Fabian Mockert, Christian M. Grams, Sebastian Lerch, Marisol Osman, Julian Quinting
Reliable forecasts of quasi‐stationary, recurrent, and persistent large‐scale atmospheric circulation patterns—so‐called weather regimes—are crucial for various socio‐economic sectors, including energy, health, and agriculture. Despite steady progress, probabilistic weather regime predictions still exhibit biases in the exact timing and amplitude of weather regimes. This study thus aims at advancing probabilistic weather regime predictions in the North Atlantic–European region through ensemble post‐processing. Here, we focus on the representation of seven year‐round weather regimes in sub‐seasonal to seasonal reforecasts of the European Centre for Medium‐Range Weather Forecasts (ECMWF). The manifestation of each of the seven regimes can be expressed by a continuous weather regime index, representing the projection of the instantaneous 500‐hPa geopotential height anomalies (A) onto the respective mean regime pattern. We apply a two‐step ensemble post‐processing involving first univariate ensemble model output statistics and second ensemble copula coupling, which restores the multivariate dependence structure. Compared with current forecast calibration practices, which rely on correcting the field by the lead‐time‐dependent mean bias, our approach extends the forecast skill horizon for daily/instantaneous regime forecasts moderately by 1 day (from 13.5 to 14.5 days). Additionally, to our knowledge our study is the first to evaluate the multivariate aspects of forecast quality systematically for weather regime forecasts. Our method outperforms current practices in the multivariate aspect, as measured by the energy and variogram score. Still, our study shows that, even with advanced post‐processing, weather regime prediction becomes difficult beyond 14 days, which likely points towards intrinsic limits of predictability for daily/instantaneous regime forecasts. The proposed method can easily be applied to operational weather regime forecasts, offering a neat alternative for cost‐ and time‐efficient post‐processing of real‐time weather regime forecasts.
{"title":"Multivariate post‐processing of probabilistic sub‐seasonal weather regime forecasts","authors":"Fabian Mockert, Christian M. Grams, Sebastian Lerch, Marisol Osman, Julian Quinting","doi":"10.1002/qj.4840","DOIUrl":"https://doi.org/10.1002/qj.4840","url":null,"abstract":"Reliable forecasts of quasi‐stationary, recurrent, and persistent large‐scale atmospheric circulation patterns—so‐called weather regimes—are crucial for various socio‐economic sectors, including energy, health, and agriculture. Despite steady progress, probabilistic weather regime predictions still exhibit biases in the exact timing and amplitude of weather regimes. This study thus aims at advancing probabilistic weather regime predictions in the North Atlantic–European region through ensemble post‐processing. Here, we focus on the representation of seven year‐round weather regimes in sub‐seasonal to seasonal reforecasts of the European Centre for Medium‐Range Weather Forecasts (ECMWF). The manifestation of each of the seven regimes can be expressed by a continuous weather regime index, representing the projection of the instantaneous 500‐hPa geopotential height anomalies (A) onto the respective mean regime pattern. We apply a two‐step ensemble post‐processing involving first univariate ensemble model output statistics and second ensemble copula coupling, which restores the multivariate dependence structure. Compared with current forecast calibration practices, which rely on correcting the field by the lead‐time‐dependent mean bias, our approach extends the forecast skill horizon for daily/instantaneous regime forecasts moderately by 1 day (from 13.5 to 14.5 days). Additionally, to our knowledge our study is the first to evaluate the multivariate aspects of forecast quality systematically for weather regime forecasts. Our method outperforms current practices in the multivariate aspect, as measured by the energy and variogram score. Still, our study shows that, even with advanced post‐processing, weather regime prediction becomes difficult beyond 14 days, which likely points towards intrinsic limits of predictability for daily/instantaneous regime forecasts. The proposed method can easily be applied to operational weather regime forecasts, offering a neat alternative for cost‐ and time‐efficient post‐processing of real‐time weather regime forecasts.