Jonathan A. Christophersen, Adam Rydbeck, Maria Flatau, Matt Janiga, Carolyn A. Reynolds, Tommy Jensen, Travis Smith
In recent years, studies have put forth various theories on the role of oceanic equatorial Rossby waves (OERW) in the subseasonal-to-seasonal (S2S) predictability of the Indian Ocean (IO). While much of the scientific literature uses data from in-situ, satellite, and/or reanalysis datasets, this study focuses on reforecast fields from the European Centre for Medium-Range Weather Forecasting's (ECMWF) S2S dataset. Evaluation of the model's predictive skill in representing OERWs and the associated variations in subsurface-to-surface interaction and air-sea coupling are discussed. This work provides a unique methodology to calculate and evaluate the predictability of OERWs from model forecast data. Our results indicate that the model forecasts OERWs with high skill (anomaly correlation > 0.8 out to 40 days), indicating they are a key source of oceanic subseasonal predictability at extended lead times. Analysis of the wavenumber-frequency spectra for the IO indicates a strong reduction in power throughout the model forecast time period in the oceanic equatorial Kelvin wave (OEKW) regime and modest reduction of the OERW power. Both Kelvin and Rossby waves are modulated by the subseasonal zonal wind stress anomalies and the reduction of power is impacted by biases in winds at longer forecast leads. The erroneous weakening of the OEKWs contributes to the weakening of the reflected oceanic equatorial Rossby waves (OERWs). Previous studies have documented that ocean heat content (OHC), particularly associated with downwelling OERWs, is important to maintaining and amplifying subseasonal precipitation in the IO. The reduced OERW power results in weaker advection of enhanced OHC anomalies by the OERWs, which has numerous implications for air-sea and subsurface-to-surface coupling, as discussed. The atmospheric response to the waning westward transport of OHC anomalies in the western IO by OERWs is associated with a weakening of intraseasonal precipitation anomalies associated with the intraseasonal oscillation.
{"title":"Oceanic Rossby Wave Predictability in ECMWF's Subseasonal-to-Seasonal Reforecasts","authors":"Jonathan A. Christophersen, Adam Rydbeck, Maria Flatau, Matt Janiga, Carolyn A. Reynolds, Tommy Jensen, Travis Smith","doi":"10.1002/qj.4636","DOIUrl":"https://doi.org/10.1002/qj.4636","url":null,"abstract":"In recent years, studies have put forth various theories on the role of oceanic equatorial Rossby waves (OERW) in the subseasonal-to-seasonal (S2S) predictability of the Indian Ocean (IO). While much of the scientific literature uses data from in-situ, satellite, and/or reanalysis datasets, this study focuses on reforecast fields from the European Centre for Medium-Range Weather Forecasting's (ECMWF) S2S dataset. Evaluation of the model's predictive skill in representing OERWs and the associated variations in subsurface-to-surface interaction and air-sea coupling are discussed. This work provides a unique methodology to calculate and evaluate the predictability of OERWs from model forecast data. Our results indicate that the model forecasts OERWs with high skill (anomaly correlation > 0.8 out to 40 days), indicating they are a key source of oceanic subseasonal predictability at extended lead times. Analysis of the wavenumber-frequency spectra for the IO indicates a strong reduction in power throughout the model forecast time period in the oceanic equatorial Kelvin wave (OEKW) regime and modest reduction of the OERW power. Both Kelvin and Rossby waves are modulated by the subseasonal zonal wind stress anomalies and the reduction of power is impacted by biases in winds at longer forecast leads. The erroneous weakening of the OEKWs contributes to the weakening of the reflected oceanic equatorial Rossby waves (OERWs). Previous studies have documented that ocean heat content (OHC), particularly associated with downwelling OERWs, is important to maintaining and amplifying subseasonal precipitation in the IO. The reduced OERW power results in weaker advection of enhanced OHC anomalies by the OERWs, which has numerous implications for air-sea and subsurface-to-surface coupling, as discussed. The atmospheric response to the waning westward transport of OHC anomalies in the western IO by OERWs is associated with a weakening of intraseasonal precipitation anomalies associated with the intraseasonal oscillation.