Formation and evolution of dusty plasma structures in the ionosphere

A self-consistent model of the formation and evolution of dusty plasma structures in the ionosphere has been developed. The effect of the initial distributions of dust particles, as well as condensation and absorption of water molecules by dust particles, on the formation of noctilucent clouds and polar mesosphere summer echoes has been demonstrated. The possibility of the formation of a layered structure of noctilucent clouds has been illustrated.     

Dust particle charging and formation of dust structures in the upper atmosphere

We investigate the dust particle charging process in the Earth’s upper atmosphere. Calculating the spectra of solar radiation, we study the influence of the photoelectric effect on the charging process. We show that both positively and negatively charged dust particles are present in the upper atmosphere. We consider the mechanisms which can be responsible for the formation of dust structures like noctilucent clouds and polar mesosphere summer echoes.     

Radar studies of ionospheric dusty plasma phenomena

We discuss the influence of charged dust on radar observations in the Earth ionosphere. This region in the upper Earth atmosphere can be described as a partially ionized, low‐temperature plasma. Plasma parameters vary by orders of magnitude spatially and in time. Dust particles influence the charge balance, in some cases dusty plasma condition is met. The polar mesospheric echoes are an example of dust plasma interactions observed with radar. The mesosphere is a region where atmospheric temperature decreases with altitude and can reach frost point temperature. The formation of the polar mesospheric radar echoes involves neutral atmosphere dynamics, which is latitude dependent and it involves charged dust particles, especially icy dust that forms in the polar summer mesosphere. Charged dust can also influence incoherent scatter that results from electromagnetic waves scattering off electrons, where the electrons are coupled to other charged components. Observers rarely report charged dust signatures in the incoherent scatter spectra; we show that there is a good chance for doing so with improved observations. The incoherent scatter can possibly also be used to estimate the amount of charged dust in the direct vicinity of a meteor, as we show based on the order of magnitude considerations. This prospect of new observational results makes theoretical investigations of radio‐wave scattering in the presence of charged dust with size distributions worthwhile.     

Retrieval of the vertical distribution of chemical components in the mesosphere from simultaneous measurements of ozone and hydroxyl distributions

We propose a method for retrieval of directly unmeasurable concentrations of minor gas constituents of the mesosphere from available experimental data using simplified models of atmospheric photochemical systems. The method is used for processing of the results of simultaneous measurements of ozone and hydroxyl concentrations within the framework of the CRISTA-MAHRSI satellite experiments. As a result, vertical distributions of concentrations of three more key chemical components of the mesosphere, namely, atomic oxygen, atomic hydrogen, and hydroperoxide, were retrieved. It is shown that a limiting altitude-dependent ratio between OH and O₃ concentrations is valid in the mesosphere and lower thermosphere. It is found that CRISTA-MAHRSI data satisfy this ratio up to an altitude of 87 km, but a strong discrepancy between theory and experiment arises in the upper region. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 9, pp. 760–769, September 2006.     

Synchrotron X-ray imaging of the onset of ultrasonic horn cavitation

High-power ultrasonic horns operating at low frequency are known to generate a cone-shaped cavitation bubble cloud beneath them. The exact physical processes resulting in the conical structure are still unclear mainly due to challenges associated with their visualization. Herein, we address the onset of the cavitation cloud by exploiting high-speed X-ray phase contrast imaging. It reveals that the cone formation is not immediate but results from a three-step phenomenology: (i) inception and oscillation of single bubbles, (ii) individual cloud formation under splitting or lens effects, and (iii) cloud merging leading to the formation of a bubble layer and, eventually, to the cone structure due to the radial pressure gradient on the horn tip.     

基于尘埃等离子体理论的极区中层分层结构研究

根据尘埃等离子体理论,考虑到尘埃粒子的充放电过程,研究了尘埃冰晶粒子吞噬效应对极区中层电子浓度分层结构及电导率和介电常数的影响。结果表明,尘埃冰晶粒子的吞噬效应造成了极区中层80~90km 高度范围内电子浓度的分层结构,并进而导致这一区域尘埃等离子体电导率、介电常数沿高度出现明显的分层,为解释和研究极区中层夏季回波现象提供参考。     

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根据尘埃等离子体理论,考虑到尘埃粒子的充放电过程,研究了尘埃冰晶粒子吞噬效应对极区中层电子浓度分层结构及电导率和介电常数的影响。结果表明,尘埃冰晶粒子的吞噬效应造成了极区中层80~90km高度范围内电子浓度的分层结构,并进而导致这一区域尘埃等离子体电导率、介电常数沿高度出现明显的分层,为解释和研究极区中层夏季回波现象提供参考。     

Roles of positively charged dust in the formation of ion-acoustic subsonic solitary waves in electron-ion-positively charged dust plasmas

The electron-ion-positively charged dust plasma system containing Boltzmann distributed electron species, cold inertial ion species, and stationary positively charged dust (pcd) species are considered. The roles of pcd species in the formation of ion-acoustic (IA) subsonic solitary waves (SWs) are investigated by the pseudo-potential approach, which is valid for arbitrary amplitude time-independent subsonic SWs, as well as by the reductive perturbation method, which is valid for the time-dependent small amplitude subsonic SWs. It is observed that the presence of the pcd species reduces the phase speed of the IA waves, and consequently supports the IA subsonic SWs with the positive wave potential in such electron-ion-pcd plasmas. This is due to the reduction of the space charge electric field by the presence of the pcd species. The applications of the work in space environments (viz. Earth's mesosphere, cometary tails, Jupiter's magnetosphere, etc.), where pcd species have been detected, are briefly discussed.     

