Potential effect of bio-surfactants on sea spray generation in tropical cyclone conditions

Abstract Despite significant improvement in computational and observational capabilities, predicting intensity and intensification of major tropical cyclones remains a challenge. In 2017 Hurricane Maria intensified to a Category 5 storm within 24 h, devastating Puerto Rico. In 2019 Hurricane Dorian, predicted to remain tropical storm, unexpectedly intensified into a Category 5 storm and destroyed the Bahamas. The official forecast and computer models were unable to predict rapid intensification of these storms. One possible reason for this is that key physics, including microscale processes at the air-sea interface, are poorly understood and parameterized in existing forecast models. Here we show that surfactants significantly affect the generation of sea spray, which provides some of the fuel for tropical cyclones and their intensification, but also provides some of the drag that limits intensity and intensification. Using a numerical model verified with a laboratory experiment, which predicts spray radii distribution starting from a 100 μm radius, we show that surfactants increase spray generation by 20–34%. We anticipate that bio-surfactants affect heat, energy, and momentum exchange through altered size distribution and concentration of sea spray, with consequences for tropical cyclone intensification or decline, particularly in areas of algal blooms and near coral reefs, as well as in areas affected by oil spills and dispersants.

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Investigating the forecast predictability for fluvial flooding from tropical cyclones

10.5194/egusphere-egu21-8888 ◽

2021 ◽

Author(s):

Helen Titley ◽

Hannah Cloke ◽

Shaun Harrigan ◽

Florian Pappenberger ◽

Christel Prudhomme ◽

...

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Decision Makers ◽

Management Service ◽

Flood Events ◽

Key Factors ◽

Ensemble Forecasts ◽

Weather Forecasts ◽

Forecast Models ◽

Landfall Location

Global ensemble forecast models have been shown to have good skill in forecasting the track probabilities of tropical cyclones worldwide, but less well-studied is their ability to predict the hazards resulting from tropical cyclones, which in the case of fluvial flooding can extend far from the landfall location traditionally focussed on in operational tropical cyclone warnings. This work aims to investigate the key factors that influence the predictability of fluvial flood severity from tropical cyclones, using forecasts from the Global Flood Awareness System (GloFAS). GloFAS is jointly developed by the European Commission and the European Centre for Medium-Range Weather Forecasts (ECMWF) and is designed to provide a global overview of upcoming flood events to decision makers as part of the Copernicus Emergency Management Service, producing probabilistic river discharge forecasts driven by global ECMWF ensemble forecasts coupled to a hydrological model. This presentation will explore the chain of uncertainty through the forecasting process for several recent tropical cyclone flood events including Hurricane Iota and Cyclone Nivar. It investigates the influence on the overall predictability and uncertainty of the fluvial flood forecasts of various components of the forecasting chain, including the track, intensity, and precipitation forecasts for the tropical cyclone, and the hydrological catchment conditions and modelling.

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Microphysics-Based Bulk Parameterizations of Enthalpy and Momentum Fluxes for Tropical Cyclones

10.5194/egusphere-egu2020-4383 ◽

2020 ◽

Author(s):

Sydney Sroka ◽

Kerry Emanuel

Keyword(s):

Boundary Layer ◽

Tropical Cyclone ◽

State Of The Art ◽

Sea Spray ◽

Wind Speeds ◽

Extreme Wind ◽

Momentum Fluxes ◽

Forecast Models ◽

Extreme Wind Speeds ◽

Tropical Cyclone Boundary Layer

Despite the powerful influence that sea spray has on air-sea enthalpy and momentum fluxes, most state-of-the-art tropical cyclone forecast models do not incorporate the microphysics of sea spray evaporation into their boundary layer flux schemes. Since the air-sea enthalpy and momentum fluxes control a tropical cyclone&#8217;s intensification rate, increasing the accuracy of the associated bulk parameterizations is crucially important for improving forecast skill. New microphysics-based bulk parameterizations for enthalpy and momentum flux through the tropical cyclone boundary layer are developed from a set of prognostic evaporation equations and numerical simulations of evaporating, multiphase flow subject to extreme wind speeds. The microphysics-based parameterizations are computationally inexpensive and are functions of the local environmental conditions; these features allow forecast models to efficiently vary the air-sea enthalpy and momentum fluxes in space and time. By developing microphysics-based bulk parameterizations, the influence that sea spray exerts on tropical cyclone intensification can be more accurately simulated and intensity forecasts could be improved.

