The “Bag Breakup” Spume Droplet Generation Mechanism at High Winds. Part I: Spray Generation Function

AbstractThis paper describes the results of an experimental and theoretical investigation into the mechanisms by which spume droplets are generated by high winds. The experiments were performed in a high-speed wind-wave flume at friction velocities between 0.8 and 1.5 m s−1 (corresponding to a 10-m wind speed of 18–33 m s−1 under field conditions). High-speed video of the air–water interface revealed that the main types of spray-generating phenomena near the interface are “bag breakup” (similar to fragmentation of droplets and jets in gaseous flows at moderate Weber numbers), breakage of liquid ligaments near the crests of breaking surface waves, and bursting of large submerged bubbles. Statistical analysis of these phenomena showed that at wind friction velocities exceeding 1.1 m s−1 (corresponding to a wind speed of approximately 22.5 m s−1), the main mechanism responsible for the generation of spume droplets is bag breakup fragmentation of small-scale disturbances that arise at the air–water interface under the strong wind. Based on the general principles of statistical physics, it was found that the number of bags arising at the water surface per unit area per unit time was dependent on the friction velocity of the wind. The statistics obtained for the bag breakup events and other data available on spray production through this type of fragmentation were employed to construct a spray generation function (SGF) for the bag breakup mechanism. The resultant bag breakup SGF is in reasonable agreement with empirical SGFs obtained under laboratory and field conditions.

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Shear instability of wind drift as the initiation mechanism for the bag-breakup fragmentation of the air-water interface at high winds.

10.5194/egusphere-egu21-8539 ◽

2021 ◽

Author(s):

Yuliya Troitskaya

Keyword(s):

High Speed ◽

Marine Boundary Layer ◽

Laboratory Data ◽

Simple Wave ◽

Field Conditions ◽

Shear Instability ◽

Small Scale ◽

Strong Wind ◽

Initiation Mechanism ◽

Wind Drift

The "bag breakup" fragmentation is the dominant mechanism for generating spray in hurricane winds, which parameters substantially affect the exchange processes between the ocean and the atmosphere and, thereby, the dynamics of the development of sea storms. This fast process can only be studied in lab using sophisticated experimental techniques based on high-speed video filming. In such circumstances, the transfer of laboratory data to field conditions requires a kind of theoretical model that describes how the initiation of disturbances occurs, which then lead to fragmentation events, what is the threshold for fragmentation, what is the volume of liquid, which determines the size of spray droplets, that undergoes fragmentation, and how it depends on wind parameters, etc. The conclusions of the model can be first verified in the laboratory experiment and then applied to field conditions.In the present work, such a model is proposed. First of all, a linear theory of small-scale disturbances on the water surface under the action of a strong wind has been built, which makes it possible to describe their structure, dispersion properties and determine the threshold value of the dynamic air flow velocity at which such disturbances become growing. These disturbances comprise small-scale ripples concentrated within the thin surface layer and growing fast due to shear instability of the wind drift flow in the water. The peculiarity of the structure of these disturbances enables one to consider the nonlinear stage of their evolution within the Riemann simple wave equation modified to describe the increasing disturbances. The analytical solution of the obtained equation suggests the scaling of the volume of liquid undergoing the "bag-breakup" fragmentation, to estimate the scale of the formed droplets and the speed of their injection into the atmosphere. The scaling correctly describes the dependencies of these quantities on the wind friction velocity obtained in laboratory experiments.The obtained results are applied for the construction of the fetch-dependent spray generation function, which is applicable in the field. Within the Lagrangian stochastic model for the inertial droplets in the marine boundary layer, the momentum, heat, moisture and enthalpy exchange coefficients are calculated. One should notice substantial &#160;feedback effect on the atmosphere caused by the presence of spray in hurricane conditions.This work was supported by RFBR grant 19-05-00249 and RSF grant 19-17-00209.&#160;

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Kinetic effects during ocean evaporation: observed relationship with wind speed

10.5194/egusphere-egu21-5516 ◽

2021 ◽

Author(s):

Daniele Zannoni ◽

Hans Christian Steen-Larsen ◽

Andrew Peters ◽

Árný Erla Sveinbjörnsdóttir

Keyword(s):

