Article
Meteorology & Atmospheric Sciences
J. M. Eissner, D. B. Mechem, M. P. Jensen, S. E. Giangrande
Summary: This study utilized observations from the ARM mobile facility in Manacapuru, Brazil, to estimate entrainment rates of shallow clouds and found uncertainties in these rates with respect to certain parameters and environmental properties.
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
(2021)
Article
Mechanics
Nick H. Wise, Gary R. Hunt
Summary: Previous mathematical models of quasi-steady turbulent plumes and fountains have described the flow resulting from a given input of buoyancy. In this study, we take a new perspective by asking what input of buoyancy would result in a plume or fountain with specific characteristics. By developing analytical solutions to the conservation equations, we show that it is possible to design synthetic plumes with desired properties without specifying the buoyancy distribution.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Geosciences, Multidisciplinary
Lei Zhu, Chunsong Lu, Shuqi Yan, Yangang Liu, Guang J. Zhang, Fan Mei, Bin Zhu, Jerome D. Fast, Alyssa Matthews, Mikhail S. Pekour
Summary: A new approach has been developed to estimate entrainment and detrainment rates in cumulus clouds based on aircraft observations, showing a decrease in rates with increasing height and correlations with environmental relative humidity. This method can be applied to obtain data sets related to cloud thermodynamic variables from other cloud observations.
GEOPHYSICAL RESEARCH LETTERS
(2021)
Article
Mechanics
D. A. Parker, H. C. Burridge, J. L. Partridge, J. N. Hacker, P. F. Linden
Summary: This study examines the flow resulting from a vertically distributed wall-source plume in both unventilated and ventilated spaces. The experiments show that negligible ambient vertical transport occurs in unventilated space and a linear ambient temperature stratification is present in ventilated space during steady state. The results have practical applications in creating linear ambient temperature stratification in a room and understanding temperature stratification in a large ventilated atrium heated by solar radiation.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
James Richardson, Gary R. Hunt
Summary: There has been no consensus on the value of the entrainment coefficient alpha for a pure plume. However, after theoretical developments, measurements, and evaluation, it is concluded that alpha = 0.11 +/- 15% should be adopted as the consensus value. This consensus value enhances the application of plume theory and allows for detailed comparison with other turbulent flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Geochemistry & Geophysics
Gaurav Dogra, Sudarsan Bera, Anupam Dewan, Sandeep Sahany
Summary: An idealized large eddy simulation (LES) using the Weather Research and Forecasting (WRF) model was conducted to investigate the dynamics of cumulus clouds over the Bay of Bengal. It was found that cumulus clouds undergo a transition from shallow to deep clouds, which is not well represented in global climate models. The findings of this study can contribute to the development of future parameterizations for cumulus clouds.
PURE AND APPLIED GEOPHYSICS
(2023)
Article
Environmental Sciences
Bipin Kumar, Rahul Ranjan, Man-Kong Yau, Sudarsan Bera, Suryachandra A. Rao
Summary: The study investigates the impact of turbulent mixing on the evolution of cloud droplet size spectrum, revealing that turbulent mixing of dry air leads to spatial supersaturation variability, which affects the evolution of the cloud droplet size spectrum. Through a 3D simulation of turbulent mixing followed by droplet evaporation/condensation processes, the thermodynamic and microphysical characteristics of droplets in high- and low-vorticity regions were analyzed. The influence of vorticity generation in turbulent flows on mixing and cloud microphysics was demonstrated.
