Droplet Spectra Research Articles

Direct Numerical Simulation of a Warm Cloud Top Model Interface: Impact of the Transient Mixing on Different Droplet Population

Turbulent mixing through atmospheric cloud and clear air interface plays an important role in the life of a cloud. Entrainment and detrainment of clear air and cloudy volume result in mixing across the interface, which broadens the cloud droplet spectrum. In this study, we simulate the transient evolution of a turbulent cloud top interface with three initial mono-disperse cloud droplet population, using a pseudo-spectral Direct Numerical Simulation (DNS) along with Lagrangian droplet equations, including collision and coalescence. Transient evolution of in-cloud turbulent kinetic energy (TKE), density of water vapour and temperature is carried out as an initial value problem exhibiting transient decay. Mixing in between the clear air and cloudy volume produced turbulent fluctuations in the density of water vapour and temperature, resulting in supersaturation fluctuations. Small scale turbulence, local supersaturation conditions and gravitational forces have different weights on the droplet population depending on their sizes. Larger droplet populations, with initial 25 and 18 μ m radii, show significant growth by droplet-droplet collision and a higher rate of gravitational sedimentation. However, the smaller droplets, with an initial 6 μ m radius, did not show any collision but a large size distribution broadening due to differential condensation/evaporation induced by the mixing, without being influenced by gravity significantly.

Infrared spectroscopy of the n-propyl and i-propyl radicals in solid para-hydrogen

We report infrared spectra of the n- and i-propyl radicals isolated in solid para-hydrogen (p-H2). Propyl radicals were produced via 248 nm irradiation of matrices formed by co-deposition of p-H2 and either 1-iodopropane (forming n-propyl) or 2-iodopropane (forming i-propyl). Secondary photolysis was used to group spectral bands arising from the same species. In addition to those observed previously in either argon matrix or helium droplet spectra, we assign approximately 20 previously unreported bands. The assignment of features to propyl radicals is made via comparisons to VPT2+K anharmonic frequency computations. In separate measurements, propyl radicals were generated via the reaction between propene and hydrogen atoms produced within the p-H2 matrix. Because the barriers are between 700 and 1500 cm−1, the H + propene reaction is necessarily under tunneling control when carried out in solid p-H2 at 3.3 K. i-Propyl radicals were produced in ∼5–20 times greater abundance than n-propyl radicals, indicating that H atom addition to the terminal carbon is faster than addition to the central carbon. The Wentzl-Kramers-Brillouin approximation is applied to one-dimensional abinitio potentials to estimate the tunneling time constants for formation of n- and i-propyl. This model predicts the rate of addition to the terminal carbon (forming i-propyl) to be 17 times faster, in qualitative agreement with the experimental branching ratio.

50 MANAGEMENT OF COFFEE LEAF MINER: SPRAY VOLUME, EFFICACY OF CARTAP HYDROCHLORIDE AND IMPACT ON PARASITISM

The leaf miner is a key pest of coffee and the use of insecticides for its control results in high water consumption. The objective in this study was to evaluate the quali-quantitative aspects of reduced spray volumes with and without the addition of adjuvant, the efficacy of the insecticide cartap hydrochloride in the control of the pest and its effects on the parasitism. Two experiments were carried out in coffee plantations in São Desiderio, BA. Initially, solution of Brilliant Blue tracer (0.15% p v-1) of the 43, 112, 146 and 309 L ha-1 volumes was sprayed with and without the soybean oil methyl ester adjuvant (0.25 % v v-1). Before spraying, water-sensitive cards were fixed to the plants and subsequently used for analyze the droplet spectrum in Gotas 1.0 software. The tracer deposit was determined by spectrophotometry. Posteriorly, the insecticide cartap hydrochloride (0.5 kg a.i. ha-1) was applied in the same volumes and types of spray used in the first test. Infestation rates of pest and parasitism were evaluated before and after application of the insecticide. The quali-quantitative aspects of the sprays were affected by the volume of spray applied, by the adjuvant and by the interaction of the factors. The intermediate volumes yielded better spraying quality without the presence of the adjuvante, with higher number and desity of drops. The spraying volume affected the depoisto the Brilliant Blue tracer in a linear and positive form. The efficacy of the insecticide was prolonged with the lowest volume spray and with adjuvant and its impact on parasitism varied with the volume applied and time after application.

