Satellite‐observed microwave radiances provide information on both surface and atmosphere. For operational weather forecasting, information on atmospheric temperature, humidity, cloud, and precipitation is inferred directly using all‐sky radiance data assimilation. In contrast, information on the surface state, such as sea‐surface temperature (SST) and sea‐ice concentration (SIC), is typically provided through third‐party retrieval products. Scientifically, this is a sub‐optimal use of the observations, and practically it has disadvantages such as time delays of more than 48 h. A better solution is to estimate the surface and atmospheric state jointly from the radiance observations. This has not been possible until now, due to incomplete knowledge of the surface state and the radiative transfer that links this to the observed radiances. A new approach based on an empirical state and an empirical sea‐ice surface emissivity model is used here to add sea‐ice state estimation, including SIC, to the European Centre for Medium‐range Weather Forecasts atmospheric data assimilation system. The sea‐ice state is estimated using augmented control variables at the observation locations. The resulting SIC estimates are of good quality and they highlight apparent defects in the existing OCEAN5 sea‐ice analysis. The SIC estimates can also be used to track giant icebergs, which may provide a novel maritime application for passive microwave radiances. Further, the SIC estimates should be suitable for onward use in coupled ocean–atmosphere data assimilation. There is also increased coverage of microwave observations in the proximity of sea ice, leading to improved atmospheric forecasts out to day 4 in the Southern Ocean.
{"title":"Joint estimation of sea ice and atmospheric state from microwave imagers in operational weather forecasting","authors":"Alan J. Geer","doi":"10.1002/qj.4797","DOIUrl":"https://doi.org/10.1002/qj.4797","url":null,"abstract":"Satellite‐observed microwave radiances provide information on both surface and atmosphere. For operational weather forecasting, information on atmospheric temperature, humidity, cloud, and precipitation is inferred directly using all‐sky radiance data assimilation. In contrast, information on the surface state, such as sea‐surface temperature (SST) and sea‐ice concentration (SIC), is typically provided through third‐party retrieval products. Scientifically, this is a sub‐optimal use of the observations, and practically it has disadvantages such as time delays of more than 48 h. A better solution is to estimate the surface and atmospheric state jointly from the radiance observations. This has not been possible until now, due to incomplete knowledge of the surface state and the radiative transfer that links this to the observed radiances. A new approach based on an empirical state and an empirical sea‐ice surface emissivity model is used here to add sea‐ice state estimation, including SIC, to the European Centre for Medium‐range Weather Forecasts atmospheric data assimilation system. The sea‐ice state is estimated using augmented control variables at the observation locations. The resulting SIC estimates are of good quality and they highlight apparent defects in the existing OCEAN5 sea‐ice analysis. The SIC estimates can also be used to track giant icebergs, which may provide a novel maritime application for passive microwave radiances. Further, the SIC estimates should be suitable for onward use in coupled ocean–atmosphere data assimilation. There is also increased coverage of microwave observations in the proximity of sea ice, leading to improved atmospheric forecasts out to day 4 in the Southern Ocean.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"29 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141548739","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}
Fundamental to the theory of data assimilation is that the data (i.e., the observations and the background) provide an unbiased estimate of the true state. There are many situations when this assumption is known to be far from valid; and without bias correction (BC), significant biases will be present in the resulting analysis. Here, we compare two methods to account for biases in the background that do not require a change to the data assimilation algorithm: explicit BC and covariance inflation (CI). When the background bias is known perfectly it is clear that the BC method outperforms the CI method, in that it can completely remove the effect of the background bias whereas the CI method can only reduce it. However, the background bias can only be estimated when unbiased observations are available. A lack of unbiased observations means that the estimate of the background bias will always be subject to sample errors and structural errors due to poor assumptions about how the bias varies in space and time. Given these difficulties in estimating the background bias, the robustness of the two methods in producing an unbiased analysis is studied within an idealised linear system. It is found that the CI method is much less sensitive to errors in the background bias estimate and that a smooth estimate of the bias is crucial to the success of the BC method. However, the CI method is more sensitive to uncorrected biases in the observations.