Radiation-Transfer Modeling of the Cloud L1544 in the HCO+ and HC18O+ Emission Lines

We study the formation of HCO⁺ and HC¹⁸O⁺ emission lines in the cloud L1544. The radiation transfer is modeled numerically, and the line intensities for different impact parameters are calculated. It is shown that a decrease in the abundances of the studied molecules toward the object center is necessary for the formation of the observed line profile in the optically thin case. We consider various hydrodynamic models allowing for compression, turbulence, and different types of cloud rotation and find a model ensuring the best agreement with the observational data. Our numerical simulations are indicative of nonuniform rotation in L1544. Assuming that the object is spherically symmetric, we estimate the density and velocity of the medium within the framework of the selected model.     

Role of surface modes in vortex formation in BEC

We study the role of surface modes in the process of vortex formation in harmonically trapped BEC. It is shown that the vortex nucleation and penetration to the inner part of the cloud occur at velocities slightly exceeding the surface mode critical velocity. Surface modes induce ripples of the order parameter; these ripples are then transformed into vortex-antivortex pairs. After this, vortices move to the inner part of the cloud, whereas antivortices go in the opposite direction     

Deformation of a water shell during free fall in air

The basic regularities of the change in the shape and sizes (the initial volume is 0.05–0.5 L) of a water shell are singled out in its deformation during free fall in air from a height of 3 m. The 3D recording of the basic stages of deformation (flattening of the shell, nucleation, growth, and destruction of bubbles, formation of the droplet cloud) is carried out using high-speed (up to 10⁵ frames per second) Phantom V411 and Phantom Miro M310 video cameras and the program complex Tema Automotive (with the function of continuous tracking). The physical model of destruction of large water bodies is formulated at free fall with the formation of the droplet cloud.     

Evolution of a dust cloud in the field of a Knudsen flow under zero gravity conditions (numerical scenarios)

We report on the results of analysis of numerical scenarios for motion of a dust cloud interacting with a Knudsen gas flow. Two types of evolution of the dust formation are observed: regular, in which the characteristic points of the cloud are attracted to attractors, or the development of instability in a bounded region.     

Impacts of fast meteoroids and a plasma–dust cloud over the lunar surface

The possibility of the formation of a plasma–dust cloud in the exosphere of the Moon owing to impacts of meteoroids on the lunar surface is discussed. Attention is focused on dust particles at large altitudes of ~10–100 km at which measurements were performed within the NASA LADEE mission. It has been shown that a melted material ejected from the lunar surface owing to the impacts of meteoroids plays an important role in the formation of the plasma–dust cloud. Drops of the melted material acquire velocities in the range between the first and second cosmic velocities for the Moon and can undergo finite motion around it. Rising over the lunar surface, liquid drops are solidified and acquire electric charges, in particular, owing to their interaction with electrons and ions of the solar wind, as well as with solar radiation. It has been shown that the number density of dust particles in the plasma–dust cloud present in the exosphere of the Moon is ?10^?8 cm^?3, which is in agreement with the LADEE measurements.     

Suppression of the effect of charge cloud in an ion mobility increment spectrometer to improve its sensitivity

The formation of a charge cloud due to ions passing through a set of electrodes that constitute an atmospheric-pressure ion mobility increment spectrometer is considered. Since this cloud disturbs the passage of ions separated in the spectrometer, it is suggested that the formation of the cloud be suppressed by shifting the central electrode or applying a voltage to the output electrode. Such a trick removes an ion trap responsible for the charge cloud. It is shown that the transparency of the instrument can be increased severalfold in this case.     

Limited transverse sizes of a droplet cloud under disintegration of a water mass during its fall from a great height

The main stages of the formation of a droplet cloud during the disintegration of water masses (with an initial volume of 0.05–1 L) during their free fall from a great height (up to 15 m) have been determined. High-speed (up to 6 × 10⁵ frames per second) video cameras were used to perform 3D video recording of the transformation and destruction of water mass with the formation of a droplet cloud. It is found that the transverse sizes of the newly formed droplet cloud rapidly increase when the mass passes the first few (up to 10) meters from the onset of falling. It is shown that the maximum cross-sectional areas of the water mass change only slightly with an increase in the discharge height at heights above 10 m. A model of limited growth of the transverse sizes of droplet cloud is developed for the first time based on the results of large-scale experiments.     

