Pub Date : 2024-03-08DOI: 10.1175/jcli-d-23-0588.1
Andrew Hoell, Xiao-Wei Quan, Rachel Robinson, Martin Hoerling
Abstract Potential predictability of two-year droughts indicated by low runoff in consecutive April-September seasons in the Upper (UMRB) and Lower (LMRB) Missouri River Basin are examined with observed estimates and climate models. The majority of annual runoff is generated in April-September, which is also the main precipitation and evapotranspiration season. Physical features related to low April-September runoff in both UMRB and LMRB include a dry land surface state indicated by low soil moisture, low snowpack indicated by low snow water equivalent, and a wave train across the Pacific-North American region that can be generated internally by the atmosphere or forced by the La Niña phase of the El Niño-Southern Oscillation. When present in March, these features increase the risk of low runoff in the following April-September warm seasons. Antecedent low soil moisture significantly increases low runoff risks in each of the following two April-September, as the dry land surfaces decrease runoff efficiency. Initial low snow water equivalent, especially in the Missouri River headwaters of Montana, generates less runoff in the subsequent warm season. La Niña increases the risk of low runoff during the warm seasons by suppressing precipitation via dynamical-induced atmospheric circulation anomalies. Model simulations that differ in their radiative forcing suggest that climate change increases the predictability of two-year droughts in the Missouri River Basin related to La Niña. The relative risk of low runoff in the second April-September following a La Niña event in March is greater in the presence of stronger radiative forcing.
{"title":"Potential Predictability of Two-Year Droughts in the Missouri River Basin","authors":"Andrew Hoell, Xiao-Wei Quan, Rachel Robinson, Martin Hoerling","doi":"10.1175/jcli-d-23-0588.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0588.1","url":null,"abstract":"Abstract Potential predictability of two-year droughts indicated by low runoff in consecutive April-September seasons in the Upper (UMRB) and Lower (LMRB) Missouri River Basin are examined with observed estimates and climate models. The majority of annual runoff is generated in April-September, which is also the main precipitation and evapotranspiration season. Physical features related to low April-September runoff in both UMRB and LMRB include a dry land surface state indicated by low soil moisture, low snowpack indicated by low snow water equivalent, and a wave train across the Pacific-North American region that can be generated internally by the atmosphere or forced by the La Niña phase of the El Niño-Southern Oscillation. When present in March, these features increase the risk of low runoff in the following April-September warm seasons. Antecedent low soil moisture significantly increases low runoff risks in each of the following two April-September, as the dry land surfaces decrease runoff efficiency. Initial low snow water equivalent, especially in the Missouri River headwaters of Montana, generates less runoff in the subsequent warm season. La Niña increases the risk of low runoff during the warm seasons by suppressing precipitation via dynamical-induced atmospheric circulation anomalies. Model simulations that differ in their radiative forcing suggest that climate change increases the predictability of two-year droughts in the Missouri River Basin related to La Niña. The relative risk of low runoff in the second April-September following a La Niña event in March is greater in the presence of stronger radiative forcing.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"55 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140076609","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 : 2024-03-06DOI: 10.1175/jcli-d-23-0374.1
William Kamp, Weiqing Han, Lei Zhang, Shoichiro Kido, Julian P. McCreary
Abstract Coastal flooding induced by sea surface High EXtreme (HEX) events is an increasing risk to human society and infrastructure as both urban growth in coastal areas and anthropogenic sea level rise continue, especially for island nations like Indonesia. This paper investigates the role of atmospheric IntraSeasonal Oscillations (ISOs), which are dominated by the Madden-Julian Oscillation (MJO), in forcing HEXs on the coasts of Indonesia bordering the Indian Ocean. We use satellite altimetry data from 1993-2021 and tide gauge observations to detect HEXs, and modeling experiments using both the Regional Ocean Modeling System and a Bayesian dynamic linear model to understand the forcing and processes. We find that HEXs exhibit strong seasonality, with most events occurring during boreal winter (December-February) and spring (March-May) that are dominated by seasonal-to-decadal and intraseasonal variability respectively. In 32% of the 56 HEX events detected, the amplitude of ISO-induced sea level anomalies (SLAs) exceeds that of seasonal-to-decadal SLAs. Surface wind stress associated with atmospheric ISOs is the major forcing for intraseasonal SLAs, and both the remote westerly wind stress from the Indian Ocean equator and northwesterly longshore wind stress at the Indonesian coasts play important roles in driving the HEXs. The MJO is the dominant cause of ISO-dominated HEXs and its impact shows strong seasonal differences. Spring MJOs are associated with stronger convective anomalies over the eastern Indian Ocean equator that drive stronger zonal winds across the equatorial basin that lead to more HEX events compared to winter MJOs when the convection is shifted southward.