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"65 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142247948","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study examines the vertical variations of cloud microphysics and their correlation with the thickness of the entrainment interfacial layer (EIL) in stratocumulus clouds, observed in the Physics of Stratocumulus Top (POST) aircraft measurement campaign. From the mixing fraction analysis, we identified EIL between the free atmosphere and cloud top for all 15 POST flights, and found that EIL thickness significantly influenced the vertical variation of cloud microphysics and thermodynamics. In several flights, a trend toward stronger homogeneous mixing traits with increasing depth from the cloud top was found, indicative of the vertical movement of mixed (i.e., entrainment‐affected and diluted) parcels. However, in one flight, this trend was limited to the middle part of the cloud only, with the correlation between virtual potential temperature and liquid water content being strongly negative near the cloud top, suggesting limited downward movement of mixed parcels. Another important finding is that there was a robust negative correlation between long‐wave cooling rate near the cloud top and EIL thickness, highlighting differences in radiative cooling rates between mixed and unmixed parcels due to differences in liquid water content between them. These insightful findings will be crucial for enhancing our understanding of the role of EIL in modulating entrainment and the vertical movement of mixed parcels in stratocumulus clouds.
本研究考察了层积云顶物理学（POST）飞机测量活动中观测到的云微观物理垂直变化及其与层积云中夹带界面层（EIL）厚度的相关性。通过混合分数分析，我们确定了所有 15 次 POST 飞行中自由大气与云顶之间的 EIL，并发现 EIL 厚度对云微观物理和热力学的垂直变化有显著影响。在几次飞行中，我们发现随着距离云顶深度的增加，均质混合特征有增强的趋势，这表明混合包裹（即受夹带影响和稀释的包裹）在垂直方向移动。然而，在一次飞行中，这种趋势仅限于云的中间部分，虚拟势温与液态水含量之间的相关性在云顶附近呈强负相关，表明混合包裹的向下运动有限。另一个重要发现是，云顶附近的长波冷却率与 EIL 厚度之间存在很强的负相关，这突出表明了混合云团与非混合云团之间由于液态水含量不同而导致的辐射冷却率差异。这些富有洞察力的发现对于加深我们对 EIL 在调节层积云中混合云团的夹带和垂直运动中的作用的理解至关重要。
{"title":"Relationship between vertical variation of cloud microphysical properties and thickness of the entrainment interfacial layer in Physics of Stratocumulus Top stratocumulus clouds","authors":"Inyeob La, Seong Soo Yum","doi":"10.1002/qj.4855","DOIUrl":"https://doi.org/10.1002/qj.4855","url":null,"abstract":"This study examines the vertical variations of cloud microphysics and their correlation with the thickness of the entrainment interfacial layer (EIL) in stratocumulus clouds, observed in the Physics of Stratocumulus Top (POST) aircraft measurement campaign. From the mixing fraction analysis, we identified EIL between the free atmosphere and cloud top for all 15 POST flights, and found that EIL thickness significantly influenced the vertical variation of cloud microphysics and thermodynamics. In several flights, a trend toward stronger homogeneous mixing traits with increasing depth from the cloud top was found, indicative of the vertical movement of mixed (i.e., entrainment‐affected and diluted) parcels. However, in one flight, this trend was limited to the middle part of the cloud only, with the correlation between virtual potential temperature and liquid water content being strongly negative near the cloud top, suggesting limited downward movement of mixed parcels. Another important finding is that there was a robust negative correlation between long‐wave cooling rate near the cloud top and EIL thickness, highlighting differences in radiative cooling rates between mixed and unmixed parcels due to differences in liquid water content between them. These insightful findings will be crucial for enhancing our understanding of the role of EIL in modulating entrainment and the vertical movement of mixed parcels in stratocumulus clouds.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"1 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142247950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Atlantic tropical cyclones (TCs) are known to develop from African easterly waves (AEWs) that propagate across North Africa and out over the Atlantic Ocean. The relationship between AEWs and TCs has been the subject of numerous previous studies. There are, however, many Atlantic TCs that do not have AEW origins. In this study, we provide a novel analysis of the characteristics and trends of Atlantic TCs both with and without AEW origins using 43 years of observational and reanalysis data. To conduct this research, we identified TCs with and without AEW origins from the observational record between 1980 and 2022, and ran objective tracking algorithms on reanalysis data to identify the AEWs and TCs during this time period. We found statistically significant differences in the characteristics and environments of TCs with and without AEW origins. TCs with AEW origins are stronger and costlier, experience more favorable environmental conditions, and are more likely to make landfall in the Gulf of Mexico and the Caribbean when compared to TCs without AEW origins. Additionally, the 43‐year increasing trend in Atlantic TC activity is primarily driven by an increase in TCs with AEW origins that is associated with increasing AEW frequency and strength, with anthropogenic aerosols potentially driving this trend. In contrast, we found no trend in TCs without AEW origins.
