Pub Date : 2024-06-21DOI: 10.1175/jcli-d-23-0388.1
Xiaoqin Yan, Wangjie Yao, Youmin Tang
Abstract Utilizing ensemble hindcast data from the Community Earth System Model (CESM) spanning the years 1900–2014, the multidecadal changes in the seasonal potential predictability of the winter Pacific–North American (PNA) teleconnection pattern and associated circulation anomalies have been investigated by using an information-based metric of relative entropy and the method of the most predictable component analysis. Results show that the seasonal potential predictability of winter PNA has significant multidecadal changes, with values much higher at the two ends of the twentieth century and much lower in between particularly in the 1930s and 1940s. The changes in the seasonal potential predictability of winter PNA are mostly reflected by the temporal evolutions of PNA rather than the location changes of active centers. Further, the changes are mostly contributed by the external forcing of El Niño–Southern Oscillation (ENSO)-related sea surface temperature anomalies in tropical central and eastern Pacific. In particular, the combined effects of lower amplitudes, reduced persistence, and a more eastward shift in warming centers lead to the reduced seasonal potential predictability of PNA and associated circulation changes in the 1930s and 1940s. Significance Statement Seasonal prediction of the winter Pacific–North American (PNA) teleconnection pattern and associated circulation anomalies is very important due to its profound climate impacts. Understanding the multidecadal fluctuations and its driving sources of the potential predictability of winter PNA and associated circulation anomalies are meaningful for skillful seasonal prediction of winter PNA and circulation anomalies as well as related climate variations. This study for the first time shows that the multidecadal fluctuations of the potential predictability of winter PNA are quite significant and the changes are mostly reflected by its temporal evolutions rather than spatial shifts of active centers. Furthermore, this study shows that the strength, persistence, and warming center locations of ENSO-related sea surface temperatures in tropical Pacific play a crucial role on the multidecadal changes of the potential predictability of winter PNA and associated circulation anomalies.
{"title":"Multidecadal Changes of the Seasonal Potential Predictability of Winter PNA and Associated Circulation Anomalies","authors":"Xiaoqin Yan, Wangjie Yao, Youmin Tang","doi":"10.1175/jcli-d-23-0388.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0388.1","url":null,"abstract":"Abstract Utilizing ensemble hindcast data from the Community Earth System Model (CESM) spanning the years 1900–2014, the multidecadal changes in the seasonal potential predictability of the winter Pacific–North American (PNA) teleconnection pattern and associated circulation anomalies have been investigated by using an information-based metric of relative entropy and the method of the most predictable component analysis. Results show that the seasonal potential predictability of winter PNA has significant multidecadal changes, with values much higher at the two ends of the twentieth century and much lower in between particularly in the 1930s and 1940s. The changes in the seasonal potential predictability of winter PNA are mostly reflected by the temporal evolutions of PNA rather than the location changes of active centers. Further, the changes are mostly contributed by the external forcing of El Niño–Southern Oscillation (ENSO)-related sea surface temperature anomalies in tropical central and eastern Pacific. In particular, the combined effects of lower amplitudes, reduced persistence, and a more eastward shift in warming centers lead to the reduced seasonal potential predictability of PNA and associated circulation changes in the 1930s and 1940s. Significance Statement Seasonal prediction of the winter Pacific–North American (PNA) teleconnection pattern and associated circulation anomalies is very important due to its profound climate impacts. Understanding the multidecadal fluctuations and its driving sources of the potential predictability of winter PNA and associated circulation anomalies are meaningful for skillful seasonal prediction of winter PNA and circulation anomalies as well as related climate variations. This study for the first time shows that the multidecadal fluctuations of the potential predictability of winter PNA are quite significant and the changes are mostly reflected by its temporal evolutions rather than spatial shifts of active centers. Furthermore, this study shows that the strength, persistence, and warming center locations of ENSO-related sea surface temperatures in tropical Pacific play a crucial role on the multidecadal changes of the potential predictability of winter PNA and associated circulation anomalies.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"85 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1175/jcli-d-23-0563.1
Chenyu Zheng, Shaojun Zheng, Ming Feng, Lingling Xie, Lei Wang, Tianyu Zhang, Li Yan
Abstract The East African Coastal Current (EACC) is an important western boundary current of the tropical South Indian Ocean and plays an important role in the ocean circulation and biogeochemical cycles in the Indian Ocean. This study investigates the interannual variability of the EACC and its dynamical mechanisms. The result shows that the EACC has interannual variability associated with the El Niño-Southern Oscillation (ENSO) during 1993-2017. The EACC shows a significantly positive correlation with the Niño3.4 index with a correlation coefficient of 0.65, lagging the Niño3.4 index by 18 months. During the decaying phases of El Niño (La Niña) events, the negative (positive) sea level anomaly (SLA) propagates westward as upwelling (downwelling) Rossby waves from the southeast Indian Ocean to the southwest Indian Ocean, and then strengthens (weakens) the EACC due to zonal SLA gradient off the East African coast under geostrophic equilibrium. The SLA gradually weakens in the southeast Indian Ocean during its westward propagation but strengthens in the southwest Indian Ocean promoted by local wind stress curl anomaly. This study can improve our understanding of the relationship between the western boundary current of the tropical South Indian Ocean and large-scale ENSO air-sea processes, and is important for managing marine fisheries and ecosystems on the East African coast.
