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Yongqi Gao - One of the best experts on this subject based on the ideXlab platform.
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the unstable connection between Atlantic Multidecadal Oscillation and indian summer monsoon in cesm le
Climate Dynamics, 2021Co-Authors: Ayesha Ahmad, Feifei Luo, Yongqi GaoAbstract:Instrumental records since the mid-1990s show that the correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) becomes non-significant or even negative. This seems to disagree with that the AMO is positively correlated with the ISM illustrated by most of previous studies, and implies an unstable connection between AMO and ISM. Given the limitation of the length of instrumental records and the substantial human impacts, what causes this instability, specially whether it originates from natural variability in climate system, is unclear. Here the pre-industrial and historical simulations from a Community Earth System Model Large Ensemble (CESM-LE) project are used to investigate this issue. The results suggest that the AMO–ISM connection variability is predominated by internal climatic processes, and an unstable connection occurs in the 1800-year pre-industrial simulation, which is positive in some decades but negative or neutral in some other decades. A regression analysis based on the selected decades when the AMO–ISM connection is positive and when it is negative suggests the substantial role of natural SST variability in the subtropical western North Pacific in modulating the linkage of the AMO with the ISM. The warm SST anomalies lead to higher pressure and easterly anomalies over the western subtropical Pacific, and then a convergence over South Asia and subsequently more precipitation in India, thus a significant positive AMO–ISM correlation; opposite anomalies are true for the significant negative correlation periods. This study provides a new insight into the AMO–ISM connection, in that the connection itself is unstable in the natural climate system and subjective to the modulation of subtropical western North Pacific SST.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon in cmip5 models
Climate Dynamics, 2018Co-Authors: Feifei Luo, Noel Keenlyside, Yongqi Gao, Lea Svendsen, Tore FurevikAbstract:A number of observational and modeling studies have shown a co-relationship between higher than normal sea surface temperatures (SSTs) in the North Atlantic and increased summer precipitation over India. However, discrepancies among the models make the robustness of the results debatable. This study examines the connections between the Atlantic Multidecadal Oscillation (AMO) and the Indian summer monsoon (ISM) in 66 “Historical” runs of 22 coupled models that were part of the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Diverse results are obtained, and correlation coefficients between the AMO and ISM range from − 0.39 to 0.66. Only 10 out of 66 members (~ 15%) show a positive correlation statistically significant at the 90% level (> 0.42), close to the observation (0.5). The models with positive AMO–ISM correlations show an AMO-related atmospheric teleconnection that involves an extratropical–tropical SST gradient in the North Pacific, as well as a more regional temperature difference between the Indian subcontinent and the tropical Indian Ocean. In comparison, the models with negative correlations fail to capture these teleconnections. Moreover, the models with higher climatological precipitation over the tropical Atlantic and warmer climatological SST in the tropical Atlantic and the North Pacific relative to multi-member ensemble, as well as a weak westerly jet, perform better at reproducing the observed teleconnections.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon since the industrial revolution is intrinsic to the climate system
Environmental Research Letters, 2018Co-Authors: Feifei Luo, Tore Furevik, Noel Keenlyside, Yongqi Gao, Lea SvendsenAbstract:Observations show a significant positive correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) over the past 100 years. Whether this connection is intrinsic to the climate system or caused by external forcing remains unclear in view of the substantial existence of anthropogenic greenhouse gases and aerosols in observations. Two state-of-the-art climate models (GFDL-CM3 and HadGEM2-ES), the historical simulations (1850–2005) of which show positive correlations between the AMO and ISM, similar to observation, are used to address this question. A significant positive AMO-ISM correlation exists in the control simulations with fixed preindustrial forcing with HadGEM2-ES, but not with GFDL-CM3. An in-depth analysis illustrates that the positive correlation in the HadGEM2-ES control run is more reasonable, since it simulates a similar teleconnection of the AMO with the North Pacific to that in both observations and previous studies. In comparison, the GFDL-CM3 control run fails to simulate the teleconnection of the AMO with the North Pacific. The positive AMO-ISM correlation in the historical simulation in GFDL-CM3 may be attributable to the role of the external forcing, since it is so strong that the AMO signals are excited additionally in the North Pacific. This study suggests that the AMO-ISM connection is intrinsic to the climate system, and highlights the crucial role played by the North Pacific in bridging such a connection.
