Abstract This article considers the role of thunder in the production of rain by gravitational processes. A previous numerical work has shown that a thunder event consisting of four consecutive thunderclaps can alone produce small but significant droplet growths in a lean cumulus cloud in less than 2 s. Here we consider, also numerically, the coalescence effects produced by both thunderclaps and gravity in a cumulus congestus cloud that had more than four times the liquid content of that lean cloud. Those effects are studied separately and in tandem, using the same set of assumptions. Therefore, the results presented here provide a basis for the comparison of the effectiveness of each type to produce droplet growth in thunderclouds. For thunder alone, these results show that a small number of thunderclaps can in less than 2 s produce mean size growths larger than 50%. For gravity alone, it is found that after 60 s, the longest time considered, gravitational coalescence increases the mean diameter of the original droplet size distribution by 20%. The tandem study considers the effects produced by gravitation on the droplet size distribution that resulted after the original distribution was modified by four or five thunderclaps. Significant increases are found in both cases. For four claps it was found that the mean size increased by 71% in 60 s. The corresponding growth for five claps was slightly larger than 100%. These substantial increases also show that the growths produced by the thunderclaps are not simply additive, but significantly accelerate those produced by gravitation. This acceleration implies that the droplet size growths produced by thunderclaps can substantially decrease the time required by gravitational coagulation to produce raindrops in rainclouds.
{"title":"Raincloud Conditioning by Thunder","authors":"Samuel Temkin","doi":"10.1002/qj.4580","DOIUrl":"https://doi.org/10.1002/qj.4580","url":null,"abstract":"Abstract This article considers the role of thunder in the production of rain by gravitational processes. A previous numerical work has shown that a thunder event consisting of four consecutive thunderclaps can alone produce small but significant droplet growths in a lean cumulus cloud in less than 2 s. Here we consider, also numerically, the coalescence effects produced by both thunderclaps and gravity in a cumulus congestus cloud that had more than four times the liquid content of that lean cloud. Those effects are studied separately and in tandem, using the same set of assumptions. Therefore, the results presented here provide a basis for the comparison of the effectiveness of each type to produce droplet growth in thunderclouds. For thunder alone, these results show that a small number of thunderclaps can in less than 2 s produce mean size growths larger than 50%. For gravity alone, it is found that after 60 s, the longest time considered, gravitational coalescence increases the mean diameter of the original droplet size distribution by 20%. The tandem study considers the effects produced by gravitation on the droplet size distribution that resulted after the original distribution was modified by four or five thunderclaps. Significant increases are found in both cases. For four claps it was found that the mean size increased by 71% in 60 s. The corresponding growth for five claps was slightly larger than 100%. These substantial increases also show that the growths produced by the thunderclaps are not simply additive, but significantly accelerate those produced by gravitation. This acceleration implies that the droplet size growths produced by thunderclaps can substantially decrease the time required by gravitational coagulation to produce raindrops in rainclouds.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"184 S488","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135775733","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 intertropical convergence zone (ITCZ) is a central component of the atmospheric general circulation, but remarkably little is known about the dynamical and thermodynamical structure of the convergence zone itself. This is true even for the structure of the low‐level convergence that gives the ITCZ its name. Following on from the major international field campaigns in the 1960s and 70s, we performed extensive atmospheric profiling of the Atlantic ITCZ during a ship‐based measurement campaign aboard the research vessel SONNE in summer 2021. Combining data collected during our north‐south crossing of the ITCZ with reanalysis data shows the ITCZ to be a meridionally extended region of intense precipitation, with enhanced surface convergence at its edges rather than in the center. Based on the location of these edges, we construct a composite view of the structure of the Atlantic ITCZ. The ITCZ, far from being simply a region of enhanced deep convection, has a rich inner life, i.e., a rich dynamical and thermodynamic structure that changes throughout the course of the year and has a northern edge that differs systematically from the southern edge. This article is protected by copyright. All rights reserved.