{"title":"Interannual variability of the East African Coastal Current associated with the El Niño-Southern Oscillation","authors":"Chenyu Zheng, Shaojun Zheng, Ming Feng, Lingling Xie, Lei Wang, Tianyu Zhang, Li Yan","doi":"10.1175/jcli-d-23-0563.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0563.1","url":null,"abstract":"Abstract The East African Coastal Current (EACC) is an important western boundary current of the tropical South Indian Ocean and plays an important role in the ocean circulation and biogeochemical cycles in the Indian Ocean. This study investigates the interannual variability of the EACC and its dynamical mechanisms. The result shows that the EACC has interannual variability associated with the El Niño-Southern Oscillation (ENSO) during 1993-2017. The EACC shows a significantly positive correlation with the Niño3.4 index with a correlation coefficient of 0.65, lagging the Niño3.4 index by 18 months. During the decaying phases of El Niño (La Niña) events, the negative (positive) sea level anomaly (SLA) propagates westward as upwelling (downwelling) Rossby waves from the southeast Indian Ocean to the southwest Indian Ocean, and then strengthens (weakens) the EACC due to zonal SLA gradient off the East African coast under geostrophic equilibrium. The SLA gradually weakens in the southeast Indian Ocean during its westward propagation but strengthens in the southwest Indian Ocean promoted by local wind stress curl anomaly. This study can improve our understanding of the relationship between the western boundary current of the tropical South Indian Ocean and large-scale ENSO air-sea processes, and is important for managing marine fisheries and ecosystems on the East African coast.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"6 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1175/jcli-d-23-0723.1
Qinghua Ding, Hailan Wang
Abstract This study aims to understand the underlying mechanism of large scale circulation control on atmospheric rivers (AR) and precipitation variability across the Contiguous United States (CONUS) in winter. The El Niño-Southern Oscillation (ENSO), known as a key driver of global circulation, has shown a modest impact on CONUS precipitation, prompting us to focus our attention on other climate drivers. Here, we find that barotropic instability over the exit region of the North Pacific subtropical jet stream plays a critical role in forming a downstream stationary Rossby wave train during winter (referred to as the West Mode). This wave pattern influences CONUS precipitation by affecting AR activity and explains approximately 50% of rainfall changes in the Western US, as well as numerous extreme wet and drought years along the West Coast, such as the wet winter in 2022/23. Over the past eight decades, the West Mode exhibited limited sensitivity to both Sea Surface Temperature (SST) and increasing anthropogenic forcing and was more influential in shaping interannual and interdecadal CONUS precipitation variability than ENSO. This result may explain why ENSO alone can only account for a limited portion of CONUS precipitation variability, thereby imposing an inherent constraint on the precision of seasonal predictions of CONUS precipitation made by climate models. Due to the significance of the West Mode in governing precipitation variability over the Western US, winter precipitation in that region may possess some resilience to the effects of global warming in the coming decades, as supported by large ensemble simulations driven by projected radiative forcing.
