Mesoscale Systems Research Articles

ИССЛЕДОВАНИЕ РАДИОЛОКАЦИОННЫХ ХАРАКТЕРИСТИК ОБЛАЧНЫХ СИСТЕМ ПРИ ВЫПАДЕНИИ СИЛЬНЫХ ДОЖДЕЙ

The paper analyzes radar characteristics of mesoscale precipitation systems associated with heavy precipitation in Western Urals. The characteristics under study, obtained from the Doppler weather radar, include the maximum height of the radar echo of clouds and precipitation, meteorological phenomena, speed and direction of the radar echo movement. An attempt was made to classify mesoscale precipitation systems with respect to their horizontal scales and geometrical features as well as precipitation patterns. Statistical features of radar characteristics of cloud systems causing heavy rain were calculated taking into account their classification by horizontal scales. Radar meteorological characteristics were obtained from instruments in the Izhevsk city and Ufa city for the warm period of 2016–2017. The results can be used during nowcasting of heavy precipitation events.

Mapping water vapour variability over a mountainous tropical island using InSAR and an atmospheric model for geodetic observations

The three dimensional distribution of water vapour around mountainous terrain can be highly variable. This variability can in turn affect local meteorological processes and geodetic techniques to measure ground surface motion. We demonstrate this general problem with the specific issues of a small tropical island, Montserrat. Over a period of 17 days in December 2014 we made observations using InSAR and GPS techniques, together with concurrent atmospheric models using the WRF code. Comparative studies of water vapour distribution and its effect on refractivity were made at high spatial resolution (300 m) over short distances (~10 km). Our results show that model simulations of the observed differences in water vapour distribution using WRF is insufficiently accurate. We suggest that better use could be made of the knowledge and observations of local water vapour conditions at different scales, specifically the Inter Tropical Convergence Zone (ITCZ), the trade wind fields and the mountain flow (~30 m) perhaps using eddy simulation. The annual perturbations of the ITCZ show that the range of humidity is approximately the same expressed as the differential phase of InSAR imaging (~100 mm). Trade wind direction and speed are particularly important at high wind speeds driving vigorous asymmetrical convection over the island's mountains. We also show that the slant angles of radar can follow distinct separate paths through the water vapour field. Our study is novel in demonstrating how synoptic-scale features and climate can advise the modelling of mesoscale systems and sub-seasonal InSAR imaging on tropical islands.

A Review of Research on Warm-Sector Heavy Rainfall in China

Warm-sector heavy rainfall (WSHR) events in China have been investigated for many years. Studies have investigated the synoptic weather conditions during WSHR formation, the categories and general features, the triggering mechanism, and structural features of mesoscale convective systems during these rainfall events. The main results of WSHR studies in recent years are summarized in this paper. However, WSHR caused by micro- to mesoscale systems often occurs abruptly and locally, making both numerical model predictions and objective forecasts difficult. Further research is needed in three areas: (1) The mechanisms controlling WSHR events need to be understood to clarify the specific effects of various factors and indicate the influences of these factors under different synoptic background circulations. This would enable an understanding of the mechanisms of formation, maintenance, and organization of the convections in WSHR events. (2) In addition to South China, WSHR events also occur during the concentrated summer precipitation in the Yangtze River-Huaihe River Valley and North China. A high spatial and temporal resolution dataset should be used to analyze the distribution and environmental conditions, and to further compare the differences and similarities of the triggering and maintenance mechanisms of WSHR events in different regions. (3) More studies of the mechanisms are required, as well as improvements to the model initial conditions and physical processes based on multi-source observations, especially the description of the triggering process and the microphysical parameterization. This will improve the numerical prediction of WSHR events.

The Role of Continental Mesoscale Convective Systems in Forecast Busts within Global Weather Prediction Systems

Despite significant, steady improvements in the skill of medium-range weather prediction systems over the past several decades, the accuracy of these forecasts are occasionally very poor. These forecast failures are referred to as “busts” or “dropouts”. The lack of a clear explanation for bust events limits the development and implementation of strategies designed to reduce their occurrence. This study seeks to explore a flow regime where forecast busts occur over Europe in association with mesoscale convective systems over North America east of the Rocky Mountains. Our investigation focuses on error growth in the European Centre for Medium-Range Weather Forecasting’s (ECMWF’s) global model during the summer 2015 PECAN (Plains Elevated Convection at Night) experiment. Observations suggest that a close, but varied interrelationship can occur between long-lived, propagating, mesoscale convection systems over the Great Plains and Rossby wave packets. Aloft, the initial error occurs in the ridge of the wave and then propagates downstream as an amplifying Rossby wave packet producing poor forecasts in middle latitudes and, in some cases, the Arctic. Our results suggest the importance of improving the representation of organized deep convection in numerical models, particularly for long-lived mesoscale convective systems that produce severe weather and propagate near the jet stream.

