Pub Date : 2024-06-25DOI: 10.1175/jcli-d-23-0477.1
Kara Hartig, Eli Tziperman
Abstract In spite of the mean warming trend over the last few decades and its amplification in the Arctic, some studies have found no robust decline or even a slight increase in wintertime cold air outbreaks over North America. But fossil evidence from warmer paleoclimate periods indicates that the interior of North America never dropped below freezing even in the depths of winter, which implies that the maintenance of cold air outbreaks is unlikely to continue indefinitely with future warming. To identify key mechanisms affecting cold air outbreaks and understand how and why they will change in a warmer climate, we examine the development of North American cold air outbreaks in both a pre-industrial and a roughly 8×CO2 scenario using the Community Earth System Model, CESM2. We observe a sharp drop-off in the wintertime temperature distribution at the freezing temperature, suppressing below-freezing conditions in the warmer climate and above-freezing conditions in the pre-industrial case. The disappearance of Arctic sea ice and loss of the near-surface temperature inversion dramatically decrease the availability of below-freezing air in source regions. Using an air parcel trajectory analysis, we demonstrate a remarkable similarity in both the dynamics and diabatic effects acting on cold air masses in the two climate scenarios. Diabatic temperature evolution along cold air outbreak trajectories is a competition between cooling from longwave radiation and warming from boundary layer mixing. Surprisingly, while both diabatic effects strengthen in the warmer climate, the balance remains the same, with a net cooling of about −6 K over 10 days.
{"title":"Suppression of cold air outbreaks over the interior of North America in a warmer climate","authors":"Kara Hartig, Eli Tziperman","doi":"10.1175/jcli-d-23-0477.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0477.1","url":null,"abstract":"Abstract In spite of the mean warming trend over the last few decades and its amplification in the Arctic, some studies have found no robust decline or even a slight increase in wintertime cold air outbreaks over North America. But fossil evidence from warmer paleoclimate periods indicates that the interior of North America never dropped below freezing even in the depths of winter, which implies that the maintenance of cold air outbreaks is unlikely to continue indefinitely with future warming. To identify key mechanisms affecting cold air outbreaks and understand how and why they will change in a warmer climate, we examine the development of North American cold air outbreaks in both a pre-industrial and a roughly 8×CO2 scenario using the Community Earth System Model, CESM2. We observe a sharp drop-off in the wintertime temperature distribution at the freezing temperature, suppressing below-freezing conditions in the warmer climate and above-freezing conditions in the pre-industrial case. The disappearance of Arctic sea ice and loss of the near-surface temperature inversion dramatically decrease the availability of below-freezing air in source regions. Using an air parcel trajectory analysis, we demonstrate a remarkable similarity in both the dynamics and diabatic effects acting on cold air masses in the two climate scenarios. Diabatic temperature evolution along cold air outbreak trajectories is a competition between cooling from longwave radiation and warming from boundary layer mixing. Surprisingly, while both diabatic effects strengthen in the warmer climate, the balance remains the same, with a net cooling of about −6 K over 10 days.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504528","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 : 2024-06-24DOI: 10.1175/jcli-d-23-0644.1
Hanzhao Yu, Tianjun Zhou, Linqiang He
Abstract The zonal wavenumber-5 circumglobal teleconnection pattern (CGT) is one of the most critical atmospheric teleconnection patterns during boreal summer over the Northern Hemisphere (NH). CGT can exert significant climatic impact across NH including Europe, East Asia and North America but how reliable coupled climate models simulate the characteristics of CGT is poorly understood. Here, twenty coupled models with their respective versions in Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 are selected to evaluate their performance on CGT simulation. We find that while both CMIP5 and CMIP6 models are able to capture the basic features of CGT in multi-model mean (MMM), there are large inter-model discrepancies in the simulation of CGT pattern among CMIP5 and CMIP6 models. High-skill models exhibit strong action center over west-central Asia, coinciding with the pattern derived from reanalysis, while the corresponding action center in low-skill models are weaker. Further analyses demonstrate that high-skill models are capable of simulating more realistic Indian Summer Monsoon (ISM) precipitation anomalies related to CGT. The resultant anomalous upper-tropospheric divergence over west-central Asia, acting as a Rossby wave source, can therefore excite the above-mentioned action center. This high- and low-skill model difference on CGT-ISM relationship is consistent in both CMIP5 and CMIP6. It is also found that high-skill models tend to simulate more realistic CGT-ENSO relationship. The relationship between simulation skills of CGT-ENSO correlation and CGT spatial pattern is attributed to the remote impact of ENSO on CGT wavetrain through affecting ISM precipitation anomalies.