{"title":"Influences of large scale circulation and atmospheric rivers on US winter precipitation beyond ENSO","authors":"Qinghua Ding, Hailan Wang","doi":"10.1175/jcli-d-23-0723.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0723.1","url":null,"abstract":"Abstract This study aims to understand the underlying mechanism of large scale circulation control on atmospheric rivers (AR) and precipitation variability across the Contiguous United States (CONUS) in winter. The El Niño-Southern Oscillation (ENSO), known as a key driver of global circulation, has shown a modest impact on CONUS precipitation, prompting us to focus our attention on other climate drivers. Here, we find that barotropic instability over the exit region of the North Pacific subtropical jet stream plays a critical role in forming a downstream stationary Rossby wave train during winter (referred to as the West Mode). This wave pattern influences CONUS precipitation by affecting AR activity and explains approximately 50% of rainfall changes in the Western US, as well as numerous extreme wet and drought years along the West Coast, such as the wet winter in 2022/23. Over the past eight decades, the West Mode exhibited limited sensitivity to both Sea Surface Temperature (SST) and increasing anthropogenic forcing and was more influential in shaping interannual and interdecadal CONUS precipitation variability than ENSO. This result may explain why ENSO alone can only account for a limited portion of CONUS precipitation variability, thereby imposing an inherent constraint on the precision of seasonal predictions of CONUS precipitation made by climate models. Due to the significance of the West Mode in governing precipitation variability over the Western US, winter precipitation in that region may possess some resilience to the effects of global warming in the coming decades, as supported by large ensemble simulations driven by projected radiative forcing.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"12 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504456","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1175/jcli-d-23-0396.1
Josep Bonsoms, Marc Oliva, Juan I. López-Moreno, Xavier Fettweis
Abstract The Greenland Ice Sheet (GrIS) meltwater runoff has increased considerably since the 1990s, leading to implications for the ice sheet mass balance and ecosystem dynamics in ice-free areas. Extreme weather events will likely continue to occur in the coming decades. Therefore, a more thorough understanding of the spatiotemporal patterns of extreme melting events is of interest. This study aims to analyze the evolution of extreme melting events acrossthe GrIS and determine the climatic factors that drive them. Specifically, we have analyzed extreme melting events (90th percentile) across the GrIS from 1950 to 2022 and examined their links to the surface energy balance (SEB) and large-scale atmospheric circulation. Extreme melting days account for approximately 35-40% of the total accumulated melting per season. We found that extreme melting frequency, intensity, and contribution to the total accumulated June, July and August (summer) melting show a statistically significant upward trend at a 95% confidence level. The largest trends are detected across the northern GrIS. The trends are independent of the extreme melting percentile rank (90th, 97th, or 99th) analyzed, and are consistent with average melting trends that exhibit an increase of similar magnitude and spatial configuration. Radiation plays a dominant role in controlling the SEB during extreme melting days. The increase in extreme melting frequency and intensity is driven by the increase of anticyclonic weather types during summer and more energy available for melting. Our results help to enhance the understanding of extreme events in the Arctic.
{"title":"Rising extreme meltwater trends in Greenland ice sheet (1950 – 2022): surface energy balance and large-scale circulation changes","authors":"Josep Bonsoms, Marc Oliva, Juan I. López-Moreno, Xavier Fettweis","doi":"10.1175/jcli-d-23-0396.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0396.1","url":null,"abstract":"Abstract The Greenland Ice Sheet (GrIS) meltwater runoff has increased considerably since the 1990s, leading to implications for the ice sheet mass balance and ecosystem dynamics in ice-free areas. Extreme weather events will likely continue to occur in the coming decades. Therefore, a more thorough understanding of the spatiotemporal patterns of extreme melting events is of interest. This study aims to analyze the evolution of extreme melting events acrossthe GrIS and determine the climatic factors that drive them. Specifically, we have analyzed extreme melting events (90th percentile) across the GrIS from 1950 to 2022 and examined their links to the surface energy balance (SEB) and large-scale atmospheric circulation. Extreme melting days account for approximately 35-40% of the total accumulated melting per season. We found that extreme melting frequency, intensity, and contribution to the total accumulated June, July and August (summer) melting show a statistically significant upward trend at a 95% confidence level. The largest trends are detected across the northern GrIS. The trends are independent of the extreme melting percentile rank (90th, 97th, or 99th) analyzed, and are consistent with average melting trends that exhibit an increase of similar magnitude and spatial configuration. Radiation plays a dominant role in controlling the SEB during extreme melting days. The increase in extreme melting frequency and intensity is driven by the increase of anticyclonic weather types during summer and more energy available for melting. Our results help to enhance the understanding of extreme events in the Arctic.