Valuation of Weather Manifested Rice Cultivation in Bangladesh: A Way Forward

Good crop yield entirely depends on good management practice and quality management of crops allied with authentic weather forecasting can reduce risk, crop damage, cost of production and increase the yield as well. Bangladesh Rice Research Institute (BRRI) had aimed this study for quantifying the financial benefit of forecasting and validating micro climatological factors and their impacts on paddy production through experimentation and arranging for weather based agro meteorological advisory service delivery to the farmers applying the tools of ICT. A next-generation meso-scale numerical weather prediction system, WRF (Weather Research and Forecasting) model was used for generating atmospheric simulations based on real data (observations, analyses or idealized conditions). Field experiment was conducted in the areas of five different agro microclimatological conditions for Boro rice production, namely; Gazipur, Habiganj, Rajshahi, Barishal and Satkhira. Then the experimental fields were managed according to the weekly management advisory based on weather forecasts. Results obtained suggest that the application of weather predictability accrued a comparative rice yield benefit of 9-12% and a 3–5% reduction in the cost of cultivation. Countrywide application of agro-meteorological advisory service may pave the way for averting adverse climatic effects on agriculture.

Meso-structural characteristics of asphalt mixture main skeleton based on meso-scale analysis

To provide a reference for the gradation design of dense skeleton asphalt mixture (DSAM), a meso-scale main skeleton structural system with a contact chain as the medium scale, composed of coarse aggregates and contact points, contact chains, and a main skeleton, is proposed in this study. Based on the theoretical analysis of the main contact chain structure stability, the statistical characteristics of the main skeleton, contact chain of the asphalt mixtures, as well as their gradual behaviour under loading, were studied using the digital image processing (DIP) techniques. At last, the corresponding meso-evaluation indices and design criteria for the main skeleton were proposed. The results indicate that the factors affecting the stability of the main contact chain include the particle size of the coarse aggregate, the length, structure, and direction of the main contact chain, and the cohesion of asphalt binder. Coarser gradation and a shorter contact chain, as well as a linear main contact chain with the same load action direction, exhibit greater stiffness and superior resistance to deformation. A lower number of contact chains and longer contact chains in the asphalt mixture result in a more perfect main skeleton. When creating asphalt mixture specimens using the wheel rolling method, the design criteria of the main skeleton structure meso-index should reach Ks ≥ 80% and Nn ≤ 37. The design criteria can be used as a reference basis for the design of DSAM with a nominal maximum particle size of 13.2 mm, ensuring that the coarse aggregates are interlocked to form a stable main skeleton.

Effects of Topographic Perturbation on the Precipitation Distribution in Sichuan

Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect effects of topographic dynamic forcing on the atmosphere. The one-dimensional weighted-average spatial spectral analysis method is used to explore topographic forcing on precipitation distribution in Sichuan. Results indicate that spectral distributions of terrain and winter precipitation in zonal direction present a typical resonance coupling pattern, while that of terrain and precipitation in other seasons drifts toward the smaller scale. In meridional direction, spectral distributions of terrain and precipitation in each season present the large-scale drift pattern. Different patterns are probably relevant to the change of circulations. In winter, due to strong zonal circulation and weak meridional circulation, atmospheric fluctuations caused by zonal topographic forcing show the most significant impact on precipitation. After that season, the zonal circulation weakens gradually in agreement with the decrease of zonal topographic forcing while the meridional flow enhances, leading to the increase of the damping of the zonal wind disturbance caused by terrain, and the pattern transforms from resonance to drift. Summer rainfall is produced by interaction among different scale systems, and terrain is one of the most important factors. The maximum topographic spectral energy in zonal direction is about an order of magnitude larger than that in meridional direction, implying that effects of topographic dynamic forcing are zonally stronger than that in meridional direction. Values of meridional and zonal topographic characteristic scales are 296.8 km and 475.8 km, respectively, which reflects the characteristic of the mesoscale topographic forcing coincident with the frequent mesoscale systems in Sichuan. The peak of the precipitation spectral energy in summer is about two orders of magnitude larger than that in winter and one order of magnitude larger than that in spring or autumn, and the characteristic scale in summer is about 150 km smaller than that in winter. It illustrates that the intensity of the zonal topographic dynamic forcing in summer is significantly increased when the scale of precipitation systems decreases, which explains the high frequency of mesoscale convective precipitation, and implies the significant impact of topographic dynamic forcing on atmosphere as well. The strongest summer precipitation in Sichuan is located at Ya'an, where larger-scale topographic perturbation is more significant than other region in Sichuan. The terrain spectra and summer precipitation spectra in meridional direction are phase-locked in identical wavelength (37.1 km), implying the critical role of terrain on the occurrence of heavy rainfall, and the effect of topographic dynamic forcing in meridional direction is dominant.