{"title":"The inner life of the Atlantic ITCZ","authors":"Julia M. Windmiller, Bjorn Stevens","doi":"10.1002/qj.4610","DOIUrl":"https://doi.org/10.1002/qj.4610","url":null,"abstract":"The intertropical convergence zone (ITCZ) is a central component of the atmospheric general circulation, but remarkably little is known about the dynamical and thermodynamical structure of the convergence zone itself. This is true even for the structure of the low‐level convergence that gives the ITCZ its name. Following on from the major international field campaigns in the 1960s and 70s, we performed extensive atmospheric profiling of the Atlantic ITCZ during a ship‐based measurement campaign aboard the research vessel SONNE in summer 2021. Combining data collected during our north‐south crossing of the ITCZ with reanalysis data shows the ITCZ to be a meridionally extended region of intense precipitation, with enhanced surface convergence at its edges rather than in the center. Based on the location of these edges, we construct a composite view of the structure of the Atlantic ITCZ. The ITCZ, far from being simply a region of enhanced deep convection, has a rich inner life, i.e., a rich dynamical and thermodynamic structure that changes throughout the course of the year and has a northern edge that differs systematically from the southern edge. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"15 12","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135933632","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}
M. Yaremchuk, C. N. Barron, W. Crawford, C. DeHaan, C. Rowley, B. Ruston, T. Townsend
In this study we assess a possibility to efficiently represent the strongly coupled increment in an ocean‐atmosphere coupled data assimilation (DA) system by applying an iterative procedure involving uncoupled solvers and the weakly coupled analysis as a first guess approximation to the strongly coupled increment. Using the output of the ensemble‐based weakly coupled DA system, we explore convergence of the approximations to the strongly coupled DA solution by applying the uncoupled solver to a sequence of innovation vectors at various spacetime locations over the global ocean grid. The results demonstrate that, in general, fewer than two iterations are required to approximate the coupled increment in the majority of the tested locations with sufficient (3%) accuracy given the uncertainty of the background error covariance estimated from the limited number of the ensemble members. We assess the impact of data thinning and hybridization of the background error covariance model on the convergence of the iterative approximations to the strongly coupled increment. An empirical relationship between the spectral radius of the expansion matrix and convergence rate is obtained. This article is protected by copyright. All rights reserved.
{"title":"Toward a strongly coupled assimilation in the ESPC system","authors":"M. Yaremchuk, C. N. Barron, W. Crawford, C. DeHaan, C. Rowley, B. Ruston, T. Townsend","doi":"10.1002/qj.4611","DOIUrl":"https://doi.org/10.1002/qj.4611","url":null,"abstract":"In this study we assess a possibility to efficiently represent the strongly coupled increment in an ocean‐atmosphere coupled data assimilation (DA) system by applying an iterative procedure involving uncoupled solvers and the weakly coupled analysis as a first guess approximation to the strongly coupled increment. Using the output of the ensemble‐based weakly coupled DA system, we explore convergence of the approximations to the strongly coupled DA solution by applying the uncoupled solver to a sequence of innovation vectors at various spacetime locations over the global ocean grid. The results demonstrate that, in general, fewer than two iterations are required to approximate the coupled increment in the majority of the tested locations with sufficient (3%) accuracy given the uncertainty of the background error covariance estimated from the limited number of the ensemble members. We assess the impact of data thinning and hybridization of the background error covariance model on the convergence of the iterative approximations to the strongly coupled increment. An empirical relationship between the spectral radius of the expansion matrix and convergence rate is obtained. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"15 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135934106","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}
Non‐hydrostatic atmospheric models often use semi‐implicit temporal discretisations in order to negate the time step limitation of explicitly resolving the fast acoustic and gravity waves. Solving the resulting system to machine precision using Newton's method is considered prohibitively expensive, and so the non‐linear solver is typically truncated to a fixed number of iterations, often using an approximate Jacobian matrix that is reassembled only once per time step. The present article studies the impact of using various third‐order, four stage Rosenbrock‐Wanner schemes, where integration weights are chosen to meet specific stability and order conditions, in comparison to a Crank‐Nicolson time discretisation, as is done in the UK Met Office's LFRic model. Rosenbrock‐Wanner schemes present a promising alternative on account of their ability to preserve their temporal order with only an approximate Jacobian, and may be constructed to be stiffly‐stable, so as to ensure the decay of fast unresolved modes. These schemes are compared for the 2D rotating shallow water equations and the 3D compressible Euler equations at both planetary and non‐hydrostatic scales and are shown to exhibit improved results in terms of their energetic profiles and stability. Results in terms of computational performance are mixed, with the Crank‐Nicolson method allowing for longer time steps and faster time to solution for the baroclinic instability test case at planetary scales, and the Rosenbrock‐Wanner methods allowing for longer time steps and faster time to solution for a rising bubble test case at non‐hydrostatic scales. This article is protected by copyright. All rights reserved.
