Mathew J. Lipson, Sue Grimmond, Martin Best, Gab Abramowitz, Andrew Coutts, Nigel Tapper, Jong‐Jin Baik, Meiring Beyers, Lewis Blunn, Souhail Boussetta, Elie Bou‐Zeid, Martin G. De Kauwe, Cécile de Munck, Matthias Demuzere, Simone Fatichi, Krzysztof Fortuniak, Beom‐Soon Han, Margaret A. Hendry, Yukihiro Kikegawa, Hiroaki Kondo, Doo‐Il Lee, Sang‐Hyun Lee, Aude Lemonsu, Tiago Machado, Gabriele Manoli, Alberto Martilli, Valéry Masson, Joe McNorton, Naika Meili, David Meyer, Kerry A. Nice, Keith W. Oleson, Seung‐Bu Park, Michael Roth, Robert Schoetter, Andrés Simón‐Moral, Gert‐Jan Steeneveld, Ting Sun, Yuya Takane, Marcus Thatcher, Aristofanis Tsiringakis, Mikhail Varentsov, Chenghao Wang, Zhi‐Hua Wang, Andy J. Pitman
Abstract Accurately predicting weather and climate in cities is critical for safeguarding human health and strengthening urban resilience. Multimodel evaluations can lead to model improvements; however, there have been no major intercomparisons of urban‐focussed land surface models in over a decade. Here, in Phase 1 of the Urban‐PLUMBER project, we evaluate the ability of 30 land surface models to simulate surface energy fluxes critical to atmospheric meteorological and air quality simulations. We establish minimum and upper performance expectations for participating models using simple information‐limited models as benchmarks. Compared with the last major model intercomparison at the same site, we find broad improvement in the current cohort's predictions of short‐wave radiation, sensible and latent heat fluxes, but little or no improvement in long‐wave radiation and momentum fluxes. Models with a simple urban representation (e.g., ‘slab’ schemes) generally perform well, particularly when combined with sophisticated hydrological/vegetation models. Some mid‐complexity models (e.g., ‘canyon’ schemes) also perform well, indicating efforts to integrate vegetation and hydrology processes have paid dividends. The most complex models that resolve three‐dimensional interactions between buildings in general did not perform as well as other categories. However, these models also tended to have the simplest representations of hydrology and vegetation. Models without any urban representation (i.e., vegetation‐only land surface models) performed poorly for latent heat fluxes, and reasonably for other energy fluxes at this suburban site. Our analysis identified widespread human errors in initial submissions that substantially affected model performances. Although significant efforts are applied to correct these errors, we conclude that human factors are likely to influence results in this (or any) model intercomparison, particularly where participating scientists have varying experience and first languages. These initial results are for one suburban site, and future phases of Urban‐PLUMBER will evaluate models across 20 sites in different urban and regional climate zones.
