Pub Date : 2024-04-18DOI: 10.1175/jcli-d-23-0286.1
Teryn J. Mueller, Christina M. Patricola, Emily Bercos-Hickey
Abstract The El Niño–Southern Oscillation (ENSO) influences seasonal Atlantic tropical cyclone (TC) activity by impacting environmental conditions important for TC genesis. However, the influence of future climate change on the teleconnection between ENSO and Atlantic TCs is uncertain, as climate change is expected to impact both ENSO and the mean climate state. We used the Weather Research and Forecasting model on a tropical channel domain to simulate 5-member ensembles of Atlantic TC seasons in historical and future climates under different ENSO conditions. Experiments were forced with idealized sea-surface temperature configurations based on the Community Earth System Model (CESM) Large Ensemble representing: a monthly-varying climatology, Eastern Pacific El Niño, Central Pacific El Niño, and La Niña. The historical simulations produced fewer Atlantic TCs during Eastern Pacific El Niño compared to Central Pacific El Niño, consistent with observations and other modeling studies. For each ENSO state, the future simulations produced a similar teleconnection with Atlantic TCs as in the historical simulations. Specifically, La Niña continues to enhance Atlantic TC activity, and El Niño continues to suppress Atlantic TCs, with greater suppression during Eastern Pacific El Niño compared to Central Pacific El Niño. In addition, we found a decrease in Atlantic TC frequency in the future relative to historical regardless of ENSO state, which was associated with a future increase in northern tropical Atlantic vertical wind shear and a future decrease in the zonal tropical Pacific SST gradient, corresponding to a more El Niño-like mean climate state. Our results indicate that ENSO will remain useful for seasonal Atlantic TC prediction in the future.
{"title":"The Influence of ENSO Diversity on Future Atlantic Tropical Cyclone Activity","authors":"Teryn J. Mueller, Christina M. Patricola, Emily Bercos-Hickey","doi":"10.1175/jcli-d-23-0286.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0286.1","url":null,"abstract":"Abstract The El Niño–Southern Oscillation (ENSO) influences seasonal Atlantic tropical cyclone (TC) activity by impacting environmental conditions important for TC genesis. However, the influence of future climate change on the teleconnection between ENSO and Atlantic TCs is uncertain, as climate change is expected to impact both ENSO and the mean climate state. We used the Weather Research and Forecasting model on a tropical channel domain to simulate 5-member ensembles of Atlantic TC seasons in historical and future climates under different ENSO conditions. Experiments were forced with idealized sea-surface temperature configurations based on the Community Earth System Model (CESM) Large Ensemble representing: a monthly-varying climatology, Eastern Pacific El Niño, Central Pacific El Niño, and La Niña. The historical simulations produced fewer Atlantic TCs during Eastern Pacific El Niño compared to Central Pacific El Niño, consistent with observations and other modeling studies. For each ENSO state, the future simulations produced a similar teleconnection with Atlantic TCs as in the historical simulations. Specifically, La Niña continues to enhance Atlantic TC activity, and El Niño continues to suppress Atlantic TCs, with greater suppression during Eastern Pacific El Niño compared to Central Pacific El Niño. In addition, we found a decrease in Atlantic TC frequency in the future relative to historical regardless of ENSO state, which was associated with a future increase in northern tropical Atlantic vertical wind shear and a future decrease in the zonal tropical Pacific SST gradient, corresponding to a more El Niño-like mean climate state. Our results indicate that ENSO will remain useful for seasonal Atlantic TC prediction in the future.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"39 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140625416","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 : 2024-04-17DOI: 10.1175/jcli-d-23-0602.1
Matthew Patterson, Christopher O’Reilly, Jon Robson, Tim Woollings
Abstract The coupled nature of the ocean-atmosphere system frequently makes understanding the direction of causality difficult in ocean-atmosphere interactions. This study presents a method to decompose turbulent surface heat fluxes into a component which is directly forced by atmospheric circulation, and a residual which is assumed to be primarily ‘ocean-forced’. This method is applied to the North Atlantic in a 500-year pre-industrial control run using the Met Office’s HadGEM3-GC3.1-MM model. The method shows that atmospheric circulation dominates interannual to decadal heat flux variability in the Labrador Sea, in contrast to the Gulf Stream where the Ocean primarily drives the variability. An empirical orthogonal function analysis identifies several residual heat flux modes associated with variations in ocean circulation. The first of these modes is characterised by the ocean warming the atmosphere along the Gulf Stream and North Atlantic Current and the second by a dipole of cooling in the western subtropical North Atlantic and warming in the sub-polar North Atlantic. Lead-lag regression analysis suggests that atmospheric circulation anomalies in prior years partly drive the ocean heat flux modes, however there is no significant atmospheric circulation response in years following the peaks of the modes. Overall, the heat flux dynamical decomposition method provides a useful way to separate the effects of the ocean and atmosphere on heat flux and could be applied to other ocean basins and to either models or reanalysis datasets.
