Investigation of sea spray effect on the vertical momentum transport using an Eulerian multi-fluid-type model

The Eulerian multi-fluid mathematical model is developed to describe the marine atmospheric boundary layer laden with sea spray under high wind condition of a hurricane. The model considers spray and air as separate continuous interacting turbulent media and employs the multi-fluid E – ε closure. Each phase is described by its own set of coupled conservation equations and characterized by its own velocity. Such an approach enables us to accurately quantify the interaction between spray and air and pinpoint the effect of spray on the vertical momentum transport much more precisely than could be done with traditional mixture-type approaches. The model consistently quantifies the effect of spray inertia and the suppression of air turbulence due to two different mechanisms: the turbulence attenuation, which results from the inability of spray droplets to fully follow turbulent fluctuations, and the vertical transport of spray against the gravity by turbulent eddies. The results of numerical and asymptotic analyses show that the turbulence suppression by spray overpowers its inertia several meters above wave crests resulting in a noticeable wind acceleration and the corresponding reduction of the drag coefficient from the reference values for a spray-free atmosphere. This occurs at a much lower than predicted previously spray volume fraction values ~ 10−5. The falloff of the drag coefficient from its reference values is stronger pronounced at higher altitudes. The drag coefficient reaches its maximum at spray volume fraction values ~ 10−4 that is several times smaller than predicted by mixture-type models.

A Wind–Wave-Dependent Sea Spray Volume Flux Model Based on Field Experiments

Sea spray can contribute significantly to the exchanges of heat and momentum across the air–sea interface. However, while critical, sea spray physics are typically not included in operational atmospheric and oceanic models due to large uncertainties in their parameterizations. In large part, this is because of the scarcity of in-situ sea spray observations which prevent rigorous validation of existing sea spray models. Moreover, while sea spray is critically produced through the fundamental interactions between wind and waves, traditionally, sea spray models are parameterized in terms of wind properties only. In this study, we present novel in-situ observations of sea spray derived from a laser altimeter through the adoption of the Beer–Lambert law. Observations of sea spray cover a broad range of wind and wave properties and are used to develop a wind–wave-dependent sea spray volume flux model. Improved performance of the model is observed when wave properties are included, in contrast to a parameterization based on wind properties alone. The novel in-situ sea spray observations and the predictive model derived here are consistent with the classic spray model in both trend and magnitude. Our model and novel observations provide opportunities to improve the prediction of air–sea fluxes in operational weather forecasting models.

Spray volume, dose and time of day of glyphosate application in the control of Urochloa brizantha

In order to optimize machinery use, the application of herbicides has been performed at different times of the day and night. Therefore, knowledge about the pesticide that will be used and how the spray volume and time of application affect the effectiveness of the product is very important. Thus, the objective of this work was to study the influence of spray volume and different time of application on the control of Urochloa brizantha by different doses of glyphosate. The treatments were arranged in a 5 x 3 x 2 factorial scheme in a randomized block design with four replications. Five doses of glyphosate (0; 1080; 1440; 1800 and 2160 g∙ha-1∙a.e.), three times of application (morning, afternoon and evening) and two spray volumes (50 and 100 L·ha-1) were evaluated. A control assessment was performed at 21 days after application, in addition to the accumulation of dry matter and the leaf area index on the regrowth. A satisfactory control of the grass was obtained for applications performed in the morning and afternoon, without interference of the volume applied and the doses tested. Evening application reduces the effectiveness of glyphosate in Urochloa brizantha burndown.

Deposition of sprayed drops in soybean in function of sowing spacing

To reach all parts of the plants can be a difficult achievement faced by the drops in several crops. Strategies in crop management such as an increment in the plant spacing can contribute to the spray application's success. This study aimed to evaluate the droplets deposition in soybean, using three different spray nozzles and application rate, in two soybean rows spacing. The experimental design used was the randomized blocks, with treatments arranged in a split-plot scheme. The plots were the interrow spacing (0.45 and 0.76 m), the subplots were the spray nozzles (JA-2 and Magno 11002 BD), and the sub-subplots were the application rate (120, 200 and 280 L ha-1). Droplets coverage was evaluated in the upper, middle and lower thirds of soybean plants. Water-sensitive papers were installed in the adaxial part of plant leaves to analyze the spray technology and evaluated using E-Sprinkle® software. Spraying was performed in plants at the R5.3 soybean stage. This experiment evaluated the following parameters: the volume median diameter, the density of droplets per cm2, the droplet coverage area, and the droplet percentage less than 150 µm. The increase in the soybean row spacing combined with the spray volume increase provided greater droplet coverage in the middle third in soybean crop. The Magno 11002 BD droplet nozzle provided the higher droplet coverage in the row spacing of 0.76 m. The spray rate of 280 L ha-1 provided the highest density of droplets per cm2 in the lower third and greater coverage in the middle-third.

