Pub Date : 2024-07-17DOI: 10.1175/jcli-d-23-0635.1
Xuan Zhou, Lu Wang, Pang-chi Hsu, Tim Li, Baoqiang Xiang
The prediction skill for individual Madden-Julian Oscillation (MJO) events is highly variable, but the key factors behind this remain unclear. Using the latest hindcast results from the Subseasonal-to-Seasonal (S2S) Phase II models, this study attempts to understand the diverse prediction skill for the MJO events with an enhanced convective anomaly over the eastern Indian Ocean (IO) at the forecast start date, by investigating the preference of the prediction skill to the MJO-associated convective anomalies and low-frequency background states (LFBS). Compared to the low-skill MJO events, the high-skill events are characterized by a stronger intraseasonal convection-circulation couplet over the IO before the forecast start date, which could result in a longer zonal propagation range during the forecast period, thereby leading to a higher score for assessing the prediction skill. The difference in intraseasonal fields can further be attributed to the LFBS of IO sea surface temperature (SST) and quasi-biannual oscillation (QBO), with the high- (low-) skill events corresponding to a warmer (colder) IO and easterly (westerly) QBO phase. The physical link is that a warm IO could increase the low-level convective instability and thus amplify MJO convection over the IO, whereas an easterly QBO phase could weaken the Maritime Continent barrier effect through weakening the static stability near the tropopause, thus favoring eastward propagation of the MJO. It is also found that the combined effects of IO SST and QBO phases are more effective in influencing MJO prediction skill than individual LFBS.
{"title":"Understanding the Factors Controlling MJO Prediction Skill across Events","authors":"Xuan Zhou, Lu Wang, Pang-chi Hsu, Tim Li, Baoqiang Xiang","doi":"10.1175/jcli-d-23-0635.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0635.1","url":null,"abstract":"\u0000The prediction skill for individual Madden-Julian Oscillation (MJO) events is highly variable, but the key factors behind this remain unclear. Using the latest hindcast results from the Subseasonal-to-Seasonal (S2S) Phase II models, this study attempts to understand the diverse prediction skill for the MJO events with an enhanced convective anomaly over the eastern Indian Ocean (IO) at the forecast start date, by investigating the preference of the prediction skill to the MJO-associated convective anomalies and low-frequency background states (LFBS). Compared to the low-skill MJO events, the high-skill events are characterized by a stronger intraseasonal convection-circulation couplet over the IO before the forecast start date, which could result in a longer zonal propagation range during the forecast period, thereby leading to a higher score for assessing the prediction skill. The difference in intraseasonal fields can further be attributed to the LFBS of IO sea surface temperature (SST) and quasi-biannual oscillation (QBO), with the high- (low-) skill events corresponding to a warmer (colder) IO and easterly (westerly) QBO phase. The physical link is that a warm IO could increase the low-level convective instability and thus amplify MJO convection over the IO, whereas an easterly QBO phase could weaken the Maritime Continent barrier effect through weakening the static stability near the tropopause, thus favoring eastward propagation of the MJO. It is also found that the combined effects of IO SST and QBO phases are more effective in influencing MJO prediction skill than individual LFBS.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.8,"publicationDate":"2024-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141829125","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 : 2024-07-11DOI: 10.1175/jcli-d-24-0097.1
Hai Lin, R. Muncaster, J. Derome, W. Merryfield, Gulilat Diro
In contrast to boreal winter when extratropical seasonal predictions benefit greatly from ENSO-related teleconnections, our understanding of forecast skill and sources of predictability in summer is limited. Based on 40 years of hindcasts of the Canadian Seasonal to Inter-annual Prediction System version 3 (CanSIPSv3), this study shows that predictions for the Northern Hemisphere summer surface air temperature are skillful more than six months in advance in several middle latitude regions, including eastern Europe–Middle East, central Siberia–Mongolia–North China, and the western United States. These midlatitude regions of statistically significant predictive skill appear to be connected to each other through an upper tropospheric circum-global wave train. Although a large part of the forecast skill for the surface air temperature and 500 hPa geopotential height is attributable to the linear trend associated with global warming, there is significant long-lead seasonal forecast skill related to interannual variability. Two additional idealized hindcast experiments are performed to help shed light on sources of the long-lead forecast skill using one of the CanSIPSv3 models and its uncoupled version. It is found that tropical ENSO related SST anomalies contribute to the forecast skill in the western United States, while land surface conditions in winter, including snow cover and soil moisture, in the Siberian and western United States regions have a delayed or long-lasting impact on the atmosphere, which leads to summer forecast skill in these regions. This implies that improving land surface initial conditions and model representation of land surface processes is crucial for further development of a seasonal forecasting system.