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"159 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504457","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The summer atmospheric heat source (AHS) over the Tibetan Plateau (TP) induces meridional circulations in TP and its surrounding areas. Previous studies mainly focused on the monsoon circulation on the south side of TP, while the formation and maintenance mechanisms of meridional circulation on its north side remain unclear. This study compared three calculation methods of the AHS, analyzed the spatial–temporal variability of the summer AHS over the TP, and discussed its influence on the interannual variability of meridional circulation on the north side of the TP based on the two-dimensional decomposition method of atmospheric circulation and sensitivity experiments. The results indicate that in the positive AHS anomalies years, the diabatic heating of condensation latent release in southeastern TP could motivate anomalous ascending motion. Simultaneously, the increased meridional temperature gradient between the mid- and high latitudes of East Asia leads to an enhanced southward westerly jet. In this context, the region on the north side of TP, located on the north side of the westerly jet entrance, is affected by negative anomalous relative vorticity advection, prevailing anomalous descending motion, which makes the descending branch of meridional circulation significantly presented. Unlike previous studies that considered the descending branch of meridional circulation as the compensation for upward flow, the results of the linear baroclinic model (LBM) verify that the descending branch is mainly influenced by the vorticity advection related to regional scale variability of the westerly jet. This study reveals the physical mechanism of meridional circulation on the north side of TP, which offers valuable implications for seasonal forecasting in TP and Northwest China.
{"title":"Impact of the Summer Atmospheric Heat Source over the Tibetan Plateau on Interannual Variability of Meridional Circulation on the North Side of the Tibetan Plateau","authors":"Hongyu Luo, Haipeng Yu, Zeyong Hu, Jie Zhou, Bofei Zhang, Yaoxian Yang, Shanling Cheng, Yongqi Gong, Yu Ren","doi":"10.1175/jcli-d-23-0599.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0599.1","url":null,"abstract":"Abstract The summer atmospheric heat source (AHS) over the Tibetan Plateau (TP) induces meridional circulations in TP and its surrounding areas. Previous studies mainly focused on the monsoon circulation on the south side of TP, while the formation and maintenance mechanisms of meridional circulation on its north side remain unclear. This study compared three calculation methods of the AHS, analyzed the spatial–temporal variability of the summer AHS over the TP, and discussed its influence on the interannual variability of meridional circulation on the north side of the TP based on the two-dimensional decomposition method of atmospheric circulation and sensitivity experiments. The results indicate that in the positive AHS anomalies years, the diabatic heating of condensation latent release in southeastern TP could motivate anomalous ascending motion. Simultaneously, the increased meridional temperature gradient between the mid- and high latitudes of East Asia leads to an enhanced southward westerly jet. In this context, the region on the north side of TP, located on the north side of the westerly jet entrance, is affected by negative anomalous relative vorticity advection, prevailing anomalous descending motion, which makes the descending branch of meridional circulation significantly presented. Unlike previous studies that considered the descending branch of meridional circulation as the compensation for upward flow, the results of the linear baroclinic model (LBM) verify that the descending branch is mainly influenced by the vorticity advection related to regional scale variability of the westerly jet. This study reveals the physical mechanism of meridional circulation on the north side of TP, which offers valuable implications for seasonal forecasting in TP and Northwest China.