{"title":"Tropical Atmospheric Intraseasonal Oscillations Leading to Sea Level Extremes in Coastal Indonesia during Recent Decades","authors":"William Kamp, Weiqing Han, Lei Zhang, Shoichiro Kido, Julian P. McCreary","doi":"10.1175/jcli-d-23-0374.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0374.1","url":null,"abstract":"Abstract Coastal flooding induced by sea surface High EXtreme (HEX) events is an increasing risk to human society and infrastructure as both urban growth in coastal areas and anthropogenic sea level rise continue, especially for island nations like Indonesia. This paper investigates the role of atmospheric IntraSeasonal Oscillations (ISOs), which are dominated by the Madden-Julian Oscillation (MJO), in forcing HEXs on the coasts of Indonesia bordering the Indian Ocean. We use satellite altimetry data from 1993-2021 and tide gauge observations to detect HEXs, and modeling experiments using both the Regional Ocean Modeling System and a Bayesian dynamic linear model to understand the forcing and processes. We find that HEXs exhibit strong seasonality, with most events occurring during boreal winter (December-February) and spring (March-May) that are dominated by seasonal-to-decadal and intraseasonal variability respectively. In 32% of the 56 HEX events detected, the amplitude of ISO-induced sea level anomalies (SLAs) exceeds that of seasonal-to-decadal SLAs. Surface wind stress associated with atmospheric ISOs is the major forcing for intraseasonal SLAs, and both the remote westerly wind stress from the Indian Ocean equator and northwesterly longshore wind stress at the Indonesian coasts play important roles in driving the HEXs. The MJO is the dominant cause of ISO-dominated HEXs and its impact shows strong seasonal differences. Spring MJOs are associated with stronger convective anomalies over the eastern Indian Ocean equator that drive stronger zonal winds across the equatorial basin that lead to more HEX events compared to winter MJOs when the convection is shifted southward.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"40 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140044077","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 : 2024-03-05DOI: 10.1175/jcli-d-23-0716.1
Lucas R. Vargas Zeppetello, Lily N. Zhang, David S. Battisti, Marysa M. Laguë
Abstract Interannual fluctuations in average summertime temperatures across the western United States are captured by a leading EOF that explains over 50% of the total observed variance. In this paper, we explain the origins of this pattern of interannual temperature variability by examining soil moisture-temperature coupling that acts across seasons in observations and climate models. We find that a characteristic pattern of coupled temperature-soil moisture climate variability accounts for 34% of the total observed variance in summertime temperature across the region. This pattern is reproduced in state-of-the-art global climate models, where experiments that eliminate soil moisture variability reduce summertime average temperature variance by a factor of three on average. We use an idealized model of the coupled atmospheric boundary layer and underlying land surface to demonstrate that feedbacks between soil moisture, boundary layer relative humidity, and precipitation can explain the observed relations between springtime soil moisture and summertime temperature. Our results suggest that antecedent soil moisture conditions and subsequent land-atmosphere interactions play an important role in interannual summertime temperature variability in the western U.S.; soil moisture variations cause distal temperature anomalies and impart predictability at timescales longer than one season. Our results indicate that 40% of the observed warming trend across the western U.S. since 1981 has been driven by wintertime precipitation trends in the U.S. southwest.