{"title":"Indian summer monsoon precipitation dominates the reproduction of Circumglobal teleconnection pattern: A comparison of CMIP5 and CMIP6 models","authors":"Hanzhao Yu, Tianjun Zhou, Linqiang He","doi":"10.1175/jcli-d-23-0644.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0644.1","url":null,"abstract":"Abstract The zonal wavenumber-5 circumglobal teleconnection pattern (CGT) is one of the most critical atmospheric teleconnection patterns during boreal summer over the Northern Hemisphere (NH). CGT can exert significant climatic impact across NH including Europe, East Asia and North America but how reliable coupled climate models simulate the characteristics of CGT is poorly understood. Here, twenty coupled models with their respective versions in Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6 are selected to evaluate their performance on CGT simulation. We find that while both CMIP5 and CMIP6 models are able to capture the basic features of CGT in multi-model mean (MMM), there are large inter-model discrepancies in the simulation of CGT pattern among CMIP5 and CMIP6 models. High-skill models exhibit strong action center over west-central Asia, coinciding with the pattern derived from reanalysis, while the corresponding action center in low-skill models are weaker. Further analyses demonstrate that high-skill models are capable of simulating more realistic Indian Summer Monsoon (ISM) precipitation anomalies related to CGT. The resultant anomalous upper-tropospheric divergence over west-central Asia, acting as a Rossby wave source, can therefore excite the above-mentioned action center. This high- and low-skill model difference on CGT-ISM relationship is consistent in both CMIP5 and CMIP6. It is also found that high-skill models tend to simulate more realistic CGT-ENSO relationship. The relationship between simulation skills of CGT-ENSO correlation and CGT spatial pattern is attributed to the remote impact of ENSO on CGT wavetrain through affecting ISM precipitation anomalies.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504453","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 : 2024-06-24DOI: 10.1175/jcli-d-23-0533.1
Sining Ling, Riyu Lu
Abstract The climatological western North Pacific summer monsoon onset, so called convection jump, occurs around 41th pentad, corresponding to an abrupt northeastward extension of strong convection. This study investigates the process of convection jump from a local perspective. Composite analyses are performed based on the onset dates that are identified in individual years. The results show that the convective inhibition (CIN) decreases dramatically around the onset dates, while the convective available potential energy (CAPE) reaches its maximum long before the onset, suggesting that the CIN, rather than CAPE, plays a dominant role in triggering convection. Further analysis indicates that the reduction of CIN is induced by the increased low-lever relative humidity, which is the result of enhanced water vapor convergence. The moisture transportation is primarily contributed by the wind transfer from easterlies to southeasterlies or southerlies along the southern boundary of convection jump region, in accordance with the monsoon trough establishment. The present observational results may be used to evaluate climate models in simulating stepwise evolution of summer monsoon.