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"29 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The poleward migration of tropical cyclone (TC) activity in recent years has been linked to the expansion of the Hadley circulation (HC). Here, we investigate the impact of the winter regional HC over the western Pacific (WPHC) on the frequency of following summer landfalling TC (LTC) in China. Results show that interannual variation of the LTC frequency has a very close connection with the northern WPHC edge (WPHCE). After removing the El Niño–Southern Oscillation signal, there still exists a significant correlation between them. When the winter WPHCE shifts poleward, the associated lower-level southwesterly (easterly) wind anomalies over the subtropical western Pacific (tropical central-eastern Pacific) induce sea surface temperature (SST) warming (cooling) anomalies therein via suppressing (enhancing) upward surface heat flux. In turn, the SST warming (cooling) excites an anomalous cyclonic (anticyclonic) circulation to its west via a Rossby wave response, thus maintaining the southwesterly (easterly) wind anomalies. In addition, the negative rainfall anomalies over the tropical central-eastern Pacific induced by negative SST anomalies can stimulate an anomalous intensive Walker circulation with anomalous upward motion around the tropical western Pacific. Through this positive air–sea interaction, the winter WPHCE signal would be preserved in the ocean and maintained to the succeeding summer, then favoring LTC genesis landward by decreasing the vertical wind shear and increasing the low-level vorticity and midlevel humidity. Meanwhile, anomalous midtropospheric easterly winds over the subtropics are favorable for steering more LTCs toward China’s coast. This study suggests that the winter WPHCE variation is a potential predictor for the prediction of the following summer LTC activity over China. Significance Statement Tropical cyclone (TC) is one of the most catastrophic high-impact weather events, which may cause great casualties and severe property losses over the coastal areas, particularly when it makes landfall. Previous research studies have related the poleward migration trend of TC locations to the Hadley circulation (HC) expansion. Compared to the long-term trend, the magnitude of the year-to-year change of the HC edge (HCE) is even larger, leading to a stronger impact on the TC activity. A recent study has suggested that the northern HCE over the western Pacific (WPHCE) in boreal winter exhibits a notable interannual variability. In this study, we reveal that the wintertime WPHCE has a very close connection with the landfalling TC (LTC) frequency over China in the following summer. After removing the El Niño–Southern Oscillation (ENSO) signal, there still exists a significant positive correlation between them. Observational evidence and numerical model experiments consistently confirm that this time-lagged association is attributable to the air–sea interaction processes in the tropical Pacific. Thus, the results of this stud
{"title":"Impact of the Winter Regional Hadley Circulation over Western Pacific on the Frequency of Following Summer Tropical Cyclone Landfalling in China","authors":"Ruping Huang, Shangfeng Chen, Wen Chen, Renguang Wu, Zhibiao Wang, Peng Hu, Liang Wu, Lei Wang, Jingliang Huangfu","doi":"10.1175/jcli-d-23-0610.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0610.1","url":null,"abstract":"Abstract The poleward migration of tropical cyclone (TC) activity in recent years has been linked to the expansion of the Hadley circulation (HC). Here, we investigate the impact of the winter regional HC over the western Pacific (WPHC) on the frequency of following summer landfalling TC (LTC) in China. Results show that interannual variation of the LTC frequency has a very close connection with the northern WPHC edge (WPHCE). After removing the El Niño–Southern Oscillation signal, there still exists a significant correlation between them. When the winter WPHCE shifts poleward, the associated lower-level southwesterly (easterly) wind anomalies over the subtropical western Pacific (tropical central-eastern Pacific) induce sea surface temperature (SST) warming (cooling) anomalies therein via suppressing (enhancing) upward surface heat flux. In turn, the SST warming (cooling) excites an anomalous cyclonic (anticyclonic) circulation to its west via a Rossby wave response, thus maintaining the southwesterly (easterly) wind anomalies. In addition, the negative rainfall anomalies over the tropical central-eastern Pacific induced by negative SST anomalies can stimulate an anomalous intensive Walker circulation with anomalous upward motion around the tropical western Pacific. Through this positive air–sea interaction, the winter WPHCE signal would be preserved in the ocean and maintained to the succeeding summer, then favoring LTC genesis landward by decreasing the vertical wind shear and increasing the low-level vorticity and midlevel humidity. Meanwhile, anomalous midtropospheric easterly winds over the subtropics are favorable for steering more LTCs toward China’s coast. This study suggests that the winter WPHCE variation is a potential predictor for the prediction of the following summer LTC activity over China. Significance Statement Tropical cyclone (TC) is one of the most catastrophic high-impact weather events, which may cause great casualties and severe property losses over the coastal areas, particularly when it makes landfall. Previous research studies have related the poleward migration trend of TC locations to the Hadley circulation (HC) expansion. Compared to