{"title":"Disentangling North Atlantic ocean-atmosphere coupling using circulation analogues","authors":"Matthew Patterson, Christopher O’Reilly, Jon Robson, Tim Woollings","doi":"10.1175/jcli-d-23-0602.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0602.1","url":null,"abstract":"Abstract The coupled nature of the ocean-atmosphere system frequently makes understanding the direction of causality difficult in ocean-atmosphere interactions. This study presents a method to decompose turbulent surface heat fluxes into a component which is directly forced by atmospheric circulation, and a residual which is assumed to be primarily ‘ocean-forced’. This method is applied to the North Atlantic in a 500-year pre-industrial control run using the Met Office’s HadGEM3-GC3.1-MM model. The method shows that atmospheric circulation dominates interannual to decadal heat flux variability in the Labrador Sea, in contrast to the Gulf Stream where the Ocean primarily drives the variability. An empirical orthogonal function analysis identifies several residual heat flux modes associated with variations in ocean circulation. The first of these modes is characterised by the ocean warming the atmosphere along the Gulf Stream and North Atlantic Current and the second by a dipole of cooling in the western subtropical North Atlantic and warming in the sub-polar North Atlantic. Lead-lag regression analysis suggests that atmospheric circulation anomalies in prior years partly drive the ocean heat flux modes, however there is no significant atmospheric circulation response in years following the peaks of the modes. Overall, the heat flux dynamical decomposition method provides a useful way to separate the effects of the ocean and atmosphere on heat flux and could be applied to other ocean basins and to either models or reanalysis datasets.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"56 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140608511","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 : 2024-04-15DOI: 10.1175/jcli-d-23-0450.1
Verónica Martín-Gómez, Belén Rodríguez-Fonseca, Irene Polo, Marta Martín-Rey
Abstract In the last decades, many efforts have been made to understand how different tropical oceanic basins are able to impact El Niño Southern Oscillation (ENSO). However, the collective connectivity among the tropical oceans and their associated influence on ENSO is less understood. Using a complex network methodology, the degree of collective connectivity among the tropical oceans is analyzed focusing on the detection of periods when the tropical basins collectively interact and Atlantic and Indian basins influence the equatorial Pacific sea surface temperatures (SST). The background state for the periods of strong collective connectivity is also investigated. Our results show a marked multidecadal variability in the tropical interbasin connection, with periods of stronger and weaker collective connectivity. These changes seem to be modulated by changes in the North Atlantic ocean mean state a decade in advance. In particular, strong connectivity occurs in periods with colder than average tropical north Atlantic surface ocean. Associated with this cooling an anomalous convergence of the vertical integral of total energy flux (VIEF) takes place over the tropical north-west Atlantic, associated with anomalous divergence of VIEF over the equatorial eastern Pacific. In turn, an anomalous zonal surface pressure gradient over the tropical Pacific weakens the trades over the western equatorial Pacific. Consequently, a shallower thermocline emerges over the western equatorial Pacific, which can enhance thermocline feedbacks, the triggering of ENSO events, and therefore, ENSO variability. By construction, our results put forward opposite conditions for periods of weak tropical basins connectivity. These results have important implications for seasonal to decadal predictions.