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Sea Spray in Air-Sea Enthalpy and Momentum Exchanges in Tropical Cyclones

10.5194/egusphere-egu21-13353 ◽

2021 ◽

Author(s):

Alexander Soloviev ◽

Breanna Vanderplow ◽

Roger Lukas ◽

Brian Haus ◽

Muhammad Sami ◽

...

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Negative Feedback ◽

Aerodynamic Drag ◽

Water Layer ◽

Breaking Waves ◽

Sea Spray ◽

Substantial Part ◽

Related Factors ◽

Turbulent Airflow

Under tropical cyclones, sea spray is produced by breaking waves and direct disruption of the air-sea interface. The influence of sea spray on tropical cyclone intensity and intensification has not been well understood. There are serious questions regarding the most appropriate methods for the incorporation of sea spray in tropical cyclone models. These include momentum and enthalpy fluxes at the air-sea interface due to spray, the airborne sea-salt particles inducing boundary layer convection and clouds (Woodcock &#160;1958, Spund &#160;et al. 2014), and other related factors. Here, we study the effect of spray on thermodynamics of tropical cyclones using a Volume of Fluid to Discrete Phase (VOF to DPM) transition model. Due to dynamic remeshing, VOF to DPM resolves spray particles ranging in size from tens of micrometers to a few millimeters. The generated water particles that satisfy the condition of asphericity are converted into Lagrangian particles involved in a two-way interaction with the airflow. This model has been partially verified at the UM RSMAS Surge Structure Atmosphere Interaction facility (Vanderplow et al. 2020). A recent addition of the ANSYS Fluent Evaporation-Condensation model also allows us to model spray evaporation and related heat and enthalpy fluxes. A substantial part of the smallest particles was suspended in the turbulent airflow and evaporated, and thus contributed less to the total air-sea enthalpy flux. The temperature of the largest particles was close to the temperature of the water layer, which contributed more to the enthalpy flux. This resembled the effect of negative feedback on the enthalpy flux (Peng and Richter 2019). Results of the numerical simulation showed a dramatic increase of spray generation under major tropical cyclones (Cat. 3-5). Under major tropical cyclones, most sea spray (including large particles-spume) is suspended in the turbulent airflow and is then subject to the negative feedback. Consequently, in major tropical cyclones the effect of sea spray is expected to be more significant in the momentum budget rather than enthalpy flux at the air-sea interface. This result may explain the nearly constant enthalpy exchange coefficient observed in laboratory and oceanic experiments on tropical cyclones. This is also consistent with the formation of an &#8220;aerodynamic drag well&#8221; around a wind speed of 60 m/s, which can explain the process of rapid storm intensification (Soloviev et al. 2017).&#160;

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Water Over the Bridge: Can We Connect Tree Rings and Overwash Deposits to Understand Regional Tropical Cyclone Variability?

10.5194/egusphere-egu21-8983 ◽

2021 ◽

Author(s):