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"25 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138573404","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 this paper, we combine Deep symbolic regression (DSR) and Ensemble Optimal Interpolation-based Data Assimilation (DA) method to correct the error in the forecasts from the numerical model, WaveWatch III. In our experiments, the DA and DSR training is performed on the hindcasts and then the model is integrated forward in time with both the numerical model and the symbolic expressions generated from the DSR procedure to generate the forecasts. The DSR method is utilized in this paper to generate the symbolic equations that correct the model error in the WaveWatch III/ DA system. The proposed algorithm takes the zonal (u) and meridional (v) wind components from Global Forecast System (GFS) forecasts, wave heights from WaveWatch III, and geographical coordinates (latitude and longitude) to model physical relationships not included in the original numerical model. The DA is performed using JASON-2 and SARAL altimeter measurements, and the independent testing uses the in situ buoys The RMSD of the proposed method is better than the numerical model with/without DA for up to 42 hours with only 12 days of assimilation spin-up cycle. The symbolic equation generated from the proposed framework can be used to correct the predictions from WaveWatch III for weather prediction.
在本文中，我们将深度符号回归（DSR）和基于集合优化插值的数据同化（DA）方法结合起来，以纠正数值模式 WaveWatch III 的预报误差。在我们的实验中，DA 和 DSR 训练是在后报上进行的，然后用数值模式和 DSR 程序生成的符号表达式对模型进行时间整合，生成预报。本文利用 DSR 方法生成符号方程，以纠正 WaveWatch III/ DA 系统中的模型误差。建议的算法采用全球预报系统（GFS）预报中的纵向风（u）和经向风（v）分量、WaveWatch III 中的波高和地理坐标（经纬度）来模拟原始数值模式中未包含的物理关系。利用 JASON-2 和 SARAL 高度计的测量数据进行了数据分析，并利用原位浮标进行了独立测试。建议框架生成的符号方程可用于修正 WaveWatch III 的天气预报预测。
{"title":"A Machine Learning and Data Assimilation forecasting framework for surface waves","authors":"Pujan Pokhrel, Mahdi Abdelguerfi, Elias Ioup","doi":"10.1002/qj.4631","DOIUrl":"https://doi.org/10.1002/qj.4631","url":null,"abstract":"In this paper, we combine Deep symbolic regression (DSR) and Ensemble Optimal Interpolation-based Data Assimilation (DA) method to correct the error in the forecasts from the numerical model, WaveWatch III. In our experiments, the DA and DSR training is performed on the hindcasts and then the model is integrated forward in time with both the numerical model and the symbolic expressions generated from the DSR procedure to generate the forecasts. The DSR method is utilized in this paper to generate the symbolic equations that correct the model error in the WaveWatch III/ DA system. The proposed algorithm takes the zonal (u) and meridional (v) wind components from Global Forecast System (GFS) forecasts, wave heights from WaveWatch III, and geographical coordinates (latitude and longitude) to model physical relationships not included in the original numerical model. The DA is performed using JASON-2 and SARAL altimeter measurements, and the independent testing uses the in situ buoys The RMSD of the proposed method is better than the numerical model with/without DA for up to 42 hours with only 12 days of assimilation spin-up cycle. The symbolic equation generated from the proposed framework can be used to correct the predictions from WaveWatch III for weather prediction.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"104 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138573467","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}
Lewis P. Blunn, Robert S. Plant, Omduth Coceal, Sylvia I. Bohnenstengel, Humphrey W. Lean, Janet F. Barlow
The UK Met Office has a 300 m grid length numerical weather prediction (NWP) model running routinely over London and in research mode city-scale hectometric grid length NWP has become commonplace. It is important to understand how moving from kilometre to hectometre scale grid length NWP influences boundary layer vertical mixing. For a clear-sky convective boundary layer (CBL) case study, using 55 m and 100 m grid length NWP, we demonstrate that CBL vertical mixing of passive scalar is almost fully resolved. Passive scalar converges near the surface after emission from an idealised pollution ground source representing city-scale emissions, and is transported in updrafts preferentially into the upper boundary layer. Approximately 8 km downstream of the source edge this causes 34% lower near-surface concentrations compared to 1.5 km grid length NWP, where vertical mixing is fully parameterised. This demonstrates that resolving ballistic type dispersion, which is not typically represented in NWP vertical mixing parameterisations, can have a leading order influence on city-scale near-surface pollution concentration. We present a simple analytical model that is able to capture diffusive and ballistic dispersion behaviour in terms of effective timescales. The timescale controlling how long it takes passive scalar to become well-mixed in the CBL is ≈ times longer for the 1.5 km compared to the 100 m and 55 m grid length NWP.
