2025
|
Mohammad Abbasian; Daniel B. Wright; Michael Notaro; Steve Vavrus; Daniel J. Vimont: Flood frequency sampling error: insights from regional analysis, stochastic storm transposition, and physics-based modeling. In: Journal of Hydrology, vol. 662 Part A, no. 133802, 2025. @article{Abbasian2025b,
title = {Flood frequency sampling error: insights from regional analysis, stochastic storm transposition, and physics-based modeling},
author = {Mohammad Abbasian and Daniel B. Wright and Michael Notaro and Steve Vavrus and Daniel J. Vimont},
url = {https://www.sciencedirect.com/science/article/abs/pii/S0022169425011400?via%3Dihub},
doi = {10.1016/j.jhydrol.2025.133802},
year = {2025},
date = {2025-07-12},
urldate = {2025-07-12},
journal = {Journal of Hydrology},
volume = {662 Part A},
number = {133802},
abstract = {Flood Frequency Analysis (FFA) typically involves fitting a probability distribution to Annual Maximum Peaks (AMPs) to estimate peak flow quantiles. While flood frequency sampling error due to small sample sizes is a well-recognized issue, this study highlights that, as flood data records lengthen, sampling error can remain as a concern. We examine the Kickapoo watershed in the north-central United States, where at-site FFA is susceptible to significant sampling errors despite a relatively long record of flood observations (90 years). We leverage a combination of at-site and regional statistical analyses of AMPs and watershed characteristics, Bulletin 17C guidelines, and a process-driven FFA approach to gain insights into flood extremes, flood frequency, and sampling errors. The process-based FFA integrates stochastic storm transposition with Monte Carlo physics-based hydrologic modeling. It employs the WRF-Hydro hydrologic model and a process-based calibration approach with Fusion, a new high-resolution forcing dataset over the continental United States. We demonstrate that three exceptionally large events, with a combined likelihood of occurrence of less than 2%, significantly affect extreme quantiles and their confidence intervals. Further, we show that while Kickapoo’s physiographic characteristics differ somewhat from neighboring watersheds, these extremes are also shaped by remarkable precipitation variability, contributing to sampling errors. While sample size has traditionally been the focal issue of sampling error, this research underscores additional factors: rare and extreme events and hydroclimate variability. It also highlights how regional analyses and advanced physics-based modeling techniques help improve understanding of flood extremes and frequency.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Flood Frequency Analysis (FFA) typically involves fitting a probability distribution to Annual Maximum Peaks (AMPs) to estimate peak flow quantiles. While flood frequency sampling error due to small sample sizes is a well-recognized issue, this study highlights that, as flood data records lengthen, sampling error can remain as a concern. We examine the Kickapoo watershed in the north-central United States, where at-site FFA is susceptible to significant sampling errors despite a relatively long record of flood observations (90 years). We leverage a combination of at-site and regional statistical analyses of AMPs and watershed characteristics, Bulletin 17C guidelines, and a process-driven FFA approach to gain insights into flood extremes, flood frequency, and sampling errors. The process-based FFA integrates stochastic storm transposition with Monte Carlo physics-based hydrologic modeling. It employs the WRF-Hydro hydrologic model and a process-based calibration approach with Fusion, a new high-resolution forcing dataset over the continental United States. We demonstrate that three exceptionally large events, with a combined likelihood of occurrence of less than 2%, significantly affect extreme quantiles and their confidence intervals. Further, we show that while Kickapoo’s physiographic characteristics differ somewhat from neighboring watersheds, these extremes are also shaped by remarkable precipitation variability, contributing to sampling errors. While sample size has traditionally been the focal issue of sampling error, this research underscores additional factors: rare and extreme events and hydroclimate variability. It also highlights how regional analyses and advanced physics-based modeling techniques help improve understanding of flood extremes and frequency.
|
Rudradutt Thaker; Stephen J. Vavrus; Christine A. Shields; Alice K. DuVivier; Michelle Maclennan; Marika M. Holland; Laura Landrum: Arctic Atmospheric Rivers in a Changing Climate and the Impacts on Sea Ice. In: JGR-Atmospheres, vol. 130, iss. 10, 2025. @article{Thaker2025b,
title = {Arctic Atmospheric Rivers in a Changing Climate and the Impacts on Sea Ice},
author = {Rudradutt Thaker and Stephen J. Vavrus and Christine A. Shields and Alice K. DuVivier and Michelle Maclennan and Marika M. Holland and Laura Landrum},
url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JD042521},
doi = {10.1029/2024JD042521},
year = {2025},
date = {2025-05-15},
urldate = {2025-05-15},
journal = {JGR-Atmospheres},
volume = {130},
issue = {10},
abstract = {Atmospheric rivers (ARs) transport heat and moisture from lower latitudes to the Arctic, contributing to sea ice loss. As climate warming and sea ice decline continue, understanding how Arctic ARs evolve is essential. While studies suggest an increase in Arctic ARs and storms, a comprehensive understanding of their changing behavior, seasonal patterns, and sea ice impacts remains incomplete. This study investigates the changing dynamics of Arctic ARs in response to a warming climate, examining the drivers of these changes and their impact on sea ice. Using the Community Earth System Model, Version 2 (CESM2), we find CESM2 effectively simulates Arctic ARs compared to ERA5. To analyze ARs under different climate conditions, we apply three detection methods: using present climate thresholds, scaling thresholds with projected future moisture changes, and calculating unique thresholds for each decade. Our results show increased AR frequency and intensity in the future, with changes strongly influenced by the chosen AR definition. Depending on the method, we find that AR frequency increases range from 30%–50% up to 400%, or even show decreases in some regions. During fall and winter, the North Atlantic experiences increased AR frequency, while more intense ARs occur in the North Pacific during summer. We also explore the effects of future ARs on sea ice, finding a net increase in sea ice loss, particularly in winter and spring. The extent of sea ice loss is highly sensitive to the AR detection method used.