{"title":"How Much Does Land-Atmosphere Coupling Influence Summertime Temperature Variability in the Western United States?","authors":"Lucas R. Vargas Zeppetello, Lily N. Zhang, David S. Battisti, Marysa M. Laguë","doi":"10.1175/jcli-d-23-0716.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0716.1","url":null,"abstract":"Abstract Interannual fluctuations in average summertime temperatures across the western United States are captured by a leading EOF that explains over 50% of the total observed variance. In this paper, we explain the origins of this pattern of interannual temperature variability by examining soil moisture-temperature coupling that acts across seasons in observations and climate models. We find that a characteristic pattern of coupled temperature-soil moisture climate variability accounts for 34% of the total observed variance in summertime temperature across the region. This pattern is reproduced in state-of-the-art global climate models, where experiments that eliminate soil moisture variability reduce summertime average temperature variance by a factor of three on average. We use an idealized model of the coupled atmospheric boundary layer and underlying land surface to demonstrate that feedbacks between soil moisture, boundary layer relative humidity, and precipitation can explain the observed relations between springtime soil moisture and summertime temperature. Our results suggest that antecedent soil moisture conditions and subsequent land-atmosphere interactions play an important role in interannual summertime temperature variability in the western U.S.; soil moisture variations cause distal temperature anomalies and impart predictability at timescales longer than one season. Our results indicate that 40% of the observed warming trend across the western U.S. since 1981 has been driven by wintertime precipitation trends in the U.S. southwest.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"57 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140036422","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 : 2024-03-05DOI: 10.1175/jcli-d-23-0130.1
Pei-Syuan Liao, Chia-Wei Lan, Yu-Chiao Liang, Min-Hui Lo
Abstract The annual range (AR) of precipitation in the Amazon River basin has increased steadily since 1979. This increase may have resulted from natural variability and/or anthropogenic forcing, such as local land-use changes and global warming, which has yet to be explored. In this study, climate model experiments using the Community Earth System Model version 2 (CESM2) were conducted to examine the relative contributions of sea surface temperatures (SSTs) variability and anthropogenic forcings to the AR changes in the Amazon rainfall. With CESM2, we design several factorial simulations, instead of actual model projection. We found that the North Atlantic SSTs fluctuation dominantly decreases the precipitation AR trend over the Amazon by −85%. In contrast, other factors, including deforestation and carbon dioxide, contribute to the trend changes, ranging from 25∼35%. The dynamic component, specifically the tendency of vertical motion, made negative contributions, along with the vertical profiles of moist static energy (MSE) tendency. Seasonal-dependent changes in atmospheric stability could be associated with variations in precipitation. It is concluded that surface ocean warming associated with the North Atlantic natural variability and global warming is the key factor in the increased precipitation AR over the Amazon from 1979 to 2014. The continuous local land use changes may potentially influence the precipitation AR in the future.
