Abstract Xinjiang suffers compound hot and drought events under global warming. However, less attention has been paid to physical mechanisms of the variability of compound hot and drought events in this region. This article investigates the interannual variation of summer (June–July–August) compound hot and drought events in Xinjiang and its relationship with the sea surface temperature (SST) over the North Atlantic. The results show that its first Empirical Orthogonal Function (EOF) mode features a spatially homogenous pattern. This mode is closely connected with the simultaneous meridional negative–positive–negative SST anomalies over the North Atlantic. The summer North Atlantic tripole SST anomalies can trigger a remarkable wave train extending from the North Atlantic to Eurasia, consequently inducing an anomalous high-pressure system over the Iran–Pamirs Plateau, which is conducive to the increase of air temperature from the surface to the upper troposphere over Xinjiang. The warmer troposphere further strengthens the western Asian subtropical meridional temperature gradient and thereby enhances the westerly wind to the north flank of the West Asian subtropical westerly jet (WASWJ). As a result, the WASWJ is displaced northward, which intensifies the sinking motion and prevents the water vapor transport to Xinjiang, leading to a decrease of precipitation in the target region. The higher temperature and less precipitation contribute to the occurrence of compound hot and drought events over Xinjiang. Numerical simulations based on the Community Atmospheric Model version 4 (CAM4) further confirm the relationship between the North Atlantic tripole SST anomalies and compound hot and drought events in Xinjiang during summer on the interannual time scale.
{"title":"Interannual variation of summer compound hot and drought events in Xinjiang and its relationship with the North Atlantic sea surface temperature","authors":"Xiaolu Zhang, Jiapeng Miao, Xiaoxin Wang, Botao Zhou","doi":"10.1175/jcli-d-24-0086.1","DOIUrl":"https://doi.org/10.1175/jcli-d-24-0086.1","url":null,"abstract":"Abstract Xinjiang suffers compound hot and drought events under global warming. However, less attention has been paid to physical mechanisms of the variability of compound hot and drought events in this region. This article investigates the interannual variation of summer (June–July–August) compound hot and drought events in Xinjiang and its relationship with the sea surface temperature (SST) over the North Atlantic. The results show that its first Empirical Orthogonal Function (EOF) mode features a spatially homogenous pattern. This mode is closely connected with the simultaneous meridional negative–positive–negative SST anomalies over the North Atlantic. The summer North Atlantic tripole SST anomalies can trigger a remarkable wave train extending from the North Atlantic to Eurasia, consequently inducing an anomalous high-pressure system over the Iran–Pamirs Plateau, which is conducive to the increase of air temperature from the surface to the upper troposphere over Xinjiang. The warmer troposphere further strengthens the western Asian subtropical meridional temperature gradient and thereby enhances the westerly wind to the north flank of the West Asian subtropical westerly jet (WASWJ). As a result, the WASWJ is displaced northward, which intensifies the sinking motion and prevents the water vapor transport to Xinjiang, leading to a decrease of precipitation in the target region. The higher temperature and less precipitation contribute to the occurrence of compound hot and drought events over Xinjiang. Numerical simulations based on the Community Atmospheric Model version 4 (CAM4) further confirm the relationship between the North Atlantic tripole SST anomalies and compound hot and drought events in Xinjiang during summer on the interannual time scale.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504518","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 : 2024-07-02DOI: 10.1175/jcli-d-23-0621.1
Sarah M. Larson, Kay McMonigal, Yuko Okumura, Dillon Amaya, Antonietta Capotondi, Katinka Bellomo, Isla R. Simpson, Amy C. Clement
Abstract To improve understanding of ocean processes impacting monthly sea surface temperature (SST) variability, we analyze a Community Earth System Model version 2 hierarchy in which models vary only in their degree of ocean complexity. The most realistic ocean is a dynamical ocean model, as part of a fully coupled model (FCM). The next most realistic ocean, from a mechanically decoupled model (MDM), is like the FCM but excludes anomalous wind stress-driven ocean variability. The simplest ocean is a slab ocean model (SOM). Inclusion of a buoyancy coupled dynamic ocean as in the MDM, which includes temperature advection and vertical mixing absent in the SOM, leads to dampening of SST variance everywhere and reduced persistence of SST anomalies in the high latitudes and equatorial Pacific compared to the SOM. Inclusion of anomalous wind stress-driven ocean dynamics as in the FCM leads to higher SST variance and longer persistence timescales in most regions compared to the MDM. The net role of the dynamic ocean, as an overall dampener or amplifier of anomalous SST variance and persistence is regionally dependent. Notably, we find that efforts to reduce the complexity of the ocean models in the SOM and MDM configurations result in changes in the magnitude of the thermodynamic forcing of SST variability compared to the FCM. These changes, in part, stem from differences in the seasonally varying mixed layer depth and should be considered when attempting to quantify the relative contribution of certain ocean mechanisms to differences in SST variability between the models.