{"title":"Observed global mean state changes modulating the collective influence of the tropical Atlantic and Indian oceans on ENSO","authors":"Verónica Martín-Gómez, Belén Rodríguez-Fonseca, Irene Polo, Marta Martín-Rey","doi":"10.1175/jcli-d-23-0450.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0450.1","url":null,"abstract":"Abstract In the last decades, many efforts have been made to understand how different tropical oceanic basins are able to impact El Niño Southern Oscillation (ENSO). However, the collective connectivity among the tropical oceans and their associated influence on ENSO is less understood. Using a complex network methodology, the degree of collective connectivity among the tropical oceans is analyzed focusing on the detection of periods when the tropical basins collectively interact and Atlantic and Indian basins influence the equatorial Pacific sea surface temperatures (SST). The background state for the periods of strong collective connectivity is also investigated. Our results show a marked multidecadal variability in the tropical interbasin connection, with periods of stronger and weaker collective connectivity. These changes seem to be modulated by changes in the North Atlantic ocean mean state a decade in advance. In particular, strong connectivity occurs in periods with colder than average tropical north Atlantic surface ocean. Associated with this cooling an anomalous convergence of the vertical integral of total energy flux (VIEF) takes place over the tropical north-west Atlantic, associated with anomalous divergence of VIEF over the equatorial eastern Pacific. In turn, an anomalous zonal surface pressure gradient over the tropical Pacific weakens the trades over the western equatorial Pacific. Consequently, a shallower thermocline emerges over the western equatorial Pacific, which can enhance thermocline feedbacks, the triggering of ENSO events, and therefore, ENSO variability. By construction, our results put forward opposite conditions for periods of weak tropical basins connectivity. These results have important implications for seasonal to decadal predictions.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"50 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140571982","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 : 2024-04-15DOI: 10.1175/jcli-d-23-0606.1
Arthur Coquereau, Florian Sévellec, Thierry Huck, Joël J.-M. Hirschi, Antoine Hochet
Abstract As well as having an impact on the background state of the climate, global warming due to human activities could affect its natural oscillations and internal variability. In this study, we use four initial-condition ensembles from the CMIP6 framework to investigate the potential evolution of internal climate variability under different warming pathways for the 21st century. Our results suggest significant changes in natural climate variability, and point to two distinct regimes driving these changes. First, a decrease of internal variability of surface air temperature at high latitudes and all frequencies, associated with a poleward shift and the gradual disappearance of sea-ice edges, which we show to be an important component of internal variability. Second, an intensification of the interannual variability of surface air temperature and precipitation at low latitudes, which appears to be associated with the El Niño–Southern Oscillation (ENSO). This second regime is particularly alarming because it may contribute to making the climate more unstable and less predictable, with a significant impact on human societies and ecosystems.
{"title":"Anthropogenic changes of interannual-to-decadal climate variability in CMIP6 multi-ensemble simulations","authors":"Arthur Coquereau, Florian Sévellec, Thierry Huck, Joël J.-M. Hirschi, Antoine Hochet","doi":"10.1175/jcli-d-23-0606.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0606.1","url":null,"abstract":"Abstract As well as having an impact on the background state of the climate, global warming due to human activities could affect its natural oscillations and internal variability. In this study, we use four initial-condition ensembles from the CMIP6 framework to investigate the potential evolution of internal climate variability under different warming pathways for the 21st century. Our results suggest significant changes in natural climate variability, and point to two distinct regimes driving these changes. First, a decrease of internal variability of surface air temperature at high latitudes and all frequencies, associated with a poleward shift and the gradual disappearance of sea-ice edges, which we show to be an important component of internal variability. Second, an intensification of the interannual variability of surface air temperature and precipitation at low latitudes, which appears to be associated with the El Niño–Southern Oscillation (ENSO). This second regime is particularly alarming because it may contribute to making the climate more unstable and less predictable, with a significant impact on human societies and ecosystems.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"19 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140571993","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 : 2024-04-11DOI: 10.1175/jcli-d-23-0296.1
Tingting Zhu, Jin-Yi Yu
Abstract Utilizing a 2200-year CESM1 pre-industrial simulation, this study examines the influence of property distinctions between single-year (SY) and multi-year (MY) La Niñas on their respective impacts on winter surface air temperatures across mid-to-high latitude continents in the model, focusing on specific teleconnection mechanisms. Distinct impacts were identified in four continent sectors: North America, Europe, Western Siberia (W-Siberia), and Eastern Siberia (E-Siberia). The typical impacts of simulated SY La Niña events are featured with anomalous warming over Europe and W&E-Siberia and anomalous cooling over North America. Simulated MY La Niña events reduce the typical anomalous cooling over North America and the typical anomalous warming over W&E-Siberia but intensify the typical anomalous warming over Europe. The distinct impacts of simulated MY La Niñas are more prominent during their first winter than during the second winter, except over W-Siberia, where the distinct impact is more pronounced during the second winter. These overall distinct impacts in the CESM1 simulation can be attributed to the varying sensitivities of these continent sectors to the differences between MY and SY La Niñas in their intensity, location, and induced sea surface temperature anomalies in the Atlantic Ocean. These property differences were linked to the distinct climate impacts through the Pacific North America, North Atlantic Oscillation, Indian Ocean-induced wave train, and Tropical North Atlantic-induced wave train mechanisms. The modeling results are then validated against observations from 1900 to 2022 to identify disparities in the CESM1 simulation.
