The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Johann H. Jungclaus - One of the best experts on this subject based on the ideXlab platform.
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winter amplification of the european Little Ice Age cooling by the subpolar gyre
Scientific Reports, 2017Co-Authors: Davide Zanchettin, Katja Lohmann, Eduardo Morenochamarro, Juerg Luterbacher, Johann H. JungclausAbstract:Climate reconstructions reveal a strong winter amplification of the cooling over central and northern continental Europe during the Little Ice Age period (LIA, here defined as c. 16th–18th centuries) via persistent, blocked atmospheric conditions. Although various potential drivers have been suggested to explain the LIA cooling, no coherent mechanism has yet been proposed for this seasonal contrast. Here we demonstrate that such exceptional wintertime conditions arose from sea Ice expansion and reduced ocean heat losses in the Nordic and Barents seas, driven by a multIcentennial reduction in the northward heat transport by the subpolar gyre (SPG). However, these anomalous oceanic conditions were largely decoupled from the European atmospheric variability in summer. Our novel dynamical explanation is derived from analysis of an ensemble of last millennium climate simulations, and is supported by reconstructions of European temperatures and atmospheric circulation variability and North Atlantic/Arctic paleoceanographic conditions. We conclude that SPG-related internal climate feedbacks were responsible for the winter amplification of the European LIA cooling. Thus, characterization of SPG dynamics is essential for understanding multIcentennial variations of the seasonal cycle in the European/North Atlantic sector.
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An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes
Climate Dynamics, 2017Co-Authors: Eduardo Moreno-chamarro, Davide Zanchettin, Katja Lohmann, Johann H. JungclausAbstract:We investigate the mechanism of a decadal-scale weakening shift in the strength of the subpolar gyre (SPG) that is found in one among three last millennium simulations with a state-of-the-art Earth system model. The SPG shift triggers multIcentennial anomalies in the North Atlantic climate driven by long-lasting internal feedbacks relating anomalous oceanic and atmospheric circulation, sea Ice extent, and upper-ocean salinity in the Labrador Sea. Yet changes throughout or after the shift are not associated with a persistent weakening of the Atlantic Meridional Overturning Circulation or shifts in the North Atlantic Oscillation. The anomalous climate state of the North Atlantic simulated after the shift agrees well with climate reconstructions from within the area, which describe a transition between a stronger and weaker SPG during the relatively warm medieval climate and the cold Little Ice Age respectively. However, model and data differ in the timing of the onset. The simulated SPG shift is caused by a rapid increase in the freshwater export from the Arctic and associated freshening in the upper Labrador Sea. Such freshwater anomaly relates to prominent thickening of the Arctic sea Ice, following the cluster of relatively small-magnitude volcanic eruptions by 1600 CE. Sensitivity experiments without volcanic forcing can nonetheless produce similar abrupt events; a necessary causal link between the volcanic cluster and the SPG shift can therefore be excluded. Instead, preconditioning by internal variability explains discrepancies in the timing between the simulated SPG shift and the reconstructed estimates for the Little Ice Age onset.
Jeffrey P. Donnelly - One of the best experts on this subject based on the ideXlab platform.
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Increased typhoon activity in the Pacific deep tropics driven by Little Ice Age circulation changes
Nature Geoscience, 2020Co-Authors: James F. Bramante, Kristopher B. Karnauskas, Murray R. Ford, Paul S. Kench, Andrew D. Ashton, Michael R. Toomey, Richard M. Sullivan, Caroline C. Ummenhofer, Jeffrey P. DonnellyAbstract:The instrumental record reveals that tropical cyclone activity is sensitive to oceanic and atmospheric variability on inter-annual and decadal scales. However, our understanding of the influence of climate on tropical cyclone behaviour is restricted by the short historical record and the sparseness of prehistorical reconstructions, particularly in the western North Pacific, where coastal communities suffer loss of life and livelihood from typhoons annually. Here, to explore past regional typhoon dynamics, we reconstruct three millennia of deep tropical North Pacific cyclogenesis. Combined with existing records, our reconstruction demonstrates that low-baseline typhoon activity prior to 1350 ce was followed by an interval of frequent storms during the Little Ice Age. This pattern, concurrent with hydroclimate proxy variability, suggests a centennial-scale link between Pacific hydroclimate and tropical cyclone climatology. An ensemble of global climate models demonstrates a migration of the Pacific Walker circulation and variability in two Pacific climate modes during the Little Ice Age, which probably contributed to enhanced tropical cyclone activity in the tropical western North Pacific. In the next century, projected changes to the Pacific Walker circulation and expansion of the tropics will invert these Little Ice Age hydroclimate trends, potentially reducing typhoon activity in the deep tropical Pacific. Atmospheric circulation shifts during the Little Ice Age led to greater typhoon generation in the tropical North Pacific according to a comparison of sediment proxy records of past storm activity and outputs of general circulation models.
Hong Yan - One of the best experts on this subject based on the ideXlab platform.
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hydrological changes in shuangchi lake hainan island tropical china during the Little Ice Age
Quaternary International, 2017Co-Authors: Wenchao Zhang, Hong Yan, Chengcheng Liu, Peng Cheng, John R Dodson, Henk Heijnis, Weijian ZhouAbstract:Abstract Hydrological changes in East Asia during the last millennium have been addressed by numerous earlier studies, but spatial characteristics and dynamics in precipitation variations during the Little Ice Age (LIA) remain unclear, perhaps especially due to the sparse coverAge of high-resolution hydrological records from tropical and sub-tropical regions in East Asia. In this study, a sediment core was obtained from Shuangchi Lake in northern Hainan Island, tropical China, of which geochemical proxies including the ratios of Rb/Sr, Rb/K, Zr/Rb and Si/Ti were analyzed using an X-ray fluorescence (XRF) core scanner. Meanwhile, the grain size distribution of sediments was also determined. The results show that the Rb/Sr and Rb/K ratios decreased significantly during the LIA, whilst the Zr/Rb and Si/Ti ratios increased along with higher median grain size. The changes of these proxies likely suggest that precipitation was enhanced during the LIA in this region, and this was consistent with other hydrological records from tropical southern China. The synthesis of hydrological records from East Asia and the tropical Pacific suggest that the co-existence of a contracted Intertropical Convergence Zone (ITCZ) and strengthened Pacific Walker circulation (PWC) could contribute synchronously to the increased precipitation in the tropical region of southern China during the LIA.
