Investigation of the action of hygroscopic particles on a warm convective cloud from the results of numerical simulation

The results of a numerical simulation of the action of hygroscopic particles on a warm convective cloud with the purpose of obtaining additional precipitation are presented. The one-dimensional numerical model considered in this work describes the evolution of the cloud medium in the central part of an axisymmetric convective cloud at the specified height-variable velocity of the upward air flow which forms the cloud. Our model comprehensively describes microphysical processes in the cloud medium with the use of the kinetic equation for the size distribution of cloud droplets. This model makes it possible to obtain the spatiotemporal pattern of the cloud formation and development and to analyze regular features in the cloud evolution under the action of hygroscopic reagents. The cloud characteristics calculated with the use of this model correspond to the cloud parameters observed in natural conditions of the atmosphere. The process of precipitation stimulation by hygroscopic particles in convective clouds with vertical thicknesses of 2.5–4.5 km was analyzed on the basis of the results of numerical calculations. The results of calculations of the dependence of the intensity and total amount of precipitation on the vertical cloud thickness and parameters of particles introduced into the cloud are presented. It is shown that hygroscopic particles with root-mean-cube radii of 1–1.5 μm are the most effective for acting on warm convective clouds with the purpose of obtaining additional precipitation. In this case, the required reagent expenditure is 100–200 kg/km². The conditions necessary for obtaining the maximal positive effect of the action are elucidated.     

Study of the possibility of stimulating precipitation from warm convective clouds by hygroscopic particles from numerical simulation

We present the results of numerical simulation of the action of hygroscopic particles on a convective cloud for obtaining additional precipitation. The correspondence of vertical profiles of cloud parameters to those actually observed under natural atmospheric conditions is achieved within a one-dimensional numerical model by parametrization of the process of heat and moisture entrainment into the upward air flow forming the cloud. The model describes in detail microphysical processes in a cloud with the use of the kinetic equation for the size distribution of cloud droplets. The processes of forming precipitation in convective clouds with a vertical thickness of 3–4 km during their natural development and during the introduction of hygroscopic particles are analyzed using numerical calculations. It is shown that it is actually possible to obtain additional precipitation from convective clouds of continental type under the action of hygroscopic particles with sizes of 1–1.5 μm. The results of calculating the intensity and total amount of precipitation as functions of the vertical thickness of a cloud and the parameters of particles introduced into it are presented. The conditions necessary for obtaining the maximum positive effect are elucidated.     

Scavenging trace gases from an arbitrary dynamical source in the below-cloud layer of the atmosphere

We consider the scavenging of trace gases in the below-cloud layer with their evaporation from droplets and atmospheric turbulent diffusion. This problem is solved by the method of splitting into physical processes where the dynamics of scavenging of trace gases is treated separately on the background of atmospheric diffusion and transport. These processes produce a dynamical background source of trace gases. We obtain a general solution of kinetic equations of scavenging for a source with an arbitrary background distribution. This solution is analyzed for two limiting cases: slow and fast time-varying sources (compared to the process of scavenging). The results of illustrative calculations are presented and practical recommendations are given on the calculation of the scavenging rate for numerical systems.     

Simulation of the indirect impact that the 11-year solar cycle has on the gas composition of the atmosphere

An interactive three-dimensional chemistry-climate model combining models of the gas composition and general circulation of the lower and middle atmosphere is used to study the impact of changes in extra-atmospheric solar radiative fluxes induced by solar activity on the stratospheric heating and subsequent temperature and ozone variations in the stratosphere and troposphere. The results have shown that a change in the atmospheric radiative heating resulting from variations in solar activity has a direct effect on the temperature and circulation of the atmosphere. Atmospheric temperature variations affect the rates of temperature-dependent chemical reactions, and this is considered the first type of indirect impact of solar activity on the atmospheric gas composition. On the other hand, as a result of the variation in atmospheric heating, its circulation changes, thus affecting the transport of minor gases into the atmosphere. This effect is considered the second type of indirect impact of solar activity on atmospheric gases. The results of our calculations have shown that both types of indirect impact of the variation in solar activity on the atmospheric gas composition are comparable in order of magnitude to the direct impact of solar activity on atmospheric gases.     