{"title":"Characteristics and trends of Atlantic tropical cyclones that do and do not develop from African easterly waves","authors":"Emily Bercos‐Hickey, Christina M. Patricola","doi":"10.1002/qj.4850","DOIUrl":"https://doi.org/10.1002/qj.4850","url":null,"abstract":"Atlantic tropical cyclones (TCs) are known to develop from African easterly waves (AEWs) that propagate across North Africa and out over the Atlantic Ocean. The relationship between AEWs and TCs has been the subject of numerous previous studies. There are, however, many Atlantic TCs that do not have AEW origins. In this study, we provide a novel analysis of the characteristics and trends of Atlantic TCs both with and without AEW origins using 43 years of observational and reanalysis data. To conduct this research, we identified TCs with and without AEW origins from the observational record between 1980 and 2022, and ran objective tracking algorithms on reanalysis data to identify the AEWs and TCs during this time period. We found statistically significant differences in the characteristics and environments of TCs with and without AEW origins. TCs with AEW origins are stronger and costlier, experience more favorable environmental conditions, and are more likely to make landfall in the Gulf of Mexico and the Caribbean when compared to TCs without AEW origins. Additionally, the 43‐year increasing trend in Atlantic TC activity is primarily driven by an increase in TCs with AEW origins that is associated with increasing AEW frequency and strength, with anthropogenic aerosols potentially driving this trend. In contrast, we found no trend in TCs without AEW origins.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"54 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142247951","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Arnab Sen, Pranab Deb, Adrian J. Matthews, Manoj M. Joshi
Tropical–Antarctic teleconnections are known to have large impacts on Antarctic climate variability at multiple timescales. Anomalous tropical convection triggers upper‐level quasi‐stationary Rossby waves, which propagate to high southern latitudes and impact the local environment. Here the teleconnection between the Indian Ocean Dipole (IOD) and Antarctica was examined using daily gridded reanalysis data and the linear response theory method (LRTM) during September–November of 1980–2015. The individual contribution of the IOD over the Antarctic climate is challenging to quantify, as positive IOD events often co‐occur with El Niño events. However, using the LRTM, the extratropical response due to a positive IOD was successfully extracted from the combined signal in the composite map of anomalous 250‐hPa geopotential height. Applying the method to a set of models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), significant differences were observed in the extratropical response to the IOD among the models, due to bias in the Rossby waveguide and IOD precipitation pattern. The LRTM was then applied to evaluate the extratropical response of the 850‐hPa temperature, wind anomalies, and sea‐ice concentration anomalies in observation data, as well as models that represented both the IOD precipitation and the extratropical waveguide adequately. The IOD induced cold southerly flow over the west of the Ross Sea, Weddell Sea, and Antarctic Peninsula, causing cold surface‐temperature anomalies and the increase of sea ice, and warm northerly flow over the east of the Ross Sea and Amundsen Sea, causing warm surface‐temperature anomalies and the decrease of sea ice. We recommend the LRTM as a complementary method to standard analysis of climate variability from observations and global climate models.