Joshua Bregy ◽

Justin Maxwell ◽

Grant Harley ◽

Emily Elliott

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Tree Ring ◽

Tree Rings ◽

Ring Width ◽

Organic Content ◽

Sensitivity Threshold ◽

The Bahamas ◽

Storm Activity ◽

Latewood Density

Despite significant advances in methods, reconstructions using multiple proxies are uncommon in paleotempestology. Studies employing multiproxy techniques often rely on homologous proxies (e.g., grain-size distribution and organic content, or total ring width and maximum latewood density) that complement one another as they often reflect similar processes occurring within tropical cyclones. Unifying seemingly diametric proxies (i.e., tree rings and overwash deposits) receives less attention as they typically record different aspects of a tropical cyclone over substantially different temporal resolutions. However, given the spatial characteristics of storm-related hazards, tree rings and overwash might be far more complementary than previously thought. Here, I present work reconstructing tropical cyclone rainfall using tree rings, from which I develop frequency curves based on the number of years receiving tropical cyclone rainfall amounts &#8805;75th percentile. Using this new metric, I compare tree-ring-based reconstructions with near-annually- to decadally-resolved sediment records from Florida and The Bahamas. Through this comparison, I demonstrate both synchronous and asynchronous behavior between records, highlighting the possible presence of regional signatures and climate controls in storm activity. While there remain numerous discrepancies between these records, this comparison serves as an example that these proxies augment one another when viewed through the lens of regional shifts in the hurricane climate. Given that trees respond to the widespread footprint of tropical cyclone rainfall, independent of storm intensity, tree rings may better capture regional changes in storm activity. As such, turning to the shorter, yet higher-resolution tree-ring record can provide additional context to active and quiescent intervals observed in overwash records, especially at sites with a higher sensitivity threshold. Comparing these two proxies is still in its infancy; however, we can use techniques unique to a particular proxy to produce analogous records of tropical cyclone activity. In addition to developing analogous records, is important to explore nontraditional signals of tropical cyclones in these proxies. In particular, I will discuss two approaches that could be key for developing holistic records of storm activity in the Gulf of Mexico. The first uses growth suppressions and geochemical signals in coastal trees in response to saltwater intrusion, while the second examines the sedimentary and geochemical signature of inland flooding from tropical cyclones. The advancement of paleotempestology necessitates developing multiproxy reconstructions. All of these novel approaches and proxies complement records of overwash, which is one of the few proxies able to provide a quantitative estimate of storm magnitude. Moreover, using these proxies in conjunction with one another is critical for understanding changes in the regional hurricane climate and reducing the manifold risks associated with tropical cyclones.

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Air-sea Interface Exchanges in Rapidly Intensifying Tropical Cyclones

10.5194/egusphere-egu2020-12109 ◽

2020 ◽

Author(s):

Alexander Soloviev ◽

Breanna Vanderplow ◽

Roger Lukas

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

Aerodynamic Drag ◽

Model Verification ◽

Intensity Change ◽

Rapid Decline ◽

Rapid Intensification ◽

Discrete Phase Model ◽

Momentum Exchange ◽

General Terms

Rapid intensification of tropical cyclones is a challenge for forecasters. In 2017, Hurricane Maria intensified to a Category 5 storm within 24 hours and devastated Puerto Rico. The official forecast and all computer models were unable to predict it. Hurricane Dorian had been predicted as a tropical storm; unexpectedly, it intensified into a Category 5 storm and destroyed the Bahamas. Soloviev et al. (2017) suggested that under the assumption of constant enthalpy exchange coefficient, rapid cyclone intensification and decay can be related to the drag coefficient dependence on wind speed including an &#8220;aerodynamic drag well&#8221; around 60 m/s. This concept is in general terms consistent with Emanuel&#8217;s (1988) theory of maximum potential intensity of a tropical cyclone and its extension by Lee et al. (2019). The influence of sea spray is still a significant uncertainty. In order to study the effect of spray on dynamics of tropical cyclones, we have implemented a Volume of Fluid to Discrete-Phase Model (VOF to DPM). This model re-meshes the areas with increased gradients or curvature, which are suspicious for the interface instability. The generated water particles that satisfy the condition of asphericity are converted into Lagrangian particles. The size distribution of spray measured in air-sea interaction facilities is used for the model verification. Due to dynamic remeshing, VOF to DPM resolves spray particle radius from ten micrometers to a few millimeters, which correspond to spume. Results of the numerical simulation show a dramatic increase of spume generation under major tropical cyclones. Though sub-micrometer and micrometer scale spray particles are not resolved in this simulation, they are likely less significant in the momentum exchange at the air-sea interface than spume. These results are expected to contribute to the parameterization and proper treatment of spray in forecasting models, including cases of rapid intensification and rapid decline of tropical cyclones. References: Emanuel, K. A. (1988). The maximum intensity of hurricanes. JAS 45, 1143&#8211;1155. Soloviev, A. V., Lukas, R., Donelan, M.A., Haus, B. K., Ginis, I. (2017). Is the state of the air-sea interface a factor in rapid intensification and rapid decline of tropical cyclones? JGR - Oceans 122, 10174-10183. Lee, W., Kim, S.&#8208;H., Chu, P.&#8208;S., Moon,I.&#8208;J., and Soloviev, A. V. (2019). An index to better estimate tropical cyclone intensity change in the western North Pacific. GRL 46, 8960-8968.