Numerical Model of Total Sediment Transport in the Yangtze Estuary

Based on the non-equilibrium suspended load transport equation,bed load transport equationand sediment transport capacity formulas derived by Dou et al.,a 2-D numerical model of total sedimenttransport in the Yangtze Estuary is presented.In the model,the actions of tidal currents and wind waves andthe effect of salinity on sediment transport are considered.An automatically generated boundary-fitted grid isused to fit the boundaries of the estuary and the boundaries of engineering projects.The verification of calcu-lations shows that the sediment concentration,the deformation of riverbed and siltation in the channels causedby typhoons can be successfully simulated.     

Numerical study on wave-induced filtration flow across the beach face and its effects on swash zone sediment transport

A numerical model, coupling an analysis of beach groundwater flow with an analysis of swash wave motion over a uniform slope, is presented. Model calculations are performed to investigate the variations of swash-induced filtration flows across the beach face for different input parameters. Swash zone sediment transport under the influence of such filtration flow across the beach face is investigated through modification of effective weight of sediment particle and modification of swash boundary layer thickness. These effects are quantified based on a bed load transport model with a modified Shields parameter.     

基于云模型的数字海图质量评估方法

提出了基于云模型的数字海图质量评估方法,通过综合云模型对各级评估指标进行运算,以质量评估云模型及其数字特征图的形式给出最终的评估结果。实验证明了该方法具有可行性。     

Modeling of Motion of Particle Clouds Formed by Dumping Dredged Material

The motion of particle clouds formed by dumping dredged material into quiescent waters is experimentally and numerically studied. In the numerical model, the particle phase is modeled by the dispersion model, and turbulence is calculated by the large eddy simulation. The governing equations, including the filtered Navier-Stokes equations and mass transport equation, are solved based on the operator-splitting algorithm and an implicit cubic spline interpolation scheme. The eddy viscosity is evaluated by the modified Smagorinsky model including the buoyancy term. Comparisons of main flow characteristics, including shape, size, average density excess, moving speed and the amount of particles deposited on the bed, between experimental and computational results show that the numerical model well predicts the motion of the cloud from the falling to spreading stage. The effects of silt-fence on the motion of the particle cloud are also investigated.     

近岸破碎波水体掺气及气泡输运过程研究

为准确探讨破碎波作用下气体如何卷入以及气泡的形成与输运特性, 文章结合粒子图像测速技术(particle image velocimetry, PIV)、高速相机和气泡测量系统, 以及基于Navier-Stokes方程的三维数值模型对气泡形成及其运动过程进行研究。研究结果表明: 文章建立的数值模型能合理地捕捉到破碎波作用下气体的卷入及其输运过程; 波浪的破碎会形成较大的气腔, 其破裂过程又将产生大量的气体微团; 气泡会增加水体的紊动, 造成水体与空气交界面附近形成大量的漩涡以及水体的飞溅; 气泡的破裂会消耗大量的水体能量, 同时发现较大的紊动动能与气泡的生成有关, 且气泡数随平均紊动动能的增加呈线性增长关系。     

Numerical simulation of the action on a warm convective cloud by hygroscopic particles

A one-dimensional numerical model of a warm convective cloud is presented. This model is used to study the effectiveness of the action on the cloud by hygroscopic particles with the aim of intensifying precipitation. The numerical simulation takes into account the processes of condensation, coagulation, and sedimentation of cloud droplets and makes it possible to obtain spatiotemporal characteristics of cloud development. A system of differential equations describing time variations in the temperature, pressure, and watervapor supersaturation during the adiabatic rise of a continuous air flow is solved. The evolution of the size distribution of cloud droplets is described by a kinetic equation. A continuous acting source of droplets with the size distribution calculated with consideration for condensation properties and dispersion characteristics of condensation nuclei (natural and additionally introduced during the action) is specified at the cloud-base level. The cloud top is formed owing to the evaporation of droplets in the barrier atmospheric layer over the cloud. The influence of changes in the barrier-layer height on the structure of cloud parameters and precipitation-formation processes is analyzed. The introduction of additional hygroscopic particles into a cloud is shown to act as a trigger mechanism initiating the processes of coagulation and sedimentation in the cloud medium. In this case, a positive effect of action by fine particles can be achieved if a certain reserve of sufficiently large droplets is present in the cloud. The results of calculating the dependence of the action effect on the height of the barrier layer, restricting cloud development, are presented.     