{"title":"The influence of resolved convective motions on scalar dispersion in hectometric scale numerical weather prediction models","authors":"Lewis P. Blunn, Robert S. Plant, Omduth Coceal, Sylvia I. Bohnenstengel, Humphrey W. Lean, Janet F. Barlow","doi":"10.1002/qj.4632","DOIUrl":"https://doi.org/10.1002/qj.4632","url":null,"abstract":"The UK Met Office has a 300 m grid length numerical weather prediction (NWP) model running routinely over London and in research mode city-scale hectometric grid length NWP has become commonplace. It is important to understand how moving from kilometre to hectometre scale grid length NWP influences boundary layer vertical mixing. For a clear-sky convective boundary layer (CBL) case study, using 55 m and 100 m grid length NWP, we demonstrate that CBL vertical mixing of passive scalar is almost fully resolved. Passive scalar converges near the surface after emission from an idealised pollution ground source representing city-scale emissions, and is transported in updrafts preferentially into the upper boundary layer. Approximately 8 km downstream of the source edge this causes 34% lower near-surface concentrations compared to 1.5 km grid length NWP, where vertical mixing is fully parameterised. This demonstrates that resolving ballistic type dispersion, which is not typically represented in NWP vertical mixing parameterisations, can have a leading order influence on city-scale near-surface pollution concentration. We present a simple analytical model that is able to capture diffusive and ballistic dispersion behaviour in terms of effective timescales. The timescale controlling how long it takes passive scalar to become well-mixed in the CBL is ≈ times longer for the 1.5 km compared to the 100 m and 55 m grid length NWP.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"253 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138573405","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}
Jasmin Vural, Claire Merker, Moritz Löffler, Daniel Leuenberger, Christoph Schraff, Olaf Stiller, Annika Schomburg, Christine Knist, Alexander Haefele, Maxime Hervo
In a joint effort, MeteoSwiss and Deutscher Wetterdienst (DWD) address the need for improving the initial state of the atmospheric boundary layer (ABL) by exploiting ground-based profiling observations that aim to fill the existing observational gap in the ABL. We implemented the brightness temperature observations from ground-based microwave radiometers (MWRs) into our data assimilation systems using a local ensemble transform Kalman filter (LETKF) with RTTOV-gb (Radiative Transfer for TOVS, ground-based) as a forward operator. We were able to obtain a positive impact on the brightness temperature first guess and analysis as well as a slight impact on the ABL humidity using two MWRs at MeteoSwiss. These results led to a subsequent operational implementation of the observing system at MeteoSwiss. Furthermore, we performed an extensive set of assimilation experiments at DWD to further investigate various aspects such as the vertical localisation of selected single channels. We obtained a positive impact on the 6 h-forecast of ABL temperature and humidity by assimilating two channels employing a dynamical localisation based on the sensitivity functions of RTTOV-gb but also with a static localisation in a single-channel setup. Our experiments indicate the importance of the vertical localisation when using more than one channel, although reliable improvements are challenging to obtain without a larger number of observations for both assimilation and verification.