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Atlantic Multidecadal Oscillation modulates the impacts of arctic sea ice decline
Geophysical Research Letters, 2018Co-Authors: Yvan J Orsolini, Huijun Wang, Yongqi GaoAbstract:The Arctic sea ice cover has been rapidly declining in the last two decades, concurrent with a shift in the Atlantic Multidecadal Oscillation (AMO) to its warm phase around 1996/1997. Here we use both observations and model simulations to investigate the modulation of the atmospheric impacts of the decreased sea ice cover in the Atlantic sector of the Arctic (AASIC) by the AMO. We find that the AASIC loss during a cold AMO phase induces increased Ural blocking activity, a southeastward-extended snowpack, and a cold continent anomaly over Eurasia in December through northerly cold air advection and moisture transport from the Arctic. The increased Ural blocking activity and more extended Eurasian snowpack strengthen the upward propagation of planetary waves over the Siberian-Pacific sector in the lower stratosphere and hence lead to a weakened stratospheric polar vortex and a negative Arctic Oscillation (AO) phase at the surface in February. However, corresponding to the AASIC loss during a warm AMO phase, one finds more widespread warming over the Arctic and a reduced snowpack over Northern Eurasia in December. The stratosphere-troposphere coupling is suppressed in early winter and no negative AO anomaly is found in February. We suggest that the cold AMO phase is important to regulate the atmospheric response to AASIC decline, and our study provides insight to the ongoing debate on the connection between the Arctic sea ice and the AO.
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modulation of the aleutian icelandic low seesaw and its surface impacts by the Atlantic Multidecadal Oscillation
Advances in Atmospheric Sciences, 2018Co-Authors: Yvan J Orsolini, Huijun Wang, Yongqi GaoAbstract:Early studies suggested that the Aleutian–Icelandic low seesaw (AIS) features Multidecadal variation. In this study, the Multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation (AMO) during late winter (February–March) is explored with observational data. It is shown that, in the cold phase of the AMO (AMO|−), a clear AIS is established, while this is not the case in the warm phase of the AMO (AMO|+). The surface climate over Eurasia is significantly influenced by the AMO’s modulation of the Aleutian low (AL). For example, the weak AL in AMO|− displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe, but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|−, but decreases over northern Europe and increases over southern Europe in AMO|+. The mechanism underlying the influence of AMO|− on the AIS can be described as follows: AMO|− weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.
Feifei Luo - One of the best experts on this subject based on the ideXlab platform.
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the unstable connection between Atlantic Multidecadal Oscillation and indian summer monsoon in cesm le
Climate Dynamics, 2021Co-Authors: Ayesha Ahmad, Feifei Luo, Yongqi GaoAbstract:Instrumental records since the mid-1990s show that the correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) becomes non-significant or even negative. This seems to disagree with that the AMO is positively correlated with the ISM illustrated by most of previous studies, and implies an unstable connection between AMO and ISM. Given the limitation of the length of instrumental records and the substantial human impacts, what causes this instability, specially whether it originates from natural variability in climate system, is unclear. Here the pre-industrial and historical simulations from a Community Earth System Model Large Ensemble (CESM-LE) project are used to investigate this issue. The results suggest that the AMO–ISM connection variability is predominated by internal climatic processes, and an unstable connection occurs in the 1800-year pre-industrial simulation, which is positive in some decades but negative or neutral in some other decades. A regression analysis based on the selected decades when the AMO–ISM connection is positive and when it is negative suggests the substantial role of natural SST variability in the subtropical western North Pacific in modulating the linkage of the AMO with the ISM. The warm SST anomalies lead to higher pressure and easterly anomalies over the western subtropical Pacific, and then a convergence over South Asia and subsequently more precipitation in India, thus a significant positive AMO–ISM correlation; opposite anomalies are true for the significant negative correlation periods. This study provides a new insight into the AMO–ISM connection, in that the connection itself is unstable in the natural climate system and subjective to the modulation of subtropical western North Pacific SST.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon in cmip5 models