Tuning Conjugated Polymers for Binder Applications in High-Capacity Magnetite Anodes

Battery electrodes are complex mesoscale systems comprising an active material, conductive agent, current collector, and polymeric binder. Although significant research on composite electrode materials for Li-ion batteries focuses on the design, synthesis, and characterization of the active particles, the binder component has been shown to critically impact stability and ensure electrode integrity during volume changes induced upon cycling. Herein, we explore the ability of water-soluble, carboxylated conjugated polymer binders to aid in electron and ion transport in magnetite-based anodes. Specifically, poly[3-(potassium-4-butanoate)thiophene] (PPBT) and a potassium carboxylate functionalized 3,4-propylenedioxythiophene (ProDOT)-based copolymer (WS-PE2) were investigated and evaluated against the control, potassium salt form of poly(acrylic acid) (PAA-K). When used in conjunction with a polyethylene glycol (PEG) surface coating for the magnetite active material, PPBT provided for overall improved electro...

Hydroeconomic optimization of mesoscale blue-green stormwater systems at the city level

The development of tools to help cities and water utility authorities communicate and plan for long-term sustainable solutions is of utmost importance in the era of a changing and uncertain climate. This study introduces a hybrid modeling concept for the cosimulation of mesoscale blue-green stormwater systems and conventional urban sewer networks. The hybrid model successfully introduces the retention/detention effects of mesoscale blue-green stormwater systems to the hydraulic dynamics of the sewer network. The cosimulation package was further facilitated with a cost-oriented multiobjective optimization algorithm. The aim of the scalar multiobjective optimization was to minimize the total cost comprising both flooding costs and action costs – both parameters solely representing the financial components of cost – through optimal placement of mesoscale blue-green systems of optimal size. The suggested methodology provides a useful platform for sustainable management of the existing sewer networks in cities from a hydroeconomic perspective.

SPATIOTEMPORAL VARIATION IN THE PRECIPITATION OF THE AMAZON COASTAL ZONE: USE OF REMOTE SENSING AND MULTIVARIATE ANALYSIS

Reliable data on the spatiotemporal variability in precipitation patterns are vital to the development of effective public policies for environmental management. The analysis of the variation in rainfall rates is currently limited severely by the dependence on data from rain gauges, in particular in regions with a relatively sparsely-distributed network of meteorological stations, as in the Amazon region. The present study investigated the variability in the precipitation and the principal rainfall patterns at different time scales in the coastal zone of the Amazon region, and associated these patterns with the precipitant meteorological systems present in the region. The study was based on the application of remote sensing (CMORPH) data taken at half-hourly intervals on a 0.088 latitude/longitude scale. The spatiotemporal variability in the region’s precipitation was analyzed at different time scales (monthly, seasonal, and annual), with distribution patterns being assessed using a Principal Components Analysis (PCA). The estimates obtained from the CMORPH data provided a satisfactory overview of the precipitation climatology of the study region at the distinct time scales. The PCA identified a precipitation gradient in the two principal pluviometric modes, which together explained 88% of the total variance in the data. The first mode explained 83% of the variance, with two distinct periods, a rainy season and a dry (or less rainy) period, which are influenced by large-scale precipitant systems, the Intertropical Convergence Zone (ITCZ) and High Level Cyclonic Vortices (HLCVs). The second mode, which explains 5% of the variance in the rainfall data, is associated with mesoscale systems that affect primarily the transition periods between the seasons, and depend on the southern extreme of the annual shift in the ITCZ. The understanding of the variation of precipitation patterns using high-resolution CMORPH data, with a comprehensive coverage in both time and space, provides an effective tool for the establishment of public policies at a municipal level, in particular the development of models, and the mediation of the vulnerability of local populations to climatic extremes.