{"title":"Teleconnection and the Antarctic response to the Indian Ocean Dipole in CMIP5 and CMIP6 models","authors":"Arnab Sen, Pranab Deb, Adrian J. Matthews, Manoj M. Joshi","doi":"10.1002/qj.4854","DOIUrl":"https://doi.org/10.1002/qj.4854","url":null,"abstract":"Tropical–Antarctic teleconnections are known to have large impacts on Antarctic climate variability at multiple timescales. Anomalous tropical convection triggers upper‐level quasi‐stationary Rossby waves, which propagate to high southern latitudes and impact the local environment. Here the teleconnection between the Indian Ocean Dipole (IOD) and Antarctica was examined using daily gridded reanalysis data and the linear response theory method (LRTM) during September–November of 1980–2015. The individual contribution of the IOD over the Antarctic climate is challenging to quantify, as positive IOD events often co‐occur with El Niño events. However, using the LRTM, the extratropical response due to a positive IOD was successfully extracted from the combined signal in the composite map of anomalous 250‐hPa geopotential height. Applying the method to a set of models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), significant differences were observed in the extratropical response to the IOD among the models, due to bias in the Rossby waveguide and IOD precipitation pattern. The LRTM was then applied to evaluate the extratropical response of the 850‐hPa temperature, wind anomalies, and sea‐ice concentration anomalies in observation data, as well as models that represented both the IOD precipitation and the extratropical waveguide adequately. The IOD induced cold southerly flow over the west of the Ross Sea, Weddell Sea, and Antarctic Peninsula, causing cold surface‐temperature anomalies and the increase of sea ice, and warm northerly flow over the east of the Ross Sea and Amundsen Sea, causing warm surface‐temperature anomalies and the decrease of sea ice. We recommend the LRTM as a complementary method to standard analysis of climate variability from observations and global climate models.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"7 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hongyi Xiao, Wei Han, Yang Han, Hao Hu, Yining Shi, Yihong Bai, Yuanyuan Liu
The Imaging/Sounding Microwave Radiometer–Improved (MTVZA‐GY) on board the Russian meteorological satellite, Meteor‐M N2‐2, launched in 2019, provides daily observations of Earth's atmosphere and surface from a polar orbit. Here, its performance in a numerical prediction model – the Global/Regional Assimilation and Prediction System–Global Forecast System (CMA_GFS), which involves the Advanced Radiative Transfer Modeling System (ARMS) – was evaluated. After supplementing some lacking information during data preprocessing, the characteristics of all available channels (24 in total) were evaluated by comparison among channels, with background fields, and with similar active instruments in CMA‐GFS, as well as between different radiative transfer models. Failed calibration was found in all window channels. Scan position biases, ascending/descending biases, and striping noises were widely discovered in temperature‐sounding channels, as well as larger biases in humidity‐sounding channels. Following quality control and bias correction, only two temperature‐sounding channels were feasible for assimilation into CMA‐GFS within the observational errors calculated by the a posteriori verification scheme. A one‐month experiment confirmed that these two channels have positive impacts on the analysis of both thermal and dynamic fields, as well as short‐term weather forecasting in the Northern Hemisphere and tropics. Short‐term global forecasting of moderate rainfall was also improved. This work is a pioneering attempt at examining the potential and impacts of assimilating MTVZA‐GY in a numerical weather prediction model system. It also provides guidance for the manufacture and usage of the instruments that will be on board the three satellites planned for launch by the Russian Federation in the next three years.