摘要 自 1979 年以来，亚马逊河流域的年降水量（AR）持续增长。这种增加可能是由于自然变率和/或人为因素（如当地土地利用变化和全球变暖）造成的，这一点还有待探讨。本研究利用共同体地球系统模式第 2 版（CESM2）进行了气候模式实验，以研究海表温度（SSTs）变化和人为作用力对亚马逊流域降雨量 AR 变化的相对贡献。利用 CESM2，我们设计了多个因子模拟，而不是实际的模型预测。我们发现，北大西洋的 SSTs 波动使亚马逊地区降水的 AR 变化趋势下降了-85%。相比之下，其他因素（包括森林砍伐和二氧化碳）对趋势变化的影响在 25% 至 35% 之间。动态成分，特别是垂直运动趋势，与湿静态能量（MSE）趋势的垂直剖面一起产生了负面影响。大气稳定性随季节的变化可能与降水量的变化有关。结论是，与北大西洋自然变率和全球变暖相关的表层海洋变暖是 1979 年至 2014 年亚马逊地区降水 AR 增加的关键因素。未来，当地土地利用的持续变化可能会对降水 AR 产生潜在影响。
{"title":"Exploring the Factors Controlling the Annual Range of Amazon Precipitation","authors":"Pei-Syuan Liao, Chia-Wei Lan, Yu-Chiao Liang, Min-Hui Lo","doi":"10.1175/jcli-d-23-0130.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0130.1","url":null,"abstract":"Abstract The annual range (AR) of precipitation in the Amazon River basin has increased steadily since 1979. This increase may have resulted from natural variability and/or anthropogenic forcing, such as local land-use changes and global warming, which has yet to be explored. In this study, climate model experiments using the Community Earth System Model version 2 (CESM2) were conducted to examine the relative contributions of sea surface temperatures (SSTs) variability and anthropogenic forcings to the AR changes in the Amazon rainfall. With CESM2, we design several factorial simulations, instead of actual model projection. We found that the North Atlantic SSTs fluctuation dominantly decreases the precipitation AR trend over the Amazon by −85%. In contrast, other factors, including deforestation and carbon dioxide, contribute to the trend changes, ranging from 25∼35%. The dynamic component, specifically the tendency of vertical motion, made negative contributions, along with the vertical profiles of moist static energy (MSE) tendency. Seasonal-dependent changes in atmospheric stability could be associated with variations in precipitation. It is concluded that surface ocean warming associated with the North Atlantic natural variability and global warming is the key factor in the increased precipitation AR over the Amazon from 1979 to 2014. The continuous local land use changes may potentially influence the precipitation AR in the future.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"194 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140036263","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 El Niño-Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical Pacific, is well known to affect the extratropical climate via atmospheric teleconnections. Extratropical atmospheric variability may in turn influence the occurrence of ENSO events. The winter North Pacific Oscillation (NPO), as the secondary dominant mode of atmospheric variability over the North Pacific, has been recognized as a potential precursor for ENSO development. This study demonstrates that the pre-existing winter NPO signal is primarily excited by sea surface temperature (SST) anomalies in the equatorial western-central Pacific. During ENSO years with a preceding winter NPO signal, which accounts for approximately 60% of ENSO events observed in 1979–2021, significant SST anomalies emerge in the equatorial western-central Pacific in the preceding autumn and winter. The concurrent presence of local convection anomalies can act as a catalyst for NPO-like atmospheric circulation anomalies. In contrast, during other ENSO years, significant SST anomalies are not observed in the equatorial western-central Pacific during the preceding winter, and correspondingly, the NPO signal is absent. Ensemble simulations using an atmospheric general circulation model driven by observed SST anomalies in the tropical western-central Pacific can well reproduce the interannual variability of observed NPO. Therefore, an alternative explanation for the observed NPO-ENSO relationship is that the preceding winter NPO is a companion to ENSO development, driven by the precursory SST signal in the equatorial western-central Pacific. Our results suggest that the lagged relationship between ENSO and the NPO involves a tropical-extratropical two-way coupling rather than a purely stochastic forcing of the extratropical atmosphere on ENSO.