Interpretation of the Tropospheric Gradients Estimated With GPS During Hurricane Harvey

During the last decade Global Positioning System (GPS) Continuous Operating Reference Stations networks have become a new important data source for meteorology. This has dramatically improved the ability to remotely sense the atmosphere under the influence of severe mesoscale and synoptic systems. The zenith tropospheric delay (ZTD) is one of the atmospheric variables continuously observed, and its horizontal variations, the horizontal tropospheric gradients, are routinely computed nowadays within the dual‐frequency GPS processing, but their interpretation and relationship with the weather is still an open question. The purpose of this paper is to contribute in this direction by studying the effect that Hurricane Harvey had on the spatial and temporal behavior of the ZTDs and gradients, when it reached Texas coast, during 18–31 August 2017. The results show that ZTD time series present a clear and rapid increase larger than 10 cm in a few hours when the hurricane reached the area. Gradients behaviors show that the hurricane also produced significant changes on them, since the magnitude and predominant directions before and after the hurricane arrived are completely different. Noticeably, the gradient vectors before the landing are consistently related to the horizontal winds and pressure fields. In this manuscript we demonstrate that the ZTD gradients can show a consistent signature under severe weather events, strongly suggesting their potential application for short‐term weather forecasting.

Study of Pre-Monsoon Thunderstorms and Associated Thermodynamic Features Over Bangladesh Using WRF-ARW Model

Thunderstorm is a mesoscale system (from a km to below thousands of km and sustaining less than one hour). Two pre-monsoon thunderstorms events are analyzed in this study which are named as event-1 (0030-0150 UTC of 19 April 2018 over Chattogram) and event-2 (0600-1000 UTC of 4 May 2018 over Dhaka). To predict these events Mean Convective Available Potential Energy (mCAPE), Mean Convective Inhibition Energy (mCINE), K Index (KI), Total totals Index (TTI), wind distribution, and relative humidity (RH) are investigated.The model simulated mCAPE and mCINE values, 18 hours before the events, are found greater than 1700 J/Kg and less than 100 J/Kg respectively which satisfies the conditions for thunderstorms to occur.The KI values are close to 400C and TTI values are greater or equal to 450C for both events. The wind patterns and the high value of mid –tropospheric RH also favors the formation of severe thunderstorm.
 Dhaka Univ. J. Sci. 67(2): 151-156, 2019 (July)

CALIOPE-Urban v1.0: coupling R-LINE with a mesoscale air quality modelling system for urban air quality forecasts over Barcelona city (Spain)

Abstract. The NO2 annual air quality limit value is systematically exceeded in many European cities. In this context, understanding human exposure, improving policy and planning, and providing forecasts requires the development of accurate air quality models at the urban (street level) scale. We describe CALIOPE-Urban, a system coupling CALIOPE – an operational mesoscale air quality forecast system based on the HERMES (emissions), WRF (meteorology) and CMAQ (chemistry) models – with the urban roadway dispersion model R-LINE. Our developments have focused on Barcelona city (Spain), but the methodology may be replicated for other cities in the future. WRF drives pollutant dispersion and CMAQ provides background concentrations to R-LINE. Key features of our system include the adaptation of R-LINE to street canyons, the use of a new methodology that considers upwind grid cells in CMAQ to avoid double counting traffic emissions, a new method to estimate local surface roughness within street canyons, and a vertical mixing parameterisation that considers urban geometry and atmospheric stability to calculate surface level background concentrations. We show that the latter is critical to correct the night-time overestimations in our system. Both CALIOPE and CALIOPE-Urban are evaluated using two sets of observations. The temporal variability is evaluated against measurements from five traffic sites and one urban background site for April–May 2013. While both systems show a fairly good agreement at the urban background site, CALIOPE-Urban shows a better agreement at traffic sites. The spatial variability is evaluated using 182 passive dosimeters that were distributed across Barcelona during 2 weeks for February–March 2017. In this case, the coupled system also shows a more realistic distribution than the mesoscale system, which systematically underpredicts NO2 close to traffic emission sources. Overall CALIOPE-Urban improves mesoscale model results, demonstrating that the combination of both scales provides a more realistic representation of NO2 spatio-temporal variability in Barcelona.