数据同化理论的基本原理是，数据（即观测数据和背景数据）提供了对真实状态的无偏估计。众所周知，在很多情况下，这一假设远远不能成立；如果不进行偏差校正（BC），结果分析中就会出现明显的偏差。在此，我们比较了两种不需要改变数据同化算法就能考虑背景偏差的方法：显式 BC 和协方差膨胀（CI）。当背景偏差完全已知时，BC 方法显然优于 CI 方法，因为它可以完全消除背景偏差的影响，而 CI 方法只能减少背景偏差的影响。然而，背景偏差只有在有无偏见观测数据的情况下才能估算出来。如果缺乏无偏的观测数据，就意味着对背景偏差的估计总是会受到样本误差和结构误差的影响，这是因为对偏差在空间和时间上如何变化的假设不充分。考虑到估计背景偏差的这些困难，我们在一个理想化的线性系统中研究了这两种方法在进行无偏分析时的稳健性。结果发现，CI 方法对背景偏差估计误差的敏感度要低得多，而平稳的偏差估计对 BC 方法的成功至关重要。然而，CI 方法对观测数据中未修正的偏差更为敏感。
{"title":"On the robustness of methods to account for background bias in data assimilation to uncertainties in the bias estimates","authors":"Alison M. Fowler","doi":"10.1002/qj.4790","DOIUrl":"https://doi.org/10.1002/qj.4790","url":null,"abstract":"Fundamental to the theory of data assimilation is that the data (i.e., the observations and the background) provide an unbiased estimate of the true state. There are many situations when this assumption is known to be far from valid; and without bias correction (BC), significant biases will be present in the resulting analysis. Here, we compare two methods to account for biases in the background that do not require a change to the data assimilation algorithm: explicit BC and covariance inflation (CI). When the background bias is known perfectly it is clear that the BC method outperforms the CI method, in that it can completely remove the effect of the background bias whereas the CI method can only reduce it. However, the background bias can only be estimated when unbiased observations are available. A lack of unbiased observations means that the estimate of the background bias will always be subject to sample errors and structural errors due to poor assumptions about how the bias varies in space and time. Given these difficulties in estimating the background bias, the robustness of the two methods in producing an unbiased analysis is studied within an idealised linear system. It is found that the CI method is much less sensitive to errors in the background bias estimate and that a smooth estimate of the bias is crucial to the success of the BC method. However, the CI method is more sensitive to uncorrected biases in the observations.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"32 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141548534","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 tropical overturning circulation is examined in a moist aquaplanet general circulation model forced using a non‐interactive sea‐surface temperature (SST) distribution that varies between a present‐day Earth‐like profile and one that is globally uniform. A Hadley cell (HC)‐like flow is observed in all experiments along with the poleward transport of heat and angular momentum. In simulations with non‐zero SST gradients, deep convection near the Equator sets up a deep tropical cell; midlatitude baroclinic Rossby waves flux heat and angular momentum poleward, reinforcing the thermally direct circulation. As the imposed SST gradient is weakened, the HC transitions from a thermally and eddy‐driven regime to one that is completely eddy‐driven. When the SST is globally uniform, equatorial waves concentrate precipitation in the Tropics and facilitate the lower‐level convergence necessary for the ascending branch of the HC. Midlatitude Rossby waves generated near the surface become very weak, but upper‐level baroclinicity generates waves that cause equatorward transport of heat and poleward transport of momentum. Moreover, these upper‐level waves induce a circulation that opposes the time‐mean HC, thus highlighting the role of tropical waves in driving an overturning circulation that looks similar to the present‐day Earth‐like case, even for the case with globally uniform SSTs. In all cases, anomalies associated with the tropical waves closely resemble those that sum to give the upper‐level zonal mean divergent outflow. Through their ability to modulate tropical rainfall and the related latent heating, equatorial waves cause considerable hemispheric asymmetry in the HC and impart synoptic and intraseasonal variability to the tropical overturning circulation.