{"title":"Equatorial western-central Pacific SST responsible for the North Pacific Oscillation-ENSO sequence","authors":"Suqiong Hu, Wenjun Zhang, Masahiro Watanabe, Feng Jiang, Fei-Fei Jin, Han-Ching Chen","doi":"10.1175/jcli-d-23-0434.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0434.1","url":null,"abstract":"Abstract El Niño-Southern Oscillation (ENSO), the dominant mode of interannual variability in the tropical Pacific, is well known to affect the extratropical climate via atmospheric teleconnections. Extratropical atmospheric variability may in turn influence the occurrence of ENSO events. The winter North Pacific Oscillation (NPO), as the secondary dominant mode of atmospheric variability over the North Pacific, has been recognized as a potential precursor for ENSO development. This study demonstrates that the pre-existing winter NPO signal is primarily excited by sea surface temperature (SST) anomalies in the equatorial western-central Pacific. During ENSO years with a preceding winter NPO signal, which accounts for approximately 60% of ENSO events observed in 1979–2021, significant SST anomalies emerge in the equatorial western-central Pacific in the preceding autumn and winter. The concurrent presence of local convection anomalies can act as a catalyst for NPO-like atmospheric circulation anomalies. In contrast, during other ENSO years, significant SST anomalies are not observed in the equatorial western-central Pacific during the preceding winter, and correspondingly, the NPO signal is absent. Ensemble simulations using an atmospheric general circulation model driven by observed SST anomalies in the tropical western-central Pacific can well reproduce the interannual variability of observed NPO. Therefore, an alternative explanation for the observed NPO-ENSO relationship is that the preceding winter NPO is a companion to ENSO development, driven by the precursory SST signal in the equatorial western-central Pacific. Our results suggest that the lagged relationship between ENSO and the NPO involves a tropical-extratropical two-way coupling rather than a purely stochastic forcing of the extratropical atmosphere on ENSO.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"51 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140025648","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 : 2024-03-04DOI: 10.1175/jcli-d-23-0490.1
Olawale James Ikuyajolu, Luke Van Roekel, Steven R Brus, Erin E Thomas, Yi Deng, James J Benedict
Abstract This study investigates the sensitivity of the Madden-Julian Oscillation (MJO) to changes to the bulk flux parameterization and the role of ocean surface waves in air-sea coupling using a fully-coupled ocean-atmosphere-wave model. The atmospheric and ocean model components of the Energy Exascale Earth System Model (E3SM) are coupled to a spectral wave model, WAVEWATCH III (WW3). Two experiments with wind speed dependent bulk algorithms, NCAR (Large and Yeager 2004, 2009) & COARE3.0a (Fairall et al. 2003), and one experiment with wave-state dependent flux (COR3.0a-WAV) were conducted. We modify COARE3.0a to include surface roughness calculated within WW3 and also account for the buffering effect of waves on the relative difference between air-side and ocean-side momentum flux. Differences in surface fluxes, primarily caused by discrepancies in drag coefficients, result in significant differences in MJO’s properties. While COARE3.0a has better convection-circulation coupling than NCAR, it exhibits anomalous MJO convection east of the dateline. The wave-state dependent flux (COR3.0-WAV) improves the MJO representation over the default COARE3.0 algorithm. Strong easterlies over the Pacific Ocean in COARE3.0a enhance the latent heat flux (LHFLX). This is responsible for the anomalous MJO propagation after the dateline. In COR3.0a-WAV, waves reduce the anomalous easterlies, leading to a decrease in LHFLX and MJO dissipation after the dateline. These findings highlight the role of surface fluxes in MJO simulation fidelity. Most importantly, we show that the proper treatment of wave-induced effects in bulk flux parameterization improves the simulation of coupled climate variability.
{"title":"Effects of Surface Turbulence Flux Parameterizations on the MJO: The Role of Ocean Surface Waves","authors":"Olawale James Ikuyajolu, Luke Van Roekel, Steven R Brus, Erin E Thomas, Yi Deng, James J Benedict","doi":"10.1175/jcli-d-23-0490.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0490.1","url":null,"abstract":"Abstract This study investigates the sensitivity of the Madden-Julian Oscillation (MJO) to changes to the bulk flux parameterization and the role of ocean surface waves in air-sea coupling using a fully-coupled ocean-atmosphere-wave model. The atmospheric and ocean model components of the Energy Exascale Earth System Model (E3SM) are coupled to a spectral wave model, WAVEWATCH III (WW3). Two experiments with wind speed dependent bulk algorithms, NCAR (Large and Yeager 2004, 2009) & COARE3.0a (Fairall et al. 2003), and one experiment with wave-state dependent flux (COR3.0a-WAV) were conducted. We modify COARE3.0a to include surface roughness calculated within WW3 and also account for the buffering effect of waves on the relative difference between air-side and ocean-side momentum flux. Differences in surface fluxes, primarily caused by discrepancies in drag coefficients, result in significant differences in MJO’s properties. While COARE3.0a has better convection-circulation coupling than NCAR, it exhibits anomalous MJO convection east of the dateline. The wave-state dependent flux (COR3.0-WAV) improves the MJO representation over the default COARE3.0 algorithm. Strong easterlies over the Pacific Ocean in COARE3.0a enhance the latent heat flux (LHFLX). This is responsible for the anomalous MJO propagation after the dateline. In COR3.0a-WAV, waves reduce the anomalous easterlies, leading to a decrease in LHFLX and MJO dissipation after the dateline. These findings highlight the role of surface fluxes in MJO simulation fidelity. Most importantly, we show that the proper treatment of wave-induced effects in bulk flux parameterization improves the simulation of coupled climate variability.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"22 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140036193","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 : 2024-03-01DOI: 10.1175/jcli-d-23-0649.1