{"title":"Evaluation of 30 urban land surface models in the Urban‐PLUMBER project: Phase 1 results","authors":"Mathew J. Lipson, Sue Grimmond, Martin Best, Gab Abramowitz, Andrew Coutts, Nigel Tapper, Jong‐Jin Baik, Meiring Beyers, Lewis Blunn, Souhail Boussetta, Elie Bou‐Zeid, Martin G. De Kauwe, Cécile de Munck, Matthias Demuzere, Simone Fatichi, Krzysztof Fortuniak, Beom‐Soon Han, Margaret A. Hendry, Yukihiro Kikegawa, Hiroaki Kondo, Doo‐Il Lee, Sang‐Hyun Lee, Aude Lemonsu, Tiago Machado, Gabriele Manoli, Alberto Martilli, Valéry Masson, Joe McNorton, Naika Meili, David Meyer, Kerry A. Nice, Keith W. Oleson, Seung‐Bu Park, Michael Roth, Robert Schoetter, Andrés Simón‐Moral, Gert‐Jan Steeneveld, Ting Sun, Yuya Takane, Marcus Thatcher, Aristofanis Tsiringakis, Mikhail Varentsov, Chenghao Wang, Zhi‐Hua Wang, Andy J. Pitman","doi":"10.1002/qj.4589","DOIUrl":"https://doi.org/10.1002/qj.4589","url":null,"abstract":"Abstract Accurately predicting weather and climate in cities is critical for safeguarding human health and strengthening urban resilience. Multimodel evaluations can lead to model improvements; however, there have been no major intercomparisons of urban‐focussed land surface models in over a decade. Here, in Phase 1 of the Urban‐PLUMBER project, we evaluate the ability of 30 land surface models to simulate surface energy fluxes critical to atmospheric meteorological and air quality simulations. We establish minimum and upper performance expectations for participating models using simple information‐limited models as benchmarks. Compared with the last major model intercomparison at the same site, we find broad improvement in the current cohort's predictions of short‐wave radiation, sensible and latent heat fluxes, but little or no improvement in long‐wave radiation and momentum fluxes. Models with a simple urban representation (e.g., ‘slab’ schemes) generally perform well, particularly when combined with sophisticated hydrological/vegetation models. Some mid‐complexity models (e.g., ‘canyon’ schemes) also perform well, indicating efforts to integrate vegetation and hydrology processes have paid dividends. The most complex models that resolve three‐dimensional interactions between buildings in general did not perform as well as other categories. However, these models also tended to have the simplest representations of hydrology and vegetation. Models without any urban representation (i.e., vegetation‐only land surface models) performed poorly for latent heat fluxes, and reasonably for other energy fluxes at this suburban site. Our analysis identified widespread human errors in initial submissions that substantially affected model performances. Although significant efforts are applied to correct these errors, we conclude that human factors are likely to influence results in this (or any) model intercomparison, particularly where participating scientists have varying experience and first languages. These initial results are for one suburban site, and future phases of Urban‐PLUMBER will evaluate models across 20 sites in different urban and regional climate zones.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"42 7","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134972575","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}
David S. Nolan, Samantha Nebylitsa, Brian D. McNoldy, Sharanya J. Majumdar
Abstract Computer model simulations are one of the most important tools in current use for understanding tropical cyclone (TC) formation and rapid intensification (RI). These include “idealized” simulations in which a TC‐like vortex is placed in a hypothetical environment with pre‐defined sea surface temperature and vertical profiles of temperature, humidity, and wind that are either constant or slowly varying across a large domain. The vast majority of such simulations begin with a perfectly circular vortex as the precursor to a TC. However, most real TCs form or intensify while interacting with asymmetric wind fields either within or external to the vortex circulation. This study introduces a method to initialize idealized TC simulations with asymmetries, and investigates the extent to which such asymmetries might delay RI in favorable environments. It is shown that mesoscale asymmetries can delay RI and reduce the fastest rates of intensification, and that these effects are statistically significantly increased when relatively low values of vertical shear of the horizontal wind are present. In some cases the asymmetries tilt the vortex directly through advection. In other cases, the wind asymmetries increase the disorganization of the convection, increase the size of the inner core wind field, and thus make the weaker TC more susceptible to environmental wind shear. The results suggest that mesoscale asymmetries of the wind field could be useful predictors for delay of RI in otherwise favorable environments. This article is protected by copyright. All rights reserved.