{"title":"Skillful long-lead seasonal predictions in the summertime Northern Hemisphere middle latitudes","authors":"Hai Lin, R. Muncaster, J. Derome, W. Merryfield, Gulilat Diro","doi":"10.1175/jcli-d-24-0097.1","DOIUrl":"https://doi.org/10.1175/jcli-d-24-0097.1","url":null,"abstract":"\u0000In contrast to boreal winter when extratropical seasonal predictions benefit greatly from ENSO-related teleconnections, our understanding of forecast skill and sources of predictability in summer is limited. Based on 40 years of hindcasts of the Canadian Seasonal to Inter-annual Prediction System version 3 (CanSIPSv3), this study shows that predictions for the Northern Hemisphere summer surface air temperature are skillful more than six months in advance in several middle latitude regions, including eastern Europe–Middle East, central Siberia–Mongolia–North China, and the western United States. These midlatitude regions of statistically significant predictive skill appear to be connected to each other through an upper tropospheric circum-global wave train. Although a large part of the forecast skill for the surface air temperature and 500 hPa geopotential height is attributable to the linear trend associated with global warming, there is significant long-lead seasonal forecast skill related to interannual variability. Two additional idealized hindcast experiments are performed to help shed light on sources of the long-lead forecast skill using one of the CanSIPSv3 models and its uncoupled version. It is found that tropical ENSO related SST anomalies contribute to the forecast skill in the western United States, while land surface conditions in winter, including snow cover and soil moisture, in the Siberian and western United States regions have a delayed or long-lasting impact on the atmosphere, which leads to summer forecast skill in these regions. This implies that improving land surface initial conditions and model representation of land surface processes is crucial for further development of a seasonal forecasting system.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.8,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141658049","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 : 2024-07-10DOI: 10.1175/jcli-d-24-0002.1
Xiao-Tong Zheng, C. Hui, Zi-Wen Han, Yue Wu
El Niño‒Southern Oscillation (ENSO) is the leading mode of interannual ocean‒atmosphere coupling in the tropical Pacific, greatly influencing the global climate system. Seasonal phase locking, which means that ENSO events usually peak in boreal winter, is a distinctive feature of ENSO. In model future projections, the ENSO sea surface temperature (SST) amplitude in winter shows no significant change with a large intermodel spread. However, whether and how ENSO phase locking will respond to global warming are not fully understood. In this study, using CESM large ensemble (CESM-LE) projections, we found that the seasonality of ENSO events, especially its peak phase, has advanced under global warming. This phenomenon corresponds to the seasonal difference in the changes in the ENSO SST amplitude with an enhanced (weakened) amplitude from boreal summer to autumn (winter). Mixed layer ocean heat budget analysis revealed that the advanced ENSO seasonality is due to intensified positive meridional advective and thermocline feedback during the ENSO developing phase, and intensified negative thermal damping during the ENSO peak phase. Furthermore, the seasonal variation in the mean El Niño-like SST warming in the tropical Pacific favors a weakened zonal advective feedback in boreal autumn-winter and earlier decay of ENSO. The advance of the ENSO peak phase is also found in most CMIP5/6 models that simulate the seasonal phase locking of ENSO well in the present climate. Thus, even though the amplitude response in the winter shows no model consensus, ENSO also significantly changes during different stages under global warming.