{"title":"Improving the representation of the atmospheric boundary layer by direct assimilation of ground-based microwave radiometer observations","authors":"Jasmin Vural, Claire Merker, Moritz Löffler, Daniel Leuenberger, Christoph Schraff, Olaf Stiller, Annika Schomburg, Christine Knist, Alexander Haefele, Maxime Hervo","doi":"10.1002/qj.4634","DOIUrl":"https://doi.org/10.1002/qj.4634","url":null,"abstract":"In a joint effort, MeteoSwiss and Deutscher Wetterdienst (DWD) address the need for improving the initial state of the atmospheric boundary layer (ABL) by exploiting ground-based profiling observations that aim to fill the existing observational gap in the ABL. We implemented the brightness temperature observations from ground-based microwave radiometers (MWRs) into our data assimilation systems using a local ensemble transform Kalman filter (LETKF) with RTTOV-gb (Radiative Transfer for TOVS, ground-based) as a forward operator. We were able to obtain a positive impact on the brightness temperature first guess and analysis as well as a slight impact on the ABL humidity using two MWRs at MeteoSwiss. These results led to a subsequent operational implementation of the observing system at MeteoSwiss. Furthermore, we performed an extensive set of assimilation experiments at DWD to further investigate various aspects such as the vertical localisation of selected single channels. We obtained a positive impact on the 6 h-forecast of ABL temperature and humidity by assimilating two channels employing a dynamical localisation based on the sensitivity functions of RTTOV-gb but also with a static localisation in a single-channel setup. Our experiments indicate the importance of the vertical localisation when using more than one channel, although reliable improvements are challenging to obtain without a larger number of observations for both assimilation and verification.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"107 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138573874","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 new limited-area numerical model (TRAM, for Triangle-based Regional Atmospheric Model) has been built using a nonhydrostatic and fully compressible version of the Navier-Stokes equations. Advection terms are solved using a Reconstruct-Evolve-Average (REA) strategy over the computational cells. These cells consist of equilateral triangles in the horizontal. The classical z-coordinate is used in the vertical, allowing arbitrary stretching (e.g. higher resolution in the Planetary Boundary Layer, PBL). Proper treatment of terrain slopes in the bottom boundary conditions allows for representing accurately the orographic forcing. To gain computational efficiency, time-splitting is used to integrate separately fast and slow terms and acoustic modes in the vertical are solved implicitly. For real cases on the globe, the Lambert map projection is applied, and all Coriolis and curvature terms are retained. No explicit filters are needed.
利用纳维-斯托克斯方程的非流体静力学和完全可压缩版本，建立了一个新的有限区域数值模型（TRAM，即基于三角形的区域大气模型）。在计算单元上采用重建-演化-平均（REA）策略解决平流项。这些单元由水平等边三角形组成。垂直方向使用传统的 Z 坐标，允许任意拉伸（例如，提高行星边界层的分辨率）。在底部边界条件中对地形坡度进行适当处理，可以准确地表示地貌作用力。为了提高计算效率，采用时间分割法对快速和慢速项分别进行积分，并对垂直方向的声学模式进行隐式求解。对于地球上的实际情况，采用兰伯特地图投影，并保留所有科里奥利和曲率项。不需要明确的滤波器。
{"title":"TRAM: A New Nonhydrostatic Fully Compressible Numerical Model Suited for All Kinds of Regional Atmospheric Predictions","authors":"R. Romero","doi":"10.1002/qj.4639","DOIUrl":"https://doi.org/10.1002/qj.4639","url":null,"abstract":"A new limited-area numerical model (TRAM, for Triangle-based Regional Atmospheric Model) has been built using a nonhydrostatic and fully compressible version of the Navier-Stokes equations. Advection terms are solved using a Reconstruct-Evolve-Average (REA) strategy over the computational cells. These cells consist of equilateral triangles in the horizontal. The classical z-coordinate is used in the vertical, allowing arbitrary stretching (e.g. higher resolution in the Planetary Boundary Layer, PBL). Proper treatment of terrain slopes in the bottom boundary conditions allows for representing accurately the orographic forcing. To gain computational efficiency, time-splitting is used to integrate separately fast and slow terms and acoustic modes in the vertical are solved implicitly. For real cases on the globe, the Lambert map projection is applied, and all Coriolis and curvature terms are retained. No explicit filters are needed.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"30 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138573407","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}