{"title":"Modulation of Tropical Cyclone Rapid Intensification by Mesoscale Asymmetries","authors":"David S. Nolan, Samantha Nebylitsa, Brian D. McNoldy, Sharanya J. Majumdar","doi":"10.1002/qj.4602","DOIUrl":"https://doi.org/10.1002/qj.4602","url":null,"abstract":"Abstract Computer model simulations are one of the most important tools in current use for understanding tropical cyclone (TC) formation and rapid intensification (RI). These include “idealized” simulations in which a TC‐like vortex is placed in a hypothetical environment with pre‐defined sea surface temperature and vertical profiles of temperature, humidity, and wind that are either constant or slowly varying across a large domain. The vast majority of such simulations begin with a perfectly circular vortex as the precursor to a TC. However, most real TCs form or intensify while interacting with asymmetric wind fields either within or external to the vortex circulation. This study introduces a method to initialize idealized TC simulations with asymmetries, and investigates the extent to which such asymmetries might delay RI in favorable environments. It is shown that mesoscale asymmetries can delay RI and reduce the fastest rates of intensification, and that these effects are statistically significantly increased when relatively low values of vertical shear of the horizontal wind are present. In some cases the asymmetries tilt the vortex directly through advection. In other cases, the wind asymmetries increase the disorganization of the convection, increase the size of the inner core wind field, and thus make the weaker TC more susceptible to environmental wind shear. The results suggest that mesoscale asymmetries of the wind field could be useful predictors for delay of RI in otherwise favorable environments. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"8 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135366435","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}
Jiachen Lu, Negin Nazarian, Melissa Anne Hart, E. Scott Krayenhoff, Alberto Martilli
Abstract We conducted large‐eddy simulations over 98 urban arrays with varying building densities and height distributions. Compared with uniform‐height urban arrays, the influence of height variability on urban flow is pronounced and acts differently in two idealized urban configurations: the low buildings induce higher wind speed and stronger turbulence over staggered arrays but act inversely over aligned building configurations. The flow motions around tall buildings generate strong dispersive fluxes, which are sometimes of similar magnitude to the turbulent momentum flux and responsible for a persistent isolated roughness flow pattern in the upper canopy regardless of the urban density. Tall buildings further contribute disproportionately to the form drag of the urban surface, reaching up to 3.9 times the form drag induced by buildings of height equal to the average building height, in dense layouts. The flow inflection points—that is, the largest wind‐speed gradient that defines the aerodynamic interface between the urban canopy flow and the surface layer flow above—are found to be displaced to the maximum building height if less than 25% of buildings are below the mean building height. These findings provide critical insight for the development of urban canopy models, where the impacts of height variability on flow are often linked to the vertical variation in urban density alone. To address this deficiency, we provide a case study that considers the drag amplification due to the impact of vertical urban structures in the urban canopy model, enabling high‐resolution regional climate models to reproduce urban air flows better.
{"title":"Representing the effects of building height variability on urban canopy flow","authors":"Jiachen Lu, Negin Nazarian, Melissa Anne Hart, E. Scott Krayenhoff, Alberto Martilli","doi":"10.1002/qj.4584","DOIUrl":"https://doi.org/10.1002/qj.4584","url":null,"abstract":"Abstract We conducted large‐eddy simulations over 98 urban arrays with varying building densities and height distributions. Compared with uniform‐height urban arrays, the influence of height variability on urban flow is pronounced and acts differently in two idealized urban configurations: the low buildings induce higher wind speed and stronger turbulence over staggered arrays but act inversely over aligned building configurations. The flow motions around tall buildings generate strong dispersive fluxes, which are sometimes of similar magnitude to the turbulent momentum flux and responsible for a persistent isolated roughness flow pattern in the upper canopy regardless of the urban density. Tall buildings further contribute disproportionately to the form drag of the urban surface, reaching up to 3.9 times the form drag induced by buildings of height equal to the average building height, in dense layouts. The flow inflection points—that is, the largest wind‐speed gradient that defines the aerodynamic interface between the urban canopy flow and the surface layer flow above—are found to be displaced to the maximum building height if less than 25% of buildings are below the mean building height. These findings provide critical insight for the development of urban canopy models, where the impacts of height variability on flow are often linked to the vertical variation in urban density alone. To address this deficiency, we provide a case study that considers the drag amplification due to the impact of vertical urban structures in the urban canopy model, enabling high‐resolution regional climate models to reproduce urban air flows better.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"3 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135461956","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}
Kimberley J. Reid, Debra Hudson, Andrew D. King, Todd P Lane, Andrew G. Marshall
Abstract Extended warning of above‐average and extreme precipitation is valuable to a wide range of stakeholders. However, the sporadic nature of precipitation makes it difficult to forecast skilfully beyond one week. Subseasonal forecasting is a growing area of science that aims to predict average weather conditions multiple weeks in advance using dynamical models. Building on recent work in this area, we test the hypothesis that using large‐scale horizontal moisture transport as a predictor for precipitation may increase the forecast skill of the above‐median and high‐precipitation weeks on subseasonal time‐scales. We analysed retrospective forecast (hindcast) sets from the Australian Bureau of Meteorology's latest operational subseasonal‐to‐seasonal forecasting model, ACCESS‐S2, to compare the forecast skill of precipitation using integrated water vapour transport (IVT) as a proxy, compared to using precipitation forecasts directly. We show that ACCESS‐S2 precipitation generally produces more skilful forecasts, except over some regions where IVT could be a useful additional diagnostic for warning of heavy precipitation events.
