Expressions of the scintillation index for optical waves propagating through weak non-Kolmogorov turbulence based on the generalized atmospheric spectral model

The high frequency “bump” which occurs in the turbulence spectral model just prior to the turbulence cell dissipation is important for the analysis of the irradiance scintillation for optical wave propagating through atmospheric turbulence. In this study, expressions of the irradiance scintillation index are developed from the generalized modified atmospheric spectral model for optical waves propagating through weak non-Kolmogorov turbulence. Compared with the expressions of the irradiance scintillation index derived from the general non-Kolmogorov spectral model, the new expressions can consider the influences of finite turbulence inner and outer scales and the influence of finite diameter aperture receiver. As the irradiance scintillation is caused mainly by the small scale turbulence cells' diffractive effects for weak turbulence, the turbulence outer scale's influence can be ignored. Numerical simulations show that variable inner scale values produce obvious effects on the irradiance scintillation for non-Kolmogorov turbulence.     

Features of interannual variations of ozone in the middle stratosphere over Moscow according to observations at millimeter waves

The features of interannual variations of ozone in the middle stratosphere over Moscow in cold half-years since 1995 to 2015 are considered. These features are most pronounced in two separated groups of winters (six winters in each group) in December–January. It appeared that the seasonal variation of ozone averaged within each group is characterized by a higher ozone concentration \({C_{{O_3}}}\) in group I (in comparison with group II) in December and lower values in January. The differences in the seasonal variation of ozone between these groups at the level of 10 mbar in December and January exceed 2 ppm. A feature of the stratosphere circulation for half-year group I is the existence of a stable polar vortex and the absence of strong midwinter perturbations and sudden stratospheric warmings. On the contrary, for cold half-years of group II, the appearance of strong stratospheric warmings in January–February is in common. The results presented provide a quantitative estimate of the effect of these stratospheric warmings on ozone of the middle stratosphere overMoscow.     

Further analysis of scintillation index for a laser beam propagating through moderate-to-strong non-Kolmogorov turbulence based on generalized effective atmospheric spectral model

A new expression of the scintillation index(SI) for a Gaussian-beam wave propagating through moderate-to-strong non-Kolmogorov turbulence is derived, using a generalized effective atmospheric spectrum and the extended Rytov approximation theory. Finite inner and outer scale parameters and high wave number "bump" are considered in the spectrum with a generalized spectral power law in the range of 3–4, instead of the fixed classical Kolmogorov power law of 11/3. The obtained SI expression is then used to analyze the effects of the spectral power law and the inner scale and outer scale on SI under various non-Kolmogorov fluctuation conditions. These results will be useful in future investigations of optical wave propagation through atmospheric turbulence.     

On the generation and maintenance of waves and turbulence in simulations of free-surface turbulence

One of the challenges in numerical simulation of wave–turbulence interaction is the precise setup and maintenance of wave and turbulence fields. In this paper, we investigate techniques for the generation and suppression of specific surface wave modes, the generation of turbulence in an inhomogeneous physical domain with a wavy boundary-fitted grid, and the generation and maintenance of waves and turbulence during the complex wave–turbulence interaction process. We apply surface pressure to generate and suppress waves. Based on the solution of linearized Cauchy–Poisson problem, we derive three pressure expressions, which lead to a δ-function method, a time-segment method, and a gradual method. Numerical experiments show that these methods generate waves as specified and eliminate spurious waves effectively. The nonlinear wave effect is accounted for with a time-relaxation method. For turbulence generation, we extend the linear forcing method to an inhomogeneous physical domain with a curvilinear computational grid. Effects of force distribution and computational grid distortion are examined. For wave–turbulence interaction, we develop an algorithm to instantaneously identify specific progressive and standing waves. To precisely control the wave amplitude in a complex turbulent flow field, we further develop an energy controlling method. Finally, a simulation example of wave–turbulence interaction is presented. Results show that turbulence has unique features in the presence of waves. Velocity fluctuations are found to be strongly dependent on the wave phase; variations of these fluctuations are explained by the pressure–strain correlation associated with the wave-induced strain field.     

Experimental investigation on the scintillation index of vortex beams propagating in simulated atmospheric turbulence

The scintillation index of vortex beam in simulated atmospheric turbulence is experimentally investigated. The fluctuation of the intensity can be effectively reduced by vortex beams. In particular, the reduction of scintillation is more pronounced for vortex beams with larger topological charge.     

The weighting-function method in the computation of solar and stellar spectra

Accurate expressions for the computation of absorption lines, both in solar and stellar spectra, can only be obtained with the help of differential weighting functions. For arbitrary absorption in the stellar flux, the integrated weighting function is only approximately applicable. Approximate formulae for the weighting functions are not required.     

A two-dimensional model of the distribution of trace gases in the stratosphere and troposphere

Summary We report the results of computations of the distribution of trace gases in the troposphere and stratosphere with a two-dimensional photochemical transport model. The region covered by the model extends from pole to pole and from 0 to 50 km. Atmospheric transport is included by using seasonal averaged values for mean meridional and vertical winds and eddy diffusion. The compounds transported in the model are N₂O, NO _x (NO+NO₂), NO _y (NO_x+HNO₃), N₂O₅, H₂O, CH₄ and H₂O₂. Odd hydrogen (OH+HO₂+H) is assumed in photoequilibrium. A simple scheme is proposed to simulate the condensation of H₂O and scavenging of other gases. Rayleigh scattering is included in the calculation of the photodissociation rates. The resulting distributions are compared whenever possible with experimental data. We attempt to discuss the stratospheric budget of water vapour taking into account photochemical sources (e.g. CH₄ oxidation) and sinks. It is shown that similarly to other models serious disagreement seems to exist between the calculated and observed mixing ratios of NO _x , NO _y and the ratios of the different compound within the family. The amount of experimental data is, however, too sparse to draw any definite conclusion.