the long-term trend, the magnitude of the year-to-year change of the HC edge (HCE) is even larger, leading to a stronger impact on the TC activity. A recent study has suggested that the northern HCE over the western Pacific (WPHCE) in boreal winter exhibits a notable interannual variability. In this study, we reveal that the wintertime WPHCE has a very close connection with the landfalling TC (LTC) frequency over China in the following summer. After removing the El Niño–Southern Oscillation (ENSO) signal, there still exists a significant positive correlation between them. Observational evidence and numerical model experiments consistently confirm that this time-lagged association is attributable to the air–sea interaction processes in the tropical Pacific. Thus, the results of this stud","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"5 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504459","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-04DOI: 10.1175/jcli-d-23-0654.1
Yifei Fan, Duo Chan, Pengfei Zhang, Laifang Li
Abstract Despite global warming, sea surface temperature (SST) in the subpolar North Atlantic has decreased since the 1900s. This local cooling, known as the North Atlantic cold blob (North Atlantic cold blob), signifies a unique role of the subpolar North Atlantic in uptaking heat and hence impacts downstream weather and climate. However, a lack of observational records and its constraints on climate models leave the North Atlantic cold blob formation mechanism inconclusive. Using simulations from the Coupled Model Intercomparison Project Phase 6, we assess the primary processes driving the North Atlantic cold blob within individual models and the consistency of mechanisms across models. We show that 11 out of 32 models, which we call “Cold Bold” models, simulate subpolar North Atlantic cooling over 1900–2014. Further analyzing the heat budget of subpolar North Atlantic SST shows that models have distinct mechanisms of cold blob formation. Whereas four out of the 11 Cold Blob models indicate decreased Oceanic Heat Transport Convergence (OHTC) as the key mechanism, another four models suggest changes in radiative processes making predominant contributions. The contribution of OHTC and radiative processes are comparable in the remaining three models. Such a model spread in the mechanism of cold blob formation may be associated with distinct base-state Atlantic Meridional Overturning Circulation (AMOC) strength, which explains about 39% of the inter-model spread in the contribution of OHTC to the simulated cold blob. Models with a stronger base-state AMOC suggest a greater role of OHTC, whereas those with a weaker base-state AMOC indicate radiative processes are more responsible. This model discrepancy suggests that the cold blob formation mechanism diagnosed from single models should be interpreted with caution.
{"title":"Disagreement on the North Atlantic Cold Blob Formation Mechanisms among Climate Models","authors":"Yifei Fan, Duo Chan, Pengfei Zhang, Laifang Li","doi":"10.1175/jcli-d-23-0654.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0654.1","url":null,"abstract":"Abstract Despite global warming, sea surface temperature (SST) in the subpolar North Atlantic has decreased since the 1900s. This local cooling, known as the North Atlantic cold blob (North Atlantic cold blob), signifies a unique role of the subpolar North Atlantic in uptaking heat and hence impacts downstream weather and climate. However, a lack of observational records and its constraints on climate models leave the North Atlantic cold blob formation mechanism inconclusive. Using simulations from the Coupled Model Intercomparison Project Phase 6, we assess the primary processes driving the North Atlantic cold blob within individual models and the consistency of mechanisms across models. We show that 11 out of 32 models, which we call “Cold Bold” models, simulate subpolar North Atlantic cooling over 1900–2014. Further analyzing the heat budget of subpolar North Atlantic SST shows that models have distinct mechanisms of cold blob formation. Whereas four out of the 11 Cold Blob models indicate decreased Oceanic Heat Transport Convergence (OHTC) as the key mechanism, another four models suggest changes in radiative processes making predominant contributions. The contribution of OHTC and radiative processes are comparable in the remaining three models. Such a model spread in the mechanism of cold blob formation may be associated with distinct base-state Atlantic Meridional Overturning Circulation (AMOC) strength, which explains about 39% of the inter-model spread in the contribution of OHTC to the simulated cold blob. Models with a stronger base-state AMOC suggest a greater role of OHTC, whereas those with a weaker base-state AMOC indicate radiative processes are more responsible. This model discrepancy suggests that the cold blob formation mechanism diagnosed from single models should be interpreted with caution.