Modelling of the ecosystem of the Black-Sea shelf zone near the estuary of the Danube

We analyze the results of numerical calculations performed according to the three-dimensional interdisciplinary model of an ecological system of the Black-Sea shelf zone near the estuary of the Danube. The complete system of equations of hydrothermodynamics is solved together with transport equations of the advection-diffusion-reaction type used to describe the transformation of a substance (nitrogen) between the components of the characteristic vectors of the ecosystem: plankton, detritus, and biogenic elements (nitrates). We describe the distinctive features of the circumcontinental distribution of components obtained as a result of numerical experiments and present arguments for the conclusion that the ecosystem of the Danube estuary water area plays the role of a buffer zone between the press of the Danubian biogenic pollutions and the neighbouring areas of the shelf zone and open sea. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

The role of sulfate aerosol in the formation of cloudiness over the sea

We estimate the impact of sulfate aerosols on cloudiness formation over the sea in the middle troposphere and the involvement of these particles in the formation of polar stratospheric clouds (PSCs) in the lower stratosphere. The first of these problems is solved using a combined model of moist convection and the formation of cloudiness and sulfate aerosols in the troposphere and lower stratosphere over the sea, incorporating natural emissions of sulfur-containing compounds. We have found that a significant source of condensation nuclei in the troposphere is the photochemical transformation of biogenic dimethyl sulfide (in addition to NaCl). The results of numerical experiments indicate that the absence of sulfate aerosols hinders the cloudiness formation over the sea in the middle and upper troposphere. The problem of sulfate aerosol involvement in the formation of supercooled ternary solutions (STSs) (PSC Type Ib) in the lower stratosphere is solved using a mathematical model of global transport of multicomponent gas pollutants and aerosols in the atmosphere. Using the combined model, numerical experiments were performed for the winter season in both hemispheres. Sulfate aerosols were found to really participate in the formation of STS particles. Without their participation, the formation of STS particles in the lower stratosphere would be hindered. We present the results of numerical calculations and discuss the distribution of concentrations of gaseous nitric and sulfuric acids, as well as mass concentrations of these components in STS particles.     

Numerical modelling of water transport processes in partially-connected tidal basins

In the paper two types of numerical models – a lumped-parameter model and a high-resolution two-dimensional hydrodynamic model – are used to analyse the response of a system of partially-connected tidal basins to inhomogeneous open sea forcing. The equations of the lumped-parameter model, suitable for an arbitrary number of basins with sloping walls, are formulated based on one-dimensional continuity and momentum equations. Numerical solutions to the equations are thoroughly examined, showing the influence of inhomogeneous open sea forcing and of geometrical parameters of the basins on the tidal range and the water transport through the system, with particular emphasis given to inter-basin water exchange and cumulative water transport through basins boundaries. The results of the lumped-parameter model simulations for the tidal basins of the German Wadden Sea are successfully compared with the results of calculations with the two-dimensional hydrodynamic model, which is used to investigate in more detail circulation patterns and the influence of specific local features of inlet bathymetry on the hydrodynamic processes in the study area. The influence of wind on the basins response is discussed as well.     

滨海输沙若干测定法及数模计算述评

本文介绍了沙质海岸滨岸输沙的一些测定方法和数模计算的研究现状，并评述其使用条件、方法可靠性的应用前景，为开展海洋泥沙运动和岸滩演变的研究工作提供新思路与借鉴。     

Dynamics of trace gases and aerosols in the atmosphere with consideration for heterogeneous processes

A combined mathematical model has been developed to reproduce space and time variations in the concentrations of multicomponent gas constituents and aerosols in the atmosphere on both regional and urban scales. This model contains blocks of transport of gas constituents and aerosols in the atmosphere with consideration for homogeneous binary nucleation, the kinetic processes of condensation/evaporation and coagulation, chemical processes occurring in both gas and liquid phases, and the processes of mass exchange during the gas-droplet (particle) interaction. A nonhydrostatic model of atmospheric mesoscale processes is used to calculate the fields of meteorological elements and turbulent characteristics. The generation of new-phase particles from precursor gases by the mechanism of homogeneous binary nucleation and their interaction with background aerosol are considered. The results of numerical experiments are compared with the data obtained from field observations of both space and time variations in the concentrations of gas constituents and aerosols and in the ionic content of aerosol particles over the Baikal region under the influence of emissions from powerful industrial sources.     