Water Vapor ◽

Wind Speed ◽

Water Interface ◽

Fractionation Factor ◽

Wind Speeds ◽

Air Water Interface ◽

Kinetic Fractionation ◽

Speed Effect ◽

Equilibrium Fractionation ◽

Non Equilibrium

Water vapor has a fundamental role in weather and climate, being the strongest natural greenhouse gas in the Earth&#8217;s atmosphere. The main source of water vapor in the atmosphere is ocean evaporation, which transfers a large amount of energy via latent heat fluxes. In the past, evaporation was intensively studied using stable isotopes because of the large fractionation effects involved during water phase changes, providing insights on processes occurring at the air-water interface. Current theories describe evaporation near the air-water interface as a combination of molecular and turbulent diffusion processes into separated sublayers. The importance of those two sublayers, in terms of total resistance to vapor transport in air, is expected to be dependent on parameters such as moisture deficit, temperature and wind speed. Non-equilibrium fractionation effects in isotopic evaporation models are then expected to be related to these physical parameters. In the last 10 years, several water vapor observations from oceanic expeditions were focused on the impact of temperature and wind speed effect, assuming the influence of those parameters on non-equilibrium fractionation in the marine boundary layer. Wind speed effect is expected to be small on total kinetic fractionation and was discussed at length but was not completely ruled out. With a gradient-diffusion approach (2 heights above the ocean surface) and Cavity Ring-Down Spectroscopy we have estimated non-equilibrium fractionation factors for 18O/16O during evaporation, showing that the wind speed effect can be detected and has no significant impact on kinetic fractionation. Results obtained for wind speeds between 0 and 10 m s-1 in the North Atlantic Ocean are consistent with the Merlivat and Jouzel (1979) parametrization for smooth surfaces (mean &#949;18=6.1&#8240;). A small monotonic decrease of the fractionation parameter is observed as a function of 10 m wind speed (slope&#160; &#8773; 0.15 &#8240; m-1 s), without any evident discontinuity. However, depending on the data filtering approach it is possible to highlight a rapid decrease of the kinetic fractionation factor at low wind speed (&#8804; 2.5 m s-1). An evident decrease of fractionation factor is also observed for wind speeds above 10 m s-1, allowing to hypothesize the possible effect of sea spray in net evaporation flux. Considering the average wind speed over the oceans, we conclude that a constant kinetic fractionation factor for evaporation is a more simple and reasonable solution than a wind-speed dependent parametrization.&#160;&#160;Merlivat, L., & Jouzel, J. (1979). Global climatic interpretation of the deuterium&#8208;oxygen 18 relationship for precipitation. Journal of Geophysical Research: Oceans, 84(C8), 5029-5033.

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Water skating in the larvae of dixella aestivalis (Diptera) and hydrobius fuscipes (Coleoptera)

Journal of Experimental Biology ◽

10.1242/jeb.202.7.845 ◽

1999 ◽

Vol 202 (7) ◽

pp. 845-853

Author(s):

J. Brackenbury

Keyword(s):

High Speed ◽

The Body ◽

Water Interface ◽

Body Movements ◽

Chironomid Larvae ◽

High Speed Video ◽

Adhesive Organ ◽

Video Recordings ◽

Air Water Interface

The kinematics of locomotion was investigated in the aquatic larvae of Dixella aestivalis and Hydrobius fuscipes with the aid of high-speed video recordings. Both insects are able to skate on the surface of the water using the dorso-apical tracheal gill as an adhesive organ or ‘foot’. Progress relies on the variable adhesion of the foot between ‘slide’ and ‘hold’ periods of the locomotory cycle. The flexural body movements underlying skating in D. aestivalis can be derived directly from the figure-of-eight swimming mechanism used in underwater swimming. The latter is shown to be similar to figure-of-eight swimming in chironomid larvae. This study shows how the deployment of a ‘foot’ enables simple side-to-side flexural movements of the body to be converted into effective locomotion at the air-water interface.

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Through-grid wicking enables high-speed cryoEM specimen preparation

Acta Crystallographica Section D Structural Biology ◽

10.1107/s2059798320012474 ◽

2020 ◽

Vol 76 (11) ◽

pp. 1092-1103

Author(s):

Yong Zi Tan ◽

John L. Rubinstein

Keyword(s):

Glass Fiber ◽

High Speed ◽

Protein Complexes ◽

Absorption Capacity ◽

Specimen Preparation ◽

Water Interface ◽

Time Resolved ◽

Glass Fiber Filter ◽

Liquid Absorption ◽

Air Water Interface

Blotting times for conventional cryoEM specimen preparation complicate time-resolved studies and lead to some specimens adopting preferred orientations or denaturing at the air–water interface. Here, it is shown that solution sprayed onto one side of a holey cryoEM grid can be wicked through the grid by a glass-fiber filter held against the opposite side, often called the `back', of the grid, producing a film suitable for vitrification. This process can be completed in tens of milliseconds. Ultrasonic specimen application and through-grid wicking were combined in a high-speed specimen-preparation device that was named `Back-it-up' or BIU. The high liquid-absorption capacity of the glass fiber compared with self-wicking grids makes the method relatively insensitive to the amount of sample applied. Consequently, through-grid wicking produces large areas of ice that are suitable for cryoEM for both soluble and detergent-solubilized protein complexes. The speed of the device increases the number of views for a specimen that suffers from preferred orientations.