{"title":"Distinguishing Impacts on Winter Temperatures in Northern Mid-to-High Latitude Continents during Multi-year and Single-year La Niña Events: A Modeling Study","authors":"Tingting Zhu, Jin-Yi Yu","doi":"10.1175/jcli-d-23-0296.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0296.1","url":null,"abstract":"Abstract Utilizing a 2200-year CESM1 pre-industrial simulation, this study examines the influence of property distinctions between single-year (SY) and multi-year (MY) La Niñas on their respective impacts on winter surface air temperatures across mid-to-high latitude continents in the model, focusing on specific teleconnection mechanisms. Distinct impacts were identified in four continent sectors: North America, Europe, Western Siberia (W-Siberia), and Eastern Siberia (E-Siberia). The typical impacts of simulated SY La Niña events are featured with anomalous warming over Europe and W&E-Siberia and anomalous cooling over North America. Simulated MY La Niña events reduce the typical anomalous cooling over North America and the typical anomalous warming over W&E-Siberia but intensify the typical anomalous warming over Europe. The distinct impacts of simulated MY La Niñas are more prominent during their first winter than during the second winter, except over W-Siberia, where the distinct impact is more pronounced during the second winter. These overall distinct impacts in the CESM1 simulation can be attributed to the varying sensitivities of these continent sectors to the differences between MY and SY La Niñas in their intensity, location, and induced sea surface temperature anomalies in the Atlantic Ocean. These property differences were linked to the distinct climate impacts through the Pacific North America, North Atlantic Oscillation, Indian Ocean-induced wave train, and Tropical North Atlantic-induced wave train mechanisms. The modeling results are then validated against observations from 1900 to 2022 to identify disparities in the CESM1 simulation.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"4 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140572032","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 : 2024-04-11DOI: 10.1175/jcli-d-23-0622.1
Ying Dai, Peter Hitchcock, Isla R. Simpson
Abstract This study evaluates the representation of the composite-mean surface response to Sudden Stratospheric Warmings (SSWs) in 28 CMIP6 models. Most models can reproduce the magnitude of the SLP response over the Arctic, although the simulated Arctic SLP response varies from model to model. Regarding the structure of the SLP response, most models exhibit a basin-symmetric negative NAM-like response with a cyclonic Pacific SLP response, whereas the reanalysis shows a highly basin-asymmetric negative NAO-like response without a robust Pacific center. We then explore the drivers of these model biases and spread by applying a multiple linear regression. The results show that the polar-cap temperature anomalies at 100 hPa (ΔT100) modulate both the magnitude of the Arctic SLP response and the cyclonic Pacific SLP response. Apart from ΔT100, the intensity and latitudinal location of the climatological eddy-driven jet in the troposphere also affect the magnitude of the Arctic SLP response. The compensation of model biases in these two tropospheric metrics and the good model representation of ΔT100 explains the good agreement between the ensemble mean and the reanalysis on the magnitude of the Arctic SLP response, as indicated by the fact that the ensemble mean lies well within the reanalysis uncertainty range and that the reanalysis mean sits well within the model distribution. The Niño-3.4 SST anomalies and North Pacific SST dipole anomalies together with ΔT100 modulate the cyclonic Pacific SLP response. In this case, biases in both oceanic drivers work in the same direction and lead to the cyclonic Pacific SLP response in models that is not present in the reanalysis.