ATMOSPHERIC CHEMISTRY AND PHYSICS
(2021)
Article
Mechanics
L. Milton-McGurk, N. Williamson, S. W. Armfield, M. P. Kirkpatrick, K. M. Talluru
Summary: This study focuses on the initial stage of negatively buoyant jets, finding that the turbulence intensity does not scale with the mean flow, and the ratio of widths of buoyancy and velocity profiles increases along the jet. The entrainment coefficient decreases with local Froude number, eventually becoming negative, indicating fluid is ejected from the jet. These observations differ from neutral or buoyant jets and plumes, which approach a constant ratio and entrainment coefficient in the far field.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
K. M. Talluru, S. Armfield, N. Williamson, M. P. Kirkpatrick, L. Milton-McGurk
Summary: High-fidelity measurements of velocity and concentration were conducted in a neutral jet and a negatively buoyant jet, revealing similarities in fluid structure at local scales but differences in development characteristics.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Megan K. Richards, Oluwaseun E. Coker, Jose Florido, Rhiannon A. M. Nicholls, Andrew N. Ross, Gabriel G. Rooney
Summary: This study investigates the flow in and around two vertically and horizontally offset plumes. An analytical potential flow model is developed using the Milne-Thomson circle theorem to represent the flow due to adjacent circular and point sources. The predictions of this model are compared against Reynolds-averaged Navier-Stokes simulations and show good agreement, including the location of the stagnation point between the two plumes.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Yadan Mao
Summary: This study provides a detailed analysis of continent motion and thermal-mechanic feedback by using a simplified model. The results reveal that plate motion characteristics and frequencies change with plate size, and these changes have significant implications for continent motion and geological evolution.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Environmental Sciences
Xiaohao Guo, Huijuan Lin, Jinyao Zhu, Fenfen Wei
Summary: This study uses the WRF model to simulate a southwest vortex precipitation process and investigates the correlations between entrainment rate and dynamical parameters in the cloud. It is found that the logarithmic liner function has a larger slope with a greater probability. The fitting function for entrainment rate in cumulus clouds is determined to include vertical wind velocity and buoyancy.
Article
Meteorology & Atmospheric Sciences
Nicolas Maury, Gregory C. Roberts, Fleur Couvreux, Titouan Verdu, Pierre Narvor, Simon Lacroix, Gautier Hattenberger
Summary: During the NEPHELAE-EUREC4A field campaign in Barbados in January and February 2020, remotely piloted aircraft were used to study the structures of trade-wind cumulus clouds. Two observation methods were tested and it was found that there are two cohabiting types of cloud population, with small-diameter clouds being less buoyant than larger clouds. Statistical analysis also revealed that cumulus clouds do not have an adiabatic core. Comparison with adaptive sampling and high-resolution large-eddy simulations showed that mixing in the whole cloud is underestimated by numerical studies.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY
(2023)
Article
Meteorology & Atmospheric Sciences
D. Oh, Y. Noh, F. Hoffmann
Summary: The study investigates the activation of aerosol particles and its impact on cloud droplet size distributions in shallow cumulus clouds. Analysis of cloud field simulation results using a Lagrangian cloud model coupled with large eddy simulation reveals the distinct characteristics of aerosol particle activation following central updraft from a cloud base and particles entrained above the cloud base. The entrainment and turbulent mixing at cloud edges cause most entrained particles to be deactivated soon after activation, limiting their lifetime and growth compared to particles following central updraft. Most of the net activation occurs at the cloud base and disappears aloft. The cloud droplet activation spectra conform to theoretical predictions at high supersaturation conditions, but deviate at low supersaturation conditions due to the transport of cloud base particles activated elsewhere.
JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES
(2023)
Article
Mechanics
Ziheng Yu, Gary R. Hunt
Summary: A theoretical model for steady multi-layered flow induced by a vertically distributed buoyancy source in a ventilated box has been presented. Boundary conditions for each layer were established by deducing the turbulent entrainment rate, and closed-form solutions for the streamfunction of the induced flow in each layer were obtained using conformal mapping techniques and Poisson's integral theorem. Re-evaluation of the flow near the ceiling and incorporation of an entraining ceiling current led to a refined stratification that matched well with experimental observations.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Meteorology & Atmospheric Sciences
Hooman Ayat, Jason P. Evans, Steven C. Sherwood, Joshua Soderholm
Summary: The study examines a coastal site in Sydney, Australia, using 20 years of radar data to establish a regional precipitation system climatology. The findings reveal that extreme storms with high translation-speed, size, and rainfall intensity usually occur in the warm season, specifically between 10 am and 8 pm. Precipitation systems are more frequent in the cold season and typically initiate over the ocean and move northward. Clustering algorithms identify five distinct precipitation system types that peak in different seasons. Although there is no overall link between rainfall statistics and climate modes, some system types show connections using a multivariate approach.