在一个潮湿的水行星大气环流模式中，利用非交互式海面温度（SST）分布对热带倾覆环流进行了研究。在所有实验中都观察到类似哈德利气室（HC）的气流以及热量和角动量的极向输送。在海温梯度不为零的模拟中，赤道附近的深层对流形成了一个深层热带气室；中纬度的巴氏罗斯比波向极地输送热量和角动量，加强了热直流环流。随着外加 SST 梯度的减弱，HC 从热力和涡流驱动系统过渡到完全由涡流驱动的系统。当 SST 全球均匀时，赤道波会将降水集中在热带地区，并促进 HC 上升分支所需的低层辐合。在地表附近产生的中纬度罗斯比波变得非常微弱，但高层气压变化产生的波会导致热量向赤道输送和动量向极地输送。此外，这些上层波引起的环流与时间均值 HC 相反，从而突出了热带波在驱动翻转环流中的作用，这种环流看起来与现在的类地球情况类似，甚至在全球均匀 SST 的情况下也是如此。在所有情况下，与热带波相关的异常都与上层带状平均发散流的异常相近。赤道波通过其调节热带降雨和相关潜热的能力，在 HC 中造成了相当大的半球不对称，并给热带翻转环流带来了同步和季节内变化。
{"title":"Investigating the role of tropical and extratropical waves in the Hadley circulation via present‐day Earth‐like to globally uniform sea‐surface temperature forcing","authors":"A.B.S. Thakur, Jai Sukhatme, Nili Harnik","doi":"10.1002/qj.4784","DOIUrl":"https://doi.org/10.1002/qj.4784","url":null,"abstract":"The tropical overturning circulation is examined in a moist aquaplanet general circulation model forced using a non‐interactive sea‐surface temperature (SST) distribution that varies between a present‐day Earth‐like profile and one that is globally uniform. A Hadley cell (HC)‐like flow is observed in all experiments along with the poleward transport of heat and angular momentum. In simulations with non‐zero SST gradients, deep convection near the Equator sets up a deep tropical cell; midlatitude baroclinic Rossby waves flux heat and angular momentum poleward, reinforcing the thermally direct circulation. As the imposed SST gradient is weakened, the HC transitions from a thermally and eddy‐driven regime to one that is completely eddy‐driven. When the SST is globally uniform, equatorial waves concentrate precipitation in the Tropics and facilitate the lower‐level convergence necessary for the ascending branch of the HC. Midlatitude Rossby waves generated near the surface become very weak, but upper‐level baroclinicity generates waves that cause equatorward transport of heat and poleward transport of momentum. Moreover, these upper‐level waves induce a circulation that opposes the time‐mean HC, thus highlighting the role of tropical waves in driving an overturning circulation that looks similar to the present‐day Earth‐like case, even for the case with globally uniform SSTs. In all cases, anomalies associated with the tropical waves closely resemble those that sum to give the upper‐level zonal mean divergent outflow. Through their ability to modulate tropical rainfall and the related latent heating, equatorial waves cause considerable hemispheric asymmetry in the HC and impart synoptic and intraseasonal variability to the tropical overturning circulation.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"38 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141552603","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}
Yinglian Guo, Zhimin Zhou, Zhaoping Kang, Minghuan Wang, Jun Li, Chunguang Cui
Based on numerical simulation, this study investigates the relationship between environmental factors and microphysical variables of a heavy precipitation event in Suizhou on August 12, 2021, aiming to provide a reference for studying the interaction mechanisms of physical processes involved at different scales. The results demonstrate that environmental instability factors give an early indication of heavy precipitation occurrence and play a crucial role in connecting microphysical processes in the middle/upper layers with water vapor uplift in the lower layers before and during heavy precipitation events. Most of the peak/valley values of both environmental factors and microphysical variables occur simultaneously with those of precipitation on the hourly time series. The vertical profile reveals that, before the occurrence of heavy precipitation, there is an initial strengthening of ascending movement in the middle to upper troposphere, leading to an increase in ice‐phase particles and cloud water within these layers. Additionally, gravity sedimentation and melting significantly contribute to increased rainwater content within the lower to middle layers. When heavy precipitation occurs, intensified vertical velocity, vorticity, and water vapor convergence results in a decrease in cloud/rain particles' peak height and an increase in graupel particles' peak height. This leads to a prolonged collision process and heightened rainfall intensity. Furthermore, enhanced water vapor convergence promotes raindrops formation through colliding and coalescing with cloud droplets. By comparing variables/factors between extreme hourly heavy precipitation and general hourly heavy precipitation, it is suggested that the strengthened self‐feedback mechanism between microphysical latent heat release and vorticity may be one of the reasons for the occurrence of extreme hourly heavy rainfall.