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Atmospheric rivers (ARs) transport heat and moisture from lower latitudes to the Arctic, contributing to sea ice loss. As climate warming and sea ice decline continue, understanding how Arctic ARs evolve is essential. While studies suggest an increase in Arctic ARs and storms, a comprehensive understanding of their changing behavior, seasonal patterns, and sea ice impacts remains incomplete. This study investigates the changing dynamics of Arctic ARs in response to a warming climate, examining the drivers of these changes and their impact on sea ice. Using the Community Earth System Model, Version 2 (CESM2), we find CESM2 effectively simulates Arctic ARs compared to ERA5. To analyze ARs under different climate conditions, we apply three detection methods: using present climate thresholds, scaling thresholds with projected future moisture changes, and calculating unique thresholds for each decade. Our results show increased AR frequency and intensity in the future, with changes strongly influenced by the chosen AR definition. Depending on the method, we find that AR frequency increases range from 30%–50% up to 400%, or even show decreases in some regions. During fall and winter, the North Atlantic experiences increased AR frequency, while more intense ARs occur in the North Pacific during summer. We also explore the effects of future ARs on sea ice, finding a net increase in sea ice loss, particularly in winter and spring. The extent of sea ice loss is highly sensitive to the AR detection method used. |
2024
|
Igor V. Polyakov; Thomas J. Ballinger; James E. Overland; Stephen J. Vavrus; Seth L. Danielson; Rick Lader; Uma S. Bhatt; Amy S. Hendricks; Franz J. Mueter: Atmospheric Pressure Rivalry Between the Arctic and Northern Pacific: Implications for Alaskan Climate Variability. In: International Journal of Climatology, 2024. @article{Polyakov2024,
title = {Atmospheric Pressure Rivalry Between the Arctic and Northern Pacific: Implications for Alaskan Climate Variability},
author = {Igor V. Polyakov and Thomas J. Ballinger and James E. Overland and Stephen J. Vavrus and Seth L. Danielson and Rick Lader and Uma S. Bhatt and Amy S. Hendricks and Franz J. Mueter},
doi = {https://doi.org/10.1002/joc.8638},
year = {2024},
date = {2024-10-23},
journal = { International Journal of Climatology},
abstract = {Located at the confluence of the Arctic and North Pacific and with Alaska at its heart, the Pacific Arctic Region (PAR) is a unique and interconnected regional climate system. Significant climatic changes in the PAR are described by a novel, mobile monthly Alaska Arctic Front (AAF) index, which is defined by sea level pressure differences between the migratory cores of the Beaufort High and Aleutian Low. Regional climate variability associated with the AAF shows prominent decadal signatures that are driven by the opposing effects of the North Pacific and the Arctic atmospheric pressure fields. Low AAF (negative phase) is dominated by North Pacific forcing, whereas high AAF (positive phase) is dominated by Arctic atmospheric processes. The recent (2011–2021) negative AAF phase, which is associated with the westward displacement of Aleutian Low explaining stronger northward winds and enhanced water transport northward through Bering Strait, is conducive to increased oceanic heat and freshwater content, reduced regional sea ice cover in the PAR, and to the expansion of Pacific species into the Arctic. These factors are all indicators of the Pacification of the Arctic Ocean, a key feature of climate change related to progression of anomalous Pacific water masses and biota into the polar basins. It is not yet clear if or when the recent phase of decadal variability will change and alter the rate of Pacification of the Arctic climate system.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Located at the confluence of the Arctic and North Pacific and with Alaska at its heart, the Pacific Arctic Region (PAR) is a unique and interconnected regional climate system. Significant climatic changes in the PAR are described by a novel, mobile monthly Alaska Arctic Front (AAF) index, which is defined by sea level pressure differences between the migratory cores of the Beaufort High and Aleutian Low. Regional climate variability associated with the AAF shows prominent decadal signatures that are driven by the opposing effects of the North Pacific and the Arctic atmospheric pressure fields. Low AAF (negative phase) is dominated by North Pacific forcing, whereas high AAF (positive phase) is dominated by Arctic atmospheric processes. The recent (2011–2021) negative AAF phase, which is associated with the westward displacement of Aleutian Low explaining stronger northward winds and enhanced water transport northward through Bering Strait, is conducive to increased oceanic heat and freshwater content, reduced regional sea ice cover in the PAR, and to the expansion of Pacific species into the Arctic. These factors are all indicators of the Pacification of the Arctic Ocean, a key feature of climate change related to progression of anomalous Pacific water masses and biota into the polar basins. It is not yet clear if or when the recent phase of decadal variability will change and alter the rate of Pacification of the Arctic climate system. |
Yanyan Yu; Jie Yu snd Haibin Wu; Feng He; Stephen J. Vavrus; Amber Johnson; Wenchao Zhang; Qin Li; Zhengtang Guo: Asynchronous Holocene human population changes in north and south China as related to animal resource utilization. In: Global and Planetary Change, vol. 235, iss. 0921-8181, pp. 104403, 2024. @article{Yu2024,
title = {Asynchronous Holocene human population changes in north and south China as related to animal resource utilization},
author = {Yanyan Yu and Jie Yu snd Haibin Wu and Feng He and Stephen J. Vavrus and Amber Johnson and Wenchao Zhang and Qin Li and Zhengtang Guo},
doi = {10.1016/j.gloplacha.2024.104403},
year = {2024},
date = {2024-04-01},
urldate = {2024-04-01},
journal = {Global and Planetary Change},
volume = {235},
issue = {0921-8181},
pages = {104403},