{"title":"Atmospheric Water Vapour Transport in <scp>ACCESS‐S2</scp> and the Potential for Enhancing Skill of Subseasonal Forecasts of Precipitation","authors":"Kimberley J. Reid, Debra Hudson, Andrew D. King, Todd P Lane, Andrew G. Marshall","doi":"10.1002/qj.4585","DOIUrl":"https://doi.org/10.1002/qj.4585","url":null,"abstract":"Abstract Extended warning of above‐average and extreme precipitation is valuable to a wide range of stakeholders. However, the sporadic nature of precipitation makes it difficult to forecast skilfully beyond one week. Subseasonal forecasting is a growing area of science that aims to predict average weather conditions multiple weeks in advance using dynamical models. Building on recent work in this area, we test the hypothesis that using large‐scale horizontal moisture transport as a predictor for precipitation may increase the forecast skill of the above‐median and high‐precipitation weeks on subseasonal time‐scales. We analysed retrospective forecast (hindcast) sets from the Australian Bureau of Meteorology's latest operational subseasonal‐to‐seasonal forecasting model, ACCESS‐S2, to compare the forecast skill of precipitation using integrated water vapour transport (IVT) as a proxy, compared to using precipitation forecasts directly. We show that ACCESS‐S2 precipitation generally produces more skilful forecasts, except over some regions where IVT could be a useful additional diagnostic for warning of heavy precipitation events.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"48 10","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135461954","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 We derive a generalization of the Kalman filter that allows for non‐Gaussian background and observation errors. The Gaussian assumption is replaced by considering that the errors come from a mixed distribution of Gaussian, lognormal, and reverse lognormal random variables. We detail the derivation for reverse lognormal errors, and extend the results to mixed distributions, where the number of Gaussian, lognormal, and reverse lognormal state variables can dynamically change every analysis time. We robustly test the dynamical mixed Kalman filter on two different systems based on the Lorenz 1963 model, and demonstrate that non‐Gaussian techniques generally improve the analysis skill if the observations are sparse and uncertain, compared to the Gaussian Kalman filter. This article is protected by copyright. All rights reserved.