{"title":"Advanced Peak Phase of ENSO under Global Warming","authors":"Xiao-Tong Zheng, C. Hui, Zi-Wen Han, Yue Wu","doi":"10.1175/jcli-d-24-0002.1","DOIUrl":"https://doi.org/10.1175/jcli-d-24-0002.1","url":null,"abstract":"\u0000El Niño‒Southern Oscillation (ENSO) is the leading mode of interannual ocean‒atmosphere coupling in the tropical Pacific, greatly influencing the global climate system. Seasonal phase locking, which means that ENSO events usually peak in boreal winter, is a distinctive feature of ENSO. In model future projections, the ENSO sea surface temperature (SST) amplitude in winter shows no significant change with a large intermodel spread. However, whether and how ENSO phase locking will respond to global warming are not fully understood. In this study, using CESM large ensemble (CESM-LE) projections, we found that the seasonality of ENSO events, especially its peak phase, has advanced under global warming. This phenomenon corresponds to the seasonal difference in the changes in the ENSO SST amplitude with an enhanced (weakened) amplitude from boreal summer to autumn (winter). Mixed layer ocean heat budget analysis revealed that the advanced ENSO seasonality is due to intensified positive meridional advective and thermocline feedback during the ENSO developing phase, and intensified negative thermal damping during the ENSO peak phase. Furthermore, the seasonal variation in the mean El Niño-like SST warming in the tropical Pacific favors a weakened zonal advective feedback in boreal autumn-winter and earlier decay of ENSO. The advance of the ENSO peak phase is also found in most CMIP5/6 models that simulate the seasonal phase locking of ENSO well in the present climate. Thus, even though the amplitude response in the winter shows no model consensus, ENSO also significantly changes during different stages under global warming.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.8,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141662688","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 : 2024-07-10DOI: 10.1175/jcli-d-24-0051.1
Cameron Dong, Y. Peings, Gudrun Magnusdottir
We analyze biases in subseasonal forecast models and their effect on Southwest United States (SWUS) precipitation prediction (2–6 week timescale). Cluster analyses identify three primary wavetrains associated with SWUS precipitation: a meridional El NiñoSouthern Oscillation-type (ENSO) wavetrain, an arching PacificNorth American-type (PNA) wavetrain, and a circumglobal zonal wavetrain. Compared to reanalysis, the models overrepresent the arching pattern, underrepresent the zonal pattern, and produce mixed results for the meridional pattern. The arching pattern overrepresentation is linked to model mean flow biases in the midlatitude-subpolar North Pacific, which cause a westward retraction of the region of forbidden linear Rossby Wave propagation. The zonal pattern underrepresentation is linked to westerly biases in the subtropical jet, which cause a westward retraction of the waveguide in the midlatitude Eastern North Pacific and divert wavetrains southward. These results are confirmed using linear, barotropic ray tracing analysis. In addition to mean state biases, the models also contain errors in their representation of the Madden-Julian Oscillation (MJO). Tropical convection anomalies associated with the MJO are too weak and incoherent at lead times greater than two weeks, when compared to reanalysis. Additionally, there is a strong SWUS precipitation signal as far out as 5 weeks after a strong MJO in reanalysis, associated with its persistent eastward propagation, but this signal is absent in the models. Our results indicate that there is still significant room for improvement in subseasonal predictions, if we can reduce model biases in the background flow and improve the representation of the MJO.