abstract = {During the Holocene, rich Neolithic and Bronze cultures developed in the middle and lower reaches of Yellow River valley (north China) and Yangtze River valley (south China), making them the core areas of past human activities. Thus, it is important to reveal the process and driving mechanism of regional population change. Agriculture development has always been taken as the key driver of population changes, and current studies mainly focus on the role that cultivation played, however, it is still unclear if animal resource utilization also contributed to regional population changes. Here, the spatiotemporal changes of population and domestic animal utilization levels in north and south China from 10 to 2 ka BP have been reconstructed based on 27,935 archaeological sites and faunal remains data from 94 sites, respectively, and the change in potential wild animal resources has been simulated by the Minimum Terrestrial Resource Model (MTRM). The results show asynchronous changes of population occurred in north and south China during 10–2 ka BP, which were correlated with regional domestic and potential wild animal resource utilization. In north China, more significant population growth corresponded to a greater increase of domestic animal ratios and a sharp decline of potential wild animal resources after 8 ka BP. In south China, less significant population growth was accompanied by a slower increase of domestic animal ratios and stable variations of potential wild animal resources. This research suggests that different changes of potential wild animal resources in north and south China contributed to spatial variations in survival pressure, utilization level of domestic animals, and population growth, which was further determined by asynchronous changes of precipitation in the two regions. This study explains the impact of climate changes on population from a new perspective.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
During the Holocene, rich Neolithic and Bronze cultures developed in the middle and lower reaches of Yellow River valley (north China) and Yangtze River valley (south China), making them the core areas of past human activities. Thus, it is important to reveal the process and driving mechanism of regional population change. Agriculture development has always been taken as the key driver of population changes, and current studies mainly focus on the role that cultivation played, however, it is still unclear if animal resource utilization also contributed to regional population changes. Here, the spatiotemporal changes of population and domestic animal utilization levels in north and south China from 10 to 2 ka BP have been reconstructed based on 27,935 archaeological sites and faunal remains data from 94 sites, respectively, and the change in potential wild animal resources has been simulated by the Minimum Terrestrial Resource Model (MTRM). The results show asynchronous changes of population occurred in north and south China during 10–2 ka BP, which were correlated with regional domestic and potential wild animal resource utilization. In north China, more significant population growth corresponded to a greater increase of domestic animal ratios and a sharp decline of potential wild animal resources after 8 ka BP. In south China, less significant population growth was accompanied by a slower increase of domestic animal ratios and stable variations of potential wild animal resources. This research suggests that different changes of potential wild animal resources in north and south China contributed to spatial variations in survival pressure, utilization level of domestic animals, and population growth, which was further determined by asynchronous changes of precipitation in the two regions. This study explains the impact of climate changes on population from a new perspective. |
2023
|
A. K. DuVivier; S. J. Vavrus; M. M. Holland; L. Landrum; C. A. Shields; R. Thaker: Investigating future Arctic sea ice loss and near-surface wind speed changes related to surface roughness using the Community Earth System Model. In: Journal of Geophysical Research: Atmospheres, vol. 128, iss. 20, 2023. @article{DuVivier2023,
title = {Investigating future Arctic sea ice loss and near-surface wind speed changes related to surface roughness using the Community Earth System Model},
author = {A. K. DuVivier and S. J. Vavrus and M. M. Holland and L. Landrum and C. A. Shields and R. Thaker},
doi = {10.1029/2023JD038824},
year = {2023},
date = {2023-09-27},
urldate = {2023-09-27},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {128},
issue = {20},
abstract = {The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gasses, including reduction in sea ice extent and thickness. There are also projected increases in near-surface Arctic wind. This study addresses how the winds trends may be driven by changing surface roughness and/or stability in different Arctic regions and seasons, something that has not yet been thoroughly investigated. We analyze 50 experiments from the Community Earth System Model Version 2 (CESM2) Large Ensemble and five experiments using CESM2 with an artificially decreased sea ice roughness to match that of the open ocean. We find that with a smoother surface there are higher mean wind speeds and slower mean ice speeds in the autumn, winter, and spring. The artificially reduced surface roughness also strongly impacts the wind speed trends in autumn and winter, and we find that atmospheric stability changes are also important contributors to driving wind trends in both experiments. In contrast to the clear impacts on winds, the sea ice mean state and trends are statistically indistinguishable, suggesting that near-surface winds are not major drivers of Arctic sea ice loss. Two major results of this work are: (a) the near-surface wind trends are driven by changes in both surface roughness and near-surface atmospheric stability that are themselves changing from sea ice loss, and (b) the sea ice mean state and trends are driven by the overall warming trend due to increasing greenhouse gas emissions and not significantly impacted by coupled feedbacks with the surface winds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gasses, including reduction in sea ice extent and thickness. There are also projected increases in near-surface Arctic wind. This study addresses how the winds trends may be driven by changing surface roughness and/or stability in different Arctic regions and seasons, something that has not yet been thoroughly investigated. We analyze 50 experiments from the Community Earth System Model Version 2 (CESM2) Large Ensemble and five experiments using CESM2 with an artificially decreased sea ice roughness to match that of the open ocean. We find that with a smoother surface there are higher mean wind speeds and slower mean ice speeds in the autumn, winter, and spring. The artificially reduced surface roughness also strongly impacts the wind speed trends in autumn and winter, and we find that atmospheric stability changes are also important contributors to driving wind trends in both experiments. In contrast to the clear impacts on winds, the sea ice mean state and trends are statistically indistinguishable, suggesting that near-surface winds are not major drivers of Arctic sea ice loss. Two major results of this work are: (a) the near-surface wind trends are driven by changes in both surface roughness and near-surface atmospheric stability that are themselves changing from sea ice loss, and (b) the sea ice mean state and trends are driven by the overall warming trend due to increasing greenhouse gas emissions and not significantly impacted by coupled feedbacks with the surface winds. |
Ryan M. Clare; Ankur R. Desai; Jonathan E. Martin; Michael Notaro; Stephen J. Vavrus : Extratropical Cyclone Response to Projected Reductions in Snow Extent over the Great Plains. In: Atmosphere, vol. 14, iss. 5, pp. 783, 2023. @article{Clare2023,