摘要 为了更好地了解海洋过程对海面温度月变化的影响，我们分析了共同体地球系统模式第 2 版的层次结构，其中的模式仅在海洋复杂程度上有所不同。最现实的海洋是动力学海洋模式，是完全耦合模式（FCM）的一部分。其次是机械解耦模式（MDM）中最逼真的海洋，与全耦合模式类似，但不包括风应力驱动的海洋异常变化。最简单的海洋是板块海洋模式（SOM）。与 SOM 相比，在 MDM 中加入浮力耦合动力海洋，包括 SOM 中没有的温度平流和垂直混合，会抑制各地的 SST 变异，并降低高纬度和赤道太平洋地区 SST 异常的持续性。与 MDM 相比，在 FCM 中加入风应力驱动的海洋动力异常会导致大部分地区的 SST 变差增大，持续时标变长。动态海洋作为异常海温变异和持续性的总体抑制器或放大器，其净作用与区域有关。值得注意的是，我们发现，在 SOM 和 MDM 配置中，降低海洋模式复杂性的努力导致 SST 变率的热动力作用力大小与 FCM 相比发生了变化。这些变化部分源于季节性变化的混合层深度的差异，在试图量化某些海洋机制对模型间 SST 变率差异的相对贡献时应加以考虑。
{"title":"Ocean Complexity Shapes Sea Surface Temperature Variability in a CESM2 Coupled Model Hierarchy","authors":"Sarah M. Larson, Kay McMonigal, Yuko Okumura, Dillon Amaya, Antonietta Capotondi, Katinka Bellomo, Isla R. Simpson, Amy C. Clement","doi":"10.1175/jcli-d-23-0621.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0621.1","url":null,"abstract":"Abstract To improve understanding of ocean processes impacting monthly sea surface temperature (SST) variability, we analyze a Community Earth System Model version 2 hierarchy in which models vary only in their degree of ocean complexity. The most realistic ocean is a dynamical ocean model, as part of a fully coupled model (FCM). The next most realistic ocean, from a mechanically decoupled model (MDM), is like the FCM but excludes anomalous wind stress-driven ocean variability. The simplest ocean is a slab ocean model (SOM). Inclusion of a buoyancy coupled dynamic ocean as in the MDM, which includes temperature advection and vertical mixing absent in the SOM, leads to dampening of SST variance everywhere and reduced persistence of SST anomalies in the high latitudes and equatorial Pacific compared to the SOM. Inclusion of anomalous wind stress-driven ocean dynamics as in the FCM leads to higher SST variance and longer persistence timescales in most regions compared to the MDM. The net role of the dynamic ocean, as an overall dampener or amplifier of anomalous SST variance and persistence is regionally dependent. Notably, we find that efforts to reduce the complexity of the ocean models in the SOM and MDM configurations result in changes in the magnitude of the thermodynamic forcing of SST variability compared to the FCM. These changes, in part, stem from differences in the seasonally varying mixed layer depth and should be considered when attempting to quantify the relative contribution of certain ocean mechanisms to differences in SST variability between the models.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504521","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 : 2024-07-02DOI: 10.1175/jcli-d-23-0625.1
Ernesto Tejedor, Lorenzo M. Polvani, Nathan J. Steiger, Mathias Vuille, Jason E. Smerdon
Abstract We critically reexamine the question of whether volcanic eruptions cause surface warming over Eurasia in winter, in the light of recent modeling studies that have suggested internal variability may overwhelm any forced volcanic response, even for the very largest eruptions during the Common Era. Focusing on the Last Millennium, we combine model output, instrumental observations, tree-ring records, and ice cores to build a new temperature reconstruction that specifically targets the boreal winter season. We focus on 20 eruptions over the Last Millennium with volcanic stratospheric sulfur injections (VSSI) larger than the 1991 Pinatubo eruption. We find that only 7 of these 20 large events are followed by warm surface temperature anomalies over Eurasia in the first post-eruption winter. Examining the 13 events that show cold post-eruption anomalies we find no correlation between the amplitude of winter cooling and VSSI mass. We also find no evidence that the North Atlantic Oscillation is correlated with VSSI in winter, a key element of the proposed mechanism through which large low-latitude eruptions might cause winter warming over Eurasia. Furthermore, by inspecting individual eruptions rather than combining events into a superposed epoch analysis, we are able to reconcile our findings with those of previous studies. Analysis of two additional paleoclimatic datasets corroborates the lack of post-eruption Eurasian winter warming. Our findings, covering the entire Last Millennium, confirm the findings of most recent modeling studies, and offer important new evidence that large low-latitude eruptions are not, in general, followed by significant surface wintertime warming over Eurasia.