Cheng Tao, Shaocheng Xie, Hsi-Yen Ma, Peter Bechtold, Zeyu Cui, Paul A. Vaillancourt, Kwinten Van Weverberg, Yi-Chi Wang, May Wong, Jing Yang, Guang J. Zhang, In-Jin Choi, Shuaiqi Tang, Jiangfeng Wei, Wen-Ying Wu, Meng Zhang, J. David Neelin, Xubin Zeng
Diurnal precipitation is a fundamental mode of variability that climate models have difficulty in accurately simulating. Here the diurnal cycle of precipitation (DCP) in participating climate models from the Global Energy and Water Exchanges’ DCP project is evaluated over the tropics and central U.S. Common model biases such as excessive precipitation over the tropics, too frequent light-to-moderate rain, and the failure to capture propagating convection in the central U.S. still exist. Over the central U.S., the issues of too weak rainfall intensity in climate runs is well improved in their hindcast runs with initial conditions from Numerical Weather Prediction analyses. But the improvement is minimal over the central Amazon. Incorporating the role of the large-scale environment in convective triggering processes helps resolve the phase-locking issue in many models where precipitation often incorrectly peaks near noon due to maximum insolation over land. Allowing air parcels to be lifted above the boundary layer improves the simulation of nocturnal precipitation which is often associated with the propagation of mesoscale systems. Including convective memory in cumulus parameterizations acts to suppress light-to-moderate rain and promote intense rainfall; however, it also weakens the diurnal variability. Simply increasing model resolution (with cumulus parameterizations still used) cannot fully resolve the biases of low-resolution climate models in DCP. The hierarchy modeling framework from this study is useful for identifying the missing physics in models and testing new development of model convective processes over different convective regimes.
{"title":"Diurnal Cycle of Precipitation Over the Tropics and Central U.S.: GCM Intercomparison","authors":"Cheng Tao, Shaocheng Xie, Hsi-Yen Ma, Peter Bechtold, Zeyu Cui, Paul A. Vaillancourt, Kwinten Van Weverberg, Yi-Chi Wang, May Wong, Jing Yang, Guang J. Zhang, In-Jin Choi, Shuaiqi Tang, Jiangfeng Wei, Wen-Ying Wu, Meng Zhang, J. David Neelin, Xubin Zeng","doi":"10.1002/qj.4629","DOIUrl":"https://doi.org/10.1002/qj.4629","url":null,"abstract":"Diurnal precipitation is a fundamental mode of variability that climate models have difficulty in accurately simulating. Here the diurnal cycle of precipitation (DCP) in participating climate models from the Global Energy and Water Exchanges’ DCP project is evaluated over the tropics and central U.S. Common model biases such as excessive precipitation over the tropics, too frequent light-to-moderate rain, and the failure to capture propagating convection in the central U.S. still exist. Over the central U.S., the issues of too weak rainfall intensity in climate runs is well improved in their hindcast runs with initial conditions from Numerical Weather Prediction analyses. But the improvement is minimal over the central Amazon. Incorporating the role of the large-scale environment in convective triggering processes helps resolve the phase-locking issue in many models where precipitation often incorrectly peaks near noon due to maximum insolation over land. Allowing air parcels to be lifted above the boundary layer improves the simulation of nocturnal precipitation which is often associated with the propagation of mesoscale systems. Including convective memory in cumulus parameterizations acts to suppress light-to-moderate rain and promote intense rainfall; however, it also weakens the diurnal variability. Simply increasing model resolution (with cumulus parameterizations still used) cannot fully resolve the biases of low-resolution climate models in DCP. The hierarchy modeling framework from this study is useful for identifying the missing physics in models and testing new development of model convective processes over different convective regimes.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"8 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138573402","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}
G. Wolf, S. Ferrett, J. Methven, T.H.A. Frame, C.E. Holloway, O. Martinez-Alvarado, S.J. Woolnough