{"title":"First trial for the assimilation of radiance data from MTVZA‐GY on board the new Russian satellite meteor‐M N2‐2 in the CMA‐GFS 4D‐VAR system","authors":"Hongyi Xiao, Wei Han, Yang Han, Hao Hu, Yining Shi, Yihong Bai, Yuanyuan Liu","doi":"10.1002/qj.4853","DOIUrl":"https://doi.org/10.1002/qj.4853","url":null,"abstract":"The Imaging/Sounding Microwave Radiometer–Improved (MTVZA‐GY) on board the Russian meteorological satellite, Meteor‐M N2‐2, launched in 2019, provides daily observations of Earth's atmosphere and surface from a polar orbit. Here, its performance in a numerical prediction model – the Global/Regional Assimilation and Prediction System–Global Forecast System (CMA_GFS), which involves the Advanced Radiative Transfer Modeling System (ARMS) – was evaluated. After supplementing some lacking information during data preprocessing, the characteristics of all available channels (24 in total) were evaluated by comparison among channels, with background fields, and with similar active instruments in CMA‐GFS, as well as between different radiative transfer models. Failed calibration was found in all window channels. Scan position biases, ascending/descending biases, and striping noises were widely discovered in temperature‐sounding channels, as well as larger biases in humidity‐sounding channels. Following quality control and bias correction, only two temperature‐sounding channels were feasible for assimilation into CMA‐GFS within the observational errors calculated by the a posteriori verification scheme. A one‐month experiment confirmed that these two channels have positive impacts on the analysis of both thermal and dynamic fields, as well as short‐term weather forecasting in the Northern Hemisphere and tropics. Short‐term global forecasting of moderate rainfall was also improved. This work is a pioneering attempt at examining the potential and impacts of assimilating MTVZA‐GY in a numerical weather prediction model system. It also provides guidance for the manufacture and usage of the instruments that will be on board the three satellites planned for launch by the Russian Federation in the next three years.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"60 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188874","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The uncertainty in numerical weather prediction models is nowadays quantified by the use of ensemble forecasts. Although these forecasts are continuously improved, they still suffer from systematic bias and dispersion errors. Statistical postprocessing methods, such as the ensemble model output statistics (EMOS), have been shown to substantially correct the forecasts. This work proposes an extension of EMOS in a time‐series framework. Besides taking account of seasonality and trend in the location and scale parameter of the predictive distribution, the autoregressive process in the mean forecast errors or the standardized forecast errors is considered. The models can be further extended by allowing generalized autoregressive conditional heteroscedasticity. Furthermore, it is outlined how to use these models for arbitrary forecast horizons. To illustrate the performance of the suggested EMOS models in time‐series fashion, we present a case study for the postprocessing of 2 m surface temperature forecasts using five different lead times and a set of observation stations in Germany. The results indicate that the time‐series EMOS extensions are able to significantly outperform the benchmark models EMOS and autoregressive EMOS (AR‐EMOS) in most of the lead time–station cases.