{"title":"A dynamical Gaussian, lognormal, and reverse lognormal Kalman filter","authors":"Senne Van Loon, Steven J. Fletcher","doi":"10.1002/qj.4595","DOIUrl":"https://doi.org/10.1002/qj.4595","url":null,"abstract":"Abstract We derive a generalization of the Kalman filter that allows for non‐Gaussian background and observation errors. The Gaussian assumption is replaced by considering that the errors come from a mixed distribution of Gaussian, lognormal, and reverse lognormal random variables. We detail the derivation for reverse lognormal errors, and extend the results to mixed distributions, where the number of Gaussian, lognormal, and reverse lognormal state variables can dynamically change every analysis time. We robustly test the dynamical mixed Kalman filter on two different systems based on the Lorenz 1963 model, and demonstrate that non‐Gaussian techniques generally improve the analysis skill if the observations are sparse and uncertain, compared to the Gaussian Kalman filter. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"17 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135883722","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}
Jae Min Yeom, Kai‐Erik Szodry, Holger Siebert, André Ehrlich, Juan Pedro Mellado, Raymond A. Shaw, Seong Soo Yum
Abstract High‐resolution measurements from the Airborne Cloud‐Turbulence Observation System (ACTOS) during the Azores Stratocumulus Measurements of Radiation, Turbulence and Aerosols (ACORES) campaign are analysed for an investigation of the vertical profiles of microphysical properties and entrainment velocity ( W e ) in marine stratocumulus clouds. The vertical profiles show the transition from the cloudy layer to free troposphere with nearly linear profiles of total water mixing ratio, liquid water potential temperature and virtual potential temperature, but the thickness of entrainment interfacial layer varies significantly. Sharp transitions of cloud microphysical and optical properties within a single horizontal flight leg are found in one stratocumulus cloud system. They seem to be related to the local environmental conditions, such as the wind shear and turbulent dissipation rate. W e values estimated by three methods show consistent tendencies in general and are clearly related to the local environmental conditions, such as vertical shear of the horizontal wind and turbulence intensity. However, the magnitudes of W e values differ by up to two orders of magnitude depending on the methods, which suggests that the estimation of W e from in situ measurements is still a challenge. Analysis of the microphysical response to entrainment suggests that inhomogeneous mixing occurs dominantly. On the other hand, the analysis results for the clouds under more humid conditions indicate a higher likelihood of homogeneous mixing.
{"title":"High‐resolution measurements of microphysics and entrainment in marine stratocumulus clouds","authors":"Jae Min Yeom, Kai‐Erik Szodry, Holger Siebert, André Ehrlich, Juan Pedro Mellado, Raymond A. Shaw, Seong Soo Yum","doi":"10.1002/qj.4586","DOIUrl":"https://doi.org/10.1002/qj.4586","url":null,"abstract":"Abstract High‐resolution measurements from the Airborne Cloud‐Turbulence Observation System (ACTOS) during the Azores Stratocumulus Measurements of Radiation, Turbulence and Aerosols (ACORES) campaign are analysed for an investigation of the vertical profiles of microphysical properties and entrainment velocity ( W e ) in marine stratocumulus clouds. The vertical profiles show the transition from the cloudy layer to free troposphere with nearly linear profiles of total water mixing ratio, liquid water potential temperature and virtual potential temperature, but the thickness of entrainment interfacial layer varies significantly. Sharp transitions of cloud microphysical and optical properties within a single horizontal flight leg are found in one stratocumulus cloud system. They seem to be related to the local environmental conditions, such as the wind shear and turbulent dissipation rate. W e values estimated by three methods show consistent tendencies in general and are clearly related to the local environmental conditions, such as vertical shear of the horizontal wind and turbulence intensity. However, the magnitudes of W e values differ by up to two orders of magnitude depending on the methods, which suggests that the estimation of W e from in situ measurements is still a challenge. Analysis of the microphysical response to entrainment suggests that inhomogeneous mixing occurs dominantly. On the other hand, the analysis results for the clouds under more humid conditions indicate a higher likelihood of homogeneous mixing.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"86 6 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135944976","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}
Eliza Karlowska, Adrian J. Matthews, Benjamin Webber, Tim Graham, Prince Xavier
The diurnal warm layer in the upper ocean develops during low surface winds and high incoming solar radiation conditions, often increasing sea surface temperatures (SSTs) by up to 1 ∘ C. The suppressed phase of the Madden–Julian Oscillation (MJO) favours the formation of such a layer. Here we analyse the coupled ocean–atmosphere and atmosphere‐only Numerical Weather Prediction systems of the UK Met Office to reveal that important differences arise from the representation of the diurnal warm layer in the coupled model. While both models are skilful in predicting the MJO to at least 7‐day lead time, the coupled model predicts approximately10% faster MJO propagation than the atmosphere‐only model due to the ability to resolve diurnal warming in the upper ocean that rectifies onto MJO‐associated SST anomalies. The diurnal warming of SST (dSST) in the coupled model leads to an increase in daily mean SST compared with the atmosphere‐only model persisted foundation SST. The strength of the dSST in the coupled model is modulated by MJO conditions. During suppressed MJO conditions on lead day 1, the dSST is enhanced leading to 0.2 ∘ C warmer daily mean MJO‐associated SST anomalies and increased convection in the coupled model by lead day 7. During active MJO convection, the dSST is suppressed, leading to 0.1 ∘ C colder MJO‐associated SST anomalies in the coupled model and reduced convection by lead day 7. This variability in dSST further amplifies the MJO propagation speed, underlining the importance of the two‐way feedback between the MJO and the diurnal cycle of SST and the need to accurately represent this process in coupled models. This article is protected by copyright. All rights reserved.