{"title":"How do forecast model biases affect large-scale teleconnections that control Southwest US precipitation? - Part I: S2S models","authors":"Cameron Dong, Y. Peings, Gudrun Magnusdottir","doi":"10.1175/jcli-d-24-0051.1","DOIUrl":"https://doi.org/10.1175/jcli-d-24-0051.1","url":null,"abstract":"\u0000We analyze biases in subseasonal forecast models and their effect on Southwest United States (SWUS) precipitation prediction (2–6 week timescale). Cluster analyses identify three primary wavetrains associated with SWUS precipitation: a meridional El NiñoSouthern Oscillation-type (ENSO) wavetrain, an arching PacificNorth American-type (PNA) wavetrain, and a circumglobal zonal wavetrain. Compared to reanalysis, the models overrepresent the arching pattern, underrepresent the zonal pattern, and produce mixed results for the meridional pattern. The arching pattern overrepresentation is linked to model mean flow biases in the midlatitude-subpolar North Pacific, which cause a westward retraction of the region of forbidden linear Rossby Wave propagation. The zonal pattern underrepresentation is linked to westerly biases in the subtropical jet, which cause a westward retraction of the waveguide in the midlatitude Eastern North Pacific and divert wavetrains southward. These results are confirmed using linear, barotropic ray tracing analysis.\u0000In addition to mean state biases, the models also contain errors in their representation of the Madden-Julian Oscillation (MJO). Tropical convection anomalies associated with the MJO are too weak and incoherent at lead times greater than two weeks, when compared to reanalysis. Additionally, there is a strong SWUS precipitation signal as far out as 5 weeks after a strong MJO in reanalysis, associated with its persistent eastward propagation, but this signal is absent in the models. Our results indicate that there is still significant room for improvement in subseasonal predictions, if we can reduce model biases in the background flow and improve the representation of the MJO.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.8,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141661593","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 : 2024-07-09DOI: 10.1175/jcli-d-23-0141.1
Isaac Davis, Funing Li, Daniel R. Chavas
Abstract The effect of warming on severe convective storm potential is commonly explained in terms of changes in vertically-integrated (“bulk”) environmental parameters, such as CAPE and 0–6-km shear. However, such events are known to depend on details of the vertical structure of the thermodynamic and kinematic environment that can change independently of these bulk parameters. This work examines how warming may affect the complete vertical structure of these environments for fixed ranges of values of high CAPE and bulk shear, using data over the central Great Plains from two high-performing climate models (CNRM and MPI). To first order, projected changes in the vertical sounding structure is consistent between the two models: the environment warms approximately uniformly with height at constant relative humidity and the shear profile remains relatively constant. The boundary layer becomes slightly drier (−2–6% relative humidity) while the free troposphere becomes slightly moister (+1–3%), with a slight increase in moist static energy deficit aloft with stronger magnitude in CNRM. CNRM indicates enhanced low-level shear and storm-relative helicity associated with stronger hodograph curvature in the lowest 2 km, whereas MPI shows near zero change. Both models strongly underestimate shear below 1 km compared to ERA5, indicating large uncertainty in projecting subtle changes in the low-level flow structure in climate models. Evaluation of the net effect of these modest thermodynamic and kinematic changes on severe convective storm outcomes cannot be ascertained here but could be explored in simulation experiments.
{"title":"Future changes in the vertical structure of severe convective storm environments over the U.S. central Great Plains","authors":"Isaac Davis, Funing Li, Daniel R. Chavas","doi":"10.1175/jcli-d-23-0141.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0141.1","url":null,"abstract":"Abstract The effect of warming on severe convective storm potential is commonly explained in terms of changes in vertically-integrated (“bulk”) environmental parameters, such as CAPE and 0–6-km shear. However, such events are known to depend on details of the vertical structure of the thermodynamic and kinematic environment that can change independently of these bulk parameters. This work examines how warming may affect the complete vertical structure of these environments for fixed ranges of values of high CAPE and bulk shear, using data over the central Great Plains from two high-performing climate models (CNRM and MPI). To first order, projected changes in the vertical sounding structure is consistent between the two models: the environment warms approximately uniformly with height at constant relative humidity and the shear profile remains relatively constant. The boundary layer becomes slightly drier (−2–6% relative humidity) while the free troposphere becomes slightly moister (+1–3%), with a slight increase in moist static energy deficit aloft with stronger magnitude in CNRM. CNRM indicates enhanced low-level shear and storm-relative helicity associated with stronger hodograph curvature in the lowest 2 km, whereas MPI shows near zero change. Both models strongly underestimate shear below 1 km compared to ERA5, indicating large uncertainty in projecting subtle changes in the low-level flow structure in climate models. Evaluation of the net effect of these modest thermodynamic and kinematic changes on severe convective storm outcomes cannot be ascertained here but could be explored in simulation experiments.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract This study explores how future SST warming in remote ocean basins may affect the western North Pacific (WNP) wet season climate by applying a high-resolution atmospheric general circulation model to conduct a series of numerical experiments. A marked precipitation and tropical cyclone (TC) activity reduction, as well as enhanced anticyclonic circulation, in the WNP is projected in AMIP experiments forced by SST change in a future warming scenario. The sensitivity experiments reveal that various SST warming phenomena (e.g., in the global SST warming pattern, the tropical ocean belt, the Indian Ocean, tropical Atlantic, the subtropical northeast Pacific) and the increase of greenhouse gas concentration could weaken the precipitation, TC activity, and circulation. By contrast, the SST warming in the WNP and eastern equatorial Pacific have opposite and mixed effects, respectively, and tend to weakly offset the dominant influences of remote ocean warming. These results indicate that the WNP, being the epicenter of the global teleconnection of divergent and rotational flow, is susceptible to the influence of the SST warming in remote ocean basins. The remote forcing as projected in future scenarios would overwhelm the enhancing effect of local SST warming and weaken the circulation, convection, and TC activity in the WNP. These findings further the understanding of how the decreased precipitation and enhanced subtropical high in the WNP may be easily triggered by remote SST warming as revealed in the AMIP-type simulations. How this effect would be affected by air-sea coupling needs further investigation.