Aire Limitée Adaptation dynamique Développement InterNational – Limited Area Ensemble Forecasting (ALADIN-LAEF)

Abstract. A meso-scale ensemble system Aire Limitée Adaptation dynamique Développement InterNational – Limited Area Ensemble Forecasting (ALADIN-LAEF) based on the limited area model ALADIN has been developed in the framework of Regional Cooperation for Limited Area modelling in Central Europe (RC LACE) consortium, focusing on short range probabilistic forecasts and profiting from advanced multi-scale ALARO physics. Its main purpose is to provide probabilistic forecast on daily basis for the national weather services of RC LACE partners. It also serves as a reliable source of probabilistic information applied to downstream hydrology and energy industry.

(Invited) Proton Pump for Solar Energy Transformation:from Nano- to Meso-Scale Architectures

Proton pumps are group of membrane proteins which carry out proton (H+) transfer across a biological membrane via energy-driven conformational changes in their structures. Light-driven proton pumps utilize sunlight energy to fuel ATP-synthase. Light is absorbed by the retinal cofactor that results in photoisomeriazation of the chromophore that leads to proton translocation through a membrane. Earlier we demonstrated that semiconductor nanoparticles can be self-assembled with membrane-proton pump complexes known as purple membranes (PM), wherein PM can be either isolated from microorganism as micron-scale patches [1,2] or synthesized cell-free as nano-sized particles [3]. These bio-inorganic constructs can be used for efficient water splitting systems in photocatalytic hydrogen production half-reaction. Catalytic activity of these assemblies can be boosted via variety of approaches, for example, control and scaling down of the soft material dimensions [3], introduction of a single atomic layer carbon material [2]. Further efforts are directed toward more complex meso-scale artificial systems for sunlight energy transformation to other fuels and useful products. 1.S. Balasubraanian, P. Wang, R. Schaller, T. Rajh, E.A. Rozhkova, NanoLetters 13, 3365−3371 (2013) P. Wang, N.M. Dimitrijevic, A.Y. Chang, R.D. Schaller, Y. Liu, T. Rajh, E.A. Rozhkova, ACS Nano, 8(8), 7995-8002 (2014)P. Wang, A. Y. Chang, V. Novosad, V. V. Chupin, R.D. Schaller, E. A. Rozhkova, ACS Nano, 11 (7), pp 6739–6745 (2017)

An experimental investigation on the electrospray characteristics in a meso-scale system at different modes

An experimental study on electrospray characteristics is carried out using a steel capillary as the nozzle and the grounded steel mesh as the collector of droplets in a meso-scale system. The liquid ethanol is atomized by the electrostatic field. Four spraying modes (pulsed-jet, cone-jet, skewed cone-jet, multi-jet) are visualized along with the increase of applied voltage on the nozzle. The droplet size, velocity and RMS (root mean square) velocity are measured using PDA (Phase Doppler Anemometer). It is found that both specific charge and axial electric field around the nozzle increase when the four different spraying modes change in sequence. The most of atomization of liquid ethanol often occurs around the nozzle outlet, which is inferred from the calculated results of axial electric field distributions. The droplet size decreases when the four different spraying modes change in sequence, because the increasing specific charge and electric field force lead to further break up of liquid droplets. At the same cross section of z = 10 mm, the axial velocity at the pulsed-jet mode is the largest and the axial velocity is nearly the same for cone-jet mode, skewed cone-jet mode and multi-jet mode. The distribution of RMS velocity at four spraying modes indicates that electrospray is fluctuant at the pulsed-jet mode and it is stable at the cone-jet mode, skewed cone-jet mode and multi-jet mode. The droplet is accelerated from the nozzle due to the stronger electric field intensity around the nozzle, but the droplet velocity has little change due to the lower electric field intensity after z = 10 mm. Theoretical analysis is performed based on the Rayleigh limit model, and it is found that the Rayleigh limit coefficient is between 0.4 and 0.6 at the cone-jet mode, between 0.2 and 0.4 at the pulsed-jet mode and the skewed cone-jet mode, and below 0.2 at the multi-jet mode.

Closing the gap between atomic-scale lattice deformations and continuum elasticity

Crystal lattice deformations can be described microscopically by explicitly accounting for the position of atoms or macroscopically by continuum elasticity. In this work, we report on the description of continuous elastic fields derived from an atomistic representation of crystalline structures that also include features typical of the microscopic scale. Analytic expressions for strain components are obtained from the complex amplitudes of the Fourier modes representing periodic lattice positions, which can be generally provided by atomistic modeling or experiments. The magnitude and phase of these amplitudes, together with the continuous description of strains, are able to characterize crystal rotations, lattice deformations, and dislocations. Moreover, combined with the so-called amplitude expansion of the phase-field crystal model, they provide a suitable tool for bridging microscopic to macroscopic scales. This study enables the in-depth analysis of elasticity effects for macroscale and mesoscale systems taking microscopic details into account.