Yuanyuan Song, Yuanlong Li, Aixue Hu, Lijing Cheng, Gaël Forget, Xiaodan Chen, Jing Duan, Fan Wang
Abstract As the major sink of anthropogenic heat, the Southern Ocean has shown quasi-symmetric, deep-reaching warming since the mid-20th century. In comparison, the shorter-term heat storage pattern of the Southern Ocean is more complex and has notable impacts on regional climate and marine ecosystems. By analyzing observational datasets and climate model simulations, this study reveals that the Southern Ocean exhibits prominent decadal (> 8 years) variability extending to ~700 m depth and is characterized by out-of-phase changes in the Pacific and Atlantic-Indian Ocean sectors. Changes in the Pacific sector are larger in magnitude than those in the Atlantic-Indian Ocean sectors and dominate the total heat storage of the Southern Ocean on decadal timescales. Instead of heat uptake through surface heat fluxes, these asymmetric variations arise primarily from wind-driven heat redistribution. Pacemaker and pre-industrial simulations of the Community Earth System Model version-1 (CESM1) suggest that these variations in Southern Ocean winds arise primarily from natural variability of the tropical Pacific, as represented by the Interdecadal Pacific Oscillation (IPO). Through atmospheric teleconnection, the positive phase of the IPO gives rise to higher-than-normal sea-level pressure and anti-cyclonic wind anomalies in the 50°–70°S band of the Pacific sector. These winds lead to warming of 0–700 m by driving the convergence of warm water. The opposite processes, involving cyclonic winds and upper-layer divergence, occur in the Atlantic-Indian Ocean sector. These findings aid our understanding of the time-varying heat storage of the Southern Ocean and provide useful implications on initialized decadal climate prediction.
{"title":"Decadal thermal variability of the upper Southern Ocean: zonal asymmetry","authors":"Yuanyuan Song, Yuanlong Li, Aixue Hu, Lijing Cheng, Gaël Forget, Xiaodan Chen, Jing Duan, Fan Wang","doi":"10.1175/jcli-d-23-0649.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0649.1","url":null,"abstract":"Abstract As the major sink of anthropogenic heat, the Southern Ocean has shown quasi-symmetric, deep-reaching warming since the mid-20th century. In comparison, the shorter-term heat storage pattern of the Southern Ocean is more complex and has notable impacts on regional climate and marine ecosystems. By analyzing observational datasets and climate model simulations, this study reveals that the Southern Ocean exhibits prominent decadal (> 8 years) variability extending to ~700 m depth and is characterized by out-of-phase changes in the Pacific and Atlantic-Indian Ocean sectors. Changes in the Pacific sector are larger in magnitude than those in the Atlantic-Indian Ocean sectors and dominate the total heat storage of the Southern Ocean on decadal timescales. Instead of heat uptake through surface heat fluxes, these asymmetric variations arise primarily from wind-driven heat redistribution. Pacemaker and pre-industrial simulations of the Community Earth System Model version-1 (CESM1) suggest that these variations in Southern Ocean winds arise primarily from natural variability of the tropical Pacific, as represented by the Interdecadal Pacific Oscillation (IPO). Through atmospheric teleconnection, the positive phase of the IPO gives rise to higher-than-normal sea-level pressure and anti-cyclonic wind anomalies in the 50°–70°S band of the Pacific sector. These winds lead to warming of 0–700 m by driving the convergence of warm water. The opposite processes, involving cyclonic winds and upper-layer divergence, occur in the Atlantic-Indian Ocean sector. These findings aid our understanding of the time-varying heat storage of the Southern Ocean and provide useful implications on initialized decadal climate prediction.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"2011 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140019911","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 : 2024-03-01DOI: 10.1175/jcli-d-23-0273.1
Jun Yin, Amilcare Porporato, Lamberto Rondoni
Abstract While the warming trends of the Earth’s mean temperature are evident at climatological scales, the local temperature at shorter timescales are highly fluctuating. Here we show that the probabilities of such fluctuations are characterized by a special symmetry typical of small systems out of equilibrium. Their nearly universal properties are linked to the fluctuation theorem and reveal that the progressive warming is accompanied by growing asymmetry of temperature distributions. These statistics allow us to project the global temperature variability in the near future, in line with predictions from climate models, providing original insight about future extremes.