{"title":"Correlation analysis between environmental factors and microphysical variables during the “Suizhou 812” heavy precipitation process in Suizhou City, Hubei Province of China","authors":"Yinglian Guo, Zhimin Zhou, Zhaoping Kang, Minghuan Wang, Jun Li, Chunguang Cui","doi":"10.1002/qj.4792","DOIUrl":"https://doi.org/10.1002/qj.4792","url":null,"abstract":"Based on numerical simulation, this study investigates the relationship between environmental factors and microphysical variables of a heavy precipitation event in Suizhou on August 12, 2021, aiming to provide a reference for studying the interaction mechanisms of physical processes involved at different scales. The results demonstrate that environmental instability factors give an early indication of heavy precipitation occurrence and play a crucial role in connecting microphysical processes in the middle/upper layers with water vapor uplift in the lower layers before and during heavy precipitation events. Most of the peak/valley values of both environmental factors and microphysical variables occur simultaneously with those of precipitation on the hourly time series. The vertical profile reveals that, before the occurrence of heavy precipitation, there is an initial strengthening of ascending movement in the middle to upper troposphere, leading to an increase in ice‐phase particles and cloud water within these layers. Additionally, gravity sedimentation and melting significantly contribute to increased rainwater content within the lower to middle layers. When heavy precipitation occurs, intensified vertical velocity, vorticity, and water vapor convergence results in a decrease in cloud/rain particles' peak height and an increase in graupel particles' peak height. This leads to a prolonged collision process and heightened rainfall intensity. Furthermore, enhanced water vapor convergence promotes raindrops formation through colliding and coalescing with cloud droplets. By comparing variables/factors between extreme hourly heavy precipitation and general hourly heavy precipitation, it is suggested that the strengthened self‐feedback mechanism between microphysical latent heat release and vorticity may be one of the reasons for the occurrence of extreme hourly heavy rainfall.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"21 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141503270","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}
Identifying and understanding various causal relations are fundamental to climate dynamics for improving the predictive capacity of Earth system modeling. In particular, causality in Earth systems has manifest temporal periodicities, like physical climate variabilities. To unravel the characteristic frequency of causality in climate dynamics, we develop a data‐analytic framework based on a combination of causality detection and Hilbert spectral analysis, using a long‐term temperature and precipitation dataset in the contiguous United States. Using the Huang–Hilbert transform, we identify the intrinsic frequencies of cross‐regional causality for precipitation and temperature, ranging from interannual to interdecadal time scales. In addition, we analyze the spectra of the physical climate variabilities, including El Niño‐Southern Oscillation and Pacific Decadal Oscillation. It is found that the intrinsic causal frequencies are positively associated with the physics of the oscillations in the global climate system. The proposed methodology provides fresh insights into the causal connectivity in Earth's hydroclimatic system and its underlying mechanism as regulated by the characteristic low‐frequency variability associated with various climatic dynamics.