Effect of insecticide formulation and adjuvant combination on agricultural spray drift

Loss of crop protection products when agricultural spray applications drift has economic and ecological consequences. Modification of the spray solution through tank additives and product formulation is an important drift reduction strategy that could mitigate these effects, but has been studied less than most other strategies. Therefore, an experimental field study was conducted to evaluate spray drift resulting from agricultural ground applications of an insecticide formulated as a suspension concentrate (SC) and as a wettable powder (WP), with and without two adjuvants. Droplet sizes were also measured in a wind tunnel to determine if indirect methods could be substituted for field experimentation to quantify spray drift from these technologies. Results suggest that spray drift was reduced by 37% when comparing the SC to the WP formulation. As much as 63% drift reduction was achieved by incorporating certain spray adjuvants, but this depended on the formulation/adjuvant combination. The wind tunnel data for droplet spectra showed strong agreement with field deposition trends, suggesting that droplet statistics could be used to estimate drift reduction of spray solutions. These findings can be used to develop a classification scheme for formulated products and tank additives based on their potential for reducing spray drift.

Water-soluble food dye of Allura Red as a tracer to determine the spray deposition of pesticide on target crops.

Quantification of spray deposition on a target crop is of vital importance to optimize pesticide application. In traditional determinations of spray deposition, a large amount of organic solvent is used to extract pesticides from the target crops. In this study, a water-soluble food dye of Allura Red was developed as a tracer to determine pesticide spray deposition on a rice target crop. The addition of Allura Red does not obviously alter the physicochemical properties of pesticides (viscosity, density and surface tension) and droplet spectra. An ultra-performance liquid chromatography (UPLC) analytical method was developed and validated to determine the deposition amount of Allura Red on rice plants. Method accuracy and precision for Allura Red were found to be satisfactory with recoveries of 96.07% to 107.48%. To validate the method, comparative deposition analyses were carried out using representative systematic and non-systematic pesticides (nitenpyram and chlorothalonil) under the same spraying scenarios using a Potter spray tower. Allura Red and pesticides showed comparable deposition under the same application conditions with ratios from 0.98 to 1.21. A field trial using an unmanned aerial vehicle sprayer further indicated that the deposition rates for Allura Red and nitenpyram on rice seedling were 13.04% and 11.07%, with corresponding relative standard deviation values (n = 5) of 16.39% and 18.79%. A laboratory test and field trial confirmed that the developed method of using Allura Red as a tracer for spray deposition assessment is feasible and practicable. © 2019 Society of Chemical Industry.

Aerial application methods control spider mites on corn in Kansas, USA.

The Banks grass mite, Oligonychus pratensis (Banks), and two-spotted spider mite, Tetranychus urticae Koch, are important chelicerae herbivores on irrigated corn in Kansas, USA. They cause loss of foliage, stalk breakage, kernel shrinkage and yield loss. Aerial application methods were evaluated to control spider mites in a commercial corn field in August, 2017, near Hoxie, Kansas. Dimethoate (0.56kg active ingredient/ha) and Lorsban Advanced (1.05kg active ingredient/ha) mixed with a nonionic surfactant, Traverse (0.25% v/v), were aerially applied using conventional flat-fan hydraulic nozzles at 28.1L/ha and aerial electrostatic nozzles at 9.3L/ha. To assess spray droplet spectra of the aerial application methods, water sensitive paper samplers were deployed at the whorl of husk leaves at the tip of the ear before aerial spray treatments were applied. Spray droplet spectra were quantified using commercial image analysis software. Treatment efficacy was assessed both objectively and subjectively. Objective efficacy evaluation incorporated the use of an active multispectral optical sensor via spectral analysis of the midrib regions of corn leaves on the abaxial surface where spider mites reside. Subjective damage ratings based upon in-field spider mite movement observations were scored by professional crop scouting consultants. Results of objective spectral analysis and subjective damage ratings indicated that both the conventional and electrostatic nozzles with 283 and 210-µm spray droplet 'volume median diameter' (VMD) at 28.1 and 9.3 L/ha, respectively, controlled spider mites compared to an untreated check.