Climate Dynamics, 2018Co-Authors: Feifei Luo, Noel Keenlyside, Yongqi Gao, Lea Svendsen, Tore FurevikAbstract:A number of observational and modeling studies have shown a co-relationship between higher than normal sea surface temperatures (SSTs) in the North Atlantic and increased summer precipitation over India. However, discrepancies among the models make the robustness of the results debatable. This study examines the connections between the Atlantic Multidecadal Oscillation (AMO) and the Indian summer monsoon (ISM) in 66 “Historical” runs of 22 coupled models that were part of the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Diverse results are obtained, and correlation coefficients between the AMO and ISM range from − 0.39 to 0.66. Only 10 out of 66 members (~ 15%) show a positive correlation statistically significant at the 90% level (> 0.42), close to the observation (0.5). The models with positive AMO–ISM correlations show an AMO-related atmospheric teleconnection that involves an extratropical–tropical SST gradient in the North Pacific, as well as a more regional temperature difference between the Indian subcontinent and the tropical Indian Ocean. In comparison, the models with negative correlations fail to capture these teleconnections. Moreover, the models with higher climatological precipitation over the tropical Atlantic and warmer climatological SST in the tropical Atlantic and the North Pacific relative to multi-member ensemble, as well as a weak westerly jet, perform better at reproducing the observed teleconnections.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon since the industrial revolution is intrinsic to the climate system
Environmental Research Letters, 2018Co-Authors: Feifei Luo, Tore Furevik, Noel Keenlyside, Yongqi Gao, Lea SvendsenAbstract:Observations show a significant positive correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) over the past 100 years. Whether this connection is intrinsic to the climate system or caused by external forcing remains unclear in view of the substantial existence of anthropogenic greenhouse gases and aerosols in observations. Two state-of-the-art climate models (GFDL-CM3 and HadGEM2-ES), the historical simulations (1850–2005) of which show positive correlations between the AMO and ISM, similar to observation, are used to address this question. A significant positive AMO-ISM correlation exists in the control simulations with fixed preindustrial forcing with HadGEM2-ES, but not with GFDL-CM3. An in-depth analysis illustrates that the positive correlation in the HadGEM2-ES control run is more reasonable, since it simulates a similar teleconnection of the AMO with the North Pacific to that in both observations and previous studies. In comparison, the GFDL-CM3 control run fails to simulate the teleconnection of the AMO with the North Pacific. The positive AMO-ISM correlation in the historical simulation in GFDL-CM3 may be attributable to the role of the external forcing, since it is so strong that the AMO signals are excited additionally in the North Pacific. This study suggests that the AMO-ISM connection is intrinsic to the climate system, and highlights the crucial role played by the North Pacific in bridging such a connection.
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weaker connection between the Atlantic Multidecadal Oscillation and indian summer rainfall since the mid 1990s
Atmospheric and Oceanic Science Letters, 2018Co-Authors: Feifei Luo, L I Shuanglin, Tore FurevikAbstract:Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) can play an important role in modulating the variability of Indian summer monsoon rainfall (ISMR) over a 50–60-yr timesc...
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simulation by cmip5 models of the Atlantic Multidecadal Oscillation and its climate impacts
Advances in Atmospheric Sciences, 2016Co-Authors: Zhe Han, Feifei Luo, Tore Furevik, Yongqi Gao, Lea SvendsenAbstract:This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal variability. 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.
Fred Kucharski - One of the best experts on this subject based on the ideXlab platform.