{"title":"Time variability and periodicities of cross‐regional hydroclimatic causation in the contiguous United States","authors":"Xueli Yang, Zhi‐Hua Wang, Qi Li, Ying‐Cheng Lai","doi":"10.1002/qj.4800","DOIUrl":"https://doi.org/10.1002/qj.4800","url":null,"abstract":"Identifying and understanding various causal relations are fundamental to climate dynamics for improving the predictive capacity of Earth system modeling. In particular, causality in Earth systems has manifest temporal periodicities, like physical climate variabilities. To unravel the characteristic frequency of causality in climate dynamics, we develop a data‐analytic framework based on a combination of causality detection and Hilbert spectral analysis, using a long‐term temperature and precipitation dataset in the contiguous United States. Using the Huang–Hilbert transform, we identify the intrinsic frequencies of cross‐regional causality for precipitation and temperature, ranging from interannual to interdecadal time scales. In addition, we analyze the spectra of the physical climate variabilities, including El Niño‐Southern Oscillation and Pacific Decadal Oscillation. It is found that the intrinsic causal frequencies are positively associated with the physics of the oscillations in the global climate system. The proposed methodology provides fresh insights into the causal connectivity in Earth's hydroclimatic system and its underlying mechanism as regulated by the characteristic low‐frequency variability associated with various climatic dynamics.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"539 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141503272","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}
Moumita Bhowmik, Anupam Hazra, Sachin D. Ghude, Sandeep Wagh, Rituparna Chowdhury, Avinash N. Parde, Gaurav Govardhan, Ismail Gultepe, M. Rajeevan
With the changing climate, the study of fog formation is essential due to the impact of the complexity of natural and anthropogenic aerosols. The evolution of the droplet size distribution in the presence of different aerosol species remains poorly understood. To make progress towards reducing the uncertainty of fog forecasts, the Eulerian–Lagrangian particle‐based small‐scale model for the diffusional growth of droplets is used to better understand the droplet activation and growth. The small‐scale model simulations are performed using observed data from the Winter Fog Experiment study over Indira Gandhi International Airport, New Delhi. The microphysical properties, such as droplet number concentrations (Nd) and liquid water content (LWC), important for fog simulation, are evaluated to gain more insights. The small‐scale simulations have shown the droplet microphysical properties at different evolutionary stages. The Nd and effective radius change with variations in LWC for different aerosol chemistries (i.e., organics, mix, and inorganic). The calculated visibility at small scale is also shown with the variation of Nd and LWC. This study compared visibility from an existing parametrization with parcel–direct numerical simulation calculation. The hygroscopicity , which is highly related to the activation of aerosols to condensation nuclei, is taken into account to demonstrate the contribution of aerosol chemistry to fog droplet formation. The results highlight that hygroscopicity is essential in the numerical model for fog and visibility prediction as the microphysical properties of fog are regulated by aerosol species.
{"title":"Is a more physical representation of aerosol chemistry needed for fog forecasting?","authors":"Moumita Bhowmik, Anupam Hazra, Sachin D. Ghude, Sandeep Wagh, Rituparna Chowdhury, Avinash N. Parde, Gaurav Govardhan, Ismail Gultepe, M. Rajeevan","doi":"10.1002/qj.4729","DOIUrl":"https://doi.org/10.1002/qj.4729","url":null,"abstract":"With the changing climate, the study of fog formation is essential due to the impact of the complexity of natural and anthropogenic aerosols. The evolution of the droplet size distribution in the presence of different aerosol species remains poorly understood. To make progress towards reducing the uncertainty of fog forecasts, the Eulerian–Lagrangian particle‐based small‐scale model for the diffusional growth of droplets is used to better understand the droplet activation and growth. The small‐scale model simulations are performed using observed data from the Winter Fog Experiment study over Indira Gandhi International Airport, New Delhi. The microphysical properties, such as droplet number concentrations (Nd) and liquid water content (LWC), important for fog simulation, are evaluated to gain more insights. The small‐scale simulations have shown the droplet microphysical properties at different evolutionary stages. The Nd and effective radius change with variations in LWC for different aerosol chemistries (i.e., organics, mix, and inorganic). The calculated visibility at small scale is also shown with the variation of Nd and LWC. This study compared visibility from an existing parametrization with parcel–direct numerical simulation calculation. The hygroscopicity , which is highly related to the activation of aerosols to condensation nuclei, is taken into account to demonstrate the contribution of aerosol chemistry to fog droplet formation. The results highlight that hygroscopicity is essential in the numerical model for fog and visibility prediction as the microphysical properties of fog are regulated by aerosol species.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"57 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141503271","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}
Sunil Kumar Pariyar, Giovanni Liguori, Christian Jakob, Martin S. Singh, Michael J. Reeder, Michael A. Barnes
Rainfall variability over Australia is revisited from the viewpoint of the atmospheric moisture budgets in three regions: the extratropics, Subtropics, and Tropics. The budgets are calculated using three‐hourly European Centre for Medium‐Range Weather Forecasts Reanalysis v5 (ERA5) and ERA5‐Land data between 1979 and 2022. The use of the moisture budget at short time‐scales enables the investigation of the relationship between synoptic weather‐scale processes and the longer term variability of the rainfall climate. The total variability in the vertically integrated moisture flux divergence (VIMD) is significantly larger than the evaporation minus precipitation (E − P), to a large extent due to the sub‐daily time‐scales. E − P is related more closely to moisture flux convergence in winter (summer) over south (north) Australia, suggesting a clear seasonality in the relationship between the two budget terms. The E − P–VIMD relationship is nearly in phase in the Tropics, whereas VIMD leads E − P by 9–15 hr with eastward‐propagating signals in the extratropics and Subtropics. Such seasonal and regional discrepancies in the relationship are attributed to the background state of moisture availability and temperature as represented by relative humidity and lifting condensation levels. The variability of the budget imbalance and its seasonality are dominated by the variability in VIMD. The imbalance reduces rapidly with temporal smoothing, with the storage term approaching zero at approximately 20 days, which can be thought of as making a transition time‐scale from high‐frequency weather‐related variability into slow‐varying background conditions. Weather‐related variability (cyclones, fronts, and thunderstorms) dominates the overall E − P variability in the extratropics and Subtropics, whereas slow‐varying background conditions contribute equally to the total variability in the Tropics.