Aircraft measurement campaign on summer cloud microphysical properties over the Tibetan Plateau

We reported the first aircraft campaign on summer cloud microphysical properties conducted in July of 2014 over the Tibetan Plateau during the third Tibetan Plateau Atmospheric Sciences Experiment (TIPEX-III), and demonstrated that the summer clouds over the Tibetan Plateau were primarily characterized as mixed-phase cumulus clouds induced by strong solar radiation heating. Moreover, the characteristic number concentration of cloud droplets (2~50 μm in diameter) in developing cumuli was around 10 cm−3, which was about 1~2 orders of magnitudes lower than other continent and ocean regions, and that for large drops (>50 μm in diameter) was around 10−3 cm−3, which was also lower than other regions. The droplet spectrum distributions (DSDs) of cloud drops were much wider than other regions, indicating that the cumulus clouds over the plateau could form precipitation easier than that in other regions. Ice microphysics was characterized as very active glaciation and riming processes with high supercooled water content, which caused the formation of high concentration of graupel particles in clouds. The findings of this study suggest that these unique cloud microphysical properties formed by the high topography and clean environment of the Tibetan Plateau could induce higher precipitation efficiency when airflow passed over the plateau, so that the plateau could act as a regional “water tower”.

Comparison of Eulerian Bin and Lagrangian Particle-Based Schemes in Simulations of Pi Chamber Dynamics and Microphysics

Abstract This paper presents a comparison of simulations applying either a traditional Eulerian bin microphysics or a novel particle-based Lagrangian approach to represent CCN activation and cloud droplet growth. The Eulerian microphysics solve the evolution equation for the spectral density function, whereas the Lagrangian approach follows computational particles referred to as superdroplets. Each superdroplet represents a multiplicity of natural droplets that makes the Lagrangian approach computationally feasible. The two schemes apply identical representation of CCN activation and use the same droplet growth equation; these make direct comparison between the two schemes practical. The comparison, the first of its kind, applies an idealized simulation setup motivated by laboratory experiments with the Pi Chamber and previous model simulations of the Pi Chamber dynamics and microphysics. The Pi Chamber laboratory apparatus considers interactions between turbulence, CCN activation, and cloud droplet growth in moist Rayleigh–Bénard convection. Simulated steady-state droplet spectra averaged over the entire chamber are similar, with the mean droplet concentration, mean radius, and spectral width close in Eulerian and Lagrangian simulations. Small differences that do exist are explained by the inherent differences between the two schemes and their numerical implementation. The local droplet spectra differ substantially, again in agreement with the inherent limitations of the theoretical foundation behind each approach. There is a general agreement between simulations and Pi Chamber observations, with simplifications of the CCN activation and droplet growth equation used in the simulations likely explaining specific differences.

Understanding aerosol–cloud interactions through modeling the development of orographic cumulus congestus during IPHEx