{"title":"A Comparison of Rosenbrock‐Wanner and Crank‐Nicolson Time Integrators for Atmospheric Modelling","authors":"David Lee","doi":"10.1002/qj.4608","DOIUrl":"https://doi.org/10.1002/qj.4608","url":null,"abstract":"Non‐hydrostatic atmospheric models often use semi‐implicit temporal discretisations in order to negate the time step limitation of explicitly resolving the fast acoustic and gravity waves. Solving the resulting system to machine precision using Newton's method is considered prohibitively expensive, and so the non‐linear solver is typically truncated to a fixed number of iterations, often using an approximate Jacobian matrix that is reassembled only once per time step. The present article studies the impact of using various third‐order, four stage Rosenbrock‐Wanner schemes, where integration weights are chosen to meet specific stability and order conditions, in comparison to a Crank‐Nicolson time discretisation, as is done in the UK Met Office's LFRic model. Rosenbrock‐Wanner schemes present a promising alternative on account of their ability to preserve their temporal order with only an approximate Jacobian, and may be constructed to be stiffly‐stable, so as to ensure the decay of fast unresolved modes. These schemes are compared for the 2D rotating shallow water equations and the 3D compressible Euler equations at both planetary and non‐hydrostatic scales and are shown to exhibit improved results in terms of their energetic profiles and stability. Results in terms of computational performance are mixed, with the Crank‐Nicolson method allowing for longer time steps and faster time to solution for the baroclinic instability test case at planetary scales, and the Rosenbrock‐Wanner methods allowing for longer time steps and faster time to solution for a rising bubble test case at non‐hydrostatic scales. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"11 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135933959","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}
Seonaid R. Anderson, Steven J. Cole, Cornelia Klein, Christopher M. Taylor, Cheikh Abdoulahat Diop, Mouhamadou Kamara
Abstract Flash flooding from intense rainfall frequently results in major damage and loss of life across Africa. In the Sahel, automatic prediction and warning systems for these events, driven by Mesoscale Convective Systems (MCSs), are limited, and Numerical Weather Prediction (NWP) forecasts continue to have little skill. The ground observation network is also sparse, and very few operational meteorological radars exist to facilitate conventional nowcasting approaches. Focusing on the western Sahel, we present a novel approach for producing probabilistic nowcasts of convective activity out to 6 h ahead, using the current location of observed convection. Convective parts of the MCS, associated with extreme and heavy precipitation, are identified from 16 years of Meteosat Second Generation thermal‐infrared cloud‐top temperature data, and an offline database of location‐conditioned probabilities calculated. From this database, real‐time nowcasts can be quickly produced with minimal calculation. The nowcasts give the probability of convection occurring within a square neighbourhood surrounding each grid point, accounting for the inherent unpredictability of convection at small scales. Compared to a climatological reference, formal verification approaches show the nowcasts to be skilful at predicting convective activity over the study region, for all times of day and out to the 6‐h lead time considered. The nowcasts are also skilful at capturing extreme 24 h rain gauge accumulations over Dakar, Senegal. The nowcast skill peaks in the afternoon, with a minimum in the evening. We find that the optimum neighbourhood size varies with lead time, from 10 km at the nowcast origin to around 100 km at a 6‐h lead time. This simple and skilful nowcasting method could be highly valuable for operational warnings across West Africa and other regions with long‐lived thunderstorms, and help to reduce the impacts from heavy rainfall and flooding. This article is protected by copyright. All rights reserved.