{"title":"The effect of diurnal warming of sea surface temperatures on the propagation speed of the Madden–Julian Oscillation","authors":"Eliza Karlowska, Adrian J. Matthews, Benjamin Webber, Tim Graham, Prince Xavier","doi":"10.1002/qj.4599","DOIUrl":"https://doi.org/10.1002/qj.4599","url":null,"abstract":"The diurnal warm layer in the upper ocean develops during low surface winds and high incoming solar radiation conditions, often increasing sea surface temperatures (SSTs) by up to 1 ∘ C. The suppressed phase of the Madden–Julian Oscillation (MJO) favours the formation of such a layer. Here we analyse the coupled ocean–atmosphere and atmosphere‐only Numerical Weather Prediction systems of the UK Met Office to reveal that important differences arise from the representation of the diurnal warm layer in the coupled model. While both models are skilful in predicting the MJO to at least 7‐day lead time, the coupled model predicts approximately10% faster MJO propagation than the atmosphere‐only model due to the ability to resolve diurnal warming in the upper ocean that rectifies onto MJO‐associated SST anomalies. The diurnal warming of SST (dSST) in the coupled model leads to an increase in daily mean SST compared with the atmosphere‐only model persisted foundation SST. The strength of the dSST in the coupled model is modulated by MJO conditions. During suppressed MJO conditions on lead day 1, the dSST is enhanced leading to 0.2 ∘ C warmer daily mean MJO‐associated SST anomalies and increased convection in the coupled model by lead day 7. During active MJO convection, the dSST is suppressed, leading to 0.1 ∘ C colder MJO‐associated SST anomalies in the coupled model and reduced convection by lead day 7. This variability in dSST further amplifies the MJO propagation speed, underlining the importance of the two‐way feedback between the MJO and the diurnal cycle of SST and the need to accurately represent this process in coupled models. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"32 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135996092","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}
Hua Lu, Andrew Orr, John King, Tony Phillips, Ella Gilbert, Steve Colwell, Thomas J. Bracegirdle
Abstract Extreme warm events in the South Orkney Islands (SOIs) are investigated using synoptic observations from Signy and Orcadas stations for 1947–1994 and 1956–2019 respectively. Defining the extremes as temperatures exceeding the 95th percentile of the temperature distribution, we reveal the characteristics and associated drivers of the warm events, especially the top 10 events in both summer and winter. At both stations, extreme warm events often involve a combined effect of atmospheric rivers (ARs) and localised föhn warming, with distinct characteristics due to the station locations relative to Coronation Island, the largest and highest island of the SOIs. For example, warm events at Signy are warmer (by an average of around 3°C) than the corresponding concurrent temperatures at Orcadas. The number of warm events per year has significantly increased over the record periods at both stations, which could potentially impact ecosystems by increasing melting of snow and ice. Extreme warm events at Signy are dominated by föhn warming in combination with ARs originating from the Southern Atlantic Ocean, where warm, moisture‐rich air is rapidly advected towards the islands by enhanced northerly winds. By contrast, the Orcadas warm extremes involve both warm‐air advection and föhn warming associated with enhanced northwesterlies/westerlies with ARs originating in the Pacific Ocean that travel across the Drake Passage. Simulation of one of the top 10 warm events for Signy station using a 1‐km grid spacing configuration of the atmosphere‐only UK Met Office Unified Model is used to disentangle the role of local versus large‐scale forcing. We find that the majority of the warming can be attributed to föhn effects for the case study. These results demonstrate the complexity of Antarctic temperature extremes.