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the importance of inter basin atmospheric teleconnection in the sst footprint of Atlantic Multidecadal Oscillation over western pacific
Climate Dynamics, 2021Co-Authors: Cheng Sun, Yusen Liu, Jiaqing Xue, Fred KucharskiAbstract:Western Pacific sea surface temperature (SST) Multidecadal fluctuations are synchronized to the Atlantic Multidecadal Oscillation (AMO) phenomenon during the instrumental period. The possible mechanism of the inter-basin synchronization of Multidecadal SST variability still remains a matter of discussion regarding the roles of external radiative forcing and internal inter-basin interaction. Here we address this issue using simulations of CMIP5 coupled models and a partially coupled model experiment with prescribed SSTs over the North Atlantic. Observational analysis suggests that in association with the warm AMO phase, prominent SST warming occurs over the western Pacific, accompanied by anomalous low pressures and ascending motion that maintain the warm SST anomalies through positive feedback of local air–sea interaction. The upward motion in the western Pacific corresponds to a significant intensification of Pacific zonal Walker circulation, which is coupled with an increase in the zonal gradient of atmospheric temperature aloft. The CMIP5 model simulated externally forced component of AMO-related changes in western Pacific SST is weak, associated with little change in Pacific zonal circulation showing an absence of anomalous upward motion over the western Pacific, and this is primarily resultant from the negligible changes in the zonal gradient of atmospheric temperature as a direct thermal response to the external radiative forcing. By contrast, the partially coupled model simulation forced by the Atlantic SST variations reasonably reproduces the observed AMO-related changes in western Pacific SST and pan-tropical atmospheric circulation. A surface radiation budget analysis for the western Pacific shows contrasting roles of AMO-related surface incoming solar radiation between the reanalysis/partially coupled model simulation and the forced signal in CMIP5, further confirming the key role of dynamically induced inter-basin atmospheric teleconnection in the Multidecadal SST footprint of AMO over the western Pacific.
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contrasting spatial structures of Atlantic Multidecadal Oscillation between observations and slab ocean model simulations
Climate Dynamics, 2019Co-Authors: Jianping Li, Fred Kucharski, Xiang LiAbstract:The spatial structure of Atlantic Multidecadal Oscillation (AMO) is analyzed and compared between the observations and simulations from slab ocean models (SOMs) and fully coupled models. The observed sea surface temperature (SST) pattern of AMO is characterized by a basin-wide monopole structure, and there is a significantly high degree of spatial coherence of decadal SST variations across the entire North Atlantic basin. The observed SST anomalies share a common decadal-scale signal, corresponding to the basin-wide average (i. e., the AMO). In contrast, the simulated AMO in SOMs (AMOs) exhibits a tripole-like structure, with the mid-latitude North Atlantic SST showing an inverse relationship with other parts of the basin, and the SOMs fail to reproduce the observed strong spatial coherence of decadal SST variations associated with the AMO. The observed spatial coherence of AMO SST anomalies is identified as a key feature that can be used to distinguish the AMO mechanism. The tripole-like SST pattern of AMOs in SOMs can be largely explained by the atmosphere-forced thermodynamics mechanism due to the surface heat flux changes associated with the North Atlantic Oscillation (NAO). The thermodynamic forcing of AMOs by the NAO gives rise to a simultaneous inverse NAO–AMOs relationship at both interannual and decadal timescales and a seasonal phase locking of the AMOs variability to the cold season. However, the NAO-forced thermodynamics mechanism cannot explain the observed NAO–AMO relationship and the seasonal phase locking of observed AMO variability to the warm season. At decadal timescales, a strong lagged relationship between NAO and AMO is observed, with the NAO leading by up to two decades, while the simultaneous correlation of NAO with AMO is weak. This lagged relationship and the spatial coherence of AMO can be well understood from the view point of ocean dynamics. A time-integrated NAO index, which reflects the variations in Atlantic meridional overturning circulation (AMOC) and northward ocean heat transport caused by the accumulated effect of NAO forcing, reasonably well captures the observed Multidecadal fluctuations in the AMO. Further analysis using the fully coupled model simulations provides direct modeling evidence that the observed spatial coherence of decadal SST variations across North Atlantic basin can be reproduced only by including the AMOC-related ocean dynamics, and the AMOC acts as a common forcing signal that results in a spatially coherent variation of North Atlantic SST.
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western tropical pacific Multidecadal variability forced by the Atlantic Multidecadal Oscillation
EGU General Assembly Conference Abstracts, 2018Co-Authors: Cheng Sun, Fred Kucharski, Insik Kang, Feifei Jin, Ruiqiang DingAbstract:Observational analysis suggests that the western tropical Pacific (WTP) sea surface temperature (SST) shows predominant variability over Multidecadal time scales, which is unlikely to be explained by the Interdecadal Pacific Oscillation. Here we show that this variability is largely explained by the remote Atlantic Multidecadal Oscillation (AMO). A suite of Atlantic Pacemaker experiments successfully reproduces the WTP Multidecadal variability and the AMO-WTP SST connection. The AMO warm SST anomaly generates an atmospheric teleconnection to the North Pacific, which weakens the Aleutian low and subtropical North Pacific westerlies. The wind changes induce a subtropical North Pacific SST warming through wind-evaporation-SST effect, and in response to this warming, the surface winds converge towards the subtropical North Pacific from the tropics, leading to anomalous cyclonic circulation and low pressure over the WTP region. The warm SST anomaly further develops due to the SST-sea level pressure-cloud-longwave radiation positive feedback. Our findings suggest that the Atlantic Ocean acts as a key pacemaker for the western Pacific decadal climate variability.