{"title":"What Drives the Spread and Bias in the Surface Impact of Sudden Stratospheric Warmings in CMIP6 Models?","authors":"Ying Dai, Peter Hitchcock, Isla R. Simpson","doi":"10.1175/jcli-d-23-0622.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0622.1","url":null,"abstract":"Abstract This study evaluates the representation of the composite-mean surface response to Sudden Stratospheric Warmings (SSWs) in 28 CMIP6 models. Most models can reproduce the magnitude of the SLP response over the Arctic, although the simulated Arctic SLP response varies from model to model. Regarding the structure of the SLP response, most models exhibit a basin-symmetric negative NAM-like response with a cyclonic Pacific SLP response, whereas the reanalysis shows a highly basin-asymmetric negative NAO-like response without a robust Pacific center. We then explore the drivers of these model biases and spread by applying a multiple linear regression. The results show that the polar-cap temperature anomalies at 100 hPa (ΔT100) modulate both the magnitude of the Arctic SLP response and the cyclonic Pacific SLP response. Apart from ΔT100, the intensity and latitudinal location of the climatological eddy-driven jet in the troposphere also affect the magnitude of the Arctic SLP response. The compensation of model biases in these two tropospheric metrics and the good model representation of ΔT100 explains the good agreement between the ensemble mean and the reanalysis on the magnitude of the Arctic SLP response, as indicated by the fact that the ensemble mean lies well within the reanalysis uncertainty range and that the reanalysis mean sits well within the model distribution. The Niño-3.4 SST anomalies and North Pacific SST dipole anomalies together with ΔT100 modulate the cyclonic Pacific SLP response. In this case, biases in both oceanic drivers work in the same direction and lead to the cyclonic Pacific SLP response in models that is not present in the reanalysis.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"8 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140572174","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 : 2024-04-11DOI: 10.1175/jcli-d-23-0200.1
F. Guo, S. C. Clemens, X. Du, X. Liu, Y. Liu, J. Sun, H. Fan, T. Wang, Y. Sun
Abstract Millennial-scale climate change is thought to be synchronous throughout the northern hemisphere and has been demonstrated to be strongly modulated by longer-term glacial-interglacial and orbital scale processes. However, processes that modulate the magnitude of millennial-scale variability (MMV) at the glacial-interglacial timescale remain unclear. We present multi-proxy evidence showing out-of-phase relationships between the MMV of East Asian and North Atlantic climate proxies at the eccentricity band. During most late Pleistocene glacial intervals, the MMV in North Atlantic SST and East Asian Monsoon proxies show a gradual weakening trend from glacial inceptions into glacial maxima, inversely proportional to that of North Atlantic ice rafted detritus record. The inverse glacial-age trends apply to both summer- and winter-monsoon proxies across the loess, speleothem, and marine archives, indicating fundamental linkages between MMV records of the North Atlantic and East Asia. We infer that intensified glacial-age iceberg discharge is accompanied by weakened Atlantic meridional overturning circulation via changes in freshwater input and water-column stability, leading to reduction in North Atlantic SST and wind anomalies, subsequently propagating dampened millennial-scale variability into the mid-latitude East Asian Monsoon region via the westerlies. Our results indicate that the impact of North Atlantic iceberg discharge and the associated variability in water-column stability at the millennial-scale is a primary influence on hydroclimate instability in East Asia.