Abstract. A new cloud parcel model (CPM) including activation, condensation, collision–coalescence, and lateral entrainment processes is used to investigate aerosol–cloud interactions (ACIs) in cumulus development prior to rainfall onset. The CPM was applied with surface aerosol measurements to predict the vertical structure of cloud development at early stages, and the model results were evaluated against airborne observations of cloud microphysics and thermodynamic conditions collected during the Integrated Precipitation and Hydrology Experiment (IPHEx) in the inner region of the southern Appalachian Mountains (SAM). Sensitivity analysis was conducted to examine the model response to variations in key ACI physiochemical parameters and initial conditions. The CPM sensitivities mirror those found in parcel models without entrainment and collision–coalescence, except for the evolution of the droplet spectrum and liquid water content with height. Simulated cloud droplet number concentrations (CDNCs) exhibit high sensitivity to variations in the initial aerosol concentration at cloud base, but weak sensitivity to bulk aerosol hygroscopicity. The condensation coefficient ac plays a governing role in determining the evolution of CDNC, liquid water content (LWC), and cloud droplet spectra (CDS) in time and with height. Lower values of ac lead to higher CDNCs and broader CDS above cloud base, and higher maximum supersaturation near cloud base. Analysis of model simulations reveals that competitive interference among turbulent dispersion, activation, and droplet growth processes modulates spectral width and explains the emergence of bimodal CDS and CDNC heterogeneity in aircraft measurements from different cloud regions and at different heights. Parameterization of nonlinear interactions among entrainment, condensational growth, and collision–coalescence processes is therefore necessary to simulate the vertical structures of CDNCs and CDSs in convective clouds. Comparisons of model predictions with data suggest that the representation of lateral entrainment remains challenging due to the spatial heterogeneity of the convective boundary layer and the intricate 3-D circulations in mountainous regions.

EFFECT OF NOZZLES, APPLICATION RATES, AND ADJUVANTS ON SPRAY DEPOSITION IN WHEAT CROPS

ABSTRACT The use of insecticides is common in pest management in wheat crops but may lead to higher production costs and environmental contamination. Therefore, a more comprehensive and uniform distribution of plant protection products in the desired target is recommended. The objective of this study is to evaluate the effect of different spray nozzles, application rates, and adjuvants on droplet spectrum and spray deposition in wheat crops. The physicochemical characteristics of the spray mixture, droplet spectrum, and spray deposition in wheat plants were evaluated. The lower application rate (75 L ha−1) combined with the use of the twin flat fan tip AS7030 and the adjuvant sodium lauryl ether sulfate (SLES) yielded droplets with a larger diameter. However, insecticide spraying using hollow cone tip MGA 015 without adjuvants provided the highest percentage of droplets susceptible to drift. SLES significantly decreased the percentage of drift by increasing droplet size, and the adjuvant silicone, d-limonene, and polyester copolymer increased spray deposition. The evaluated adjuvants increased the electrical conductivity and reduced the surface tension of the spray mixtures. These results indicate that it is possible to reduce the application rate from 150 to 75 L ha−1 without affecting spray deposition on wheat leaves.

Droplet distribution spectrum effects on dry ice growth on cylinders

A detailed parametric analytical study along with a series of viscid multiphase numerical simulations of ice accretion were performed in comparison with experimental data of ice accretion on a 30 mm diameter cylinder. The study was performed for droplet distribution spectra, Langmuir (A-J), in addition to an experimental droplet distribution obtained in an icing tunnel. Analysis shows that droplet distribution spectrum has a pronounced effect on cloud impingement parameters, such as droplet overall collision efficiency (E), droplet local collision efficiency (β0), droplet maximum impingement angle (θ), droplet impact velocity (V0), accreted ice mass and density. The values of these parameters can significantly change at the same operating conditions and median volume diameter (MVD) with a change of droplet distribution spectrum. These differences are more pronounced at low values of droplet inertia parameter, (K). Further experimental, analytical and numerical investigations into those aspects at lower values of droplet inertia parameter are deemed necessary in order to expand the understanding of different cloud impingement parameters on the ice accretion process and performance of current icing theory in cases with low values of K. For the low values of K, which correspond to the values of E ≤ 0.10, the use of the full droplet spectrum is recommended in calculations instead of monodispersed. In addition, based on the results of this and previous works the Langmuir D distribution is recommended as standard or “first guess” distribution.