title = {Extratropical Cyclone Response to Projected Reductions in Snow Extent over the Great Plains},
author = {Ryan M. Clare and Ankur R. Desai and Jonathan E. Martin and Michael Notaro and Stephen J. Vavrus },
doi = {https://doi.org/10.3390/atmos14050783},
year = {2023},
date = {2023-04-26},
journal = {Atmosphere},
volume = {14},
issue = {5},
pages = {783},
abstract = {Extratropical cyclones develop in regions of enhanced baroclinicity and progress along climatological storm tracks. Numerous studies have noted an influence of terrestrial snow cover on atmospheric baroclinicity. However, these studies have less typically examined the role that continental snow cover extent and changes anticipated with anthropogenic climate change have on cyclones’ intensities, trajectories, and precipitation characteristics. Here, we examined how projected future poleward shifts in North American snow extent influence extratropical cyclones. We imposed 10th, 50th, and 90th percentile values of snow retreat between the late 20th and 21st centuries as projected by 14 Coupled Model Intercomparison Project Phase Five (CMIP5) models to alter snow extent underlying 15 historical cold-season cyclones that tracked over the North American Great Plains and were faithfully reproduced in control model cases, providing a comprehensive set of model runs to evaluate hypotheses. Simulations by the Advanced Research version of the Weather Research and Forecast Model (WRF-ARW) were initialized at four days prior to cyclogenesis. Cyclone trajectories moved on average poleward (μ = 27 +/− σ = 17 km) in response to reduced snow extent while the maximum sea-level pressure deepened (μ = −0.48 +/− σ = 0.8 hPa) with greater snow removed. A significant linear correlation was observed between the area of snow removed and mean trajectory deviation (r2 = 0.23), especially in mid-winter (r2 = 0.59), as well as a similar relationship for maximum change in sea-level pressure (r2 = 0.17). Across all simulations, 82% of the perturbed simulation cyclones decreased in average central sea-level pressure (SLP) compared to the corresponding control simulation. Near-surface wind speed increased, as did precipitation, in 86% of cases with a preferred phase change from the solid to liquid state due to warming, although the trends did not correlate with the snow retreat magnitude. Our results, consistent with prior studies noting some role for the enhanced baroclinity of the snow line in modulating storm track and intensity, provide a benchmark to evaluate future snow cover retreat impacts on mid-latitude weather systems.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Extratropical cyclones develop in regions of enhanced baroclinicity and progress along climatological storm tracks. Numerous studies have noted an influence of terrestrial snow cover on atmospheric baroclinicity. However, these studies have less typically examined the role that continental snow cover extent and changes anticipated with anthropogenic climate change have on cyclones’ intensities, trajectories, and precipitation characteristics. Here, we examined how projected future poleward shifts in North American snow extent influence extratropical cyclones. We imposed 10th, 50th, and 90th percentile values of snow retreat between the late 20th and 21st centuries as projected by 14 Coupled Model Intercomparison Project Phase Five (CMIP5) models to alter snow extent underlying 15 historical cold-season cyclones that tracked over the North American Great Plains and were faithfully reproduced in control model cases, providing a comprehensive set of model runs to evaluate hypotheses. Simulations by the Advanced Research version of the Weather Research and Forecast Model (WRF-ARW) were initialized at four days prior to cyclogenesis. Cyclone trajectories moved on average poleward (μ = 27 +/− σ = 17 km) in response to reduced snow extent while the maximum sea-level pressure deepened (μ = −0.48 +/− σ = 0.8 hPa) with greater snow removed. A significant linear correlation was observed between the area of snow removed and mean trajectory deviation (r2 = 0.23), especially in mid-winter (r2 = 0.59), as well as a similar relationship for maximum change in sea-level pressure (r2 = 0.17). Across all simulations, 82% of the perturbed simulation cyclones decreased in average central sea-level pressure (SLP) compared to the corresponding control simulation. Near-surface wind speed increased, as did precipitation, in 86% of cases with a preferred phase change from the solid to liquid state due to warming, although the trends did not correlate with the snow retreat magnitude. Our results, consistent with prior studies noting some role for the enhanced baroclinity of the snow line in modulating storm track and intensity, provide a benchmark to evaluate future snow cover retreat impacts on mid-latitude weather systems. |
Yanyan Yu; Feng He; Stephen J. Vavrus; Amber Johnson; Haibin Wu; Wenchao Zhang; Qiuzhen Yin; Junyi Ge; Chenglong Deng; Michael D. Petraglia; Zhengtang Guo: Climatic factors and human population changes in Eurasia between the Last Glacial Maximum and the early Holocene. In: Global and Planetary Change, vol. 221, pp. 104054, 2023. @article{Yu2023,
title = {Climatic factors and human population changes in Eurasia between the Last Glacial Maximum and the early Holocene},
author = {Yanyan Yu and Feng He and Stephen J. Vavrus and Amber Johnson and Haibin Wu and Wenchao Zhang and Qiuzhen Yin and Junyi Ge and Chenglong Deng and Michael D. Petraglia and Zhengtang Guo},
url = {https://www.sciencedirect.com/science/article/pii/S0921818123000279},
doi = {https://doi.org/10.1016/j.gloplacha.2023.104054},
year = {2023},
date = {2023-02-01},
journal = {Global and Planetary Change},
volume = {221},
pages = {104054},