{"title":"Nowcasting convective activity for the Sahel: A simple probabilistic approach using real‐time and historical satellite data on cloud‐top temperature","authors":"Seonaid R. Anderson, Steven J. Cole, Cornelia Klein, Christopher M. Taylor, Cheikh Abdoulahat Diop, Mouhamadou Kamara","doi":"10.1002/qj.4607","DOIUrl":"https://doi.org/10.1002/qj.4607","url":null,"abstract":"Abstract Flash flooding from intense rainfall frequently results in major damage and loss of life across Africa. In the Sahel, automatic prediction and warning systems for these events, driven by Mesoscale Convective Systems (MCSs), are limited, and Numerical Weather Prediction (NWP) forecasts continue to have little skill. The ground observation network is also sparse, and very few operational meteorological radars exist to facilitate conventional nowcasting approaches. Focusing on the western Sahel, we present a novel approach for producing probabilistic nowcasts of convective activity out to 6 h ahead, using the current location of observed convection. Convective parts of the MCS, associated with extreme and heavy precipitation, are identified from 16 years of Meteosat Second Generation thermal‐infrared cloud‐top temperature data, and an offline database of location‐conditioned probabilities calculated. From this database, real‐time nowcasts can be quickly produced with minimal calculation. The nowcasts give the probability of convection occurring within a square neighbourhood surrounding each grid point, accounting for the inherent unpredictability of convection at small scales. Compared to a climatological reference, formal verification approaches show the nowcasts to be skilful at predicting convective activity over the study region, for all times of day and out to the 6‐h lead time considered. The nowcasts are also skilful at capturing extreme 24 h rain gauge accumulations over Dakar, Senegal. The nowcast skill peaks in the afternoon, with a minimum in the evening. We find that the optimum neighbourhood size varies with lead time, from 10 km at the nowcast origin to around 100 km at a 6‐h lead time. This simple and skilful nowcasting method could be highly valuable for operational warnings across West Africa and other regions with long‐lived thunderstorms, and help to reduce the impacts from heavy rainfall and flooding. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"28 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135272360","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}
Abstract Tropical cyclone (TC)–induced remote moisture transport is the fundamental cause of TC‐induced remote precipitation. However, despite increasing attention having been paid to TC‐induced remote moisture transport over the past few decades, a method for the objective identification of TC remote moisture transport remains lacking, which is crucial to understanding the complex rainfall mechanisms associated with TC‐induced remote moisture transport over recent decades. We set out to solve this issue in the present study by using a series of newly developed processing algorithms. Firstly, we identified vertically integrated water vapor transport (IVT) pathways using spatially smoothed moving window quantiles, and then used the maximum gradient method to segment IVT clusters from pathways. Relationship digraphs were constructed for IVT clusters to flexibly interpret the spatiotemporal merging and splitting processes among them. Finally, TC clusters (TCCs) and TC remote Clusters (TRCs) were identified in succession based on the TC tracks and diagraphs of IVT clusters. Applications of these processing algorithms showed that the TCCs and TRCs at the same timestep can be identified successfully by applying our method. The generality of the objective identification method was validated using data covering four decades. Our algorithms revealed discontinuous and uneven moisture transport, especially those associated with TCs, which benefits studies of remote rainfall associated with TCs. Furthermore, it facilitates the construction of IVT pathway and cluster datasets covering the past several decades, which can be used for analyzing related characteristics and thereby revealing possible physical mechanisms underlying the nature of TRCs. This article is protected by copyright. All rights reserved.
{"title":"Objective Identification of Tropical Cyclone–induced Remote Moisture Transport using Digraphs","authors":"Shiqi Xiao, Aoqi Zhang, Yilun Chen, Weibiao Li","doi":"10.1002/qj.4612","DOIUrl":"https://doi.org/10.1002/qj.4612","url":null,"abstract":"Abstract Tropical cyclone (TC)–induced remote moisture transport is the fundamental cause of TC‐induced remote precipitation. However, despite increasing attention having been paid to TC‐induced remote moisture transport over the past few decades, a method for the objective identification of TC remote moisture transport remains lacking, which is crucial to understanding the complex rainfall mechanisms associated with TC‐induced remote moisture transport over recent decades. We set out to solve this issue in the present study by using a series of newly developed processing algorithms. Firstly, we identified vertically integrated water vapor transport (IVT) pathways using spatially smoothed moving window quantiles, and then used the maximum gradient method to segment IVT clusters from pathways. Relationship digraphs were constructed for IVT clusters to flexibly interpret the spatiotemporal merging and splitting processes among them. Finally, TC clusters (TCCs) and TC remote Clusters (TRCs) were identified in succession based on the TC tracks and diagraphs of IVT clusters. Applications of these processing algorithms showed that the TCCs and TRCs at the same timestep can be identified successfully by applying our method. The generality of the objective identification method was validated using data covering four decades. Our algorithms revealed discontinuous and uneven moisture transport, especially those associated with TCs, which benefits studies of remote rainfall associated with TCs. Furthermore, it facilitates the construction of IVT pathway and cluster datasets covering the past several decades, which can be used for analyzing related characteristics and thereby revealing possible physical mechanisms underlying the nature of TRCs. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"8 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135325751","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 a recent study, Benestad et al. (2022) found that the distribution of global precipitation variability in ERA5 appears to have shifted towards smaller spatial scales over the course of the twentieth century. Using an alternative wavelet‐based analysis, we demonstrate that the trends are located almost entirely over the tropical oceans. The phenomenon can be explained by a remarkable shift from parameterized to explicitly resolved convection in this region. The slightly coarser resolved JRA‐55 reanalysis data set exhibits no such trend. A comparison with the conventional data only version JRA‐55C reveals that assimilated satellite data can introduce an additional trend in tropical precipitation amount, but does not, on its own, alter the characteristics of tropical precipitation in JRA‐55. An artificial dual‐diurnal cycle in ERA5 total precipitation and CAPE leads us to the conclusion that the unexpected regime shift is primarily induced by changes in the observation system and not real‐world climate change. This article is protected by copyright. All rights reserved.