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Catch Characteristics of Precipitation Gauges in High-Latitude Regions with High Winds

Journal of Hydrometeorology ◽

10.1175/jhm542.1 ◽

2006 ◽

Vol 7 (5) ◽

pp. 984-994 ◽

Cited By ~ 21

Author(s):

Konosuke Sugiura ◽

Tetsuo Ohata ◽

Daqing Yang

Keyword(s):

Wind Speed ◽

High Latitude ◽

Cold Climate ◽

Strong Wind ◽

Blowing Snow ◽

High Wind ◽

Wind Speeds ◽

Solid Precipitation ◽

High Winds ◽

Correction Equations

Abstract Intercomparison of solid precipitation measurement at Barrow, Alaska, has been carried out to examine the catch characteristics of various precipitation gauges in high-latitude regions with high winds and to evaluate the applicability of the WMO precipitation correction procedures. Five manual precipitation gauges (Canadian Nipher, Hellmann, Russian Tretyakov, U.S. 8-in., and Wyoming gauges) and a double fence intercomparison reference (DFIR) as an international reference standard have been installed. The data collected in the last three winters indicates that the amount of solid precipitation is characteristically low, and the zero-catch frequency of the nonshielded gauges is considerably high, 60%–80% of precipitation occurrences. The zero catch in high-latitude high-wind regions becomes a significant fraction of the total precipitation. At low wind speeds, the catch characteristics of the gauges are roughly similar to the DFIR, although it is noteworthy that the daily catch ratios decreased more rapidly with increasing wind speed compared to the WMO correction equations. The dependency of the daily catch ratios on air temperature was confirmed, and the rapid decrease in the daily catch ratios is due to small snow particles caused by the cold climate. The daily catch ratio of the Wyoming gauge clearly shows wind-induced losses. In addition, the daily catch ratios are considerably scattered under strong wind conditions due to the influence of blowing snow. This result suggests that it is not appropriate to extrapolate the WMO correction equations for the shielded gauges in high-latitude regions for high wind speed of over 6 m s−1.

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Simulation of Air–Water Interface Effects for High-speed Planing Hull

Journal of Marine Science and Application ◽

10.1007/s11804-020-00172-0 ◽

2020 ◽

Vol 19 (3) ◽

pp. 398-414

Author(s):

Naga Venkata Rakesh Nimmagadda ◽

Lokeswara Rao Polisetty ◽

Anantha Subramanian Vaidyanatha Iyer

Keyword(s):

High Speed ◽

Water Interface ◽

Fluid Forces ◽

Transition Speed ◽

High Speeds ◽

Air Water Interface ◽

Practical Design ◽

Actual Flow ◽

Wetted Surface Area ◽

Interface Effects

Abstract High-speed planing crafts have successfully evolved through developments in the last several decades. Classical approaches such as inviscid potential flow–based methods and the empirically based Savitsky method provide general understanding for practical design. However, sometimes such analyses suffer inaccuracies since the air–water interface effects, especially in the transition phase, are not fully accounted for. Hence, understanding the behaviour at the transition speed is of fundamental importance for the designer. The fluid forces in planing hulls are dominated by phenomena such as flow separation at various discontinuities viz., knuckles, chines and transom, with resultant spray generation. In such cases, the application of potential theory at high speeds introduces limitations. This paper investigates the simulation of modelling of the pre-planing behaviour with a view to capturing the air–water interface effects, with validations through experiments to compare the drag, dynamic trim and wetted surface area. The paper also brings out the merits of gridding strategies to obtain reliable results especially with regard to spray generation due to the air–water interface effects. The verification and validation studies serve to authenticate the use of the multi-gridding strategies on the basis of comparisons with simulations using model tests. It emerges from the study that overset/chimera grids give better results compared with single unstructured hexahedral grids. Two overset methods are investigated to obtain reliable estimation of the dynamic trim and drag, and their ability to capture the spray resulting from the air–water interaction. The results demonstrate very close simulation of the actual flow kinematics at steady-speed conditions in terms of spray at the air–water interface, drag at the pre-planing and full planing range and dynamic trim angles.