{"title":"Time‐series‐based ensemble model output statistics for temperature forecasts postprocessing","authors":"David Jobst, Annette Möller, Jürgen Groß","doi":"10.1002/qj.4844","DOIUrl":"https://doi.org/10.1002/qj.4844","url":null,"abstract":"The uncertainty in numerical weather prediction models is nowadays quantified by the use of ensemble forecasts. Although these forecasts are continuously improved, they still suffer from systematic bias and dispersion errors. Statistical postprocessing methods, such as the ensemble model output statistics (EMOS), have been shown to substantially correct the forecasts. This work proposes an extension of EMOS in a time‐series framework. Besides taking account of seasonality and trend in the location and scale parameter of the predictive distribution, the autoregressive process in the mean forecast errors or the standardized forecast errors is considered. The models can be further extended by allowing generalized autoregressive conditional heteroscedasticity. Furthermore, it is outlined how to use these models for arbitrary forecast horizons. To illustrate the performance of the suggested EMOS models in time‐series fashion, we present a case study for the postprocessing of 2 m surface temperature forecasts using five different lead times and a set of observation stations in Germany. The results indicate that the time‐series EMOS extensions are able to significantly outperform the benchmark models EMOS and autoregressive EMOS (AR‐EMOS) in most of the lead time–station cases.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"19 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the summers of 2020 and 2022, the Western Pacific Subtropical High (WPSH) intensified extremely and extended westward. However, in summer 2020, the Yangtze River Valley (YRV) witnessed record‐breaking floods, while in 2022, an unprecedented and prolonged heatwave occurred. Distinctly, these two extreme events were caused by different effects of the WPSH: one is enhancement of the transportation of water vapor and the other is adiabatic heating caused by the descending airflow. In June–July 2020, the stable extension of the WPSH ridge line to South China directed a southwesterly airflow along its northwest flank, leading to sustained precipitation in the YRV. Additionally, the midlatitude circulation pattern featured two troughs and two ridges. Such a circulation configuration, combined with the strong and westward WPSH, enabled the continuous southward intrusion of cold air and northward transport of warm moist air, converging over the YRV, and thus influenced extreme persistent precipitation. In contrast, the WPSH covered the YRV almost entirely during summer 2022. Under this influence, the clear‐sky condition and descending airflow through adiabatic warming directly resulted in the heatwave. In addition, local land–atmosphere feedback was crucial in its development and persistence. The soil moisture deficit induced by high temperatures increased the sensible heat flux between the soil and atmosphere upward, further enhanced the surface air temperature and strengthened the heat dry condition.
{"title":"Differentiated influences of anomalous subtropical high on extreme persistent precipitation and heatwave events in the Yangtze River Valley","authors":"Yu Peng, Qian Wang, Panmao Zhai","doi":"10.1002/qj.4845","DOIUrl":"https://doi.org/10.1002/qj.4845","url":null,"abstract":"In the summers of 2020 and 2022, the Western Pacific Subtropical High (WPSH) intensified extremely and extended westward. However, in summer 2020, the Yangtze River Valley (YRV) witnessed record‐breaking floods, while in 2022, an unprecedented and prolonged heatwave occurred. Distinctly, these two extreme events were caused by different effects of the WPSH: one is enhancement of the transportation of water vapor and the other is adiabatic heating caused by the descending airflow. In June–July 2020, the stable extension of the WPSH ridge line to South China directed a southwesterly airflow along its northwest flank, leading to sustained precipitation in the YRV. Additionally, the midlatitude circulation pattern featured two troughs and two ridges. Such a circulation configuration, combined with the strong and westward WPSH, enabled the continuous southward intrusion of cold air and northward transport of warm moist air, converging over the YRV, and thus influenced extreme persistent precipitation. In contrast, the WPSH covered the YRV almost entirely during summer 2022. Under this influence, the clear‐sky condition and descending airflow through adiabatic warming directly resulted in the heatwave. In addition, local land–atmosphere feedback was crucial in its development and persistence. The soil moisture deficit induced by high temperatures increased the sensible heat flux between the soil and atmosphere upward, further enhanced the surface air temperature and strengthened the heat dry condition.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"11 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188878","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Matthew Patterson, Daniel J. Befort, Christopher H. O'Reilly, Antje Weisheimer
The European summer (June–August) 2022 was characterised by warm and dry anomalies across much of the continent, likely influenced by a northward‐shifted jet stream. These general features were well predicted by European Centre for Medium‐Range Weather Forecasts' system 5 seasonal forecast, initialised on May 1. Such successful predictions for European summers are relatively uncommon, particularly for atmospheric circulation. In this study, a set of hindcast experiments is employed to investigate the role that initialisation of the ocean, atmosphere, and land surface played in the 2022 forecast. We find that the trend from external forcing was the strongest contributor to the forecast near‐surface temperature anomalies, with atmospheric circulation and land‐surface interactions playing a secondary role. On the other hand, atmospheric circulation made a strong contribution to precipitation anomalies. Modelled Euro‐Atlantic circulation anomalies in 2022 were consistent with a La Niña‐forced teleconnection from the tropical Pacific. However, a northward jet trend in the model hindcasts with increasing greenhouse gas concentrations also contributed to the predicted circulation anomalies in 2022. In contrast, the observed linear trend in the jet over the past four decades was a southward shift, though it is unclear whether this trend was driven by external forcings or natural variability. Nevertheless, this case study demonstrates that important features of at least some European summers are predictable at the seasonal time‐scale.