The efficiency of Brazilian oat cultivars in reducing fungicide use for greater environmental quality and food safety

Oat cultivars more efficient at reducing fungicide can prevent contamination of soil, water and food. The objective of the study is to measure the efficiency of oat cultivars recommended for growing in Brazil by reducing the number of fungicide applications, considering favorable and unfavorable crop season conditions for productivity and progress of the main leaf diseases. The study was conducted in 2015, 2016 and 2017, in Augusto Pestana, RS, Brazil. The experimental design was a randomized block with three replications in a 22 x 4 factorial scheme, for 22 oat cultivars and 4 conditions of fungicide use [without application; an application at 60 days after emergence; two applications at 60 and 75 days after emergence; and three applications at 60, 75 and 90 days after emergence]. The fungicide FOLICUR® CE was used in 2015 and 2016 and the fungicide PRIMO® in 2017 in the dosage of 0.75 and 0.3 liters ha-1, respectively. The plots were sprayed using BD 04 fan nozzle with 45 PSI pressure, and spray volume close to 120 liters ha-1. The condition of a crop season favorable to the progress of leaf diseases identifies with quality cultivars more efficient in reducing the use of fungicide, enabling processes with lower environmental impacts with food security. Under favorable agricultural year conditions and unfavorable to the productivity and progress of the main leaf diseases of oats, the most efficient cultivars to reduce the use of fungicide are URS Altiva and URS Guria

Volume Rate Adjustment for Pesticide Applications against Aonidiella aurantii in Citrus: Validation of CitrusVol in the Growers’ Practice

Aonidiella aurantii is one of the most damaging armored scales in citrus crops worldwide. To control this pest, high water volume rates are conventionally used. In order to rationalize the pesticide applications in citrus, IVIA developed CitrusVol, a tool that recommends the optimal volume rate based on the vegetation, the pest or disease and the active ingredient. In this study the objectives were: (i) validate CitrusVol as a tool to adjust the spray volume to control A. aurantii and (ii) quantify its environmental and economical advantages. For this, the spray volume adjusted with CitrusVol was compared with the one conventionally used by farmers in 18 applications in seven orchards during two years. The following parameters were evaluated: (i) spray distribution in the canopy, (ii) A. aurantii males trapped per day, and (iii) number of scales per fruit at harvest. CitrusVol reduced the spray volume and the amount of pesticide by 35% on average. Despite this reduction, a satisfactory spray distribution was achieved, and the volume was found to control the pest in a comparable way to the conventional volume. Moreover, CitrusVol saved per application and on average 31.25 h/100 ha of spray operating time, 241.83 L/100 ha of fuel consumption and consequently, the reduction of emissions of CO2 was 631.18 kg/100 ha. Therefore, CitrusVol allows for efficient, low-input and low-impact pesticide applications.

Variable-rate Spray Technology Optimizes Pesticide Application by Adjusting for Seasonal Shifts in Deciduous Perennial Crops

To optimize pesticide applications to the canopies of deciduous perennial crops, spray volume should be adjusted throughout the year to match the changes in canopy volume and density. Machine-vision, computer-controlled, variable-rate sprayers are now commercially available and claim to provide adequate coverage with decreased spray volumes compared with constant-rate sprayers. However, there is little research comparing variable- and constant-rate spray applications as crop characteristics change throughout a growing season. This study evaluated spray volume, spray quality (e.g., coverage and deposit density), and off-target spray losses of variable- and constant-rate sprayers across multiple phenophases in an apple (Malus domestica) orchard and a grape (Vitis vinifera) vineyard. The variable-rate sprayer mode applied 67% to 74% less volume in the orchard and 61% to 80% less volume in the vineyard. Spray coverage (percent), measured by water-sensitive cards (WSC), was consistently greater in the constant-rate mode compared with the variable-rate mode, but in many cases, excessive coverage (i.e., over-spray) was recorded. The variable-rate sprayer reduced off-target losses, measured by WSC coverage, up to 40% in the orchard and up to 33% in the vineyard. Spray application deposit densities (droplets per square centimeter) on target canopies were typically greater in variable-rate mode. However, the deposit densities were confounded in over-spray conditions because droplets coalesced on the WSC resulting in artificially low values (i.e., few, very large droplets). Spray efficiencies were most improved early in the growing season, when canopy density was lowest, demonstrating the importance of tailoring spray volume to plant canopy characteristics.