abstract = {Archaeological records document a significant expansion of populations from the Last Glacial Maximum (LGM, ∼23–19 ka) to the early Holocene (EH, ∼9 ka) in Eurasia, which is often attributed to the influence of orbital-scale climate changes. Yet, information remains limited concerning the climatic factor(s) which were responsible for conditioning demographic patterns. Here, we present results from an improved Minimalist Terrestrial Resource Model (MTRM), forced by a transient climate simulation from the LGM to the EH. Simulated potential hunter-gatherer population densities and spatial distributions across Eurasia are supported by observed archaeological sites in Europe and China. In the low latitudes, potential population size change was predominantly controlled by precipitation and its strong influence on plant and animal resources. In the middle-high latitudes, temperature was the dominant driver in influencing potential population size change and animal resource availability. Different regional responses of potential populations to climate change across Eurasia - owing to variations in available food resources between the LGM and EH - provide a better understanding of human dispersal during the Late Pleistocene.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Archaeological records document a significant expansion of populations from the Last Glacial Maximum (LGM, ∼23–19 ka) to the early Holocene (EH, ∼9 ka) in Eurasia, which is often attributed to the influence of orbital-scale climate changes. Yet, information remains limited concerning the climatic factor(s) which were responsible for conditioning demographic patterns. Here, we present results from an improved Minimalist Terrestrial Resource Model (MTRM), forced by a transient climate simulation from the LGM to the EH. Simulated potential hunter-gatherer population densities and spatial distributions across Eurasia are supported by observed archaeological sites in Europe and China. In the low latitudes, potential population size change was predominantly controlled by precipitation and its strong influence on plant and animal resources. In the middle-high latitudes, temperature was the dominant driver in influencing potential population size change and animal resource availability. Different regional responses of potential populations to climate change across Eurasia - owing to variations in available food resources between the LGM and EH - provide a better understanding of human dispersal during the Late Pleistocene. |
S. J. Vavrus; S. Kruse; A. Puz,; J. A. Patz: Applying climate change science: From extreme weather events to sea level rise. In: Climate Change and Public Health, Second Edition, 2023. @article{Vavrus2023,
title = {Applying climate change science: From extreme weather events to sea level rise},
author = {S. J. Vavrus and S. Kruse and A. Puz, and J. A. Patz},
year = {2023},
date = {2023-01-01},
journal = {Climate Change and Public Health, Second Edition},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2022
|
Jennifer A. Francis; Natasa Skific; Steven J. Vavrus; Judah Cohen
: Measuring “Weather Whiplash” Events in North America: A New Large-Scale Regime Approach. In: Journal of Geophysical Research: Atmospheres, vol. 127, iss. 17, pp. e2022JD036717, 2022. @article{nokey,
title = {Measuring “Weather Whiplash” Events in North America: A New Large-Scale Regime Approach},
author = {Jennifer A. Francis and Natasa Skific and Steven J. Vavrus and Judah Cohen
},
doi = { https://doi.org/10.1029/2022JD036717},
year = {2022},
date = {2022-09-07},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {127},
issue = {17},
pages = {e2022JD036717},
abstract = {The term “weather whiplash” was recently coined to describe abrupt swings in weather conditions from one extreme to another, such as from a prolonged, frigid cold spell to anomalous warmth or from drought to heavy precipitation. These events are often highly disruptive to agriculture, ecosystems, and daily activities. In this study, we propose and demonstrate a novel metric to identify weather whiplash events (WWEs) and track their frequency over time. We define a WWE as a transition from one persistent continental-scale circulation regime to another distinctly different pattern, as determined using an objective pattern clustering analysis called self-organizing maps. We focus on the domain spanning North America and the eastern N. Pacific Ocean. A matrix of representative atmospheric patterns in 500-hPa geopotential height anomalies is created from 72 years of daily fields. We analyze the occurrence of WWEs originating with long-duration events (LDEs) (defined as lasting four or more days) in each pattern, as well as the associated extremes in temperature and precipitation. A WWE is detected when the pattern 2 days following a LDE is substantially different, measured using internal matrix distances and thresholds. Changes in WWE frequency are assessed objectively based on reanalysis and historical climate model simulations, and for the future using climate model projections. Temporal changes in the future under representative concentration pathway 8.5 forcing are more robust than those in recent decades. We find consistent increases in WWEs originating in patterns with an anomalously warm Arctic and decreases in cold-Arctic patterns.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The term “weather whiplash” was recently coined to describe abrupt swings in weather conditions from one extreme to another, such as from a prolonged, frigid cold spell to anomalous warmth or from drought to heavy precipitation. These events are often highly disruptive to agriculture, ecosystems, and daily activities. In this study, we propose and demonstrate a novel metric to identify weather whiplash events (WWEs) and track their frequency over time. We define a WWE as a transition from one persistent continental-scale circulation regime to another distinctly different pattern, as determined using an objective pattern clustering analysis called self-organizing maps. We focus on the domain spanning North America and the eastern N. Pacific Ocean. A matrix of representative atmospheric patterns in 500-hPa geopotential height anomalies is created from 72 years of daily fields. We analyze the occurrence of WWEs originating with long-duration events (LDEs) (defined as lasting four or more days) in each pattern, as well as the associated extremes in temperature and precipitation. A WWE is detected when the pattern 2 days following a LDE is substantially different, measured using internal matrix distances and thresholds. Changes in WWE frequency are assessed objectively based on reanalysis and historical climate model simulations, and for the future using climate model projections. Temporal changes in the future under representative concentration pathway 8.5 forcing are more robust than those in recent decades. We find consistent increases in WWEs originating in patterns with an anomalously warm Arctic and decreases in cold-Arctic patterns. |
S. J. Vavrus; C. Kucharik; F. He; J. E. Kutzbach; W. F. Ruddiman: Did agriculture beget agriculture during the past several millennia?. In: The Holocene, vol. 32, iss. 7, pp. 680-689, 2022. @article{Vavrus2022b,
title = {Did agriculture beget agriculture during the past several millennia?},
author = {S. J. Vavrus and C. Kucharik and F. He and J. E. Kutzbach and W. F. Ruddiman},
url = {https://journals.sagepub.com/doi/10.1177/09596836221088231},
doi = {10.1177/09596836221088231},
year = {2022},
date = {2022-05-01},
urldate = {2022-05-01},
journal = { The Holocene},
volume = {32},
issue = {7},
pages = {680-689},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
S. J. Vavrus; F. Wang; P. Block: Rainy season precipitation forecasts in coastal Peru from the North American Multi-Model Ensemble (NMME). In: International Journal of Climatology, 2022. @article{Vavrus2022,