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Machine Learning in Tropical Cyclone Forecast Modeling: A Review

Atmosphere ◽

10.3390/atmos11070676 ◽

2020 ◽

Vol 11 (7) ◽

pp. 676

Author(s):

Rui Chen ◽

Weimin Zhang ◽

Xiang Wang

Keyword(s):

Machine Learning ◽

Tropical Cyclone ◽

Tropical Cyclones ◽

Numerical Models ◽

Weather Forecasts ◽

Dynamic Mechanisms ◽

Forecast Models ◽

Strong Winds ◽

The Many ◽

Axisymmetric Structures

Tropical cyclones have always been a concern of meteorologists, and there are many studies regarding the axisymmetric structures, dynamic mechanisms, and forecasting techniques from the past 100 years. This research demonstrates the ongoing progress as well as the many remaining problems. Machine learning, as a means of artificial intelligence, has been certified by many researchers as being able to provide a new way to solve the bottlenecks of tropical cyclone forecasts, whether using a pure data-driven model or improving numerical models by incorporating machine learning. Through summarizing and analyzing the challenges of tropical cyclone forecasts in recent years and successful cases of machine learning methods in these aspects, this review introduces progress based on machine learning in genesis forecasts, track forecasts, intensity forecasts, extreme weather forecasts associated with tropical cyclones (such as strong winds and rainstorms, and their disastrous impacts), and storm surge forecasts, as well as in improving numerical forecast models. All of these can be regarded as both an opportunity and a challenge. The opportunity is that at present, the potential of machine learning has not been completely exploited, and a large amount of multi-source data have also not been fully utilized to improve the accuracy of tropical cyclone forecasting. The challenge is that the predictable period and stability of tropical cyclone prediction can be difficult to guarantee, because tropical cyclones are different from normal weather phenomena and oceanographic processes and they have complex dynamic mechanisms and are easily influenced by many factors.

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Author Correction: Potential effect of bio-surfactants on sea spray generation in tropical cyclone conditions

Scientific Reports ◽

10.1038/s41598-021-88354-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Breanna Vanderplow ◽

Alexander V. Soloviev ◽

Cayla W. Dean ◽

Brian K. Haus ◽

Roger Lukas ◽

...

Keyword(s):

Tropical Cyclone ◽

Potential Effect ◽

Sea Spray ◽

Correction Potential

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Numerical Simulations of the Evaporating Sea Surface Under Extreme Winds

10.5194/egusphere-egu21-13543 ◽

2021 ◽

Author(s):

Sydney Sroka ◽

Kerry Emanuel

Keyword(s):

Tropical Cyclone ◽

Numerical Simulations ◽

State Of The Art ◽

Wind Forcing ◽

Sea Surface ◽

Sea Spray ◽

Strong Wind ◽

Momentum Fluxes ◽

Forecast Models ◽

Extreme Winds

Since air-sea enthalpy and momentum fluxes control a tropical cyclone&#8217;s intensification rate, increasing the accuracy of the associated bulk parameterizations is crucially important for improving forecast skill. Despite the powerful influence that sea spray has on air-sea enthalpy and momentum fluxes, most state-of-the-art tropical cyclone forecast models do not incorporate the microphysics of sea spray evaporation into their boundary layer flux schemes. We present the results from direct numerical simulations of the evaporating sea surface subject to a strong wind forcing to help evaluate the parameterizations of bulk exchange coefficients of momentum and enthalpy. By developing microphysics-based bulk parameterizations, the influence that sea spray exerts on tropical cyclone intensification can be more accurately simulated and intensity forecasts could be improved.

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