Article
Meteorology & Atmospheric Sciences
David Fuchs, Steven C. Sherwood, Darryn Waugh, Vishal Dixit, Matthew H. England, Yi-Ling Hwong, Olivier Geoffroy
Summary: Midlatitude weather is influenced by midlatitude jets, whose properties, especially latitudes, are poorly understood. Climate models show a spread in their simulated jet latitudes and predicted poleward shift under global warming. Models with more poleward jets have more moisture and warmer upper troposphere, potentially due to differences in moist convection and microphysics. Turning off deep or shallow convective parameterizations in atmospheric model runs suggests that more shallow convection leads to poleward jet positioning in Southern Hemisphere (SH) summer, while favoring deep convection leads to equatorward positioning. This explains 60% of the spread in jet position during austral summer. Similar biases are observed in the Northern Hemisphere boreal summer. Shallow convection in midlatitudes reduces SH jet shift in a warmer climate, consistent with the correlation between jet position and shift in this season. These results highlight the unexpected role of atmospheric moist convection in midlatitude circulation.
JOURNAL OF CLIMATE
(2023)
Article
Meteorology & Atmospheric Sciences
Timothy H. H. Raupach, Joshua Soderholm, Alain Protat, Steven C. C. Sherwood
Summary: The performance of proxies designed to identify hail and severe storm-prone atmospheric conditions in Australia was evaluated. It was found that the existing proxies overestimated the probability of hail occurrence, particularly in Australia's tropical north. A new proxy was developed based on the relationship between instability-shear space and melting-level height, which outperformed the tested existing proxies in detecting hail-prone conditions in Australia. Additional conditions were also identified to efficiently reduce false alarms.
MONTHLY WEATHER REVIEW
(2023)
Article
Biology
Charlotte M. Waudby, Steven C. Sherwood, Nicholas J. Osborne, Paul J. Beggs, Jane Al-Kouba, Elizabeth E. Ebert, David J. Muscatello
Summary: This study determined the typical grass pollen concentrations in the Sydney basin and analyzed their correlation with meteorological variables. It found that most grass pollen originated from local sources and there was no strong evidence of long-distance transport into the metropolitan area. The study also highlighted the importance of monitoring sudden increases in grass pollen concentrations, which can put a strain on the healthcare system.
Article
Meteorology & Atmospheric Sciences
Deepashree Dutta, Steven C. Sherwood, Martin Jucker, Alex Sen Gupta, Katrin J. Meissner
Summary: Climate models underestimate Arctic warming in past warm climates like the early Cretaceous and Paleogene periods, indicating missing or poorly represented physical processes. Previous studies suggest that wintertime Arctic polar stratospheric clouds (PSCs) could promote Arctic amplification through additional greenhouse warming. This study explores PSC changes under high methane levels, preindustrial carbon dioxide, and polar-amplified surface warming, finding that PSCs could play an important role in Arctic warming in a warmer-than-present-day climate, but only if methane levels were higher than suggested by previous modeling studies for past warm climates.
JOURNAL OF CLIMATE
(2023)
Article
Meteorology & Atmospheric Sciences
J. M. Windmiller, J. Bao, S. C. Sherwood, T. D. Schanzer, D. Fuchs
Summary: Precipitation has a significant impact on convective downdrafts, primarily through its influence on updraft properties. Among the various environmental factors, lapse rate is a key predictor for downdraft characteristics.
JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS
(2023)
Article
Geosciences, Multidisciplinary
Moutassem El Rafei, Steven Sherwood, Jason Evans, Andrew Dowdy
Summary: Extreme wind gusts cause significant socioeconomic damage. It is challenging to analyze these rare and localized events using either modeling or empirical approaches. A 23-year long data record from 29 automatic weather stations in eastern Australia was used to study the distribution, frequency, and average recurrence intervals of extreme gusts. The study confirms the dominant role of thunderstorms in producing the most extreme gusts in the region and shows that wind risk varies strongly with distance from the coast.