{"title":"Drivers of the ECMWF SEAS5 seasonal forecast for the hot and dry European summer of 2022","authors":"Matthew Patterson, Daniel J. Befort, Christopher H. O'Reilly, Antje Weisheimer","doi":"10.1002/qj.4851","DOIUrl":"https://doi.org/10.1002/qj.4851","url":null,"abstract":"The European summer (June–August) 2022 was characterised by warm and dry anomalies across much of the continent, likely influenced by a northward‐shifted jet stream. These general features were well predicted by European Centre for Medium‐Range Weather Forecasts' system 5 seasonal forecast, initialised on May 1. Such successful predictions for European summers are relatively uncommon, particularly for atmospheric circulation. In this study, a set of hindcast experiments is employed to investigate the role that initialisation of the ocean, atmosphere, and land surface played in the 2022 forecast. We find that the trend from external forcing was the strongest contributor to the forecast near‐surface temperature anomalies, with atmospheric circulation and land‐surface interactions playing a secondary role. On the other hand, atmospheric circulation made a strong contribution to precipitation anomalies. Modelled Euro‐Atlantic circulation anomalies in 2022 were consistent with a La Niña‐forced teleconnection from the tropical Pacific. However, a northward jet trend in the model hindcasts with increasing greenhouse gas concentrations also contributed to the predicted circulation anomalies in 2022. In contrast, the observed linear trend in the jet over the past four decades was a southward shift, though it is unclear whether this trend was driven by external forcings or natural variability. Nevertheless, this case study demonstrates that important features of at least some European summers are predictable at the seasonal time‐scale.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"41 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188877","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Chaim I. Garfinkel, Jeff Knight, Masakazu Taguchi, Chen Schwartz, Judah Cohen, Wen Chen, Amy H. Butler, Daniela I. V. Domeisen
Subseasonal forecast models are shown to suffer from the same inconsistency in the signal‐to‐noise ratio evident in climate models. Namely, predictable signals in these models are too weak, yet there is a relatively high level of agreement with observed variability of the atmospheric circulation. The net effect is subseasonal forecast models show higher correlation with observed variability than with their own simulations; that is, the signal‐to‐noise paradox. Also, similar to climate models, this paradox is particularly evident in the North Atlantic sector. The paradox is not evident in week 1 or week 2 forecasts, and hence is limited to subseasonal time‐scales. The paradox appears to be related to an overly fast decay of northern annular mode regimes. Three possible causes of this overly fast decay and for the paradox in the Northern Hemisphere are identified: a too‐fast decay of polar stratospheric signals, overly weak downward coupling from the stratosphere to the surface in some models, and overly weak transient synoptic eddy feedbacks. Though the paradox is clearly evident in the North Atlantic, it is relatively muted in the Southern Hemisphere: southern annular mode regimes persist realistically, the stratospheric signal is well maintained, and eddy feedback is, if anything, too strong and zonal.