{"title":"No evidence of winter warming in Eurasia following large, low-latitude volcanic eruptions during the Last Millennium","authors":"Ernesto Tejedor, Lorenzo M. Polvani, Nathan J. Steiger, Mathias Vuille, Jason E. Smerdon","doi":"10.1175/jcli-d-23-0625.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0625.1","url":null,"abstract":"Abstract We critically reexamine the question of whether volcanic eruptions cause surface warming over Eurasia in winter, in the light of recent modeling studies that have suggested internal variability may overwhelm any forced volcanic response, even for the very largest eruptions during the Common Era. Focusing on the Last Millennium, we combine model output, instrumental observations, tree-ring records, and ice cores to build a new temperature reconstruction that specifically targets the boreal winter season. We focus on 20 eruptions over the Last Millennium with volcanic stratospheric sulfur injections (VSSI) larger than the 1991 Pinatubo eruption. We find that only 7 of these 20 large events are followed by warm surface temperature anomalies over Eurasia in the first post-eruption winter. Examining the 13 events that show cold post-eruption anomalies we find no correlation between the amplitude of winter cooling and VSSI mass. We also find no evidence that the North Atlantic Oscillation is correlated with VSSI in winter, a key element of the proposed mechanism through which large low-latitude eruptions might cause winter warming over Eurasia. Furthermore, by inspecting individual eruptions rather than combining events into a superposed epoch analysis, we are able to reconcile our findings with those of previous studies. Analysis of two additional paleoclimatic datasets corroborates the lack of post-eruption Eurasian winter warming. Our findings, covering the entire Last Millennium, confirm the findings of most recent modeling studies, and offer important new evidence that large low-latitude eruptions are not, in general, followed by significant surface wintertime warming over Eurasia.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504520","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 : 2024-07-02DOI: 10.1175/jcli-d-24-0072.1
Shanling Cheng, Haipeng Yu, Jie Zhou, Bofei Zhang, Yu Ren, Hongyu Luo, Siyu Chen, Yongqi Gong, Ming Peng, Yunsai Zhu
Abstract Eurasia is a sensitive and high-risk region for global climate changes, where climate anomalies significantly influence natural ecosystems, human health, and economic development. The North Atlantic tripole (NAT) sea surface temperature anomaly is crucial to interannual precipitation variations in Eurasia. Several studies have focused on the link between the NAT and climate anomalies in winter and spring. However, the mechanism by which the summer NAT impacts climate anomalies in Eurasia remains unclear. This study examines how the NAT impacts interannual variations of summer precipitation in mid-high-latitude Eurasia. Precipitation variations are associated with the atmospheric teleconnection triggered by the NAT. When the NAT is in its positive phase, the anomalous atmospheric diabatic heating over the North Atlantic excites an equivalent-barotropic Rossby wave train response that propagates eastward toward the Eurasia, resulting in atmospheric circulation anomalies over the region. The combined effects of atmospheric circulation, radiative forcing, and water vapor transport anomalies lead to decreased precipitation across Northern Europe and central Eurasia, with higher precipitation anomalies over the Northeast Asia. Finally, numerical experiments verify that the summer NAT excites atmospheric teleconnections that propagate downstream, affecting precipitation anomalies in mid-high-latitude Eurasia. This study provides a scientific basis for predicting Eurasian summer precipitation and strengthening disaster management strategies.
