 42394130the Fundamental Research Funds for the Central Universities(202261002)+2 种基金supported by the Germany-Sino Joint Project(ACE,Nos.2019YFE0125000 and 01LP2004A)MHESRF Scientific Task No.FMWE-2024-0028the MIPT Development Program(Priority-2030).
文摘The Atlantic Multidecadal Oscillation(AMO)is the leading mode of low-frequency variability in sea surface temperatures in the Atlantic,affecting global climate.Higher-resolution models substantially improve AMO simulations,closely matching observed periods and amplitudes,yet the reason for the improvement remains unclear.Here,using 4 experiments conducted within the Alfred Wegener Institute Climate Model with different atmospheric and oceanic resolutions,we found that models with a high-resolution ocean capture the positive feedback between the AMO and the Fram Strait sea ice export mediated by the Atlantic Meridional Overturning Circulation through a more realistic simulation of North Atlantic currents,extending the AMO period to 40 to 80 years.Further increasing the atmospheric resolution results in an AMO amplitude closer to observations due to stronger coupling between atmospheric blocking and Arctic sea ice.This indicates the importance of higher resolution in models for simulating the interaction between synoptic-scale atmospheric processes and long-term ocean variability,which is crucial for AMO simulations.
基金supported by the AWI INSPIRES program of“Changing Earth-Sustaining our Future”and the Deutsche Forschungsgemeinschaft(Excellence Cluster“EXC 2077:The Ocean Floor-Earth’s Uncharted Interface”,project no.390741603)。
文摘A wide range of evidence reveals that the tropical belt is expanding.Several mechanisms have been proposed to contribute to this expansion,some of which even contradict each other.The study of Yang et al.suggests that the poleward advancing mid-latitude meridional temperature gradient(MTG),originating from enhanced subtropical ocean warming,plays a leading role in driving tropical expansion.However,the abrupt4xCO_(2) experiment indicates that tropical expansion occurs at a faster rate than is indicated by changes related to ocean temperature rise.The idealized amip4K experiment illustrates that without introducing any ocean warming pattern,uniform ocean surface warming also drives tropical expansion.The results based on these idealized experiments seem to contradict the hypothesis proposed by Yang et al.In this study,we revisit these 2 experiments and show that both experiments actually support the hypothesis that MTG migration is driving tropical expansion.More specifically,in the abrupt4xCO_(2) experiment,although the rate of ocean warming is relatively slow,the poleward shift of the MTG is as rapid as tropical expansion.In the amip4K experiment,although ocean surface warming is uniform,the heating effect of the ocean on the atmosphere is nonuniform because of the nonlinear relationship between temperature,evaporation,and thermal radiation.The nonuniform oceanic heating to the atmosphere introduces a poleward shift of the MTG within the upper troposphere and drives a shift in the jet streams.By conducting an additional idealized experiment in which tropical expansion occurs under both a migrating MTG and a cooling climate,we argue that the migration of the MTG,rather than global warming,is the key mechanism in driving tropical expansion.