title = {Rainy season precipitation forecasts in coastal Peru from the North American Multi-Model Ensemble (NMME)},
author = {S. J. Vavrus and F. Wang and P. Block},
url = {https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.7586},
doi = {10.1002/joc.7586},
year = {2022},
date = {2022-02-23},
urldate = {2022-02-23},
journal = {International Journal of Climatology},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2021
|
S. J. Vavrus; R. Alkama: Future trends of Arctic surface wind speeds and their relationship with sea ice in CMIP5 climate model simulations. In: Climate Dynamics, vol. 59, pp. 1833-1848, 2021. @article{Vavrus2021,
title = {Future trends of Arctic surface wind speeds and their relationship with sea ice in CMIP5 climate model simulations},
author = {S. J. Vavrus and R. Alkama},
url = {https://link.springer.com/article/10.1007/s00382-021-06071-6},
doi = {10.1007/s00382-021-06071-6},
year = {2021},
date = {2021-12-02},
urldate = {2021-12-02},
journal = {Climate Dynamics},
volume = {59},
pages = {1833-1848},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
S. J. Vavrus; M. M. Holland: When will the Arctic Ocean become ice-free?. In: Arctic, Antarctic, and Alpine Research, vol. 53, iss. 1, pp. 217-218, 2021. @article{nokey,
title = {When will the Arctic Ocean become ice-free?},
author = {S. J. Vavrus and M. M. Holland},
url = {https://www.tandfonline.com/doi/full/10.1080/15230430.2021.1941578},
doi = {10.1080/15230430.2021.1941578},
year = {2021},
date = {2021-10-12},
urldate = {2021-10-12},
journal = {Arctic, Antarctic, and Alpine Research},
volume = {53},
issue = {1},
pages = {217-218},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
J. Francis; S. Vavrus: How is rapid Arctic warming influencing weather patterns in lower latitudes?. In: Arctic, Antarctic, and Alpine Research, vol. 53, iss. 1, pp. 219-220, 2021. @article{Francis2021,
title = {How is rapid Arctic warming influencing weather patterns in lower latitudes?},
author = {J. Francis and S. Vavrus},
url = {https://www.tandfonline.com/doi/full/10.1080/15230430.2021.1942400},
doi = {10.1080/15230430.2021.1942400},
year = {2021},
date = {2021-10-12},
urldate = {2021-10-12},
journal = {Arctic, Antarctic, and Alpine Research},
volume = {53},
issue = {1},
pages = {219-220},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
M. Notaro; Y. Zhong; P. Xue; C. Peters-Lidard; C. Cruz; E. Kemp; D. Kristovich; M. Kulie; J. Wang; C. Huang; S.V. Vavrus: Cold season performance of the NU-WRF regional climate model in the Great Lakes region. . In: Journal of Hydrometeorology, vol. 22, pp. 2423-2454, 2021. @article{doi.org/10.1175/JHM-D-21-0025.1,
title = {Cold season performance of the NU-WRF regional climate model in the Great Lakes region. },
author = {M. Notaro and Y. Zhong and P. Xue and C. Peters-Lidard and C. Cruz and E. Kemp and D. Kristovich and M. Kulie and J. Wang and C. Huang and S.V. Vavrus},
url = {https://doi.org/10.1175/JHM-D-21-0025.1},
doi = {10.1175/JHM-D-21-0025.1},
year = {2021},
date = {2021-09-14},
urldate = {2021-09-14},
journal = {Journal of Hydrometeorology},
volume = {22},
pages = {2423-2454},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
|
2020
|
J Cohen; X Zhang; J Francis; T Jung; R Kwok; J Overland; T J Ballinger; U S Bhatt; H W Chen; D Coumou; S Feldstein; H Gu; D Handorf; G Henderson; M Ionita; M Kretschmer; F Laliberte; S Lee; H W Linderholm; W Maslowski; Y Peings; K Pfeiffer; I Rigor; T Semmler; J Stroeve; P C Taylor; S Vavrus; T Vihma; S Wang; M Wendisch; Y Wu; J Yoon: Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather. In: Nature Climate Change, vol. 10, no. 1, pp. 20-29, 2020, ISSN: 1758-6798. @article{Cohen2020,
title = {Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather},
author = {J Cohen and X Zhang and J Francis and T Jung and R Kwok and J Overland and T J Ballinger and U S Bhatt and H W Chen and D Coumou and S Feldstein and H Gu and D Handorf and G Henderson and M Ionita and M Kretschmer and F Laliberte and S Lee and H W Linderholm and W Maslowski and Y Peings and K Pfeiffer and I Rigor and T Semmler and J Stroeve and P C Taylor and S Vavrus and T Vihma and S Wang and M Wendisch and Y Wu and J Yoon},
url = {https://www.nature.com/articles/s41558-019-0662-y},
doi = {10.1038/s41558-019-0662-y},
issn = {1758-6798},
year = {2020},
date = {2020-12-23},
journal = {Nature Climate Change},
volume = {10},
number = {1},
pages = {20-29},
abstract = {The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather variability. Observational studies overwhelmingly support that AA is contributing to winter continental cooling. Although some model experiments support the observational evidence, most modelling results show little connection between AA and severe midlatitude weather or suggest the export of excess heating from the Arctic to lower latitudes. Divergent conclusions between model and observational studies, and even intramodel studies, continue to obfuscate a clear understanding of how AA is influencing midlatitude weather.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather variability. Observational studies overwhelmingly support that AA is contributing to winter continental cooling. Although some model experiments support the observational evidence, most modelling results show little connection between AA and severe midlatitude weather or suggest the export of excess heating from the Arctic to lower latitudes. Divergent conclusions between model and observational studies, and even intramodel studies, continue to obfuscate a clear understanding of how AA is influencing midlatitude weather. |
Ramdane Alkama; Ernest N Koffi; Stephen J Vavrus; Thomas Diehl; Jennifer Ann Francis; Julienne Stroeve; Giovanni Forzieri; Timo Vihma; Alessandro Cescatti: Wind amplifies the polar sea ice retreat. In: Environmental Research Letters, vol. 15, no. 12, pp. 124022, 2020. @article{Alkama_2020,
title = {Wind amplifies the polar sea ice retreat},
author = {Ramdane Alkama and Ernest N Koffi and Stephen J Vavrus and Thomas Diehl and Jennifer Ann Francis and Julienne Stroeve and Giovanni Forzieri and Timo Vihma and Alessandro Cescatti},
url = {https://doi.org/10.1088/1748-9326/abc379},
doi = {10.1088/1748-9326/abc379},
year = {2020},
date = {2020-12-01},
journal = {Environmental Research Letters},
volume = {15},
number = {12},
pages = {124022},
publisher = {IOP Publishing},