{"title":"Impact of Summer North Atlantic Sea Surface Temperature Tripole on Precipitation over Mid–high-latitude Eurasia","authors":"Shanling Cheng, Haipeng Yu, Jie Zhou, Bofei Zhang, Yu Ren, Hongyu Luo, Siyu Chen, Yongqi Gong, Ming Peng, Yunsai Zhu","doi":"10.1175/jcli-d-24-0072.1","DOIUrl":"https://doi.org/10.1175/jcli-d-24-0072.1","url":null,"abstract":"Abstract Eurasia is a sensitive and high-risk region for global climate changes, where climate anomalies significantly influence natural ecosystems, human health, and economic development. The North Atlantic tripole (NAT) sea surface temperature anomaly is crucial to interannual precipitation variations in Eurasia. Several studies have focused on the link between the NAT and climate anomalies in winter and spring. However, the mechanism by which the summer NAT impacts climate anomalies in Eurasia remains unclear. This study examines how the NAT impacts interannual variations of summer precipitation in mid-high-latitude Eurasia. Precipitation variations are associated with the atmospheric teleconnection triggered by the NAT. When the NAT is in its positive phase, the anomalous atmospheric diabatic heating over the North Atlantic excites an equivalent-barotropic Rossby wave train response that propagates eastward toward the Eurasia, resulting in atmospheric circulation anomalies over the region. The combined effects of atmospheric circulation, radiative forcing, and water vapor transport anomalies lead to decreased precipitation across Northern Europe and central Eurasia, with higher precipitation anomalies over the Northeast Asia. Finally, numerical experiments verify that the summer NAT excites atmospheric teleconnections that propagate downstream, affecting precipitation anomalies in mid-high-latitude Eurasia. This study provides a scientific basis for predicting Eurasian summer precipitation and strengthening disaster management strategies.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504519","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 : 2024-07-01DOI: 10.1175/jcli-d-23-0179.1
Xiaolu Li, Toby Ault, Andrew D. Richardson, Steve Frolking, Dimitris A. Herrera, Mark A. Friedl, Carlos M. Carrillo, Colin P. Evans
Abstract Plant phenology influences both the terrestrial carbon cycle and land-atmosphere interactions, and therefore can potentially modify large-scale circulations in the atmosphere. However, considerable discrepancies are present among models and between model simulations and observations of plant phenology, adding large uncertainties to future climate projections. Here we modified plant phenology in the Northern Hemisphere in the Community Earth System Model and conducted simulations to characterize how differences in plant phenology influence land-atmosphere coupling. Plant phenology changes the land surface and land-atmosphere interactions by directly modulating absorbed solar radiation and evapotranspiration and indirectly modifying cloud feedback and snow-albedo feedback. Over the Northern Hemisphere, the largest effects occur from March to June when seasonal deciduous phenology is modified from satellite-derived values to model simulations, which results in a >3K increase in surface temperature that propagates to 500hPa (~5km height). Phenology-induced changes in canopy evapotranspiration and surface temperature depend on soil moisture availability during the growing season. Surface temperature decreases significantly due to increasing latent heat flux and cloud reflection where soil moisture is abundant, while soil moisture control over evapotranspiration increases and surface temperature remains little-changed or even increases in more arid regions. Characterizing the influence of phenology on biogeophysical processes is critical, as significant impacts are present both at the land surface and in the atmospheric layers above.