{"title":"Nonequilibrium fluctuations of global warming","authors":"Jun Yin, Amilcare Porporato, Lamberto Rondoni","doi":"10.1175/jcli-d-23-0273.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0273.1","url":null,"abstract":"Abstract While the warming trends of the Earth’s mean temperature are evident at climatological scales, the local temperature at shorter timescales are highly fluctuating. Here we show that the probabilities of such fluctuations are characterized by a special symmetry typical of small systems out of equilibrium. Their nearly universal properties are linked to the fluctuation theorem and reveal that the progressive warming is accompanied by growing asymmetry of temperature distributions. These statistics allow us to project the global temperature variability in the near future, in line with predictions from climate models, providing original insight about future extremes.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"19 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010393","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 : 2024-03-01DOI: 10.1175/jcli-d-22-0930.1
J. Michael Battalio, Juan M. Lora
Abstract Changes in the vertical and meridional temperature gradients of the atmosphere drive competing influences on storm track activity. We apply local eddy energetics to the ERA5, JRA55, MERRA2, and NCEP2 reanalyses during 1980–2020 to determine the locations, magnitudes, and trends of the energy transfer mechanisms for synoptic-scale eddies. Eddy kinetic energy (EKE) increases more rapidly in the Southern Hemisphere at all altitudes and seasons, with larger increases during austral winter and spring. In the Northern Hemisphere, increases occur within the Atlantic and Pacific storm tracks at pressures below 300 hPa but only during boreal winter and spring and confined within a narrow zonal band; EKE decreases during boreal summer and fall. Most EKE changes correspond with trends in baroclinic energy conversion upstream of storm tracks and appear to align with increases in the growth rate of the most unstable baroclinic mode. Barotropic energy conversion of EKE to the mean flow becomes locally more intense downstream of the storm tracks. Conversion of EKE to long-period eddies plays a minor role averaged over a hemisphere but can be important locally. The primary strengthening pathway for removal of EKE is a combination of surface friction and viscous dissipation. The increased baroclinic conversion in the Southern Hemisphere appears related to upper-level tropical temperature increases. In the Northern Hemisphere, baroclinic conversion is enabled by a combination of increased vertical heat fluxes and a region of temperature increases within 30°–60°N.