Article
Environmental Sciences
Sanaa Hobeichi, Nidhi Nishant, Yawen Shao, Gab Abramowitz, Andy Pitman, Steve Sherwood, Craig Bishop, Samuel Green
Summary: Global climate models (GCMs) are often downscaled to understand local climate change, but the computational cost of regional climate models (RCMs) limits downscaled GCMs. This study combines dynamical and statistical downscaling approaches to build an emulator that predicts fine-scale variables using coarse-scale predictors and land characteristics. The emulators achieve good performance in downscaled evapotranspiration and outperform traditional statistical downscaling methods. The framework offers a cheap and quick way to downscale large ensembles of GCMs, enabling higher-resolution climate projections and better support for adaptation planning.
Article
Multidisciplinary Sciences
Alan M. Seltzer, Pierre-Henri Blard, Steven C. Sherwood, Masa Kageyama
Summary: Terrestrial amplification of land warming relative to oceans is important for predicting future warming and water availability. However, the theoretical basis for this has never been tested outside the short instrumental period, and the spatial pattern and amplitude of terrestrial amplification remain uncertain. This study investigates terrestrial amplification during the Last Glacial Maximum and provides crucial new support for its existence.
Article
Meteorology & Atmospheric Sciences
Moutassem El Rafei, Steven Sherwood, Jason P. Evans, Fei Ji
Summary: The study examines extreme wind gust events in eastern Australia using long-term reanalysis data and station observations. By utilizing the generalised Pareto distribution and a decision tree model, the study estimates return values and distinguishes between convective and synoptic gust events. The reanalysis data proves to be valuable, especially in regions with limited observational coverage.
WEATHER AND CLIMATE EXTREMES
(2023)
Article
Environmental Sciences
Nidhi Nishant, Sanaa Hobeichi, Steven Sherwood, Gab Abramowitz, Yawen Shao, Craig Bishop, Andy Pitman
Summary: In this study, a machine learning approach using a multi-layer perceptron (MLP) is implemented to downscale coarse-resolution precipitation. The results show that the MLP outperforms the dynamical downscaling method in capturing rainfall climatology, frequency distribution, and spatiotemporal variability of daily precipitation. When the scale is coarsened, the skill of the MLP decreases slightly but remains comparable to or better than the dynamical downscaling method.
ENVIRONMENTAL RESEARCH LETTERS
(2023)
Article
Geosciences, Multidisciplinary
Moutassem El Rafei, Steven Sherwood, Jason Evans, Andrew Dowdy, Fei Ji
Summary: Preparing for environmental risks requires estimating the frequencies of extreme events, often from data records that are too short to confirm them directly. Fitting a statistical distribution to the data is necessary, but pooling data from neighboring sites into single samples can introduce unexpected biases in typical situations. Previous analyses may have overestimated the likelihood of extreme events arising from natural weather variability.
GEOPHYSICAL RESEARCH LETTERS
(2023)
Article
Meteorology & Atmospheric Sciences
Timothy H. Raupach, Joshua S. Soderholm, Robert A. Warren, Steven C. Sherwood
Summary: This study provides a comprehensive analysis of hail hazard changes in Australia. It reveals a decrease in hail-prone days across most of the country, but an increase in heavily populated areas. Changes in atmospheric instability are driving these trends. Radar observations support the findings and show substantial increases in hail frequency in major Australian cities.
NPJ CLIMATE AND ATMOSPHERIC SCIENCE
(2023)
Article
Meteorology & Atmospheric Sciences
Alejandro Casallas-Garcia, Daniel Hernandez-Deckers, Hector Mora-Paez
Summary: We studied convective storms in the Sabana de Bogota, a high-altitude and heavily populated area in the Colombian tropical Andes, using satellite images and precipitation data. The study found that although early-afternoon westerly winds are present in most rainy season days, they only occasionally generate storms. Additionally, the analysis suggests that moisture convergence occurs locally instead of being advected from the west.
Article
Meteorology & Atmospheric Sciences
Y. -L. Hwong, M. Colin, P. Aglas-Leitner, C. J. Muller, S. C. Sherwood
Summary: This study investigates the memory behavior of convection and compares the behavior of single-column models in two idealized tests. The results show that existing convection schemes fail to fully reproduce the behavior of cloud-resolving models because they neglect the memory effect of convection. The study also finds that the memory strength in convection schemes is related to the growth rate of subgrid structures.
JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS
(2023)