abstract = {The rapid polar sea ice retreat and its drivers are challenging and still unresolved questions in climate change research. In particular, the relationship between near-surface wind speed and sea ice extent remains unclear for two main reasons: (1) observed wind speeds over Polar Regions are very sparse, and (2) simulated winds by climate models are dependent on subjective parameterizations of boundary layer stratification, ultimately leading to large uncertainty. Here, we use observation-based data (passive microwave sea ice concentration and six different reanalysis datasets) together with output from 26 climate models (from the CMIP5 archive) to quantify the relationships between near-surface wind speed and sea ice concentration over the past 40 years. We find strong inverse relationships between near-surface wind speed and sea ice concentration that are consistent among the six reanalysis datasets. The poleward wind component is particularly increasing in years of reduced sea ice concentration, which contributes to the enhancement of the atmospheric (surface oceanic) poleward heat flux by up to 24 ± 1% (29 ± 2%) in the Arctic and 37 ± 3% (51 ± 3%) in the Antarctic seas, therefore boosting the impact of polar sea ice loss and contributing to polar amplification of climate warming. In addition, our results show a marginal contribution of the dynamical (pushing/opening/compacting) effects of wind on sea ice compared to the thermodynamic effects which in turn play a lower role than the associated change in local surface Autumn–Winter turbulent and Spring–Summer radiative fluxes. Climate models generally produce similar results but with lower magnitude, and one model even simulates the opposite relationship wind/sea-ice. Given the rapid changes in polar climate and the potential impacts on the mid-latitudes, it is urgent that model developments make use of evidence from satellite observations and reanalysis datasets to reduce uncertainties in the representation of relationships between polar winds and sea ice.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The rapid polar sea ice retreat and its drivers are challenging and still unresolved questions in climate change research. In particular, the relationship between near-surface wind speed and sea ice extent remains unclear for two main reasons: (1) observed wind speeds over Polar Regions are very sparse, and (2) simulated winds by climate models are dependent on subjective parameterizations of boundary layer stratification, ultimately leading to large uncertainty. Here, we use observation-based data (passive microwave sea ice concentration and six different reanalysis datasets) together with output from 26 climate models (from the CMIP5 archive) to quantify the relationships between near-surface wind speed and sea ice concentration over the past 40 years. We find strong inverse relationships between near-surface wind speed and sea ice concentration that are consistent among the six reanalysis datasets. The poleward wind component is particularly increasing in years of reduced sea ice concentration, which contributes to the enhancement of the atmospheric (surface oceanic) poleward heat flux by up to 24 ± 1% (29 ± 2%) in the Arctic and 37 ± 3% (51 ± 3%) in the Antarctic seas, therefore boosting the impact of polar sea ice loss and contributing to polar amplification of climate warming. In addition, our results show a marginal contribution of the dynamical (pushing/opening/compacting) effects of wind on sea ice compared to the thermodynamic effects which in turn play a lower role than the associated change in local surface Autumn–Winter turbulent and Spring–Summer radiative fluxes. Climate models generally produce similar results but with lower magnitude, and one model even simulates the opposite relationship wind/sea-ice. Given the rapid changes in polar climate and the potential impacts on the mid-latitudes, it is urgent that model developments make use of evidence from satellite observations and reanalysis datasets to reduce uncertainties in the representation of relationships between polar winds and sea ice. |
Jennifer Ann Francis; Natasa Skific; Stephen J Vavrus: Increased persistence of large-scale circulation regimes over Asia in the era of amplified Arctic warming, past and future. In: Scientific Reports, vol. 10, no. 1, pp. 14953, 2020, ISSN: 2045-2322. @article{Francis2020,
title = {Increased persistence of large-scale circulation regimes over Asia in the era of amplified Arctic warming, past and future},
author = {Jennifer Ann Francis and Natasa Skific and Stephen J Vavrus},
url = {https://www.nature.com/articles/s41598-020-71945-4},
doi = {10.1038/s41598-020-71945-4},
issn = {2045-2322},
year = {2020},
date = {2020-09-11},
journal = {Scientific Reports},
volume = {10},
number = {1},
pages = {14953},
abstract = {Extreme weather events in Asia have been occurring with increasing frequency as the globe warms in response to rising concentrations of greenhouse gases. Many of these events arise from weather regimes that persist over a region for days or even weeks, resulting in disruptive heatwaves, droughts, flooding, snowfalls, and cold spells. We investigate changes in the persistence of large-scale weather systems through a pattern-recognition approach based on daily 500 hPa geopotential height anomalies over the Asian continent. By tracking consecutive days that the atmosphere resides in a particular pattern, we identify long-duration events (LDEs), defined as lasting longer than three days, and measure their frequency of occurrence over time in each pattern. We find that regimes featuring positive height anomalies in high latitudes are occurring more often as the Arctic warms faster than mid-latitudes, both in the recent past and in model projections for the twenty-first century assuming unabated greenhouse gas emissions. The increased dominance of these patterns corresponds to a higher likelihood of LDEs, suggesting that persistent weather conditions will occur more frequently. By mapping observed temperature and precipitation extremes onto each atmospheric regime, we gain insight into the types of disruptive weather events that will become more prevalent as particular patterns become more common.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Extreme weather events in Asia have been occurring with increasing frequency as the globe warms in response to rising concentrations of greenhouse gases. Many of these events arise from weather regimes that persist over a region for days or even weeks, resulting in disruptive heatwaves, droughts, flooding, snowfalls, and cold spells. We investigate changes in the persistence of large-scale weather systems through a pattern-recognition approach based on daily 500 hPa geopotential height anomalies over the Asian continent. By tracking consecutive days that the atmosphere resides in a particular pattern, we identify long-duration events (LDEs), defined as lasting longer than three days, and measure their frequency of occurrence over time in each pattern. We find that regimes featuring positive height anomalies in high latitudes are occurring more often as the Arctic warms faster than mid-latitudes, both in the recent past and in model projections for the twenty-first century assuming unabated greenhouse gas emissions. The increased dominance of these patterns corresponds to a higher likelihood of LDEs, suggesting that persistent weather conditions will occur more frequently. By mapping observed temperature and precipitation extremes onto each atmospheric regime, we gain insight into the types of disruptive weather events that will become more prevalent as particular patterns become more common. |