{"title":"Diagnosis of atmospheric processes from a local perspective for the western North Pacific summer monsoon onset","authors":"Sining Ling, Riyu Lu","doi":"10.1175/jcli-d-23-0533.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0533.1","url":null,"abstract":"Abstract The climatological western North Pacific summer monsoon onset, so called convection jump, occurs around 41th pentad, corresponding to an abrupt northeastward extension of strong convection. This study investigates the process of convection jump from a local perspective. Composite analyses are performed based on the onset dates that are identified in individual years. The results show that the convective inhibition (CIN) decreases dramatically around the onset dates, while the convective available potential energy (CAPE) reaches its maximum long before the onset, suggesting that the CIN, rather than CAPE, plays a dominant role in triggering convection. Further analysis indicates that the reduction of CIN is induced by the increased low-lever relative humidity, which is the result of enhanced water vapor convergence. The moisture transportation is primarily contributed by the wind transfer from easterlies to southeasterlies or southerlies along the southern boundary of convection jump region, in accordance with the monsoon trough establishment. The present observational results may be used to evaluate climate models in simulating stepwise evolution of summer monsoon.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504530","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 : 2024-06-21DOI: 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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
Pub Date : 2024-06-14DOI: 10.1175/jcli-d-23-0555.1
Hongqing Yang, Ke Fan
The subseasonal variability of winter air temperature in China during 2021/22 underwent significant changes, showing warm, warm, and cold anomalies during 2–23 December 2021 (P1), 1–27 January 2022 (P2), and 28 January–24 February 2022 (P3). The strong (weak) zonal circulation over East Asia led to positive (negative) surface air temperature anomalies (SATA) during P1 and P2 (P3). The position of the Siberian high affected the distribution of the warmest center of SATA over northeastern and northwestern China in P1 and P2, respectively. Further investigations indicated that intraseasonal components (10–90 days) primarily drove the warm-to-cold transition in China during P2 and P3, contributing to 79.5% of the variance in SATA in winter 2021/22. Strong (weak) East Asian intraseasonal zonal circulations corresponded to positive (negative) meridional wind anomalies over China–Lake Baikal, affecting the guidance of cold air into China during P2 (P3). East Asian circulation alternations from P2 to P3 were associated with a shift in intraseasonal geopotential height anomalies over the North Atlantic region from positive to negative in the mid-to-high troposphere through the propagation of north and south branch wave trains. The reversal of the North Atlantic geopotential height anomalies between P2 and P3 was modulated by intraseasonal higher-latitude SST anomalies over the North Atlantic and the location of intraseasonal stratospheric polar vortex. Furthermore, the intensified south branch wave train from the Indian Peninsula to China in the mid-to-high troposphere was associated with active convection over the tropical western Indian Ocean during P3. These processes could be verified by using the Linear Baroclinic Model.
{"title":"The Causes of Intraseasonal Alternating Warm and Cold Variations over China in Winter 2021/22","authors":"Hongqing Yang, Ke Fan","doi":"10.1175/jcli-d-23-0555.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0555.1","url":null,"abstract":"\u0000The subseasonal variability of winter air temperature in China during 2021/22 underwent significant changes, showing warm, warm, and cold anomalies during 2–23 December 2021 (P1), 1–27 January 2022 (P2), and 28 January–24 February 2022 (P3). The strong (weak) zonal circulation over East Asia led to positive (negative) surface air temperature anomalies (SATA) during P1 and P2 (P3). The position of the Siberian high affected the distribution of the warmest center of SATA over northeastern and northwestern China in P1 and P2, respectively. Further investigations indicated that intraseasonal components (10–90 days) primarily drove the warm-to-cold transition in China during P2 and P3, contributing to 79.5% of the variance in SATA in winter 2021/22. Strong (weak) East Asian intraseasonal zonal circulations corresponded to positive (negative) meridional wind anomalies over China–Lake Baikal, affecting the guidance of cold air into China during P2 (P3). East Asian circulation alternations from P2 to P3 were associated with a shift in intraseasonal geopotential height anomalies over the North Atlantic region from positive to negative in the mid-to-high troposphere through the propagation of north and south branch wave trains. The reversal of the North Atlantic geopotential height anomalies between P2 and P3 was modulated by intraseasonal higher-latitude SST anomalies over the North Atlantic and the location of intraseasonal stratospheric polar vortex. Furthermore, the intensified south branch wave train from the Indian Peninsula to China in the mid-to-high troposphere was associated with active convection over the tropical western Indian Ocean during P3. These processes could be verified by using the Linear Baroclinic Model.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141338920","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":null,"pages":null},"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}
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