{"title":"Tropical convection in ERA5 has partly shifted from parameterized to resolved","authors":"Sebastian Buschow","doi":"10.1002/qj.4604","DOIUrl":"https://doi.org/10.1002/qj.4604","url":null,"abstract":"In a recent study, Benestad et al. (2022) found that the distribution of global precipitation variability in ERA5 appears to have shifted towards smaller spatial scales over the course of the twentieth century. Using an alternative wavelet‐based analysis, we demonstrate that the trends are located almost entirely over the tropical oceans. The phenomenon can be explained by a remarkable shift from parameterized to explicitly resolved convection in this region. The slightly coarser resolved JRA‐55 reanalysis data set exhibits no such trend. A comparison with the conventional data only version JRA‐55C reveals that assimilated satellite data can introduce an additional trend in tropical precipitation amount, but does not, on its own, alter the characteristics of tropical precipitation in JRA‐55. An artificial dual‐diurnal cycle in ERA5 total precipitation and CAPE leads us to the conclusion that the unexpected regime shift is primarily induced by changes in the observation system and not real‐world climate change. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"69 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135326095","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}
Xiaohui Zhong, Fei Du, Lei Chen, Zhibin Wang, Hao Li
Abstract High‐resolution and accurate prediction of near‐surface weather parameters based on numerical weather prediction (NWP) models is essential for many downstream and real‐world applications. Traditional dynamical or statistical downscaling methods are insufficient to derive high‐resolution data from operational NWP forecasts, making it essential to devise new approaches. In recent years, an increasing number of researchers have explored the implementations of deep learning (DL) based models for spatial downscaling, motivated by the similarity between the super‐resolution (SR) problem in computer vision (CV) and downscaling. Furthermore, while transformer‐based models have become state‐of‐the‐art models for many SR tasks, they are rarely applied for downscaling of weather forecasts or climate projections. This study adapted transformer‐based models such as SwinIR and Uformer to downscale the temperature at 2 m () and wind speed at 10 m () over Eastern Inner Mongolia, encompassing the area from 39.6–46°N latitude and 111.6–118°E longitude. We used high‐resolution forecast (HRES) data from the European Centre for Medium‐range Weather Forecast (ECMWF) with a spatial resolution of 0.1° as the input and gridded observation data from the China Meteorological Administration (CMA) Land Data Assimilation System (CLDAS) at a spatial resolution of 0.01° as the target. Given that the models use observation data rather than a coarse‐grained version of forecast data as the target, they accomplish both bias correction and spatial downscaling. The results demonstrate that the performance of SwinIR and Uformer is superior to that of two convolutional neural network (CNN) based models (UNet and RCAN). Additionally, we introduced a novel module to extract features of varying resolution from the high‐resolution topography data and applied a multiscale feature fusion module to merge features of different scales, contributing to further enhancement of Uformer's performance.