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western tropical pacific Multidecadal variability forced by the Atlantic Multidecadal Oscillation
Nature Communications, 2017Co-Authors: Fred Kucharski, Jianping Li, Insik Kang, Ruiqiang DingAbstract:Observational analysis suggests that the western tropical Pacific (WTP) sea surface temperature (SST) shows predominant variability over Multidecadal time scales, which is unlikely to be explained by the Interdecadal Pacific Oscillation. Here we show that this variability is largely explained by the remote Atlantic Multidecadal Oscillation (AMO). A suite of Atlantic Pacemaker experiments successfully reproduces the WTP Multidecadal variability and the AMO–WTP SST connection. The AMO warm SST anomaly generates an atmospheric teleconnection to the North Pacific, which weakens the Aleutian low and subtropical North Pacific westerlies. The wind changes induce a subtropical North Pacific SST warming through wind–evaporation–SST effect, and in response to this warming, the surface winds converge towards the subtropical North Pacific from the tropics, leading to anomalous cyclonic circulation and low pressure over the WTP region. The warm SST anomaly further develops due to the SST–sea level pressure–cloud–longwave radiation positive feedback. Our findings suggest that the Atlantic Ocean acts as a key pacemaker for the western Pacific decadal climate variability. The western tropical Pacific is a main source of heat and moisture for the global atmosphere, yet the mechanism for the Multidecadal sea surface temperature variability in this region remains unknown. Here, the authors show that this variability is forced by the remote Atlantic Multidecadal Oscillation
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enso amplitude modulation associated with the mean sst changes in the tropical central pacific induced by Atlantic Multidecadal Oscillation
Journal of Climate, 2014Co-Authors: Insik Kang, Fred KucharskiAbstract:AbstractThe mechanism associated with the modulation of the El Nino–Southern Oscillation (ENSO) amplitude caused by the Atlantic Multidecadal Oscillation (AMO) is investigated by using long-term historical observational data and various types of models. The observational data for the period 1900–2013 show that the ENSO variability weakened during the positive phase of the AMO and strengthened in the negative phase. Such a relationship between the AMO and ENSO amplitude has been reported by a number of previous studies. In the present study the authors demonstrate that the weakening of the ENSO amplitude during the positive phase of the AMO is related to changes of the SST cooling in the eastern and central Pacific accompanied by the easterly wind stress anomalies in the equatorial central Pacific, which were reproduced reasonably well by coupled general circulation model (CGCM) simulations performed with the Atlantic Ocean SST nudged perpetually with the observed SST representing the positive phase of the...