{"title":"Development of the signal‐to‐noise paradox in subseasonal forecasting models: When? Where? Why?","authors":"Chaim I. Garfinkel, Jeff Knight, Masakazu Taguchi, Chen Schwartz, Judah Cohen, Wen Chen, Amy H. Butler, Daniela I. V. Domeisen","doi":"10.1002/qj.4822","DOIUrl":"https://doi.org/10.1002/qj.4822","url":null,"abstract":"Subseasonal forecast models are shown to suffer from the same inconsistency in the signal‐to‐noise ratio evident in climate models. Namely, predictable signals in these models are too weak, yet there is a relatively high level of agreement with observed variability of the atmospheric circulation. The net effect is subseasonal forecast models show higher correlation with observed variability than with their own simulations; that is, the signal‐to‐noise paradox. Also, similar to climate models, this paradox is particularly evident in the North Atlantic sector. The paradox is not evident in week 1 or week 2 forecasts, and hence is limited to subseasonal time‐scales. The paradox appears to be related to an overly fast decay of northern annular mode regimes. Three possible causes of this overly fast decay and for the paradox in the Northern Hemisphere are identified: a too‐fast decay of polar stratospheric signals, overly weak downward coupling from the stratosphere to the surface in some models, and overly weak transient synoptic eddy feedbacks. Though the paradox is clearly evident in the North Atlantic, it is relatively muted in the Southern Hemisphere: southern annular mode regimes persist realistically, the stratospheric signal is well maintained, and eddy feedback is, if anything, too strong and zonal.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"47 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Stephen R. Foskey, Naoko Sakaeda, Jeffrey Basara, Jason C. Furtado
Despite its substantial impacts on human society, winter weather is difficult to predict on subseasonal‐to‐seasonal (S2S) timescales. To improve its predictability at longer timescales, this study examines whether the Madden–Julian Oscillation (MJO) has a significant impact on the frequency of extreme winter weather (i.e., heavy accumulations of snow, ice pellets, and freezing rain) over the contiguous United States. We find an increased frequency of extreme winter weather in the Ohio Valley and Mid‐Atlantic regions when MJO enhanced convection is over Africa and the western Indian Ocean, due to imposed lower 850‐hPa temperatures associated with MJO teleconnections. More frequent subfreezing temperatures lead to an increased likelihood of frozen precipitation compared with liquid, increasing the frequency of extreme winter weather. The MJO also increases the frequency of winter weather in the Central Great Plains region of the United States when MJO enhanced convection is over the eastern Indian Ocean and the Maritime Continent. Rather than through effects on temperature, the likely mechanism of increased winter weather over this region is enhanced synoptic forcing that increases overall precipitation. These effects can be seen up to 15 days in advance, suggesting the utility of using the MJO in S2S forecasting of extreme winter weather.
{"title":"The impact of the Madden–Julian oscillation on extreme winter weather over the contiguous United States","authors":"Stephen R. Foskey, Naoko Sakaeda, Jeffrey Basara, Jason C. Furtado","doi":"10.1002/qj.4848","DOIUrl":"https://doi.org/10.1002/qj.4848","url":null,"abstract":"Despite its substantial impacts on human society, winter weather is difficult to predict on subseasonal‐to‐seasonal (S2S) timescales. To improve its predictability at longer timescales, this study examines whether the Madden–Julian Oscillation (MJO) has a significant impact on the frequency of extreme winter weather (i.e., heavy accumulations of snow, ice pellets, and freezing rain) over the contiguous United States. We find an increased frequency of extreme winter weather in the Ohio Valley and Mid‐Atlantic regions when MJO enhanced convection is over Africa and the western Indian Ocean, due to imposed lower 850‐hPa temperatures associated with MJO teleconnections. More frequent subfreezing temperatures lead to an increased likelihood of frozen precipitation compared with liquid, increasing the frequency of extreme winter weather. The MJO also increases the frequency of winter weather in the Central Great Plains region of the United States when MJO enhanced convection is over the eastern Indian Ocean and the Maritime Continent. Rather than through effects on temperature, the likely mechanism of increased winter weather over this region is enhanced synoptic forcing that increases overall precipitation. These effects can be seen up to 15 days in advance, suggesting the utility of using the MJO in S2S forecasting of extreme winter weather.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"35 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142188880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：