{"title":"Impacts of Local and Remote SST Warming on Summer Circulation Changes in the Western North Pacific","authors":"Chao-An Chen, Huang-Hsiung Hsu, Hsin-Chien Liang, Yu-Luen Chen, Ping-Gin Chiu, Chia-Ying Tu","doi":"10.1175/jcli-d-23-0403.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0403.1","url":null,"abstract":"Abstract This study explores how future SST warming in remote ocean basins may affect the western North Pacific (WNP) wet season climate by applying a high-resolution atmospheric general circulation model to conduct a series of numerical experiments. A marked precipitation and tropical cyclone (TC) activity reduction, as well as enhanced anticyclonic circulation, in the WNP is projected in AMIP experiments forced by SST change in a future warming scenario. The sensitivity experiments reveal that various SST warming phenomena (e.g., in the global SST warming pattern, the tropical ocean belt, the Indian Ocean, tropical Atlantic, the subtropical northeast Pacific) and the increase of greenhouse gas concentration could weaken the precipitation, TC activity, and circulation. By contrast, the SST warming in the WNP and eastern equatorial Pacific have opposite and mixed effects, respectively, and tend to weakly offset the dominant influences of remote ocean warming. These results indicate that the WNP, being the epicenter of the global teleconnection of divergent and rotational flow, is susceptible to the influence of the SST warming in remote ocean basins. The remote forcing as projected in future scenarios would overwhelm the enhancing effect of local SST warming and weaken the circulation, convection, and TC activity in the WNP. These findings further the understanding of how the decreased precipitation and enhanced subtropical high in the WNP may be easily triggered by remote SST warming as revealed in the AMIP-type simulations. How this effect would be affected by air-sea coupling needs further investigation.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569966","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 : 2024-07-04DOI: 10.1175/jcli-d-22-0924.1
Sicheng He, Tetsuya Takemi
Abstract Extreme precipitation is expected to pose a more severe threat to human society in the future. This work assessed the historical performance and future changes of extreme precipitation and related atmospheric conditions in a large ensemble climate prediction dataset, the database for Policy Decision-making for Future climate change (d4PDF), over East Asia. Compared with the TRMM and ERA5 datasets, the historical climate in d4PDF represents favorably the precipitation characteristics and the atmospheric conditions, although some differences are notable in the moisture, vertical motion, and cloud water fields. The future climate projection indicates that both the frequency and intensity of heavy precipitation events over East Asia increase compared with those in the present climate. However, when comparing the atmospheric conditions in the historical and future climates for the same precipitation intensity range, the future climate indicates smaller relatively humidity, weaker ascent, less cloud water content, and smaller temperature lapse rate, which negatively affect generating extreme precipitation events. The comparison of the precipitation intensity at the same amount of precipitable water between the historical and future climates indicates that extreme precipitation is weaker in the future, because of the more stabilized troposphere in the future. The general increase in extreme precipitation under future climate is primarily due to the enhanced increase in precipitable water in the higher temperature ranges, which counteracts the negative conditions of the stabilized troposphere.