Swash overtopping and sediment overwash on a truncated beach

New experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach, approximating the conditions at the crest of a beach berm or inter-tidal ridge-runnel. The experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale. Overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model, both of which are restricted to individual swash events. The analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed. Modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates. Calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport. Additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f_w = 0.024. This is in good agreement with a broad range of published field and laboratory data. However, the influence of long waves and irregular wave run-up on the overtopping and overwash remains to be assessed. The good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone, which has application in predicting the growth and height of beach berms.     

Simulating the influence of an atmospheric fine inhomogeneous structure on long-range propagation of pulsed acoustic signals

The results of simulating the influence of an atmospheric fine structure on the characteristics of acoustic signals propagating throughout the atmosphere for long distances from their sources are presented. A numerical model of an atmospheric fine inhomogeneous structure within the height range z = 20…120 km is proposed to perform calculations. This model and its numerical parameters are based on the current notions of the formation of an atmospheric fine structure due to internal gravity waves. The numerical calculations were performed using the parabolic-equation method. A spatial structure of the acoustic field and the structure of an acoustic signal at long distances from a pulsed source were calculated. It is shown that the presence of an atmospheric fine structure results in a scattering of acoustic signals and their recording in the geometric shadow region. The results of calculations of signal forms are in a satisfactory agreement with data on signals recorded in the geometric shadow region which is formed at a distance of about 300 km from an experimental explosion.     

Influence of vertical motions on maintaining the nitrate balance in the Black Sea based on numerical simulation

The upwelling of deep water associated with the influence of cyclonic wind curl and the difference in the buoyancy of the inflows in the lower and upper water layers is observed in the central part of the Black Sea. The resulting vertical water motions contribute to the transport of ammonium to the upper boundary of the anaerobic zone. In the suboxic zone, ammonium is converted to nitrate via nitrite as a result of the nitrification, and thus it can supply the nitrocline in the water basin. Within the framework of this paper we discuss the effectiveness of this mechanism on the basis of the numerical simulation. The calculations were performed using a one-dimensional physical-biogeochemical model for the upper 600-m sea water layer, which takes into account seasonal variations in atmospheric parameters and vertical motions. The model describes the biological and redox processes in the suboxic zone. We have estimated the contribution of different constituents into the balance of nitrogen compounds in the euphotic water layer. It is shown that ammonium nitrogen coming from the deep water due to vertical water motion plays a significant role in maintaining the balance of nitrates in the central part of the Black Sea.     

台风“莫拉菲”潜热的数值模拟研究

WRF天气研究和预报模式是新一代中尺度数值预报模式,本文采用最细2公里的网格距对台风“莫拉菲”内核的宏观、微观以及潜热过程进行数值模拟。通过对台风路径、风速大小、降水形态以及内核热力和动力结构的验证,证实了单向六参数WSM6方案的合理性。本文通过计算台风过程中的潜热加热率,揭示了总潜热主要来源于0℃层以下的凝结潜热和0℃层以上的凝华潜热。证实了与霰有关的云微物理过程是对总潜热贡献最重要的因子。除此之外,在本次台风“莫拉菲”的模拟中,其他重要的潜热贡献因子分别是水汽凝结成云水、云冰的凝华增长、雪的凝华增长、云冰的初始化、霰的凝华增长、云水被雪和霰收集、云水和雨水的蒸发、雪的升华、霰的升华、霰的融化以及云冰的升华。总体而言,本文模拟的潜热加热率廓线和TRMM卫星的廓线基本一致,尽管具体数值略有不同。     

稀有气体在电离区压缩特性研究

采用Saha方程加Debye-Hückel修正简单近似模型,给出了稀有气体He, Ne, Ar, Kr, Xe在电离区的物态方程以及离化度.计算结果与已有实验和理论计算进行比较,验证了模型的可靠性.通过对稀有气体等温和冲击压缩特性理论分析,讨论了其压缩和电离的规律性.论证了在稀有气体He, Ne, Ar, Kr, Xe中,气体Xe具有较好的抗压缩性.