Recent work has demonstrated that skillful hybrid statistical-dynamical forecasts of heavy rainfall events in Southeast Asia can be made by combining model forecasts of the phases and amplitudes of Kelvin, Rossby and Westward Moving Rossby Gravity waves with climatological rainfall statistics conditioned on these waves. This study explores the sensitivity of this hybrid forecast to its parameter choices and compares its skill in forecasting extreme rainfall events in the Philippines, Malaysia, Indonesia and Vietnam to that of the Met Office Global and Regional Ensemble Prediction System (MOGREPS). The hybrid forecast is found to outperform both the global and convection-permitting ensemble in some regions when forecasting the most extreme events, however for less extreme events the ensemble is found more skillful. A weighted blend of the MOGREPS forecasts and the hybrid forecast was found to have the highest skill of all for almost all definitions of extreme event and in most regions. To quantify the influence of errors in the predicted wave state on the skill of the hybrid forecast, the skill of a hypothetical best case forecast was also calculated using reanalysis data to specify the wave amplitudes and phases. This best case forecast indicates that errors in the forecasts of all wave types reduce the skill of hybrid forecast, however the reduction in skill is largest for Kelvin waves. The skill in convection-permitting models is greater than for global models in the regions where Kelvin waves dominate, but the added-value of limited area high resolution forecasts is hampered by the poor representation of Kelvin waves in the parent global model.
{"title":"Comparison of probabilistic forecasts of extreme precipitation for a global and convection-permitting ensemble and hybrid statistical-dynamical method based on equatorial wave information","authors":"G. Wolf, S. Ferrett, J. Methven, T.H.A. Frame, C.E. Holloway, O. Martinez-Alvarado, S.J. Woolnough","doi":"10.1002/qj.4627","DOIUrl":"https://doi.org/10.1002/qj.4627","url":null,"abstract":"Recent work has demonstrated that skillful hybrid statistical-dynamical forecasts of heavy rainfall events in Southeast Asia can be made by combining model forecasts of the phases and amplitudes of Kelvin, Rossby and Westward Moving Rossby Gravity waves with climatological rainfall statistics conditioned on these waves. This study explores the sensitivity of this hybrid forecast to its parameter choices and compares its skill in forecasting extreme rainfall events in the Philippines, Malaysia, Indonesia and Vietnam to that of the Met Office Global and Regional Ensemble Prediction System (MOGREPS). The hybrid forecast is found to outperform both the global and convection-permitting ensemble in some regions when forecasting the most extreme events, however for less extreme events the ensemble is found more skillful. A weighted blend of the MOGREPS forecasts and the hybrid forecast was found to have the highest skill of all for almost all definitions of extreme event and in most regions. To quantify the influence of errors in the predicted wave state on the skill of the hybrid forecast, the skill of a hypothetical best case forecast was also calculated using reanalysis data to specify the wave amplitudes and phases. This best case forecast indicates that errors in the forecasts of all wave types reduce the skill of hybrid forecast, however the reduction in skill is largest for Kelvin waves. The skill in convection-permitting models is greater than for global models in the regions where Kelvin waves dominate, but the added-value of limited area high resolution forecasts is hampered by the poor representation of Kelvin waves in the parent global model.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"2083 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138532436","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 explores the morphology of convective cold pools, i. e., their size, shape, and structure, as well as factors controlling their growth using surface-based observations of the Field Experiment on Sub-mesoscale Spatio Temporal Variability in Lindenberg (FESSTVaL). FESSTVaL featured a dense network of 99 custom-built, low-cost measurement stations covering a circular area of 30 km in diameter at sub-mesoscale resolution (distances between 0.1 km and 4.8 km) and was held at the Lindenberg observatory near Berlin (Germany) from May to August 2021. The station network sampled 42 cold-pool events during the 103-d measurement period. The morphological properties of cold pools are derived by spatially interpolating the temperature observations to a Cartesian grid and defining cold pools as individual objects at a given time with a temperature perturbation ΔT stronger than -2 K. The sample of 1232 cold-pool objects whose extents are sufficiently captured by the network has a median equivalent diameter of 8.5 km. The objects exhibit aspect ratios between 1.5 and 1.6 independent of their size and strength, meaning they are generally not circularly shaped. On average, ΔT is strongest at the cold-pool center and decreases linearly towards the edge. For the growth phase of four selected events, the cold-pool object area ACP scales linearly with the radar-observed, area-integrated rainfall accumulation, while object-mean temperature perturbation strengthens most efficiently early in the life cycle. The global, radial expansion velocity decreases as the cold pool gets stronger and larger, in contradiction with density-current theory. Instead, ACP is a better predictor of the expansion rate. These findings identify the cold-air import by precipitation, both through evaporative cooling and convective downdrafts, as the dominant driver of the observed growth.