{"title":"Future Changes of Extreme Precipitation and Related Atmospheric Conditions in East Asia under Global Warming Projected in Large Ensemble Climate Prediction Data","authors":"Sicheng He, Tetsuya Takemi","doi":"10.1175/jcli-d-22-0924.1","DOIUrl":"https://doi.org/10.1175/jcli-d-22-0924.1","url":null,"abstract":"Abstract Extreme precipitation is expected to pose a more severe threat to human society in the future. This work assessed the historical performance and future changes of extreme precipitation and related atmospheric conditions in a large ensemble climate prediction dataset, the database for Policy Decision-making for Future climate change (d4PDF), over East Asia. Compared with the TRMM and ERA5 datasets, the historical climate in d4PDF represents favorably the precipitation characteristics and the atmospheric conditions, although some differences are notable in the moisture, vertical motion, and cloud water fields. The future climate projection indicates that both the frequency and intensity of heavy precipitation events over East Asia increase compared with those in the present climate. However, when comparing the atmospheric conditions in the historical and future climates for the same precipitation intensity range, the future climate indicates smaller relatively humidity, weaker ascent, less cloud water content, and smaller temperature lapse rate, which negatively affect generating extreme precipitation events. The comparison of the precipitation intensity at the same amount of precipitable water between the historical and future climates indicates that extreme precipitation is weaker in the future, because of the more stabilized troposphere in the future. The general increase in extreme precipitation under future climate is primarily due to the enhanced increase in precipitable water in the higher temperature ranges, which counteracts the negative conditions of the stabilized troposphere.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569967","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 : 2024-07-04DOI: 10.1175/jcli-d-23-0769.1
Xiang Han, Tao Lian, Dake Chen, Ruikun Hu, Ting Liu, Qucheng Chu, Baosheng Li
Abstract The Pacific Meridional Mode (PMM) is one of dominant coupled modes in the northeastern tropical Pacific (NETP), characterized by a strip-like sea surface temperature (SST) anomalies spanning from Baja California to the central equatorial Pacific. While the majority of the El Niño events follow a positive PMM, only a few La Niña events are preceded by a negative PMM. Such an asymmetric activity of PMM before the onset of El Niño-Southern Oscillation (ENSO) was previously attributed to the inherent nonlinear response of the wind-evaporation-SST (WES) feedback to trade winds in NETP. Through data analysis and coupled model experiments, we pointed out that PMM is in fact a highly symmetric phenomenon, and the asymmetry of PMM before ENSO onset thus must be associated with ENSO. On the one hand, the nonlinear response of deep convection over the equator to symmetric ENSO forcing in the central equatorial Pacific permits a stronger Pacific North America (PNA) pattern in El Niño years than in La Niña years. On the other hand, since the majority of La Niña events are preceded by a sharp decay of an El Niño, the warm equatorial SST anomalies associated with the preceding El Niño provides another source to trigger PNA before La Niña onset. The two mechanisms modulate the trade winds and heat fluxes in NETP more heavily before La Niña onset than the El Niño onset, and equally contribute to PMM asymmetry before ENSO onset.