Tore Furevik - One of the best experts on this subject based on the ideXlab platform.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon in cmip5 models
Climate Dynamics, 2018Co-Authors: Feifei Luo, Noel Keenlyside, Yongqi Gao, Lea Svendsen, Tore FurevikAbstract:A number of observational and modeling studies have shown a co-relationship between higher than normal sea surface temperatures (SSTs) in the North Atlantic and increased summer precipitation over India. However, discrepancies among the models make the robustness of the results debatable. This study examines the connections between the Atlantic Multidecadal Oscillation (AMO) and the Indian summer monsoon (ISM) in 66 “Historical” runs of 22 coupled models that were part of the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Diverse results are obtained, and correlation coefficients between the AMO and ISM range from − 0.39 to 0.66. Only 10 out of 66 members (~ 15%) show a positive correlation statistically significant at the 90% level (> 0.42), close to the observation (0.5). The models with positive AMO–ISM correlations show an AMO-related atmospheric teleconnection that involves an extratropical–tropical SST gradient in the North Pacific, as well as a more regional temperature difference between the Indian subcontinent and the tropical Indian Ocean. In comparison, the models with negative correlations fail to capture these teleconnections. Moreover, the models with higher climatological precipitation over the tropical Atlantic and warmer climatological SST in the tropical Atlantic and the North Pacific relative to multi-member ensemble, as well as a weak westerly jet, perform better at reproducing the observed teleconnections.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon since the industrial revolution is intrinsic to the climate system
Environmental Research Letters, 2018Co-Authors: Feifei Luo, Tore Furevik, Noel Keenlyside, Yongqi Gao, Lea SvendsenAbstract:Observations show a significant positive correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) over the past 100 years. Whether this connection is intrinsic to the climate system or caused by external forcing remains unclear in view of the substantial existence of anthropogenic greenhouse gases and aerosols in observations. Two state-of-the-art climate models (GFDL-CM3 and HadGEM2-ES), the historical simulations (1850–2005) of which show positive correlations between the AMO and ISM, similar to observation, are used to address this question. A significant positive AMO-ISM correlation exists in the control simulations with fixed preindustrial forcing with HadGEM2-ES, but not with GFDL-CM3. An in-depth analysis illustrates that the positive correlation in the HadGEM2-ES control run is more reasonable, since it simulates a similar teleconnection of the AMO with the North Pacific to that in both observations and previous studies. In comparison, the GFDL-CM3 control run fails to simulate the teleconnection of the AMO with the North Pacific. The positive AMO-ISM correlation in the historical simulation in GFDL-CM3 may be attributable to the role of the external forcing, since it is so strong that the AMO signals are excited additionally in the North Pacific. This study suggests that the AMO-ISM connection is intrinsic to the climate system, and highlights the crucial role played by the North Pacific in bridging such a connection.
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weaker connection between the Atlantic Multidecadal Oscillation and indian summer rainfall since the mid 1990s
Atmospheric and Oceanic Science Letters, 2018Co-Authors: Feifei Luo, L I Shuanglin, Tore FurevikAbstract:Previous studies have shown that the Atlantic Multidecadal Oscillation (AMO) can play an important role in modulating the variability of Indian summer monsoon rainfall (ISMR) over a 50–60-yr timesc...
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simulation by cmip5 models of the Atlantic Multidecadal Oscillation and its climate impacts
Advances in Atmospheric Sciences, 2016Co-Authors: Zhe Han, Feifei Luo, Tore Furevik, Yongqi Gao, Lea SvendsenAbstract:This study focuses on the climatic impacts of the Atlantic Multidecadal Oscillation (AMO) as a mode of internal variability. 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.
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air sea coupling enhances the east asian winter climate response to the Atlantic Multidecadal Oscillation
Advances in Atmospheric Sciences, 2015Co-Authors: Xiaomin Zhou, Feifei Luo, Yongqi Gao, Tore FurevikAbstract:A simple air–sea coupled model, the atmospheric general circulation model (AGCM) of the National Centers for Environmental Prediction coupled to a mixed-layer slab ocean model, is employed to investigate the impact of air–sea coupling on the signals of the Atlantic Multidecadal Oscillation (AMO). A regional coupling strategy is applied, in which coupling is switched off in the extratropical North Atlantic Ocean but switched on in the open oceans elsewhere. The coupled model is forced with warm-phase AMO SST anomalies, and the modeled responses are compared with those from parallel uncoupled AGCM experiments with the same SST forcing. The results suggest that the regionally coupled responses not only resemble the AGCM simulation, but also have a stronger intensity. In comparison, the coupled responses bear greater similarity to the observational composite anomaly. Thus, air–sea coupling enhances the responses of the East Asian winter climate to the AMO. To determine the mechanism responsible for the coupling amplification, an additional set of AGCM experiments, forced with the AMO-induced tropical SST anomalies, is conducted. The SST anomalies are extracted from the simulated AMO-induced SST response in the regionally coupled model. The results suggest that the SST anomalies contribute to the coupling amplification. Thus, tropical air–sea coupling feedback tends to enhance the responses of the East Asian winter climate to the AMO.