Development of Dust Storm Modeling for Use in Freeway Safety and Operations Management: An Arizona Case Study

Extreme weather conditions such as strong winds, hail, heavy rainfall, heavy snowfall, and high air temperature impact roads, traffic, and operational decisions. Strong winds in arid regions may pick up fine dust particles and create massive blowing plumes dramatically reducing the visibility. This reduced visibility severely impairs driving ability causing catastrophic crashes. The purpose of this research was to investigate the impacts of dust storms on freeway safety and operations. Interstates 8, 10, 15, 17, 19, and 40 running through Arizona were studied in relation to dust loading and crash risks. To achieve this, nine severe Arizona dust storms (2009–2016) were modeled using Weather Research and Forecasting (WRF) model coupled with a chemistry module (WRF-Chem). WRF is a mesoscale numerical weather prediction system with a software architecture allowing for parallel computation. When coupled with a chemistry module (WRF-Chem), it could be used to model the fate and transport of the particulate matter. Dust hot spots were calculated based on Getis-Ord Gi* statistical method and were correlated to dust storm caused crashes. It was shown that a positive Gi* accompanied by dust loading of at least 50 kgm–2 will result in a crash with a 90% confidence level. The outcome of this research could be used by local and federal transportation agencies to communicate warnings to drivers for improved safety.

Spatiotemporal Distribution Characteristics of Mesoscale Convective Systems Producing Short-Duration Heavy Rainfall over the Tianshan Mountain Area

Based on hourly precipitation data and FY-2 satellite infrared (IR) digital satellite imagery collected during the warm season from 2005 to 2015 in the Tianshan Mountains and the adjacent areas in Xinjiang, China, the definition of mesoscale convective systems (MCSs) was revised based on short-duration heavy precipitation processes. The spatiotemporal development of MCSs in terms of the initiation, maturation, dissipation, duration, and movement was statistically analyzed. Most mesoscale systems in the area were dominated by meso-β convective systems (MβCSs), which was in line with the annual heavy precipitation frequency. In meso-α convective systems (MαCSs), persistent elongated convective systems (PECSs) occurred more commonly than mesoscale convective complexes (MCCs). MCSs were common in summer, with the peak frequency of MαCS occurrence in June and the peak frequency of MβCS occurrence mainly in July and August. From the perspective of diurnal variations, MCSs initiated in the late afternoon, developed during the evening, and dissipated before midnight. MCSs in general lasted 6∼9 h between June and July and 9∼11 h in August. The MαCSs lasted approximately 14 h, and the MβCSs lasted from 7 h to 12 h. The development and termination stages of MCSs lasted 3∼6 h and 2∼7 h, respectively. In low-elevation areas and on the windward slope of the mountains, MCSs initiated more easily and more frequently over the northern and western slopes than that over the southern and eastern slopes. The central area of the Junggar basin hosted the development of MCSs, but the distribution of the convective systems at different scales varied. During the termination stage, these mesoscale systems were mainly located at the basin edges. In terms of tracks, most MCSs moved eastward under the influence of the westerlies and the MαCSs moved faster but in a more scattered manner than the MβCSs. Additionally, some unusual tracks appeared because of the effects of the underlying surface topography and environmental wind.

Optical forces and torques exerted on coupled silica nanospheres: novel contributions due to multiple scattering

When illuminated by light, optically coupled nanoparticles suffer the action of multiple electromagnetic forces. In general, two kinds of forces are assumed: binding forces that make the particles attract/repel each other and scattering forces that push the system forwards. Tangential forces and orbital torques can also be induced to align the interacting particles with the electric field. In this work, new degrees of freedom were found for two coupled silica nanospheres under illumination with linearly-polarized plane waves. The results have a general validity for arbitrary mesoscale systems: multiple scattering of light induces unusual torques and deviation forces. These torques include spin contributions to the movement of the whole system. The results are supported by previous works and pave the way for the engineering of nanoscale devices and nanorotators. Any application based on photonics at mesoscales should take into account the new movements predicted here.