Spray Coverage and Biological Efficacy of Single, Twin Symmetrical, and Twin Asymmetrical Flat Fan Nozzles

Proper selection of nozzle type and spray volume is essential to optimize herbicide dose, reducing its adverse environmental effects. It has not been sufficiently evaluated which nozzle type (twin symmetrical flat fan nozzle or the twin asymmetrical one) is more efficient and whether pinoxaden application is more efficient at a low or high spray volume. The spray coverage of a single, twin symmetrical, and twin asymmetrical flat fan nozzles, each in the sizes of 110015, 11002, 110025, 11003, 11004, and 11005 on the moisture-sensitive papers (MSPs) was investigated. The biological efficacy of treatments using pinoxaden against wild oat was investigated. Unlike other nozzle types, the single flat fan nozzle could not cover MSP placed vertically behind the nozzle trajectory. Except for the latter, each nozzle type could cover the MSPs more efficiently with increase in nozzle size. Generally, the nozzles’ performance was twin symmetrical > single = twin asymmetrical flat fan nozzles. A larger nozzle size improved the coverage of MSPs but increased the effective dose (ED50; dose that gives a 50% reduction in dry weight), indicating a decrease in the efficacy of pinoxaden. Among all treatments, the lowest ED50 value was obtained by the twin symmetrical flat fan nozzle 110015 (5.2 g a.i. ha−1). The smaller, more concentrated droplets are required to achieve optimal pinoxaden efficacy against wild oat, which can be provided by a twin symmetrical flat fan nozzle with a smaller size.

The estimation of sea spray at wind speeds ranging from light to extreme

<p>As one of typical elements in the air-sea boundary layer, sea spray is expected to mediate energy flux exchange in the air and ocean boundary layers, and therefore it is of crucial importance to the meteorology, oceanology, and regional climatology. In addition, the spray is also considered as one of the missing physical mechanisms in atmospheric and oceanic numerical models. Hence, it is necessary to accurately predict how much sea spray is produced at the air-sea boundary layer. Though spray has been studied for a number of decades, large uncertainties still linger. For instance, uncertainties in qualifying how much spray is produced on the sea surface reach 10<sup>6</sup> times. This is because of the rarity of spray observations in the field, especially under strong wind condition.</p><p>To give a reliable spray production model, scientists tried to employ laser-based facilities in the field to observe sea spray by interpreting infrared laser-beam intensity into sea spray volume flux over the water surface. Hence, in the current study, we collected datasets in the field measured by laser-based facilities on the North-West Shelf of the coast of Western Australia, thereafter, further analyzed, and calibrated them through a series of academic, statistical, and physical analysis to ensure the data quality. After that, assuming the existence of spray drops in the air-sea layer would attenuate the infrared laser-beam intensity, the weakening extends of laser-beam intensity is used to estimate the volume flux of sea spray above the ocean surface at winds speed ranging from light to extreme during the passage of Tropical Cyclone Olwyn (2015). It should be noted that our observations of sea spray volume flux are within the ranges of existing models and are consistent with the model proposed by Andreas (1992) in both trend and magnitude.</p><p>Using the field observations of the sea spray volume flux, a sea spray volume flux model can be constructed. Given that sea spray droplets are generated at the ocean surface through breaking waves and wind shear, the sea spray volume flux is expected to be dominated by the properties of the local wind and wave field. For physical consistency across the wide range of scales observed in the field and laboratory, non-dimensional parameters (i.e., non-dimensional wind speed and the mean wave steepness) were adopted to construct the model. Consequently, a power-law non-dimensional spray volumetric flux model is suggested based on the estimation of the spray volume flux. It should be noted that one sensitive test was conducted to substantiate the inclusion of wave breaking process, here simply included with the mean wave steepness, improves spray volume flux parameterization.</p>