{"title":"Investigating transformer‐based models for spatial downscaling and correcting biases of near‐surface temperature and wind speed forecast","authors":"Xiaohui Zhong, Fei Du, Lei Chen, Zhibin Wang, Hao Li","doi":"10.1002/qj.4596","DOIUrl":"https://doi.org/10.1002/qj.4596","url":null,"abstract":"Abstract High‐resolution and accurate prediction of near‐surface weather parameters based on numerical weather prediction (NWP) models is essential for many downstream and real‐world applications. Traditional dynamical or statistical downscaling methods are insufficient to derive high‐resolution data from operational NWP forecasts, making it essential to devise new approaches. In recent years, an increasing number of researchers have explored the implementations of deep learning (DL) based models for spatial downscaling, motivated by the similarity between the super‐resolution (SR) problem in computer vision (CV) and downscaling. Furthermore, while transformer‐based models have become state‐of‐the‐art models for many SR tasks, they are rarely applied for downscaling of weather forecasts or climate projections. This study adapted transformer‐based models such as SwinIR and Uformer to downscale the temperature at 2 m () and wind speed at 10 m () over Eastern Inner Mongolia, encompassing the area from 39.6–46°N latitude and 111.6–118°E longitude. We used high‐resolution forecast (HRES) data from the European Centre for Medium‐range Weather Forecast (ECMWF) with a spatial resolution of 0.1° as the input and gridded observation data from the China Meteorological Administration (CMA) Land Data Assimilation System (CLDAS) at a spatial resolution of 0.01° as the target. Given that the models use observation data rather than a coarse‐grained version of forecast data as the target, they accomplish both bias correction and spatial downscaling. The results demonstrate that the performance of SwinIR and Uformer is superior to that of two convolutional neural network (CNN) based models (UNet and RCAN). Additionally, we introduced a novel module to extract features of varying resolution from the high‐resolution topography data and applied a multiscale feature fusion module to merge features of different scales, contributing to further enhancement of Uformer's performance.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"57 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136134046","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}
J. K. Brooke, M. J. Best, A. P. Lock, S. R. Osborne, J. Price, J. Cuxart, A. Boone, G. Canut‐Rocafort, O. K. Hartogensis, A. Roy
Abstract The Land surface Interactions with the Atmosphere over the Iberian Semi‐arid Environment (LIAISE) campaign was conducted in July 2021, primarily to investigate the role of irrigation in modulating the boundary‐layer evolution in the Catalan region of northeastern Spain. Contrasts in near‐surface meteorological parameters and boundary‐layer thermodynamic profiles at an irrigated and rainfed (arid) site were established during the morning transition. Evapotranspriation dominated the flux partitioning at the irrigated site (Bowen ratio of 0.07–1.1), whilst sensible heat flux dominated at the rainfed (arid) site (Bowen ratio greater than 10.0). The cumulative evapotranspiration during July 2021 was a factor of 10 greater at the irrigated site than at the rainfed (arid) site. The presence of irrigation was shown to modulate the vertical gradients of turbulence, temperature, and moisture. Irrigation is shown to have a significant effect on the development of the boundary layer, including during the morning transition. The morning transition mean buoyancy flux was 2.8 times smaller at the irrigated site (1.1 ms) compared with the rainfed (arid) site (3.1 ms), with a resultant delay in the near‐surface buoyancy‐flux crossover time (30–90 min) at the irrigated site. At the start of the morning transition (sunrise), the average screen‐level (50‐m) temperature was K ( K) colder at the irrigated site relative to the rainfed (arid) site. The colder temperatures at sunrise at the irrigated site are predominantly the result of a colder boundary‐layer thermodynamic profile from the previous day. At the end of the morning transition (convective onset), temperature differences between the two sites extend through much of the boundary layer and increase in magnitude. The average screen‐level (50‐m) temperature difference was K ( K) colder at the irrigated site relative to the rainfed (arid) site. There was considerable day‐to‐day variability in temperature contrasts at a regional level ( to K).