Aircraft measurements of aerosol distribution, warm cloud microphysical properties, and their relationship over the Eastern Loess Plateau in China

In situ aircraft measurements of aerosols and clouds were performed over the eastern Loess Plateau in Shanxi Province, China. The microphysical properties of both aerosols and warm clouds, including aerosol number concentration (Na), particle effective diameter (ED), number concentration of cloud droplets (Nc), cloud droplet diameter (Dc), and liquid water content (LWC) of clouds, determined through six flight observations performed in May 2013 were obtained and analysed. The mean magnitude of measured Na over the six flights was 103 cm−3, and accumulation mode particles dominated the majority. Most EDs of aerosol particles were less than 1 μm. Large amounts of fine aerosol particles were constrained to the lower layer, with ED smaller than 0.5 μm, and Na decreased with height. The base heights of warm clouds ranged from 1000 to 2800 m. The maximum and average values of the measured Nc ranged from 147 to 311 cm−3 and 51 to 157 cm−3, respectively. The maximum and average Dc ranged from 13.5 to 28.9 and 5.8 to 13.1 μm, respectively. The average LWC of warm clouds was 0.05 g·m−3. Na was negatively correlated with Nc either in the vertical or horizontal direction. Nc was higher with a smaller size of cloud droplets under high aerosol loading conditions. A small number of cloud droplets with larger size were formed under low aerosol loading conditions. At a certain range of LWC, Nc and Dc showed a negative correlation. The increase in LWC was related to an increase in the size of cloud droplets rather than the number of cloud droplets. The cloud droplet size distribution showed that small droplets dominated the total cloud droplet concentration. A bimodal lognormal distribution function can be efficiently used to describe the average spectrum of warm cloud droplets.

Spray Application Efficiency from a Multi-Rotor Unmanned Aerial Vehicle Configured for Aerial Pesticide Application

HighlightsThe swath pattern was measured from an Agras MG-1 UAV spraying fine and extra-coarse droplet spectra.The recommended lane separation of 3.6 m did not differ for the two droplet size classes tested in this study.The applied spray deposited within the swath was higher with extra-coarse (>90%) than with fine (73%) droplets.There was potential for substantial downwind drift with fine droplets, even when flying close to the ground at low speed.Abstract. While there is increasing interest in the use of small, multi-rotor UAVs for application of agrichemicals, there is also uncertainty about their performance. Consequently, the purpose of this study was to quantify the performance of an Agras MG-1 with modified nozzle positions that, at the time of writing, was being used for commercial spraying in New Zealand. The approach was to release spray from the UAV along a single 50 m line. Spray deposits were measured using horizontal collectors placed on the ground in three 15 m transects centered on, and perpendicular to, the flight line. Airborne deposits were measured with a 10 m mast that supported spherical samplers at 1 m vertical intervals. Analysis of deposition data was undertaken to quantify factors influencing overall swath pattern variability, lane separation associated with a coefficient of variation (CV) of deposition of 30%, and spray application efficiency, which is the proportion of applied spray deposited within the swath. For two droplet size classes (extra-coarse and fine), the lane separation associated with a CV of 30% was about 3.6 m, with no significant effect of droplet size. This is a surprising result and may reflect the relatively small range of environmental conditions experienced during the field tests, including wind speed, which was relatively low for all tests. We speculate that this result may also be a consequence of the strong downwash. The swath width was positively correlated with wind speed. Spray efficiency was shown to be high (>90%) for the extra-coarse droplets but dropped significantly (73%) with the fine droplet spectrum. Combining in-swath deposition with the amount of airborne spray sampled in a 10 m vertical profile close to the edge of the swath accounted for 98.0% of the spray released with the extra-coarse spectrum but only 88.6% of the spray with the fine droplet spectrum. These results highlight that even with UAVs flying relatively close to the ground at a low forward speed, there is potential for substantial drift downwind of the swath when using smaller droplet size classes. Overall, the swath pattern was reasonably consistent across the two droplet size classes and for the narrow range of operational and meteorological conditions tested. Keywords: Aerial spraying, Pesticides, Spray application efficiency, Spray deposition, Swath pattern, UAV, Unmanned aerial vehicle.