Stephen J Vavrus; Feng He; John E Kutzbach; William F Ruddiman: Rapid neoglaciation on Ellesmere Island promoted by enhanced summer snowfall in a transient climate model simulation of the middle-late-Holocene. In: The Holocene, vol. 30, no. 10, pp. 1474-1480, 2020. @article{doi:10.1177/0959683620932967,
title = {Rapid neoglaciation on Ellesmere Island promoted by enhanced summer snowfall in a transient climate model simulation of the middle-late-Holocene},
author = {Stephen J Vavrus and Feng He and John E Kutzbach and William F Ruddiman},
url = {https://doi.org/10.1177/0959683620932967},
doi = {10.1177/0959683620932967},
year = {2020},
date = {2020-06-12},
journal = {The Holocene},
volume = {30},
number = {10},
pages = {1474-1480},
abstract = {Arctic neoglaciation following the Holocene Thermal Maximum is an important feature of late-Holocene climate. We investigated this phenomenon using a transient 6000-year simulation with the CESM-CAM5 climate model driven by orbital forcing, greenhouse gas concentrations, and a land use reconstruction. During the first three millennia analyzed here (6–3 ka), mean Arctic snow depth increases, despite enhanced greenhouse forcing. Superimposed on this secular trend is a very abrupt increase in snow depth between 5 and 4.9 ka on Ellesmere Island and the Greenland coasts, in rough agreement with the timing of observed neoglaciation in the region. This transition is especially extreme on Ellesmere Island, where end-of-summer snow coverage jumps from nearly 0 to virtually 100% in 1 year, and snow depth increases to the model’s imposed maximum within 15 years. This climatic shift involves more than the Milankovitch-based expectation of cooler summers causing less snow melt. Coincident with the onset of the cold regime are two consecutive summers with heavy snowfall on Ellesmere Island that help to short-circuit the normal seasonal melt cycle. These heavy snow seasons are caused by synoptic-scale, cyclonic circulation anomalies over the Arctic Ocean and Canadian Archipelago, including an extremely positive phase of the Arctic Oscillation. Our study reveals that a climate model can produce sudden climatic transitions in this region prone to glacial inception and exceptional variability, due to a dynamic mechanism (more summer snowfall induced by an extreme circulation anomaly) that augments the traditional Milankovitch thermodynamic explanation of orbitally induced glacier development.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Arctic neoglaciation following the Holocene Thermal Maximum is an important feature of late-Holocene climate. We investigated this phenomenon using a transient 6000-year simulation with the CESM-CAM5 climate model driven by orbital forcing, greenhouse gas concentrations, and a land use reconstruction. During the first three millennia analyzed here (6–3 ka), mean Arctic snow depth increases, despite enhanced greenhouse forcing. Superimposed on this secular trend is a very abrupt increase in snow depth between 5 and 4.9 ka on Ellesmere Island and the Greenland coasts, in rough agreement with the timing of observed neoglaciation in the region. This transition is especially extreme on Ellesmere Island, where end-of-summer snow coverage jumps from nearly 0 to virtually 100% in 1 year, and snow depth increases to the model’s imposed maximum within 15 years. This climatic shift involves more than the Milankovitch-based expectation of cooler summers causing less snow melt. Coincident with the onset of the cold regime are two consecutive summers with heavy snowfall on Ellesmere Island that help to short-circuit the normal seasonal melt cycle. These heavy snow seasons are caused by synoptic-scale, cyclonic circulation anomalies over the Arctic Ocean and Canadian Archipelago, including an extremely positive phase of the Arctic Oscillation. Our study reveals that a climate model can produce sudden climatic transitions in this region prone to glacial inception and exceptional variability, due to a dynamic mechanism (more summer snowfall induced by an extreme circulation anomaly) that augments the traditional Milankovitch thermodynamic explanation of orbitally induced glacier development. |
W F Ruddiman; F He; S J Vavrus; J E Kutzbach: The early anthropogenic hypothesis: A review. In: Quaternary Science Reviews, vol. 240, pp. 106386, 2020, ISSN: 0277-3791. @article{RUDDIMAN2020106386,
title = {The early anthropogenic hypothesis: A review},
author = {W F Ruddiman and F He and S J Vavrus and J E Kutzbach},
url = {https://www.sciencedirect.com/science/article/pii/S0277379120303486},
doi = {https://doi.org/10.1016/j.quascirev.2020.106386},
issn = {0277-3791},
year = {2020},
date = {2020-01-01},
journal = {Quaternary Science Reviews},
volume = {240},
pages = {106386},
abstract = {The ‘early anthropogenic hypothesis’ (EAH), published in 2003, proposed that early agricultural humans transformed planet Earth by adding CO2 to the atmosphere by deforestation after 7000 years ago and by adding CH4 to the atmosphere by wet-rice farming and livestock tending after 5000 years ago. Later work led to the insight that the resulting warming of the atmosphere and the ocean would have contributed additional CO2 feedback by reducing CO2 solubility in the global ocean and by boosting ventilation from the Antarctic Ocean surface due to suppressed Antarctic sea-ice extent. This paper summarizes new findings from multiple scientific disciplines that document how the steadily spreading human influence transformed their environment after 7000 years ago. We blend this new evidence into a revised version of the EAH, and we also evaluate proposed alternatives to the anthropogenic explanation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The ‘early anthropogenic hypothesis’ (EAH), published in 2003, proposed that early agricultural humans transformed planet Earth by adding CO2 to the atmosphere by deforestation after 7000 years ago and by adding CH4 to the atmosphere by wet-rice farming and livestock tending after 5000 years ago. Later work led to the insight that the resulting warming of the atmosphere and the ocean would have contributed additional CO2 feedback by reducing CO2 solubility in the global ocean and by boosting ventilation from the Antarctic Ocean surface due to suppressed Antarctic sea-ice extent. This paper summarizes new findings from multiple scientific disciplines that document how the steadily spreading human influence transformed their environment after 7000 years ago. We blend this new evidence into a revised version of the EAH, and we also evaluate proposed alternatives to the anthropogenic explanation. |