{"title":"Increases in the Local Eddy Energetics of the Extratropical Atmosphere over the Last Four Decades","authors":"J. Michael Battalio, Juan M. Lora","doi":"10.1175/jcli-d-22-0930.1","DOIUrl":"https://doi.org/10.1175/jcli-d-22-0930.1","url":null,"abstract":"Abstract Changes in the vertical and meridional temperature gradients of the atmosphere drive competing influences on storm track activity. We apply local eddy energetics to the ERA5, JRA55, MERRA2, and NCEP2 reanalyses during 1980–2020 to determine the locations, magnitudes, and trends of the energy transfer mechanisms for synoptic-scale eddies. Eddy kinetic energy (EKE) increases more rapidly in the Southern Hemisphere at all altitudes and seasons, with larger increases during austral winter and spring. In the Northern Hemisphere, increases occur within the Atlantic and Pacific storm tracks at pressures below 300 hPa but only during boreal winter and spring and confined within a narrow zonal band; EKE decreases during boreal summer and fall. Most EKE changes correspond with trends in baroclinic energy conversion upstream of storm tracks and appear to align with increases in the growth rate of the most unstable baroclinic mode. Barotropic energy conversion of EKE to the mean flow becomes locally more intense downstream of the storm tracks. Conversion of EKE to long-period eddies plays a minor role averaged over a hemisphere but can be important locally. The primary strengthening pathway for removal of EKE is a combination of surface friction and viscous dissipation. The increased baroclinic conversion in the Southern Hemisphere appears related to upper-level tropical temperature increases. In the Northern Hemisphere, baroclinic conversion is enabled by a combination of increased vertical heat fluxes and a region of temperature increases within 30°–60°N.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"69 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010460","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 : 2024-02-29DOI: 10.1175/jcli-d-23-0345.1
Soumik Ghosh, Orli Lachmy, Yohai Kaspi
Abstract Climate models generally predict a poleward shift of the midlatitude circulation in response to climate change induced by increased greenhouse gas concentration, but the inter-model spread of the eddy-driven jet shift is large and poorly understood. Recent studies point to the significance of midlatitude mid-tropospheric diabatic heating for the inter-model spread in the jet latitude. To examine the role of diabatic heating in the jet response to climate change, a series of simulations are performed using an idealized aquaplanet model. It is found that both increased CO2 concentration and increased saturation vapor pressure induce a similar warming response, leading to a poleward and upward shift of the midlatitude circulation. An exception to this poleward shift is found for a certain range of temperatures, where the eddy-driven jet shifts equatorward, while the latitude of the eddy heat flux remains essentially unchanged. This equatorward jet shift is explained by the connection between the zonal mean momentum and heat budgets: increased diabatic heating in the midlatitude mid-troposphere balances the cooling by the Ferrel cell ascending branch, enabling an equatorward shift of the Ferrel cell streamfunction and eddy-driven jet, while the latitude of the eddy heat flux remains unchanged. The equatorward jet shift and the strengthening of the midlatitude diabatic heating are found to be sensitive to the model resolution. The implications of these results for a potential reduction in the jet shift uncertainty through the improvement of convective parameterizations are discussed.
{"title":"The role of diabatic heating in the midlatitude atmospheric circulation response to climate change","authors":"Soumik Ghosh, Orli Lachmy, Yohai Kaspi","doi":"10.1175/jcli-d-23-0345.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0345.1","url":null,"abstract":"Abstract Climate models generally predict a poleward shift of the midlatitude circulation in response to climate change induced by increased greenhouse gas concentration, but the inter-model spread of the eddy-driven jet shift is large and poorly understood. Recent studies point to the significance of midlatitude mid-tropospheric diabatic heating for the inter-model spread in the jet latitude. To examine the role of diabatic heating in the jet response to climate change, a series of simulations are performed using an idealized aquaplanet model. It is found that both increased CO2 concentration and increased saturation vapor pressure induce a similar warming response, leading to a poleward and upward shift of the midlatitude circulation. An exception to this poleward shift is found for a certain range of temperatures, where the eddy-driven jet shifts equatorward, while the latitude of the eddy heat flux remains essentially unchanged. This equatorward jet shift is explained by the connection between the zonal mean momentum and heat budgets: increased diabatic heating in the midlatitude mid-troposphere balances the cooling by the Ferrel cell ascending branch, enabling an equatorward shift of the Ferrel cell streamfunction and eddy-driven jet, while the latitude of the eddy heat flux remains unchanged. The equatorward jet shift and the strengthening of the midlatitude diabatic heating are found to be sensitive to the model resolution. The implications of these results for a potential reduction in the jet shift uncertainty through the improvement of convective parameterizations are discussed.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":"19 1","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-02-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140010501","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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