{"title":"PNA nonlinearity and ENSO transition asymmetry weaken PMM before La Niña onset","authors":"Xiang Han, Tao Lian, Dake Chen, Ruikun Hu, Ting Liu, Qucheng Chu, Baosheng Li","doi":"10.1175/jcli-d-23-0769.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0769.1","url":null,"abstract":"Abstract The Pacific Meridional Mode (PMM) is one of dominant coupled modes in the northeastern tropical Pacific (NETP), characterized by a strip-like sea surface temperature (SST) anomalies spanning from Baja California to the central equatorial Pacific. While the majority of the El Niño events follow a positive PMM, only a few La Niña events are preceded by a negative PMM. Such an asymmetric activity of PMM before the onset of El Niño-Southern Oscillation (ENSO) was previously attributed to the inherent nonlinear response of the wind-evaporation-SST (WES) feedback to trade winds in NETP. Through data analysis and coupled model experiments, we pointed out that PMM is in fact a highly symmetric phenomenon, and the asymmetry of PMM before ENSO onset thus must be associated with ENSO. On the one hand, the nonlinear response of deep convection over the equator to symmetric ENSO forcing in the central equatorial Pacific permits a stronger Pacific North America (PNA) pattern in El Niño years than in La Niña years. On the other hand, since the majority of La Niña events are preceded by a sharp decay of an El Niño, the warm equatorial SST anomalies associated with the preceding El Niño provides another source to trigger PNA before La Niña onset. The two mechanisms modulate the trade winds and heat fluxes in NETP more heavily before La Niña onset than the El Niño onset, and equally contribute to PMM asymmetry before ENSO onset.","PeriodicalId":15472,"journal":{"name":"Journal of Climate","volume":null,"pages":null},"PeriodicalIF":4.9,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141569968","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 Marine Isotope Stage 3 (MIS 3) is characterized by significant millennial-scale climatic oscillations between cold stadials and mild interstadials, which presents a valuable case for understanding hydrological response to abrupt climate change. Through a set of coupled model simulations, our results broadly show an anti-phased interhemispheric change in land monsoonal precipitation during the present-day relative to MIS 3 interstadial and the stadial-interstadial transition, with a general decrease in the Northern Hemisphere but an increase in the Southern Hemisphere. The anti-phased pattern is largely caused by the change in orbital insolation during the present-day relative to MIS 3 interstadial whereas by the weakened Atlantic Meridional Overturning Circulation during the interstadial-stadial transition. However, there are obvious discrepancies in precipitation response and underlying mechanisms among individual monsoon domains and across different periods. Based on the moisture budget analysis, we indicate that the dynamic factor mainly explains the decreased monsoonal rainfall in the Northern Hemisphere during the present-day relative to the MIS 3 interstadial, whereas the thermodynamic term is largely responsible for the increased precipitation in the Southern Hemisphere. In contrast, the dynamic factor plays an important role in the variation of precipitation over all the monsoon zones from the MIS 3 interstadial to stadial states, with the thermodynamic term mainly contributing to the decreased tropical monsoonal precipitation in the colder Northern Hemisphere. Our results help improve the understanding of global monsoon variations under intermediate glacial climate conditions and shed light on their behaviors under potentially rapid climate change in the future.
摘要 海洋同位素阶段 3（MIS 3）的特点是在寒冷的恒年期和温和的间冰期之间出现显著的千年尺度气候振荡，这为了解水文对气候突变的响应提供了一个有价值的案例。通过一组耦合模型模拟，我们的结果大致显示，在现今相对于 MIS 3 间期和间期-间期过渡期间，陆地季风降水量出现了反阶段的半球间变化，北半球降水量普遍减少，而南半球则有所增加。这种反相模式主要是由于现今相对于 MIS 3 间期的轨道日照变化造成的，而在间期-恒星过渡期间，大西洋经向翻转环流减弱也是造成这种反相模式的原因。然而，不同季风域和不同时期的降水响应及其内在机制存在明显差异。根据水汽预算分析，我们发现，相对于 MIS 3 间期，动态因子主要解释了现今北半球季风降水量减少的原因，而热力学因子则是南半球降水量增加的主要原因。与此相反，动态因子在所有季风区从 MIS 3 间期到恒定期的降水量变化中发挥了重要作用，而热力学因子主要导致了较冷的北半球热带季风降水量的减少。我们的研究结果有助于加深对冰川中期气候条件下全球季风变化的理解，并揭示了未来可能发生的快速气候变化下季风的行为。
{"title":"Deciphering the variations and mechanisms of global land monsoons during Marine Isotope Stage 3","authors":"Jinzhe Zhang, Qing Yan, Nanxuan Jiang, Chuncheng Guo","doi":"10.1175/jcli-d-23-0584.