{"title":"North Atlantic influence on the glacial amplitude of East Asian millennial-scale monsoon variability","authors":"F. Guo, S. C. Clemens, X. Du, X. Liu, Y. Liu, J. Sun, H. Fan, T. Wang, Y. Sun","doi":"10.1175/jcli-d-23-0200.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0200.1","url":null,"abstract":"Abstract Millennial-scale climate change is thought to be synchronous throughout the northern hemisphere and has been demonstrated to be strongly modulated by longer-term glacial-interglacial and orbital scale processes. However, processes that modulate the magnitude of millennial-scale variability (MMV) at the glacial-interglacial timescale remain unclear. We present multi-proxy evidence showing out-of-phase relationships between the MMV of East Asian and North Atlantic climate proxies at the eccentricity band. During most late Pleistocene glacial intervals, the MMV in North Atlantic SST and East Asian Monsoon proxies show a gradual weakening trend from glacial inceptions into glacial maxima, inversely proportional to that of North Atlantic ice rafted detritus record. The inverse glacial-age trends apply to both summer- and winter-monsoon proxies across the loess, speleothem, and marine archives, indicating fundamental linkages between MMV records of the North Atlantic and East Asia. We infer that intensified glacial-age iceberg discharge is accompanied by weakened Atlantic meridional overturning circulation via changes in freshwater input and water-column stability, leading to reduction in North Atlantic SST and wind anomalies, subsequently propagating dampened millennial-scale variability into the mid-latitude East Asian Monsoon region via the westerlies. Our results indicate that the impact of North Atlantic iceberg discharge and the associated variability in water-column stability at the millennial-scale is a primary influence on hydroclimate instability in East Asia.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"43 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140572078","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 Focusing on summer precipitation over the Tibetan Plateau (TP), this study mainly investigates the joint impacts of the North African and the Western Pacific subtropical highs (i.e., NASH and WPSH) through examining circulation and moisture anomalies. Results show that there are several boundary combination types of the two subtropical highs. The anomalous vertical motion with sufficient moisture transport under different boundary types plays the dominant role in TP precipitation anomaly. When the WPSH strengthens westward approaching to the TP, it can transport water vapor northward from Northwest Pacific and North Indian Oceans to the south edge of the TP and induce ascending motion over the southeastern TP, contributing to more precipitation there. When the NASH enhances and extends eastward, it can transport water vapor eastward from North Atlantic Ocean to the southwest eastern TP and give rise to ascending motion there, inducing positive precipitation anomaly over the southwest eastern TP. When the two subtropical highs simultaneously intensify and extend to the TP, water vapor can be transported to the TP widely from the North Atlantic Ocean, the North Indian Ocean and the northwest Pacific Ocean with the strengthening of the westerly, resulting in the location of the ascending motion and rain belt shifting obviously northward. Further analyses indicate that the pre-winter ENSO and summer North Atlantic air–sea interaction are two indispensable possible modulation factors for the joint impact of the two subtropical highs on TP precipitation.
{"title":"Joint Impacts of the North African and the Western Pacific subtropical highs on summer precipitation over the Tibetan Plateau","authors":"Fang Zhou, Siseho Christonette Siseho, Minghong Liu, Dapeng Zhang, Haoxin Zhang","doi":"10.1175/jcli-d-23-0560.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0560.1","url":null,"abstract":"Abstract Focusing on summer precipitation over the Tibetan Plateau (TP), this study mainly investigates the joint impacts of the North African and the Western Pacific subtropical highs (i.e., NASH and WPSH) through examining circulation and moisture anomalies. Results show that there are several boundary combination types of the two subtropical highs. The anomalous vertical motion with sufficient moisture transport under different boundary types plays the dominant role in TP precipitation anomaly. When the WPSH strengthens westward approaching to the TP, it can transport water vapor northward from Northwest Pacific and North Indian Oceans to the south edge of the TP and induce ascending motion over the southeastern TP, contributing to more precipitation there. When the NASH enhances and extends eastward, it can transport water vapor eastward from North Atlantic Ocean to the southwest eastern TP and give rise to ascending motion there, inducing positive precipitation anomaly over the southwest eastern TP. When the two subtropical highs simultaneously intensify and extend to the TP, water vapor can be transported to the TP widely from the North Atlantic Ocean, the North Indian Ocean and the northwest Pacific Ocean with the strengthening of the westerly, resulting in the location of the ascending motion and rain belt shifting obviously northward. Further analyses indicate that the pre-winter ENSO and summer North Atlantic air–sea interaction are two indispensable possible modulation factors for the joint impact of the two subtropical highs on TP precipitation.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"47 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140572121","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 : 2024-04-09DOI: 10.1175/jcli-d-23-0125.1
P. J. Tuckman, Jane Smyth, Nicholas J. Lutsko, John Marshall
Abstract The Intertropical Convergence Zone (ITCZ) is associated with a zonal band of strong precipitation that migrates meridionally over the seasonal cycle. Tropical precipitation also migrates zonally; such as from the South Asian monsoon in Northern Hemisphere summer (JJA) to the precipitation maximum of the West Pacific in Northern Hemisphere winter (DJF). To explore this zonal movement in the Indo-Pacific sector, we analyze the seasonal cycle of tropical precipitation using a 2D energetic framework and study idealized atmosphere-ocean simulations with and without ocean dynamics. In the observed seasonal cycle, an atmospheric energy and precipitation anomaly forms over South Asia in northern spring and summer due to heating over land. It is then advected eastward into the West Pacific in northern autumn and remains there due to interactions with the Pacific cold tongue and equatorial easterlies. We interpret this phenomenon as a “monsoonal mode,” a zonally propagating moist energy anomaly of continental and seasonal scale. To understand the behavior of the monsoonal mode, we develop and explore an analytical model in which the monsoonal mode is advected by low-level winds, is sustained by interaction with the ocean, and decays due to free tropospheric mixing of energy.