{"title":"Extreme warm events in the South Orkney Islands, Southern Ocean: Compounding influence of atmospheric rivers and föhn conditions","authors":"Hua Lu, Andrew Orr, John King, Tony Phillips, Ella Gilbert, Steve Colwell, Thomas J. Bracegirdle","doi":"10.1002/qj.4578","DOIUrl":"https://doi.org/10.1002/qj.4578","url":null,"abstract":"Abstract Extreme warm events in the South Orkney Islands (SOIs) are investigated using synoptic observations from Signy and Orcadas stations for 1947–1994 and 1956–2019 respectively. Defining the extremes as temperatures exceeding the 95th percentile of the temperature distribution, we reveal the characteristics and associated drivers of the warm events, especially the top 10 events in both summer and winter. At both stations, extreme warm events often involve a combined effect of atmospheric rivers (ARs) and localised föhn warming, with distinct characteristics due to the station locations relative to Coronation Island, the largest and highest island of the SOIs. For example, warm events at Signy are warmer (by an average of around 3°C) than the corresponding concurrent temperatures at Orcadas. The number of warm events per year has significantly increased over the record periods at both stations, which could potentially impact ecosystems by increasing melting of snow and ice. Extreme warm events at Signy are dominated by föhn warming in combination with ARs originating from the Southern Atlantic Ocean, where warm, moisture‐rich air is rapidly advected towards the islands by enhanced northerly winds. By contrast, the Orcadas warm extremes involve both warm‐air advection and föhn warming associated with enhanced northwesterlies/westerlies with ARs originating in the Pacific Ocean that travel across the Drake Passage. Simulation of one of the top 10 warm events for Signy station using a 1‐km grid spacing configuration of the atmosphere‐only UK Met Office Unified Model is used to disentangle the role of local versus large‐scale forcing. We find that the majority of the warming can be attributed to föhn effects for the case study. These results demonstrate the complexity of Antarctic temperature extremes.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136078562","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}
Athul Rasheeda Satheesh, Peter Knippertz, Andreas H. Fink, Eva‐Maria Walz, Tilmann Gneiting
Abstract Numerical‐model‐based forecasts of precipitation exhibit poor skill over northern tropical Africa when compared with climatology‐based forecasts and with other tropical regions. However, as recently demonstrated, purely data‐driven forecasts based on spatio‐temporal dependences inferred from gridded satellite rainfall estimates show promise for the prediction of the 24‐hr precipitation occurrence rate in this region. The present work explores this potential further by advancing the statistical model and providing meteorological interpretations of the performance results. Advances include (a) the use of a recently developed correlation metric, the Coefficient of Predictive Ability (CPA), to identify predictors, (b) forecast evaluation with robust reliability diagrams and score decompositions, (c) a study domain over tropical Africa nested in a considerably enlarged spatio‐temporal domain to identify coherent propagating features, and (d) the introduction of a novel coherent‐linear‐propagation factor to quantify the coherence of propagating signals. The statistical forecast is compared with a climatology‐based benchmark, the European Centre for Medium‐Range Weather Forecasts (ECMWF) operational ensemble forecast, and a statistically postprocessed ensemble forecast. All methods show poor skill within the main rainbelt over northern tropical Africa, where differences in Brier scores between the different approaches are hardly statistically significant. However, the data‐driven forecast outperforms the other methods along the fringes of the rainbelt, where meridional rainfall gradients are large. The coherent‐linear‐propagation factor, in concert with metrics of convective available potential energy and convective instability, reveals that high stochasticity in the rainbelt limits predictability. At the fringes of the rainbelt, the data‐driven approach leverages coherent precipitation features associated with propagating tropical weather systems such as African Easterly Waves.