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"25 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141259335","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract The precipitation changes in arid and semi-arid Central Asia have great impacts on the local fragile ecosystem. The summer precipitation in Central Asia shows obvious interannual variations, but the corresponding crucial moisture transporting processes remain unclear. Therefore, this study employs the Lagrangian model FLEXPART to achieve this goal. Results show that the moisture of climatological summer precipitation in Central Asia is mainly from the local regions, the surrounding Western and Northern Eurasian regions. The contribution of local evaporation from Western Central Asia is about two times of that from Eastern Central Asia. At the interannual timescale, the moisture variations are mainly influenced by the local regions and the Western Eurasia, while the local evaporation is mainly from western Central Asia. Totally, the Eurasian evaporation plays a dominant role in the interannual variations of Central Asian summer precipitation by contributing more than 90% of the total moisture. The moisture transports associated with Central Asian summer precipitation interannual variations are impacted by the anomalous cyclones over western and northeastern part of Central Asia during the wet years, which enhance the moisture convergence and hence increase the summer precipitation in Central Asia. The anomalous cyclone over western part of Central Asia is correlated with the changes in intensity of Eurasian Summer Subtropical Westerly Jet (ESSWJ), while the anomalous cyclone over northeastern part of Central Asia is correlated with both ESSWJ and the British–Baikal Corridor pattern teleconnection in association with the polar front jet.
{"title":"Dominant role of Eurasian evaporation on the moisture sources of the interannual variations in Central Asian summer precipitation","authors":"Dongdong Peng, Tianjun Zhou, Xin Huang, Chao He, Lixia Zhang","doi":"10.1175/jcli-d-23-0515.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0515.1","url":null,"abstract":"Abstract The precipitation changes in arid and semi-arid Central Asia have great impacts on the local fragile ecosystem. The summer precipitation in Central Asia shows obvious interannual variations, but the corresponding crucial moisture transporting processes remain unclear. Therefore, this study employs the Lagrangian model FLEXPART to achieve this goal. Results show that the moisture of climatological summer precipitation in Central Asia is mainly from the local regions, the surrounding Western and Northern Eurasian regions. The contribution of local evaporation from Western Central Asia is about two times of that from Eastern Central Asia. At the interannual timescale, the moisture variations are mainly influenced by the local regions and the Western Eurasia, while the local evaporation is mainly from western Central Asia. Totally, the Eurasian evaporation plays a dominant role in the interannual variations of Central Asian summer precipitation by contributing more than 90% of the total moisture. The moisture transports associated with Central Asian summer precipitation interannual variations are impacted by the anomalous cyclones over western and northeastern part of Central Asia during the wet years, which enhance the moisture convergence and hence increase the summer precipitation in Central Asia. The anomalous cyclone over western part of Central Asia is correlated with the changes in intensity of Eurasian Summer Subtropical Westerly Jet (ESSWJ), while the anomalous cyclone over northeastern part of Central Asia is correlated with both ESSWJ and the British–Baikal Corridor pattern teleconnection in association with the polar front jet.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"21 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141259330","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-04DOI: 10.1175/jcli-d-23-0475.1
Dazhi Xi, Ning Lin, Renzhi Jing, Patrick Harr, Michael Oppenheimer
Abstract North Atlantic tropical cyclone (TC) activity under a high-emission scenario is projected using a statistical synthetic storm model coupled with nine Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models. The ensemble projection shows that the annual frequency of TCs generated in the basin will decrease from 15.91 (1979-2014) to 12.16 (2075-2100), and TC activity will shift poleward and coast-ward. The mean of lifetime maximum intensity will increase from 66.50 knots to 75.04 knots. Large discrepancies in TC frequency and intensity projections are found among the nine CMIP6 climate models. The uncertainty in the projection of wind shear is the leading cause of the discrepancies in the TC climatology projection, dominating the uncertainties in the projection of thermodynamic parameters such as potential intensity and saturation deficit. The uncertainty in the projection of wind shear may be related to the different projections of horizontal gradient of vertically integrated temperature in the climate models, which can be induced by different parameterizations of physical processes including surface process, sea ice, and cloud feedback. Informed by the uncertainty analysis, a surrogate model is developed to provide the first-order estimation of TC activity in climate models based on large-scale environmental features.