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Pub Date : 2024-04-08DOI: 10.1175/jcli-d-23-0382.1
Xianghui Fang, Henk Dijkstra, Claudia Wieners, Francesco Guardamagna
Abstract As the strongest year-to-year fluctuation of the global climate system, El Niño-Southern Oscillation (ENSO) exhibits spatial-temporal diversity, which challenges the classical ENSO theories that mainly focus on the canonical eastern Pacific (EP) type. Besides, the complicated interplay between the interannual anomaly fields and the decadally varying mean state is another difficulty in current ENSO theory. To better account for these issues, the nonlinear two-region recharge paradigm model is extended to a three-region full-field conceptual model to capture the physics in the western Pacific (WP), central Pacific (CP) and EP regions. The results show that the extended conceptual model displays a rich dynamical behavior as parameters setting the efficiencies of upwelling and zonal advection are varied. The model can not only generate El Niño bursting behavior, but also simulate the statistical asymmetries between the two types of El Niño and the warm and cold phases of ENSO. Finally, since both the anomaly fields and mean states are simulated by the model, it provides a simple tool to investigate their interactions. The strengthening of the upwelling efficiency, which can be seen as an analogy to a cooling thermocline associated with the oceanic tunnel to the mid-latitudes, will increase the zonal gradient of the mean state temperature between the WP and EP, i.e., resembling a negative Pacific Decadal Oscillation (PDO) pattern along the equatorial Pacific. The influence of the zonal advection efficiency is quite the opposite, i.e., its strengthening will reduce the zonal gradient of the mean state temperature along the equatorial Pacific.
摘要 作为全球气候系统中最强的逐年波动，厄尔尼诺-南方涛动（ENSO）在时空上表现出多样性，这对以典型的东太平洋（EP）类型为主的经典ENSO理论提出了挑战。此外，年际异常场与十年变化的平均状态之间复杂的相互作用是当前 ENSO 理论的另一个难点。为了更好地解释这些问题，将非线性的两区补给范式模式扩展为三区全场概念模型，以捕捉西太平洋（WP）、中太平洋（CP）和东太平洋（EP）区域的物理现象。结果表明，当设定上升流和带状平流效率的参数发生变化时，扩展的概念模型显示出丰富的动力学行为。该模式不仅能产生厄尔尼诺爆发行为，还能模拟两种厄尔尼诺现象之间的统计不对称以及厄尔尼诺/南方涛动的冷暖阶段。最后，由于异常场和平均状态都是由模型模拟的，因此它为研究它们之间的相互作用提供了一个简单的工具。上升流效率的加强（可视为与通往中纬度的海洋隧道相关的冷却热层）将增加 WP 和 EP 之间平均态温度的带状梯度，即类似于沿赤道太平洋的负太平洋十年涛动（PDO）模式。而区带平流效率的影响则恰恰相反，即区带平流效率的增强将减小赤道太平洋沿岸平均温度的区带梯度。
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