{"title":"Morphology and growth of convective cold pools observed by a dense station network in Germany","authors":"Bastian Kirsch, Cathy Hohenegger, Felix Ament","doi":"10.1002/qj.4626","DOIUrl":"https://doi.org/10.1002/qj.4626","url":null,"abstract":"This study explores the morphology of convective cold pools, i. e., their size, shape, and structure, as well as factors controlling their growth using surface-based observations of the Field Experiment on Sub-mesoscale Spatio Temporal Variability in Lindenberg (FESSTVaL). FESSTVaL featured a dense network of 99 custom-built, low-cost measurement stations covering a circular area of 30 km in diameter at sub-mesoscale resolution (distances between 0.1 km and 4.8 km) and was held at the Lindenberg observatory near Berlin (Germany) from May to August 2021. The station network sampled 42 cold-pool events during the 103-d measurement period. The morphological properties of cold pools are derived by spatially interpolating the temperature observations to a Cartesian grid and defining cold pools as individual objects at a given time with a temperature perturbation Δ<i>T</i> stronger than -2 K. The sample of 1232 cold-pool objects whose extents are sufficiently captured by the network has a median equivalent diameter of 8.5 km. The objects exhibit aspect ratios between 1.5 and 1.6 independent of their size and strength, meaning they are generally not circularly shaped. On average, Δ<i>T</i> is strongest at the cold-pool center and decreases linearly towards the edge. For the growth phase of four selected events, the cold-pool object area <i>A</i><sub>CP</sub> scales linearly with the radar-observed, area-integrated rainfall accumulation, while object-mean temperature perturbation strengthens most efficiently early in the life cycle. The global, radial expansion velocity decreases as the cold pool gets stronger and larger, in contradiction with density-current theory. Instead, <i>A</i><sub>CP</sub> is a better predictor of the expansion rate. These findings identify the cold-air import by precipitation, both through evaporative cooling and convective downdrafts, as the dominant driver of the observed growth.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"15 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138532505","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}
Xingli Mao, Li Xing, Wei Shang, Shuangshuang Li, Keqin Duan
The abundant precipitation over Pamirs Plateau (PP) in spring and winter plays a vital role in the water resources over the arid areas of Central Asia. Understanding the moisture sources and water vapor transportation associated with precipitation are very important, but there were few studies investigating the moisture sources of PP. We used a Lagrangian model driven with the Weather Research and Forecasting (WRF) output to analyze the moisture sources at Northern Pamirs Plateau (NPP) and Southern Pamirs Plateau (SPP) in spring, 2016, 2009, and 2001, and in winter, 2016, 2010, and 2017, as the seasonal precipitation in PP were the largest, median, and lowest during 2001 to 2018, and the precipitation in spring and winter was much higher than that in summer and autumn. The moisture sources from four regions were quantified: Atlantic-Europe-Africa, Arctic-Northern Asia, Indian Ocean, and moisture recycling from the PP. Atlantic-Europe-Africa and Indian Ocean are the dominant moisture source regions in spring and winter, which contribute more than 70% to the total moisture affecting the precipitation at PP. The contributions of Indian Ocean are higher at SPP than those at NPP in spring and winter. The contributions from Arctic-Northern Asia and PP are generally low, except that the moisture from PP region contributed 19% to the spring precipitation at NPP, indicating the importance of local moisture source in enhancing the spring precipitation at NPP. The moisture contributions originating from the different source regions show great difference between winter and spring. The moisture transportation is affected by westerlies, and the zonal winds in spring affect the moisture transportation, while the meridional winds over the Arabian Peninsula mainly affect the moisture transportation in winter.