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0584.1","url":null,"abstract":"Abstract Marine Isotope Stage 3 (MIS 3) is characterized by significant millennial-scale climatic oscillations between cold stadials and mild interstadials, which presents a valuable case for understanding hydrological response to abrupt climate change. Through a set of coupled model simulations, our results broadly show an anti-phased interhemispheric change in land monsoonal precipitation during the present-day relative to MIS 3 interstadial and the stadial-interstadial transition, with a general decrease in the Northern Hemisphere but an increase in the Southern Hemisphere. The anti-phased pattern is largely caused by the change in orbital insolation during the present-day relative to MIS 3 interstadial whereas by the weakened Atlantic Meridional Overturning Circulation during the interstadial-stadial transition. However, there are obvious discrepancies in precipitation response and underlying mechanisms among individual monsoon domains and across different periods. Based on the moisture budget analysis, we indicate that the dynamic factor mainly explains the decreased monsoonal rainfall in the Northern Hemisphere during the present-day relative to the MIS 3 interstadial, whereas the thermodynamic term is largely responsible for the increased precipitation in the Southern Hemisphere. In contrast, the dynamic factor plays an important role in the variation of precipitation over all the monsoon zones from the MIS 3 interstadial to stadial states, with the thermodynamic term mainly contributing to the decreased tropical monsoonal precipitation in the colder Northern Hemisphere. Our results help improve the understanding of global monsoon variations under intermediate glacial climate conditions and shed light on their behaviors under potentially rapid climate change in the future.","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":"141504517","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 : 2024-07-03DOI: 10.1175/jcli-d-23-0470.1
Annika Reintges, Jon I. Robson, Rowan Sutton, Stephen G. Yeager
Abstract The Atlantic Meridional Overturning Circulation (AMOC) plays an important role in climate, transporting heat and salt to the subpolar North Atlantic. The AMOC’s variability is sensitive to atmospheric forcing, especially the North Atlantic Oscillation (NAO). Because AMOC observations are short, climate models are a valuable tool to study the AMOC’s variability. Yet, there are known issues with climate models, like uncertainties and systematic biases. To investigate this, pre-industrial control experiments from models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) are evaluated. There is large, but correlated, spread in the models’ subpolar gyre mean surface temperature and salinity. By splitting models into groups of either a warm-salty or cold-fresh subpolar gyre, it is shown that warm-salty models have a lower sea ice cover in the Labrador Sea and, hence, enable a larger heat loss during a positive NAO. Stratification in the Labrador Sea is also weaker in warm-salty models, such that the larger NAO-related heat loss can also affect greater depths. As a result, subsurface density anomalies are much stronger in the warm-salty models than in those that tend to be cold and fresh. As these anomalies propagate southward along the western boundary, they establish a zonal density gradient anomaly that promotes a stronger delayed AMOC response to the NAO in the warm-salty models. These findings demonstrate how model mean state errors are linked across variables and affect variability, emphasizing the need for improvement of the subpolar North Atlantic mean states in models.
{"title":"Subpolar North Atlantic mean state affects the response of the Atlantic Meridional Overturning Circulation to the North Atlantic Oscillation in CMIP6 models","authors":"Annika Reintges, Jon I. Robson, Rowan Sutton, Stephen G. Yeager","doi":"10.1175/jcli-d-23-0470.1","DOIUrl":"https://doi.org/10.1175/jcli-d-23-0470.1","url":null,"abstract":"Abstract The Atlantic Meridional Overturning Circulation (AMOC) plays an important role in climate, transporting heat and salt to the subpolar North Atlantic. The AMOC’s variability is sensitive to atmospheric forcing, especially the North Atlantic Oscillation (NAO). Because AMOC observations are short, climate models are a valuable tool to study the AMOC’s variability. Yet, there are known issues with climate models, like uncertainties and systematic biases. To investigate this, pre-industrial control experiments from models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) are evaluated. There is large, but correlated, spread in the models’ subpolar gyre mean surface temperature and salinity. By splitting models into groups of either a warm-salty or cold-fresh subpolar gyre, it is shown that warm-salty models have a lower sea ice cover in the Labrador Sea and, hence, enable a larger heat loss during a positive NAO. Stratification in the Labrador Sea is also weaker in warm-salty models, such that the larger NAO-related heat loss can also affect greater depths. As a result, subsurface density anomalies are much stronger in the warm-salty models than in those that tend to be cold and fresh. As these anomalies propagate southward along the western boundary, they establish a zonal density gradient anomaly that promotes a stronger delayed AMOC response to the NAO in the warm-salty models. These findings demonstrate how model mean state errors are linked across variables and affect variability, emphasizing the need for improvement of the subpolar North Atlantic mean states in models.","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":"141504522","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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