利用地基红外高光谱发射率数据进行云参数反演(2): 云滴有效半径和云水路径反演

云滴有效半径和云水路径等微物理参数是了解云的形成过程、辐射效应以及云、气溶胶和降水相互作用等问题的重要数据。利用地基红外高光谱辐射数据开展了云微物理参数反演方法研究。针对光谱数据的特点,进行了基于云层发射率光谱和辐射光谱的敏感性分析,在此基础上建立了云微物理参数与云发射率光谱差值和斜率等特征参数有关的查找表关系。具体特征参数包括：热红外波段862.1和934.9 cm-1的云层发射率之差、中红外波段1 900.1和2 170.1 cm-1的云层发射率之差、热红外波段900～1 000 cm-1区间的发射率光谱斜率和辐射值光谱斜率、1 100～1 200 cm-1区间的发射率光谱斜率和辐射值光谱斜率等。研究了臭氧波段云层透过率的计算方法及对查找关系的约束性,选择了1 050～1 060 cm-1区间的云层透过率平均值作为约束特征参数。实现了基于逐步搜索法的多重查找反演云滴有效半径和光学厚度,并可通过经验关系计算云水路径。研究表明,该算法得到的水云的云滴有效半径与ARM计划中的MICROBASE产品基本相当,冰云的云滴有效半径相对偏小,两者的云水路径反演结果差异较大。该反演算法较适合于光学厚度小于6的薄云。     

Near infrared reflection spectra of ammonia frost: Interpretation of the upper clouds of Saturn

Models of the uppermost cloud layer on Saturn indicate that the cloud is composed of solid ammonia, with the cloud particles being initially formed at about 150 K, and subsequently transported upward by convection to colder regions of the atmosphere. For the purpose of comparison with Saturn's near-i.r. reflection spectrum, we have obtained laboratory reflection spectra of ammonia frost corresponding to a variety of deposition rates and deposition temperatures.We find that the spectral location of the strong 3 μm absorption band of solid ammonia is highly dependent upon the manner in which the frost layer is formed. For rapid deposition on a 150 K cryosurface, which closely simulates what we believe to be the cloud formation process on Saturn, the band is centered at 3.29 μm. This band location, together with the apparent absence of gaseous ammonia overlying the solid ammonia cloud, is consistent with Saturn's observed reflection spectrum in the vicinity of 3 μm.Comparison of Saturn's reflection spectrum with that of Jupiter, in the vicinity of 1.3 and 1.6 μm, also supports the hypothesis of a Saturnian ammonia ice cloud. Differences in the two observed reflection spectra are interpreted as due to gaseous ammonia absorption bands for Jupiter being replaced by solid ammonia absorption features, at displaced wavelengths, for Saturn.An important conclusion of this study is that, for the purposes of either cloud interpretation or cloud radiation modeling, the polycrystalline phase of solid ammonia, and in turn its spectrum, is highly dependent upon the manner in which the soled is formed.     

Atmospheric Turbulence and Internal Gravity Waves Examined by the Method of Artificial Periodic Irregularities

A method for studying the Earth’s ionosphere at altitudes of the mesosphere and lower thermosphere based on creating artificial periodic irregularities in the ionospheric plasma by means of powerful radio waves is breafly described. Methods for determining the temperature and density of the neutral component and the velocity of vertical and turbulent motions by measuring the characteristics of the signal backscattered by the irregularities are described. The results of experiments performed on a SURA heating facility aimed at a comprehensive investigation of the natural processes occurring in the Earth’s lower ionosphere due to the propagation of atmospheric waves and turbulent phenomena are examined. Based on measurements of the amplitude and phase of the signal scattered by periodic irregularities, the most important characteristics of the neutral and plasma components of the Earth’s atmosphere at altitudes of the mesosphere and lower thermosphere are determined. Further research on the subject is discussed.     

Experimental measurements of velocity dissipation and neutral-drag effects during the formation of a dusty plasma

Stereoscopic particle image velocimety is used to make measurements of the formation of a dust cloud of 1.2 microm alumina particles in an argon dc glow discharge plasma. These measurements show a clear redistribution of particle velocities during the cloud formation process. Furthermore, these measurements suggest that the particle cloud reaches an equilibrium on a time scale over 100 times slower than expected due to neutral-drag effects.     

Kinetic potential and barrier crossing: a model for warm cloud drizzle formation

The kinetic potential of nucleation theory is used to describe droplet growth processes in a cloud. Drizzle formation is identified as a statistical barrier-crossing phenomenon that transforms cloud droplets to drizzle size with a rate dependent on turbulent diffusion, droplet collection, and size distribution. Steady-state and transient drizzle rates are calculated for typical cloud conditions. We find drizzle more likely under transient conditions. The model quantifies an important indirect effect of aerosols on climate-drizzle suppression in clouds of higher droplet concentration.