{"title":"Moisture sources for precipitation over the Pamirs Plateau in winter and spring","authors":"Xingli Mao, Li Xing, Wei Shang, Shuangshuang Li, Keqin Duan","doi":"10.1002/qj.4624","DOIUrl":"https://doi.org/10.1002/qj.4624","url":null,"abstract":"The abundant precipitation over Pamirs Plateau (PP) in spring and winter plays a vital role in the water resources over the arid areas of Central Asia. Understanding the moisture sources and water vapor transportation associated with precipitation are very important, but there were few studies investigating the moisture sources of PP. We used a Lagrangian model driven with the Weather Research and Forecasting (WRF) output to analyze the moisture sources at Northern Pamirs Plateau (NPP) and Southern Pamirs Plateau (SPP) in spring, 2016, 2009, and 2001, and in winter, 2016, 2010, and 2017, as the seasonal precipitation in PP were the largest, median, and lowest during 2001 to 2018, and the precipitation in spring and winter was much higher than that in summer and autumn. The moisture sources from four regions were quantified: Atlantic-Europe-Africa, Arctic-Northern Asia, Indian Ocean, and moisture recycling from the PP. Atlantic-Europe-Africa and Indian Ocean are the dominant moisture source regions in spring and winter, which contribute more than 70% to the total moisture affecting the precipitation at PP. The contributions of Indian Ocean are higher at SPP than those at NPP in spring and winter. The contributions from Arctic-Northern Asia and PP are generally low, except that the moisture from PP region contributed 19% to the spring precipitation at NPP, indicating the importance of local moisture source in enhancing the spring precipitation at NPP. The moisture contributions originating from the different source regions show great difference between winter and spring. The moisture transportation is affected by westerlies, and the zonal winds in spring affect the moisture transportation, while the meridional winds over the Arabian Peninsula mainly affect the moisture transportation in winter.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"113 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138532434","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}
Coherent structures are characterized in high-resolution simulations of three atmospheric boundary layers: dry convection, marine cumulus, and stratocumulus. Based on radioactive-decaying tracers emitted at different altitudes (surface, top of well-mixed layer, and cloud top), a object-oriented methodology allows individual characterization of coherent tridimensional plumes within the flow.
{"title":"Coherent subsiding structures in large eddy simulations of atmospheric boundary layers","authors":"Florent Brient, Fleur Couvreux, Catherine Rio, Rachel Honnert","doi":"10.1002/qj.4625","DOIUrl":"https://doi.org/10.1002/qj.4625","url":null,"abstract":"Coherent structures are characterized in high-resolution simulations of three atmospheric boundary layers: dry convection, marine cumulus, and stratocumulus. Based on radioactive-decaying tracers emitted at different altitudes (surface, top of well-mixed layer, and cloud top), a object-oriented methodology allows individual characterization of coherent tridimensional plumes within the flow.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"26 1","pages":""},"PeriodicalIF":8.9,"publicationDate":"2023-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138532430","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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