{"title":"Northern hemisphere land-atmosphere feedback from prescribed plant phenology in CESM","authors":"Xiaolu Li, Toby Ault, Andrew D. Richardson, Steve Frolking, Dimitris A. Herrera, Mark A. Friedl, Carlos M. Carrillo, Colin P. Evans","doi":"10.1175/jcli-d-23-0179.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0179.1","url":null,"abstract":"Abstract Plant phenology influences both the terrestrial carbon cycle and land-atmosphere interactions, and therefore can potentially modify large-scale circulations in the atmosphere. However, considerable discrepancies are present among models and between model simulations and observations of plant phenology, adding large uncertainties to future climate projections. Here we modified plant phenology in the Northern Hemisphere in the Community Earth System Model and conducted simulations to characterize how differences in plant phenology influence land-atmosphere coupling. Plant phenology changes the land surface and land-atmosphere interactions by directly modulating absorbed solar radiation and evapotranspiration and indirectly modifying cloud feedback and snow-albedo feedback. Over the Northern Hemisphere, the largest effects occur from March to June when seasonal deciduous phenology is modified from satellite-derived values to model simulations, which results in a >3K increase in surface temperature that propagates to 500hPa (~5km height). Phenology-induced changes in canopy evapotranspiration and surface temperature depend on soil moisture availability during the growing season. Surface temperature decreases significantly due to increasing latent heat flux and cloud reflection where soil moisture is abundant, while soil moisture control over evapotranspiration increases and surface temperature remains little-changed or even increases in more arid regions. Characterizing the influence of phenology on biogeophysical processes is critical, as significant impacts are present both at the land surface and in the atmospheric layers above.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504524","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 : 2024-07-01DOI: 10.1175/jcli-d-23-0605.1
Ting-Chen Chen, Christoph Braun, Aiko Voigt, Joaquim G. Pinto
Abstract To understand how extratropical cyclones (ETCs) may change in a warmer climate, we conduct idealized baroclinic life cycle simulations using the ICON-NWP model with varied initial conditions. With respect to a present-day climate, two experiments are highlighted: a 4K uniform warming and a more realistic late 21st-century warming pattern projected by a CMIP6 model. Different ETC deepening mechanisms, especially by diabatic processes, are quantified via the pressure tendency equation analysis, and the horizontal model resolution dependency is examined by contrasting coarse-grid (80 km) and convection-permitting (2.5 km) simulations. While our simulated ETCs are primarily baroclinically driven, dominated by the horizontal warm-air advection in the air column above the surface low, such an effect only strengthens by 10% in both warming experiments. However, the direct contribution of diabatic heating to surface pressure drop almost doubles, which likely feeds back positively to horizontal warm-air advection. Although their combined response to warming is pronounced, it is largely offset by the strengthened adiabatic cooling (17%) due to enhanced upward motions in warmer and moister ETCs, leading to a marginal ETC deepening at maturity (lowers by ~ 1.5–4 hPa). Nevertheless, the near-surface impacts strongly increase, particularly the local extreme precipitation (up to 56%). The convection-permitting and the coarse-grid simulations show qualitatively consistent ETC responses to global warming. We suggest that the systematically weaker ETCs (with higher central pressure) in 2.5 km compared to 80 km simulations might be primarily caused by model uncertainty in representing the convective-diabatic heating over the warm front near the cyclone core.
{"title":"Changes of intense extratropical cyclone deepening mechanisms in a warmer climate in idealized simulations","authors":"Ting-Chen Chen, Christoph Braun, Aiko Voigt, Joaquim G. Pinto","doi":"10.1175/jcli-d-23-0605.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0605.1","url":null,"abstract":"Abstract To understand how extratropical cyclones (ETCs) may change in a warmer climate, we conduct idealized baroclinic life cycle simulations using the ICON-NWP model with varied initial conditions. With respect to a present-day climate, two experiments are highlighted: a 4K uniform warming and a more realistic late 21st-century warming pattern projected by a CMIP6 model. Different ETC deepening mechanisms, especially by diabatic processes, are quantified via the pressure tendency equation analysis, and the horizontal model resolution dependency is examined by contrasting coarse-grid (80 km) and convection-permitting (2.5 km) simulations. While our simulated ETCs are primarily baroclinically driven, dominated by the horizontal warm-air advection in the air column above the surface low, such an effect only strengthens by 10% in both warming experiments. However, the direct contribution of diabatic heating to surface pressure drop almost doubles, which likely feeds back positively to horizontal warm-air advection. Although their combined response to warming is pronounced, it is largely offset by the strengthened adiabatic cooling (17%) due to enhanced upward motions in warmer and moister ETCs, leading to a marginal ETC deepening at maturity (lowers by ~ 1.5–4 hPa). Nevertheless, the near-surface impacts strongly increase, particularly the local extreme precipitation (up to 56%). The convection-permitting and the coarse-grid simulations show qualitatively consistent ETC responses to global warming. We suggest that the systematically weaker ETCs (with higher central pressure) in 2.5 km compared to 80 km simulations might be primarily caused by model uncertainty in representing the convective-diabatic heating over the warm front near the cyclone core.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504523","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 : 2024-06-28DOI: 10.1175/jcli-d-23-0731.1
Chanil Park, Seok-Woo Son
Abstract East Asian atmospheric rivers (ARs) exhibit the most pronounced activity in summer with significant impacts on monsoon rainfall. However, their detailed characteristics from a synoptic perspective are yet to be revealed. In this study, we unravel the inherently complex nature of East Asian summer ARs by applying a multiscale index that quantifies the relative importance of high- (HF) and low-frequency (LF) moisture transports in AR development. It is found that both HF and LF processes contribute to shaping the summertime ARs in East Asia, contrasting to the wintertime ARs dominated by HF processes. Stratification of ARs with the multiscale index reveals that HF-dominant ARs are driven by baroclinically-deepening extratropical cyclones, analogous to the widely-accepted definition of canonical ARs. In contrast, LF-dominant ARs result from enhanced monsoon southwesterly between a quasi-stationary cyclone and anticyclone with the latter being the anomalous expansion of the western North Pacific subtropical high, reminiscent of the classical monsoon rainband. While HF-dominant ARs are transient, LF-dominant ARs are quasi-stationary with a higher potential for prolonged local impacts. The intermediate ARs, constituting a majority of East Asian summer ARs, exhibit synoptic conditions that combine HF- and LF-dominant ARs. Therefore, East Asian summer ARs cannot be explained by a single mechanism but should be considered as a continuum of extratropical cyclone-induced and fluctuating monsoon flow-induced moisture plumes. This finding would serve as a base for the advanced understanding of hydrological impacts, variability, and projected change of East Asian ARs.