从大气水分预算的角度，重新审视了澳大利亚三个地区的降雨变化：外热带地区、亚热带地区和热带地区。这些预算是利用 1979 年至 2022 年期间每三小时一次的欧洲中期天气预报中心再分析 v5（ERA5）和 ERA5-Land 数据计算得出的。利用短时尺度的水汽预算可以研究天气尺度的同步过程与降雨气候的长期变化之间的关系。垂直综合水汽通量分异（VIMD）的总变异性明显大于蒸发量减去降水量（E - P），这在很大程度上是由于采用了亚日时间尺度。E - P 与澳大利亚南部（北部）冬季（夏季）的水汽通量辐合关系更为密切，表明这两个预算项之间的关系具有明显的季节性。在热带地区，E-P-VIMD 关系几乎是同步的，而在外向热带和亚热带地区，VIMD 则以 9-15 小时的东向传播信号领先于 E-P。这种季节性和区域性的差异归因于相对湿度和凝结水平所代表的水汽供应和温度的背景状态。预算失衡的变化及其季节性主要受 VIMD 变化的影响。随着时间的平滑化，不平衡迅速减小，储存项在大约 20 天时接近于零，可以认为这是从与天气相关的高频变率向缓慢变化的背景条件过渡的时间尺度。与天气有关的变率（气旋、锋面和雷暴）在外向热带和亚热带地区的整个 E - P 变率中占主导地位，而慢变背景条件在热带地区的总变率中占同样的比例。
{"title":"A moisture budget perspective on Australian rainfall variability","authors":"Sunil Kumar Pariyar, Giovanni Liguori, Christian Jakob, Martin S. Singh, Michael J. Reeder, Michael A. Barnes","doi":"10.1002/qj.4778","DOIUrl":"https://doi.org/10.1002/qj.4778","url":null,"abstract":"Rainfall variability over Australia is revisited from the viewpoint of the atmospheric moisture budgets in three regions: the extratropics, Subtropics, and Tropics. The budgets are calculated using three‐hourly European Centre for Medium‐Range Weather Forecasts Reanalysis v5 (ERA5) and ERA5‐Land data between 1979 and 2022. The use of the moisture budget at short time‐scales enables the investigation of the relationship between synoptic weather‐scale processes and the longer term variability of the rainfall climate. The total variability in the vertically integrated moisture flux divergence (VIMD) is significantly larger than the evaporation minus precipitation (<jats:italic>E</jats:italic> − <jats:italic>P</jats:italic>), to a large extent due to the sub‐daily time‐scales. <jats:italic>E</jats:italic> − <jats:italic>P</jats:italic> is related more closely to moisture flux convergence in winter (summer) over south (north) Australia, suggesting a clear seasonality in the relationship between the two budget terms. The <jats:italic>E</jats:italic> − <jats:italic>P</jats:italic>–VIMD relationship is nearly in phase in the Tropics, whereas VIMD leads <jats:italic>E</jats:italic> − <jats:italic>P</jats:italic> by 9–15 hr with eastward‐propagating signals in the extratropics and Subtropics. Such seasonal and regional discrepancies in the relationship are attributed to the background state of moisture availability and temperature as represented by relative humidity and lifting condensation levels. The variability of the budget imbalance and its seasonality are dominated by the variability in VIMD. The imbalance reduces rapidly with temporal smoothing, with the storage term approaching zero at approximately 20 days, which can be thought of as making a transition time‐scale from high‐frequency weather‐related variability into slow‐varying background conditions. Weather‐related variability (cyclones, fronts, and thunderstorms) dominates the overall <jats:italic>E</jats:italic> − <jats:italic>P</jats:italic> variability in the extratropics and Subtropics, whereas slow‐varying background conditions contribute equally to the total variability in the Tropics.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"2013 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141526696","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}
A. P. Lock, M. Whitall, A. J. Stirling, K. D. Williams, S. L. Lavender, C. Morcrette, K. Matsubayashi, P. R. Field, G. Martin, M. Willett, J. Heming
The impact on global simulations of a new package of physical parametrizations in the Met Office Unified Model is documented. The main component of the package is an entirely new convection scheme, CoMorph. This has a mass‐flux structure that allows initiation of buoyant ascent from any level and the ability for plumes of differing originating levels to coexist in a grid box. It has a different form of closure, where the mass flux of initiation is dependent on local instability, and an implicit numerical solution for detrainment that yields smooth timestep behaviour. The scheme is coupled more consistently to the cloud, microphysics, and boundary‐layer parametrizations and, as a result, significant changes to these have also been made. The package, called CoMorph‐A, has