Electrostatically charged aerial application improved spinosad deposition on early season cotton

Spinosad (Tracer™), produced by an actinomycete, Saccharopolyspora spinosa, was aerially applied on early season cotton at a spray rate of 9.35 L ha−1 with a bipolar electrostatic aerial spray system, charged on and off. The charge-to-mass ratio (Q/M) for spinosad was 0.7714 mC kg−1 at ±9.0 kV charging voltage. Electrostatically charged sprays significantly increased deposition on an artificial collector by 34.5% compared to uncharged sprays. Spray droplet spectra was significantly greater for the electrostatically charged application than that for the uncharged application. This study can provide guidance to aerial applicators for increasing spray deposits on early season cotton.

CFD water spray model development and physical parameter study on the evaporative cooling

Polydisperse evaporating spray study is complex due to the influence of a large number of physical parameters. Several studies have performed CFD simulations to investigate the cooling performance of water spray systems, but a few have investigated their impact upon heat exchangers. For industrial applications, developing a new and simple approach to simulate polydisperse evaporating sprays upon complex 3D geometries is of great interest. Thus this paper is the first contribution to a CFD numerical tool development to study water spray impact on heat exchangers and presents a CFD water spray model. The spray model is divided into two steps: the spray formation and its dispersion in air flow. The spray development step describes the moment from droplet injection to the position where droplet velocity equals air velocity. This position and the spray dimension are accessed through the droplet trajectory analysis, while the amount of liquid water evaporated is obtained by integrating the droplet size decrease equation. This first part provides boundary conditions for the second step used in a 3D CFD software: Code_Saturne. This CFD code solves the Navier-Stokes equations for the spray with the k-ε turbulence model. Three transport variables are introduced: the liquid potential temperature, θL, the total water specific humidity, qw, which are conservative variables for the evaporation processes; and the total number, of droplets, Nc. The droplet evaporation is added to the Nc equation through a source term approach. A lognormal law is also used to represent and follow the evolution of the droplet spectra. The model results are compared with experimental results from droplets injected in counter-flow configurations in a wind tunnel. Temperature fields show good agreements with the experimental data. Finally, this paper provides a parametric analysis of water evaporation and air cooling upon a specified surface. The impacts of the relative humidity, spray angle, water mass flow rate and droplet size distribution are investigated. Our approach is an alternative to classical Lagrangian approaches used in spray applications. It provides accurate and consistent results with low computational time in comparison with the literature.

Observational Study on the Supercooled Fog Droplet Spectrum Distribution and Icing Accumulation Mechanism in Lushan, Southeast China

A fog monitor, hotplate total precipitation sensor, weather identifier and visibility sensor, ultrasonic wind speed meter, an icing gradient observation frame, and an automated weather station were involved in the observations at the Lushan Meteorological Bureau of Jiangxi Province, China. In this study, for the icing process under a cold surge from 20–25 January 2016, the duration, frequency, and spectrum distribution of agglomerate fog were analyzed. The effects of rain, snow, and supercooled fog on icing growth were studied and the icing and meteorological conditions at two heights (10 m and 1.5 m) were compared. There were 218 agglomerate fogs in this icing process, of which agglomerate fogs with durations less than and greater than 10 min accounted for 91.3% and 8.7%, respectively. The average time interval was 10.3 min. The fog droplet number concentration for sizes 2–15 μm and 30–50 μm increased during rainfall, and that for 2–27 μm decreased during snowfall. Icing grew rapidly (1.3 mm h−1) in the freezing rain phase but slowly (0.1 mm h−1) during the dry snow phase. Intensive supercooled fog, lower temperatures and increased wind speed all favored icing growth during dry snow (0.5 mm h−1). There were significant differences in the thickness, duration, density, and growth mechanism of icing at the heights of 10 m and 1.5 m. Differences in temperature and wind speed between the two heights were the main reasons for the differences in icing conditions, which indicated that icing was strongly affected by height.