摘要 东亚大气河流（ARs）在夏季表现出最明显的活动，对季风降雨有重大影响。然而，从同步角度来看，它们的详细特征尚待揭示。在本研究中，我们采用了一种多尺度指数，量化了高频（HF）和低频（LF）水汽输送在 AR 发展过程中的相对重要性，从而揭示了东亚夏季 AR 的内在复杂性。研究发现，高频和低频过程都有助于形成东亚夏季的大气环流，这与高频过程主导的冬季大气环流形成鲜明对比。用多尺度指数对ARs进行分层显示，高频主导的ARs是由气压加深的外热带气旋驱动的，这与广泛接受的典型ARs定义相似。与此相反，LF 主导的自回归现象是由准静止气旋和反气旋之间增强的季风西南气流造成的，后者是北太平洋西部副热带高压的异常扩张，让人联想到经典的季风雨带。以高频为主的反气旋是短暂的，而以低频为主的反气旋则是准静止的，更有可能对局部地区造成长期影响。构成东亚夏季季候风大部分的中间型季候风表现出结合高频和低频主导型季候风的同步条件。因此，东亚夏季气旋不能用单一机制来解释，而应将其视为外热带气旋诱发和季风气流诱发水汽羽流波动的连续体。这一发现将为进一步了解东亚夏季气旋的水文影响、变异性和预测变化提供基础。
{"title":"Atmospheric rivers in East Asia summer as the continuum of extratropical and monsoonal moisture plumes","authors":"Chanil Park, Seok-Woo Son","doi":"10.1175/jcli-d-23-0731.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0731.1","url":null,"abstract":"Abstract East Asian atmospheric rivers (ARs) exhibit the most pronounced activity in summer with significant impacts on monsoon rainfall. However, their detailed characteristics from a synoptic perspective are yet to be revealed. In this study, we unravel the inherently complex nature of East Asian summer ARs by applying a multiscale index that quantifies the relative importance of high- (HF) and low-frequency (LF) moisture transports in AR development. It is found that both HF and LF processes contribute to shaping the summertime ARs in East Asia, contrasting to the wintertime ARs dominated by HF processes. Stratification of ARs with the multiscale index reveals that HF-dominant ARs are driven by baroclinically-deepening extratropical cyclones, analogous to the widely-accepted definition of canonical ARs. In contrast, LF-dominant ARs result from enhanced monsoon southwesterly between a quasi-stationary cyclone and anticyclone with the latter being the anomalous expansion of the western North Pacific subtropical high, reminiscent of the classical monsoon rainband. While HF-dominant ARs are transient, LF-dominant ARs are quasi-stationary with a higher potential for prolonged local impacts. The intermediate ARs, constituting a majority of East Asian summer ARs, exhibit synoptic conditions that combine HF- and LF-dominant ARs. Therefore, East Asian summer ARs cannot be explained by a single mechanism but should be considered as a continuum of extratropical cyclone-induced and fluctuating monsoon flow-induced moisture plumes. This finding would serve as a base for the advanced understanding of hydrological impacts, variability, and projected change of East Asian ARs.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504525","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 : 2024-06-27DOI: 10.1175/jcli-d-23-0120.1
Yingfei Fang, Song Yang, Xiaoming Hu, Shuheng Lin, James A. Screen, Shangfeng Chen
Abstract The Ross Ice Shelf (RIS) experiences surface melt events in summer, which could accelerate ice loss and destabilize the ice sheet in a warming world. This study links the interannual variability of RIS surface melt to the northerly wind anomaly over the Ross Sea sector, which is established in association with the quasi-geostrophic barotropic Rossby wave trains from the tropical Pacific and subtropical Australia toward West Antarctica. Atmospheric general circulation model experiments suggest that these Rossby wave trains are regulated by El Niño-related sea surface temperature (SST) anomalies in the tropical central-eastern Pacific and atmospheric heating anomalies over western Australia. El Niño provides an important forcing of the atmospheric circulation anomalies over the Ross Sea via inducing a Rossby wave train, and most surface melt events over the RIS happen during El Niño years. In addition, the anomalous atmospheric heating over western Australia, which is independent of El Niño, is another important forcing that triggers a Rossby wave train extending from subtropical Australia to Ross Sea. The northerly flow towards the Ross Sea induces strong poleward moisture and heat transport, which further contributes to surface melt over the RIS.