Noel Keenlyside - One of the best experts on this subject based on the ideXlab platform.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon in cmip5 models
Climate Dynamics, 2018Co-Authors: Feifei Luo, Noel Keenlyside, Yongqi Gao, Lea Svendsen, Tore FurevikAbstract:A number of observational and modeling studies have shown a co-relationship between higher than normal sea surface temperatures (SSTs) in the North Atlantic and increased summer precipitation over India. However, discrepancies among the models make the robustness of the results debatable. This study examines the connections between the Atlantic Multidecadal Oscillation (AMO) and the Indian summer monsoon (ISM) in 66 “Historical” runs of 22 coupled models that were part of the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Diverse results are obtained, and correlation coefficients between the AMO and ISM range from − 0.39 to 0.66. Only 10 out of 66 members (~ 15%) show a positive correlation statistically significant at the 90% level (> 0.42), close to the observation (0.5). The models with positive AMO–ISM correlations show an AMO-related atmospheric teleconnection that involves an extratropical–tropical SST gradient in the North Pacific, as well as a more regional temperature difference between the Indian subcontinent and the tropical Indian Ocean. In comparison, the models with negative correlations fail to capture these teleconnections. Moreover, the models with higher climatological precipitation over the tropical Atlantic and warmer climatological SST in the tropical Atlantic and the North Pacific relative to multi-member ensemble, as well as a weak westerly jet, perform better at reproducing the observed teleconnections.
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the connection between the Atlantic Multidecadal Oscillation and the indian summer monsoon since the industrial revolution is intrinsic to the climate system
Environmental Research Letters, 2018Co-Authors: Feifei Luo, Tore Furevik, Noel Keenlyside, Yongqi Gao, Lea SvendsenAbstract:Observations show a significant positive correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) over the past 100 years. Whether this connection is intrinsic to the climate system or caused by external forcing remains unclear in view of the substantial existence of anthropogenic greenhouse gases and aerosols in observations. Two state-of-the-art climate models (GFDL-CM3 and HadGEM2-ES), the historical simulations (1850–2005) of which show positive correlations between the AMO and ISM, similar to observation, are used to address this question. A significant positive AMO-ISM correlation exists in the control simulations with fixed preindustrial forcing with HadGEM2-ES, but not with GFDL-CM3. An in-depth analysis illustrates that the positive correlation in the HadGEM2-ES control run is more reasonable, since it simulates a similar teleconnection of the AMO with the North Pacific to that in both observations and previous studies. In comparison, the GFDL-CM3 control run fails to simulate the teleconnection of the AMO with the North Pacific. The positive AMO-ISM correlation in the historical simulation in GFDL-CM3 may be attributable to the role of the external forcing, since it is so strong that the AMO signals are excited additionally in the North Pacific. This study suggests that the AMO-ISM connection is intrinsic to the climate system, and highlights the crucial role played by the North Pacific in bridging such a connection.
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caribbean coral tracks Atlantic Multidecadal Oscillation and past hurricane activity
Geology, 2008Co-Authors: Steffen Hetzinger, Miriam Pfeiffer, Wolfchristian Dullo, Noel Keenlyside, Mojib Latif, Jens ZinkeAbstract:It is highly debated whether global warming contributed to the strong hurricane activity observed during the last decade. The crux of the recent debate is the limited length of the reliable instrumental record that exacerbates the detection of possible long-term changes in hurricane activity, which naturally exhibits strong Multidecadal variations that are associated with the Atlantic Multidecadal Oscillation (AMO). The AMO, itself a major mode of climate variability, remains also poorly understood because of limited data. Here, we present the first coral-based proxy record (δ18O) that clearly captures Multidecadal variations in the AMO and the hurricane activity. Our record, obtained from a brain coral situated in the Atlantic hurricane domain, is equally sensitive to variations in sea surface temperature (SST) and seawater δ18O, with the latter being strongly linked to precipitation, by this means amplifying large-scale climate signals in coral δ18O. The SST and precipitation signals in the coral provide the longest, thus far, continuous proxy-based record of hurricane activity that interestingly exhibits a long-term increase over the last century. As Multidecadal SST variations in this region are closely related to the AMO, this study raises new possibilities to extend the limited observations and to gain new insights into the mechanisms underlying the AMO and long-term hurricane variations.