{"title":"Irrigation contrasts through the morning transition","authors":"J. K. Brooke, M. J. Best, A. P. Lock, S. R. Osborne, J. Price, J. Cuxart, A. Boone, G. Canut‐Rocafort, O. K. Hartogensis, A. Roy","doi":"10.1002/qj.4590","DOIUrl":"https://doi.org/10.1002/qj.4590","url":null,"abstract":"Abstract The Land surface Interactions with the Atmosphere over the Iberian Semi‐arid Environment (LIAISE) campaign was conducted in July 2021, primarily to investigate the role of irrigation in modulating the boundary‐layer evolution in the Catalan region of northeastern Spain. Contrasts in near‐surface meteorological parameters and boundary‐layer thermodynamic profiles at an irrigated and rainfed (arid) site were established during the morning transition. Evapotranspriation dominated the flux partitioning at the irrigated site (Bowen ratio of 0.07–1.1), whilst sensible heat flux dominated at the rainfed (arid) site (Bowen ratio greater than 10.0). The cumulative evapotranspiration during July 2021 was a factor of 10 greater at the irrigated site than at the rainfed (arid) site. The presence of irrigation was shown to modulate the vertical gradients of turbulence, temperature, and moisture. Irrigation is shown to have a significant effect on the development of the boundary layer, including during the morning transition. The morning transition mean buoyancy flux was 2.8 times smaller at the irrigated site (1.1 ms) compared with the rainfed (arid) site (3.1 ms), with a resultant delay in the near‐surface buoyancy‐flux crossover time (30–90 min) at the irrigated site. At the start of the morning transition (sunrise), the average screen‐level (50‐m) temperature was K ( K) colder at the irrigated site relative to the rainfed (arid) site. The colder temperatures at sunrise at the irrigated site are predominantly the result of a colder boundary‐layer thermodynamic profile from the previous day. At the end of the morning transition (convective onset), temperature differences between the two sites extend through much of the boundary layer and increase in magnitude. The average screen‐level (50‐m) temperature difference was K ( K) colder at the irrigated site relative to the rainfed (arid) site. There was considerable day‐to‐day variability in temperature contrasts at a regional level ( to K).","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"57 11","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136134045","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}
Abstract Tropical cyclone (TC)‐induced sea surface temperature (SST) cooling plays an important role in controlling the intensity of TCs in ocean basins and can modulate the local weather. This study examined the seasonal differences in TC‐induced SST cooling, especially between summer (June–August) and autumn (September–November), in the western North Pacific for the period 1992–2021. The analysis shows that the average maximum TC‐induced SST cooling along the TC track in autumn is 0.18°C less than in summer, although the mean TC intensity in autumn is 14 knots higher than in summer. This is because in autumn, the average mixed layer depth is 10–13 m deeper than in summer, and the TC track shifts equatorward, preventing the entrainment of cooler subsurface water to the surface, thereby causing less SST cooling in autumn at the same TC intensity. Given the negative feedback of TC‐induced SST cooling on TC intensity, these results are crucial to understand the seasonal differences in the intensity of TC in this basin. This article is protected by copyright. All rights reserved.
热带气旋(TC)诱导的海表温度(SST)冷却在控制海洋盆地TC强度和调节当地天气方面起着重要作用。本研究考察了1992-2021年期间北太平洋西部高温诱发海温降温的季节差异，特别是夏季(6 - 8月)和秋季(9 - 11月)之间的差异。分析表明，秋季沿TC路径的最大平均温度冷却比夏季低0.18°C，但平均TC强度比夏季高14节。这是因为在秋季，平均混合层深度比夏季深10-13 m, TC轨道向赤道移动，阻止了较冷的地下水夹带到地面，从而导致在相同TC强度下，秋季海温冷却较少。考虑到高温引起的海温冷却对高温强度的负反馈，这些结果对于理解该盆地高温强度的季节差异至关重要。这篇文章受版权保护。版权所有。
{"title":"Seasonal differences in tropical cyclone–induced sea surface cooling in the western North Pacific","authors":"Vineet Kumar Singh, Hye‐Ji Kim, Il‐Ju Moon","doi":"10.1002/qj.4606","DOIUrl":"https://doi.org/10.1002/qj.4606","url":null,"abstract":"Abstract Tropical cyclone (TC)‐induced sea surface temperature (SST) cooling plays an important role in controlling the intensity of TCs in ocean basins and can modulate the local weather. This study examined the seasonal differences in TC‐induced SST cooling, especially between summer (June–August) and autumn (September–November), in the western North Pacific for the period 1992–2021. The analysis shows that the average maximum TC‐induced SST cooling along the TC track in autumn is 0.18°C less than in summer, although the mean TC intensity in autumn is 14 knots higher than in summer. This is because in autumn, the average mixed layer depth is 10–13 m deeper than in summer, and the TC track shifts equatorward, preventing the entrainment of cooler subsurface water to the surface, thereby causing less SST cooling in autumn at the same TC intensity. Given the negative feedback of TC‐induced SST cooling on TC intensity, these results are crucial to understand the seasonal differences in the intensity of TC in this basin. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134905675","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}
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