Numerical investigations for the impacts of triple-moment and double-moment condensation schemes on the warm rain formation

ABSTRACTThe initiation and intensity of warm rain are processes dominated by the evolution of cloud droplet spectra. To treat the cloud condensation process properly is a fundamental step for the simulation of warm rain formation. Double-moment bulk schemes with a limited number of prognostic variables cannot simulate the evolution of droplet spectra properly. A triple-moment bulk scheme, however, should overcome the problem of spurious cloud droplet spectrum broadening induced by double-moment schemes. To compare the effects of a newly developed triple-moment scheme with double-moment schemes on warm rain formation, the authors conducted WRF-LES numerical simulations to investigate the impacts of the two types of condensation scheme on rain initiation and intensity. In the early stage of raindrop formation, the simulation with the triple-moment scheme delays the raindrop initiation and produces droplet spectra with smaller average radii than those with the double-moment scheme. In the developing stage, t...

CCN Spectral Shape and Stratus Cloud and Drizzle Microphysics

AbstractThe shapes of high‐resolution cloud condensation nucleus (CCN) spectra are compared with cloud and precipitation characteristics observed in the Marine Stratus/Stratocumulus Experiment. These high‐resolution spectra often revealed bimodality that is usually caused by in‐cloud processing. Bimodal CCN spectra were associated with clouds that had as much as double the concentrations of droplets with narrower distributions and as much as an order of magnitude less drizzle than clouds associated with the most extreme unimodal CCN spectra. We introduce objective CCN spectral metrics: (1) CCN concentration differences between the two modes, unprocessed (Aitken, Nu) and processed (accumulation, Np), and (2) slopes of cumulative CCN spectra. Both of these CCN spectral shape classifications show similar cloud droplet concentration (Nc) trends to that of an earlier subjective modal rating system. When there are two modes, they are separated either by minimal concentrations or concentration inflections. Enhancement of Nc is traced to greater CCN bimodality that causes narrower droplet spectra that suppress drizzle. These effects could augment indirect aerosol effects and can only be revealed by high‐resolution CCN spectral shape comparisons with cloud and drizzle microphysics.

INSECTICIDE SPRAYING IN SOYBEAN PLANTS: DIFFERENT NOZZLES MODELS AND AGROMETEOROLOGICAL CONDITIONS

ABSTRACT The aim of the experiment was to evaluate the quality of the spraying by the spray volume deposit provided by different nozzles models in two agrometeorological conditions of application. Four parameters related to spray quality were evaluated: spray volume deposit, droplet size, surface tension and contact angle. The treatments consisted of three nozzle models (AXI Twin 12002, TTJ 110015 and JAI 120015) and two application times (between 02:00 p.m. and 04:00 p.m. and between 08:00 a.m. and 09:30 a.m.). The spray volume deposit in the upper portion of the soybean plants was similar, but the JAI 120015 nozzle model produces more uniform droplet spectra and is safer than the AXI Twin 12002 and TTJ 110015 due to the highest drift risk. It is necessary to study alternatives that increase spray deposits in the lower portion of the crop, since in this study the distribution uniformity of the mixture in the portions of the soybean plant was low and the agrometeorological conditions interferes in the deposits of the sprayed mixture but is dependent on the selected nozzle model.

Towards an enhanced droplet activation scheme for multi-moment bulk microphysics schemes

Initial droplet spectra produced upon activation impact the ensuing chain of microphysical processes and therefore play a crucial role in cloud evolution. This work re-examines dependencies of newly formed cloud droplet size distribution (CDSD) characteristics on environmental and aerosol properties via parcel model simulations that serve as the basis for a multi-moment bulk microphysics droplet activation scheme suitable for a cloud-resolving model (CRM). It is found that applying a fixed size threshold to define activated droplets versus employing physical considerations can lead to erroneous activation and overly broad CDSDs for high aerosol concentration and weak updraft conditions. Aerosol distributions characterized by larger median sizes and/or increased solubility can result in greater activated droplet numbers, whereas impacts of these parameters on CDSD spectral width depend on both aerosol number concentration and updraft velocity. An expansion of the activation scheme to include CDSD spectral width is proposed to aid efforts to extend high-order moment prediction to cloud droplet categories in CRMs as well as better represent variability in the activation process on the cloud scale.