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Drifting-snow studies over an instrumented mountainous site: II. Measurements and numerical model at small scale

Annals of Glaciology ◽

10.3189/172756401781819364 ◽

2001 ◽

Vol 32 ◽

pp. 175-181 ◽

Cited By ~ 9

Author(s):

Jean-Luc Michaux ◽

Florence Naaim-Bouvet ◽

Mohamed Naaim

Keyword(s):

Wind Speed ◽

Numerical Model ◽

Small Scale ◽

Wind Gust ◽

Strong Wind ◽

Experimental Site ◽

In Situ Data ◽

Drifting Snow ◽

Mean Wind Speed ◽

Gust Factors

AbstractThe Érosion torrentielle, neige et avalanche (Etna) unit of CEMAGREF and the Centre d’Etudes de la Neige of Météo-France have been working on snowdrift for 10 years. A numerical model was developed at CEMAGREF to simulate snowdrift (Naaim and others, 1998). To validate this model on in situ data, a high-altitude experimental site was developed, located at 2700 m a.s.l. at the Lac Blanc Pass near the Alpe d’Huez ski resort. It is a nearly flat area and faces winds primarily from north and south. After describing the experimental site, we present the processed data of winter 1998/99. First, we analyze the data from CEMAGREF’s acoustic snowdrift sensor. It is sensitive to snow depth and snow-particle type, so additional calibration is necessary. Nevertheless, it allowed us to study non- stationary aspects of drifting snow. An analysis of gust factors for wind and drifting snow indicates that strong wind-gust factors exist in the mountains, and that drifting snow is more important during a regular and strong wind episode than during high wind-gust periods. Therefore, the numerical model presented here uses only the recorded mean wind speed. The model, which attempts to reproduce several days of storm, takes into account the modification of input parameters (e.g wind speed) as a function of time. The comparison between numerical results and measurements for a given meteorological event shows good agreement.

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Gas Exchange Rate Measurements in Natural Systems

Radiocarbon ◽

10.1017/s0033822200010043 ◽

1980 ◽

Vol 22 (3) ◽

pp. 676-683 ◽

Cited By ~ 35

Author(s):

W S Broecker ◽

T-H Peng ◽

G Mathieu ◽

R Hesslein ◽

T Torgersen

Keyword(s):

Exchange Rate ◽

Wind Speed ◽

Wind Tunnel ◽

Sea Water ◽

Water Interface ◽

Satisfactory Explanation ◽

Natural Systems ◽

Air Water Interface ◽

Gas Exchange Rate ◽

Mean Wind Speed

Rates of CO2 exchange across the air-water interface in oceans and lakes measured to date by the L-DGO group are summarized. They range from 3 to 38 moles/m2/yr. The possible causes for this range include the differences in salinity, mean wind speed, and pH. Wind tunnel studies comparing fresh water and sea water are required before a satisfactory explanation can be found.

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The Effects of SST-Induced Surface Wind Speed and Direction Gradients on Midlatitude Surface Vorticity and Divergence

Journal of Climate ◽

10.1175/2009jcli2613.1 ◽

2010 ◽

Vol 23 (2) ◽

pp. 255-281 ◽

Cited By ~ 91

Author(s):

Larry W. O’Neill ◽

Dudley B. Chelton ◽

Steven K. Esbensen

Keyword(s):

Wind Speed ◽

Wind Direction ◽

Spatial Scales ◽

Kuroshio Extension ◽

Surface Wind ◽

Surface Wind Speed ◽

Small Scale ◽

Strong Wind ◽

Sst Variability ◽

Seawinds Scatterometer

Abstract The effects of surface wind speed and direction gradients on midlatitude surface vorticity and divergence fields associated with mesoscale sea surface temperature (SST) variability having spatial scales of 100–1000 km are investigated using vector wind observations from the SeaWinds scatterometer on the Quick Scatterometer (QuikSCAT) satellite and SST from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) Aqua satellite. The wind–SST coupling is analyzed over the period June 2002–August 2008, corresponding to the first 6+ years of the AMSR-E mission. Previous studies have shown that strong wind speed gradients develop in response to persistent mesoscale SST features associated with the Kuroshio Extension, Gulf Stream, South Atlantic, and Agulhas Return Current regions. Midlatitude SST fronts also significantly modify surface wind direction; the surface wind speed and direction responses to typical SST differences of about 2°–4°C are, on average, about 1–2 m s−1 and 4°–8°, respectively, over all four regions. Wind speed perturbations are positively correlated and very nearly collocated spatially with the SST perturbations. Wind direction perturbations, however, are displaced meridionally from the SST perturbations, with cyclonic flow poleward of warm SST and anticyclonic flow poleward of cool SST. Previous observational analyses have shown that small-scale perturbations in the surface vorticity and divergence fields are related linearly to the crosswind and downwind components of the SST gradient, respectively. When the vorticity and divergence fields are analyzed in curvilinear natural coordinates, the wind speed contributions to the SST-induced vorticity and divergence depend equally on the crosswind and downwind SST gradients, respectively. SST-induced wind direction gradients also significantly modify the vorticity and divergence fields, weakening the vorticity response to crosswind SST gradients while enhancing the divergence response to downwind SST gradients.

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