{"title":"Remote Forcing for Circulation Pattern Favorable to Surface Melt over the Ross Ice Shelf","authors":"Yingfei Fang, Song Yang, Xiaoming Hu, Shuheng Lin, James A. Screen, Shangfeng Chen","doi":"10.1175/jcli-d-23-0120.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0120.1","url":null,"abstract":"Abstract The Ross Ice Shelf (RIS) experiences surface melt events in summer, which could accelerate ice loss and destabilize the ice sheet in a warming world. This study links the interannual variability of RIS surface melt to the northerly wind anomaly over the Ross Sea sector, which is established in association with the quasi-geostrophic barotropic Rossby wave trains from the tropical Pacific and subtropical Australia toward West Antarctica. Atmospheric general circulation model experiments suggest that these Rossby wave trains are regulated by El Niño-related sea surface temperature (SST) anomalies in the tropical central-eastern Pacific and atmospheric heating anomalies over western Australia. El Niño provides an important forcing of the atmospheric circulation anomalies over the Ross Sea via inducing a Rossby wave train, and most surface melt events over the RIS happen during El Niño years. In addition, the anomalous atmospheric heating over western Australia, which is independent of El Niño, is another important forcing that triggers a Rossby wave train extending from subtropical Australia to Ross Sea. The northerly flow towards the Ross Sea induces strong poleward moisture and heat transport, which further contributes to surface melt over the RIS.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504526","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 : 2024-06-26DOI: 10.1175/jcli-d-23-0699.1
Joanna Rodgers, Vasubandhu Misra, C. B. Jayasankar
Abstract We introduce a simple method to define the start and the end of the rainiest part of the year as the first and the last day of the year when the daily rain rate is more or less than the annual mean climatological rain rate for a region or at a given grid point of the rainfall analysis, respectively. A novelty of this work is the adoption of a perturbation technique to generate a total of 1001 ensemble members to account for observational and analysis uncertainties. This allows for a probabilistic estimate of the start and retreat dates of the rainy season at the granularity of the Integrated Multi-Satellite Retrievals for Global Precipitation Mission version 6 (IMERG) rainfall analysis over Central America. The seasonal cycle of the IMERG rainfall analysis is also found to verify with in situ observations in the region. Many large scale climate drivers affect regional rainfall, often with complex interactions that affect the onset date, retreat date, and magnitude of the seasonal rainfall cycle, making it difficult to predict the length or total quantity of seasonal rainfall using climate drivers alone. Once an onset date is established, however, this metric alone can be more indicative of both the length and total seasonal rainfall anomaly than predicting how the climate drivers will interact to affect the quantity and duration of upcoming seasonal rainfall. The local relationships of the start date with seasonal length and rainfall anomaly are leveraged to produce effective seasonal outlooks of the rainy season for the region by just monitoring the start date variations.