been tested in a variety of single‐column and idealized regimes. Here we test it in global configurations and evaluate it against observations using a range of standard metrics. Overall it is found to perform well against the control. Biases in the climatologies of the radiative fluxes are significantly reduced across the Tropics and subtropics, tropical and extratropical cyclone statistics are improved, and the Madden–Julian oscillation and other propagating tropical waves are strengthened. It also improves overall scores in numerical weather prediction trials, without revisions to the data assimilation. There is still work to do to improve the diurnal cycle of precipitation over land, where the peak remains too close to the middle of the day.
{"title":"The performance of the CoMorph‐A convection package in global simulations with the Met Office Unified Model","authors":"A. P. Lock, M. Whitall, A. J. Stirling, K. D. Williams, S. L. Lavender, C. Morcrette, K. Matsubayashi, P. R. Field, G. Martin, M. Willett, J. Heming","doi":"10.1002/qj.4781","DOIUrl":"https://doi.org/10.1002/qj.4781","url":null,"abstract":"The impact on global simulations of a new package of physical parametrizations in the Met Office Unified Model is documented. The main component of the package is an entirely new convection scheme, CoMorph. This has a mass‐flux structure that allows initiation of buoyant ascent from any level and the ability for plumes of differing originating levels to coexist in a grid box. It has a different form of closure, where the mass flux of initiation is dependent on local instability, and an implicit numerical solution for detrainment that yields smooth timestep behaviour. The scheme is coupled more consistently to the cloud, microphysics, and boundary‐layer parametrizations and, as a result, significant changes to these have also been made. The package, called CoMorph‐A, has been tested in a variety of single‐column and idealized regimes. Here we test it in global configurations and evaluate it against observations using a range of standard metrics. Overall it is found to perform well against the control. Biases in the climatologies of the radiative fluxes are significantly reduced across the Tropics and subtropics, tropical and extratropical cyclone statistics are improved, and the Madden–Julian oscillation and other propagating tropical waves are strengthened. It also improves overall scores in numerical weather prediction trials, without revisions to the data assimilation. There is still work to do to improve the diurnal cycle of precipitation over land, where the peak remains too close to the middle of the day.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"40 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141526697","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}
Thomas J. Hintz, Kelly Y. Huang, Sebastian W. Hoch, Stef L. Bardoel, Saša Gaberšek, Ismail Gultepe, Jesus Ruiz‐Plancarte, Eric R. Pardyjak, Qing Wang, Harindra J. S. Fernando
Transitional changes in the atmospheric boundary layer (ABL) are known to facilitate the onset of terrestrial fog, which is defined as a condition with near‐surface visibility <1 km due to airborne water droplets. In particular, the evening transition from a daytime convective ABL to a night‐time stable ABL provides favorable conditions for fog. This article describes a local fog event observed during the evening transition at a Canadian islet in the north Atlantic known as Sable Island during the “Fog and Turbulence Interactions in the Marine Atmosphere (Fatima)” field campaign. The comprehensive set of data collected using a myriad of instruments covering a wide range of scales allowed identification of a novel mechanism underlying this fog event. Therein an ocean–land discontinuity created a flow regime consisting of several stacked boundary layers, interplay of which produced a thin low‐level cloud that then diffused downward to the surface, causing visibility reduction. This mechanism offers useful insights on the role of boundary layers, stratification, and turbulence in fog genesis over oceanic islands.