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This study investigates the skill of the COSMO model (v5.7) at 1.1 km horizontal grid size in simulating the near‐surface foehn properties and evolution for five south foehn events and a 5‐year‐long climatology. A significant near‐surface cold bias is found during foehn, with an average bias of ‐3 K in the Rhine Valley in the five foehn cases, and of ‐1.8 K in the major northern foehn valleys in the 5‐year foehn climatology. The cold bias tends to be larger in the stronger and moister deep foehn events. Sensitivity experiments are carried out to examine the possible causes of the cold bias, including changes to the parameterization of the land‐atmosphere interaction, to the 1D turbulence parameterization, and to the horizontal grid spacing. Most sensitivity experiments have only a very minor impact on the cold bias, except for the model run with a horizontal grid spacing of 550 m. The 550 m COSMO run shows a reduced cold bias during foehn hours and also an improvement in the simulated foehn duration and northward foehn extent. By inspecting the vertical dimension, we found that the near‐surface cold bias downstream might partly originate upstream. A further contribution to the downstream cold bias is likely due to insufficient vertical mixing in the foehn flow. The latter is possibly enhanced in the 550 m model run, leading to a less stably stratified atmosphere in the lower few hundred meters of the atmosphere and a reduction of the reported model cold bias. This article is protected by copyright. All rights reserved.
本文研究了在1.1 km水平网格尺度上COSMO模式(v5.7)在模拟5次南焚风事件和5年气候条件下近地表焚风性质和演变的能力。在焚风期间发现了明显的近地表冷偏，在5年的焚风气候中，莱茵河谷的平均偏度为‐3 K，在主要的北部焚风山谷中为‐1.8 K。在较强、较湿的深风事件中，冷偏倾向较大。进行了敏感性实验以检验冷偏的可能原因，包括陆地-大气相互作用参数化的变化、一维湍流参数化的变化和水平网格间距的变化。除了水平网格间距为550 m的模型运行外，大多数灵敏度实验对冷偏差的影响很小。550 m COSMO运行表明，焚风时间的冷偏减小，模拟焚风持续时间和向北的焚风范围也有所改善。通过对垂直尺度的考察，我们发现下游近地表冷偏可能部分来源于上游。对下游冷偏的进一步贡献可能是由于焚风流的垂直混合不足。后者可能在550米模式运行中增强，导致低层几百米的大气分层不太稳定，并减少了报告的模式冷偏。这篇文章受版权保护。版权所有。
{"title":"A station‐based evaluation of near‐surface south foehn evolution in COSMO‐1","authors":"Yue Tian, Julian Quimbayo Duarte, Juerg Schmidli","doi":"10.1002/qj.4597","DOIUrl":"https://doi.org/10.1002/qj.4597","url":null,"abstract":"This study investigates the skill of the COSMO model (v5.7) at 1.1 km horizontal grid size in simulating the near‐surface foehn properties and evolution for five south foehn events and a 5‐year‐long climatology. A significant near‐surface cold bias is found during foehn, with an average bias of ‐3 K in the Rhine Valley in the five foehn cases, and of ‐1.8 K in the major northern foehn valleys in the 5‐year foehn climatology. The cold bias tends to be larger in the stronger and moister deep foehn events. Sensitivity experiments are carried out to examine the possible causes of the cold bias, including changes to the parameterization of the land‐atmosphere interaction, to the 1D turbulence parameterization, and to the horizontal grid spacing. Most sensitivity experiments have only a very minor impact on the cold bias, except for the model run with a horizontal grid spacing of 550 m. The 550 m COSMO run shows a reduced cold bias during foehn hours and also an improvement in the simulated foehn duration and northward foehn extent. By inspecting the vertical dimension, we found that the near‐surface cold bias downstream might partly originate upstream. A further contribution to the downstream cold bias is likely due to insufficient vertical mixing in the foehn flow. The latter is possibly enhanced in the 550 m model run, leading to a less stably stratified atmosphere in the lower few hundred meters of the atmosphere and a reduction of the reported model cold bias. This article is protected by copyright. All rights reserved.","PeriodicalId":49646,"journal":{"name":"Quarterly Journal of the Royal Meteorological Society","volume":"2011 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135803848","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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