{"title":"Using the observed variations of the start date of the rainy season over Central America for its reliable seasonal outlook","authors":"Joanna Rodgers, Vasubandhu Misra, C. B. Jayasankar","doi":"10.1175/jcli-d-23-0699.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0699.1","url":null,"abstract":"Abstract We introduce a simple method to define the start and the end of the rainiest part of the year as the first and the last day of the year when the daily rain rate is more or less than the annual mean climatological rain rate for a region or at a given grid point of the rainfall analysis, respectively. A novelty of this work is the adoption of a perturbation technique to generate a total of 1001 ensemble members to account for observational and analysis uncertainties. This allows for a probabilistic estimate of the start and retreat dates of the rainy season at the granularity of the Integrated Multi-Satellite Retrievals for Global Precipitation Mission version 6 (IMERG) rainfall analysis over Central America. The seasonal cycle of the IMERG rainfall analysis is also found to verify with in situ observations in the region. Many large scale climate drivers affect regional rainfall, often with complex interactions that affect the onset date, retreat date, and magnitude of the seasonal rainfall cycle, making it difficult to predict the length or total quantity of seasonal rainfall using climate drivers alone. Once an onset date is established, however, this metric alone can be more indicative of both the length and total seasonal rainfall anomaly than predicting how the climate drivers will interact to affect the quantity and duration of upcoming seasonal rainfall. The local relationships of the start date with seasonal length and rainfall anomaly are leveraged to produce effective seasonal outlooks of the rainy season for the region by just monitoring the start date variations.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504529","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 : 2024-06-26DOI: 10.1175/jcli-d-24-0074.1
Donghyun Lee, Sarah Sparrow, Nicholas Leach, Scott Osprey, Jinah Lee, Myles Allen
Abstract The importance of extreme event attribution rises as climate change causes severe damage to populations resulting from unprecedented events. In February 2019, a planetary wave shifted along the U.S.-Canadian border, simultaneously leading to troughing with anomalous cold events and ridging over Alaska and northern Canada with abnormal warm events. Also, a dry-stabilized anticyclonic circulation over low latitudes induced warm extreme events over Mexico and U.S. Florida. Most attribution studies compare the climate model simulations under natural or actual forcing conditions and assess probabilistically from a climatological point of view. However, in this study, we use multiple ensembles from an operational forecast model, promising statistical as well as dynamically constrained attribution assessment, often referred to as the storyline approach to extreme event attribution. In the globally averaged results, increasing CO2 concentrations lead to distinct warming signals at the surface, resulting mainly from diabatic heating. Our study finds that CO2-induced warming eventually affects the possibility of extreme events in North America, quantifying the impact of anthropogenic forcing over less than a week’s forecast simulation. Our study assesses the validity of the storyline approach conditional on the forecast lead times, which is hindered by rising noise in CO2 signals and the declining performance of the forecast model. The forecast-based storyline approach is valid for at least half of the land area within a six-day lead time before the target extreme occurrence. Our attribution results highlight the importance of achieving net-zero emissions ahead of schedule to reduce the occurrence of severe heatwaves.
{"title":"The attribution of February extremes over North America: A forecast-based storyline study","authors":"Donghyun Lee, Sarah Sparrow, Nicholas Leach, Scott Osprey, Jinah Lee, Myles Allen","doi":"10.1175/jcli-d-24-0074.1","DOIUrl":"https://doi.org/10.1175/jcli-d-24-0074.1","url":null,"abstract":"Abstract The importance of extreme event attribution rises as climate change causes severe damage to populations resulting from unprecedented events. In February 2019, a planetary wave shifted along the U.S.-Canadian border, simultaneously leading to troughing with anomalous cold events and ridging over Alaska and northern Canada with abnormal warm events. Also, a dry-stabilized anticyclonic circulation over low latitudes induced warm extreme events over Mexico and U.S. Florida. Most attribution studies compare the climate model simulations under natural or actual forcing conditions and assess probabilistically from a climatological point of view. However, in this study, we use multiple ensembles from an operational forecast model, promising statistical as well as dynamically constrained attribution assessment, often referred to as the storyline approach to extreme event attribution. In the globally averaged results, increasing CO2 concentrations lead to distinct warming signals at the surface, resulting mainly from diabatic heating. Our study finds that CO2-induced warming eventually affects the possibility of extreme events in North America, quantifying the impact of anthropogenic forcing over less than a week’s forecast simulation. Our study assesses the validity of the storyline approach conditional on the forecast lead times, which is hindered by rising noise in CO2 signals and the declining performance of the forecast model. The forecast-based storyline approach is valid for at least half of the land area within a six-day lead time before the target extreme occurrence. Our attribution results highlight the importance of achieving net-zero emissions ahead of schedule to reduce the occurrence of severe heatwaves.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504527","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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