{"title":"A mechanism for coastal fog genesis at evening transition","authors":"Thomas J. Hintz, Kelly Y. Huang, Sebastian W. Hoch, Stef L. Bardoel, Saša Gaberšek, Ismail Gultepe, Jesus Ruiz‐Plancarte, Eric R. Pardyjak, Qing Wang, Harindra J. S. Fernando","doi":"10.1002/qj.4732","DOIUrl":"https://doi.org/10.1002/qj.4732","url":null,"abstract":"Transitional changes in the atmospheric boundary layer (ABL) are known to facilitate the onset of terrestrial fog, which is defined as a condition with near‐surface visibility <1 km due to airborne water droplets. In particular, the evening transition from a daytime convective ABL to a night‐time stable ABL provides favorable conditions for fog. This article describes a local fog event observed during the evening transition at a Canadian islet in the north Atlantic known as Sable Island during the “Fog and Turbulence Interactions in the Marine Atmosphere (Fatima)” field campaign. The comprehensive set of data collected using a myriad of instruments covering a wide range of scales allowed identification of a novel mechanism underlying this fog event. Therein an ocean–land discontinuity created a flow regime consisting of several stacked boundary layers, interplay of which produced a thin low‐level cloud that then diffused downward to the surface, causing visibility reduction. This mechanism offers useful insights on the role of boundary layers, stratification, and turbulence in fog genesis over oceanic islands.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"73 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141503273","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}
Kianusch Vahid Yousefnia, Tobias Bölle, Isabella Zöbisch, Thomas Gerz
Thunderstorms pose a major hazard to society and the economy, which calls for reliable thunderstorm forecasts. In this work, we introduce SALAMA, a feedforward neural network model for identifying thunderstorm occurrence in numerical weather prediction (NWP) data. The model is trained on convection‐resolving ensemble forecasts over central Europe and lightning observations. Given only a set of pixel‐wise input parameters that are extracted from NWP data and related to thunderstorm development, SALAMA infers the probability of thunderstorm occurrence in a reliably calibrated manner. For lead times up to 11 h, we find a forecast skill superior to classification based only on NWP reflectivity. Varying the spatiotemporal criteria by which we associate lightning observations with NWP data, we show that the time‐scale for skillful thunderstorm predictions increases linearly with the spatial scale of the forecast.
{"title":"A machine‐learning approach to thunderstorm forecasting through post‐processing of simulation data","authors":"Kianusch Vahid Yousefnia, Tobias Bölle, Isabella Zöbisch, Thomas Gerz","doi":"10.1002/qj.4777","DOIUrl":"https://doi.org/10.1002/qj.4777","url":null,"abstract":"Thunderstorms pose a major hazard to society and the economy, which calls for reliable thunderstorm forecasts. In this work, we introduce SALAMA, a feedforward neural network model for identifying thunderstorm occurrence in numerical weather prediction (NWP) data. The model is trained on convection‐resolving ensemble forecasts over central Europe and lightning observations. Given only a set of pixel‐wise input parameters that are extracted from NWP data and related to thunderstorm development, SALAMA infers the probability of thunderstorm occurrence in a reliably calibrated manner. For lead times up to 11 h, we find a forecast skill superior to classification based only on NWP reflectivity. Varying the spatiotemporal criteria by which we associate lightning observations with NWP data, we show that the time‐scale for skillful thunderstorm predictions increases linearly with the spatial scale of the forecast.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"10 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2024-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141526698","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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