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dynamics of the intertropical convergence zone over the western pacific during the Little Ice Age
Nature Geoscience, 2015Co-Authors: Hong Yan, Wei Wei, Willie Soon, Weijian Zhou, Zhonghui Liu, Yuhong Wang, Robert M CarterAbstract:Precipitation patterns in the western Pacific changed at the onset of the Little Ice Age. A synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone.
Eduardo Morenochamarro - One of the best experts on this subject based on the ideXlab platform.
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winter amplification of the european Little Ice Age cooling by the subpolar gyre
Scientific Reports, 2017Co-Authors: Davide Zanchettin, Katja Lohmann, Eduardo Morenochamarro, Juerg Luterbacher, Johann H. JungclausAbstract:Climate reconstructions reveal a strong winter amplification of the cooling over central and northern continental Europe during the Little Ice Age period (LIA, here defined as c. 16th–18th centuries) via persistent, blocked atmospheric conditions. Although various potential drivers have been suggested to explain the LIA cooling, no coherent mechanism has yet been proposed for this seasonal contrast. Here we demonstrate that such exceptional wintertime conditions arose from sea Ice expansion and reduced ocean heat losses in the Nordic and Barents seas, driven by a multIcentennial reduction in the northward heat transport by the subpolar gyre (SPG). However, these anomalous oceanic conditions were largely decoupled from the European atmospheric variability in summer. Our novel dynamical explanation is derived from analysis of an ensemble of last millennium climate simulations, and is supported by reconstructions of European temperatures and atmospheric circulation variability and North Atlantic/Arctic paleoceanographic conditions. We conclude that SPG-related internal climate feedbacks were responsible for the winter amplification of the European LIA cooling. Thus, characterization of SPG dynamics is essential for understanding multIcentennial variations of the seasonal cycle in the European/North Atlantic sector.
Weijian Zhou - One of the best experts on this subject based on the ideXlab platform.
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hydrological changes in shuangchi lake hainan island tropical china during the Little Ice Age
Quaternary International, 2017Co-Authors: Wenchao Zhang, Hong Yan, Chengcheng Liu, Peng Cheng, John R Dodson, Henk Heijnis, Weijian ZhouAbstract:Abstract Hydrological changes in East Asia during the last millennium have been addressed by numerous earlier studies, but spatial characteristics and dynamics in precipitation variations during the Little Ice Age (LIA) remain unclear, perhaps especially due to the sparse coverAge of high-resolution hydrological records from tropical and sub-tropical regions in East Asia. In this study, a sediment core was obtained from Shuangchi Lake in northern Hainan Island, tropical China, of which geochemical proxies including the ratios of Rb/Sr, Rb/K, Zr/Rb and Si/Ti were analyzed using an X-ray fluorescence (XRF) core scanner. Meanwhile, the grain size distribution of sediments was also determined. The results show that the Rb/Sr and Rb/K ratios decreased significantly during the LIA, whilst the Zr/Rb and Si/Ti ratios increased along with higher median grain size. The changes of these proxies likely suggest that precipitation was enhanced during the LIA in this region, and this was consistent with other hydrological records from tropical southern China. The synthesis of hydrological records from East Asia and the tropical Pacific suggest that the co-existence of a contracted Intertropical Convergence Zone (ITCZ) and strengthened Pacific Walker circulation (PWC) could contribute synchronously to the increased precipitation in the tropical region of southern China during the LIA.
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cosmogenic 10be surface exposure dating of Little Ice Age glacial events in the mount jaggang area central tibet
The Holocene, 2017Co-Authors: Guocheng Dong, Weijian Zhou, Li Zhang, Qian ZhangAbstract:The timing and extent of ‘Little Ice Age’ (LIA) glacial advances on the Tibetan Plateau (TP) are critical for understanding climate during the past millennium. However, the lack of LIA chronologies in central Tibet makes it difficult to fully understand the nature of LIA throughout the TP. In this study, two presumed LIA moraines in the east of Mount Jaggang, Xainza range, the central TP, were examined and dated using 10Be surface exposure dating. Eight boulders from the two moraines yielded apparent 10Be exposure-Ages ranging from 41 ± 31 to 529 ± 130 years. These 10Be exposure-Ages indicate that glaciers advanced at least once in the Mount Jaggang area during the LIA. A relatively extensive glacial advance occurred around 267 ± 36 years, a relatively humid period as indicated by proxy data from lake sediments in the central TP. A glacial standstill might have occurred around 151 ± 36 years. The two LIA glacial events are comparable with those across the TP. However, much more efforts should be made on d...
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dynamics of the intertropical convergence zone over the western pacific during the Little Ice Age
Nature Geoscience, 2015Co-Authors: Hong Yan, Wei Wei, Willie Soon, Weijian Zhou, Zhonghui Liu, Yuhong Wang, Robert M CarterAbstract:Precipitation patterns in the western Pacific changed at the onset of the Little Ice Age. A synthesis of precipitation reconstructions suggests that this change resulted from a contraction of the intertropical convergence zone.