{"title":"Uncertainties Inherent from Large-Scale Climate Projections in the Statistical Downscaling Projection of North Atlantic Tropical Cyclone Activity","authors":"Dazhi Xi, Ning Lin, Renzhi Jing, Patrick Harr, Michael Oppenheimer","doi":"10.1175/jcli-d-23-0475.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0475.1","url":null,"abstract":"Abstract North Atlantic tropical cyclone (TC) activity under a high-emission scenario is projected using a statistical synthetic storm model coupled with nine Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models. The ensemble projection shows that the annual frequency of TCs generated in the basin will decrease from 15.91 (1979-2014) to 12.16 (2075-2100), and TC activity will shift poleward and coast-ward. The mean of lifetime maximum intensity will increase from 66.50 knots to 75.04 knots. Large discrepancies in TC frequency and intensity projections are found among the nine CMIP6 climate models. The uncertainty in the projection of wind shear is the leading cause of the discrepancies in the TC climatology projection, dominating the uncertainties in the projection of thermodynamic parameters such as potential intensity and saturation deficit. The uncertainty in the projection of wind shear may be related to the different projections of horizontal gradient of vertically integrated temperature in the climate models, which can be induced by different parameterizations of physical processes including surface process, sea ice, and cloud feedback. Informed by the uncertainty analysis, a surrogate model is developed to provide the first-order estimation of TC activity in climate models based on large-scale environmental features.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"30 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141259331","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract This study investigates the interannual variability of Marine Heatwaves (MHWs) in the Bay of Bengal (BOB) associated with the Indian Ocean Dipole (IOD) from 1982 to 2021. The results revealed a significant positive correlation at the 95% confidence level between the IOD and MHW days in the central bay at the peak of the IOD in autumn. During positive IOD (pIOD) events, the central bay experienced more MHW days in autumn, with an average increase of 7.4 days. The increased MHW days in the central bay could be primarily attributed to the enhanced net heat flux (TQ), which is 9.7 times the contribution of ocean dynamic processes (horizontal advection + entrainment). The reduced latent heat flux loss and enhanced shortwave radiation due to the anomalous atmospheric low-level high pressure associated with the pIOD account for 63% and 50%, respectively, of the anomalous enhanced TQ, while the longwave radiation and sensible heat flux make smaller contributions of −20% and 7%. In addition, thermocline deepening in the southwestern bay, caused by this anomalous high pressure and associated anticyclonic wind anomalies, favors the occurrence and persistence of MHWs by reducing the mixed-layer cooling rate. In addition to the influence of the IOD, the El Niño-Southern Oscillation mainly affects MHWs from winter to the following summer, which confirms the result of a previous study.
{"title":"An increase in autumn marine heatwaves caused by the Indian Ocean Dipole in the Bay of Bengal","authors":"Kunming Liang, Yun Qiu, Xinyu Lin, Wenshu Lin, Xutao Ni, Yijun He","doi":"10.1175/jcli-d-23-0541.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0541.1","url":null,"abstract":"Abstract This study investigates the interannual variability of Marine Heatwaves (MHWs) in the Bay of Bengal (BOB) associated with the Indian Ocean Dipole (IOD) from 1982 to 2021. The results revealed a significant positive correlation at the 95% confidence level between the IOD and MHW days in the central bay at the peak of the IOD in autumn. During positive IOD (pIOD) events, the central bay experienced more MHW days in autumn, with an average increase of 7.4 days. The increased MHW days in the central bay could be primarily attributed to the enhanced net heat flux (TQ), which is 9.7 times the contribution of ocean dynamic processes (horizontal advection + entrainment). The reduced latent heat flux loss and enhanced shortwave radiation due to the anomalous atmospheric low-level high pressure associated with the pIOD account for 63% and 50%, respectively, of the anomalous enhanced TQ, while the longwave radiation and sensible heat flux make smaller contributions of −20% and 7%. In addition, thermocline deepening in the southwestern bay, caused by this anomalous high pressure and associated anticyclonic wind anomalies, favors the occurrence and persistence of MHWs by reducing the mixed-layer cooling rate. In addition to the influence of the IOD, the El Niño-Southern Oscillation mainly affects MHWs from winter to the following summer, which confirms the result of a previous study.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"30 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141259202","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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