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Riassunto Si riportano i rusultati sulla distribuzione di gas minori nella stratosfera e troposfera, ottenuti con un modello bidimensionale, fotochimico con trasporto. Il modello si estende da 0 a 50 km in quota e da polo a polo in latitudine. Del trasporto si tiene conto usando i valori medi stagionali dei venti meridionali e verticali e dei coefficienti di diffusione turbolenta. Il modello tratta il trasporto per i seguenti composti: N₂O, NO _x (NO+NO₂), NO _y (NO _x +HNO₃), N₂O₅, H₂O, CH₄ e H₂O₂. L'idrogeno dispari (H+OH+HO₄) è calcolato all'equilibrio fotochimico. Un semplice meccanismo è proposto per simulare la condensazione del vapor d'acqua e di altri gas. I coefficienti di fotodissociazione sono calcolati tenendo conto dello scattering di Rayleigh. Le distribuzioni ottenute per i vari gas sono confrontate, ove ciò è possible, con i dati sperimentali. Si discute inoltre il bilancio stratosferico del vapor d'acqua tenendo conto delle sorgenti fotochimiche (cioè l'ossidazione del CH₄) e dei pozzi. Si conclude che, analogamente ad altri modelli, esistono delle importanti differenze fra i rappporti di mescolamento calcolati e qualli osservati di NO _x e NO _y . I dati sperimentali sono comunque ancora troppo scarsi per arrivare a conclusioni definitive.

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Резюме Мы приводим результаты вычислений распределения прослеживаемых газов в тропосфере и стратосфере с помощью двумерной фотохимической модели переноса. Область, которую покрывает модель, распостраняется от полюса до полюса и от нуля до 50 км. Атмосферный перенос включает сезонные усредненные значения для средних меридиональных и вертикальных ветров и диффзию вихрей. Переносимые соединения в этой модели являются: N₂O, NO _x (NO+NO₂), NO _y (NO _x +HNO₃), N₂O₅, H₂O, CH₄ и H₂O₂. Предполагается, что нечетный водород (OH+HO₂+H) находится в фоторавновесии. Предлагается простая схема для моделирования конденсации H₂O и удаления другин газов. При вьчислении интенсивностей фотодиссоциации учитывается релеевское рассеяние. Полученные распределения сравниваются с имеющимися экспериментальными данными. Мы пытаемся обсудить стратосферный бюджет водяных паров, учитывая фотохимические источники (т.е. окисление CH₄) и стоки. Показывается, что аналогично другим моделям, по-видимому, существует существенное расхождение между вычисленными и измеренными отношениями перемешивания NO _x , NO _y и отношениями для различных соединений. Однако экспериментальные данные являются слишком разбросанными, чтобы сделать определенные выводы.

     

基于行波管螺旋导电面模型的空间电荷场研究

通过分析行波管螺旋导电面模型中的电磁场，给出了色散和耦合阻抗计算公式，并深入研究了非线性理论中的空间电荷降低因子.结果表明，螺旋导电面模型相对理想导电圆筒中的空间电荷降低因子在较高频段变化不大.空间电荷降低因子的变化反映了螺旋线外电磁场对电子注的作用，同样的慢波结构，较高频率的电磁场应有较大的影响.因此，使用螺旋导电面模型在较高频段计算空间电荷降低因子是不合适的. 关键词： 行波管 非线性 螺旋导电面 空间电荷降低因子 色散 耦合阻抗     

Energy spectra of quantum turbulence in He II and 3He-B: A unified view

Quantum turbulence in superfluid He II and in ³He-B that can be regarded as nearly isothermal, isotropic, and homogeneous is discussed within the two-fluid model. A general form of the 3D energy spectrum is proposed: at large length scales, where normal and superfluid eddies are locked together by the mutual friction force, the energy spectrum is essentially classical and includes an inertial range of a Kolmogorov K62 form. With increasing wavenumber k, the normal fluid part of the spectrum terminates due to finite viscosity, while the superfluid part of the spectral energy density changes towards k ⁻³ and then back into Kolmogorov-like k ^−5/3 again. Agreement with computer simulations and experiments is claimed if account is taken of the turbulent box size and of the energy decay rate. The text was submitted by the author in English.     

Chemical turbulence and standing waves in a surface reaction model: The influence of global coupling and wave instabilities

Among heterogeneously catalyzed chemical reactions, the CO oxidation on the Pt(110) surface under vacuum conditions offers probably the greatest wealth of spontaneous formation of spatial patterns. Spirals, fronts, and solitary pulses were detected at low surface temperatures (T<500 K), in line with the standard phenomenology of bistable, excitable, and oscillatory reaction-diffusion systems. At high temperatures (T greater, similar 540 K), more surprising features like chemical turbulence and standing waves appeared in the experiments. Herein, we study a realistic reaction-diffusion model of this system, with respect to the latter phenomena. In particular, we deal both with the influence of global coupling through the gas phase on the oscillatory reaction and the possibility of wave instabilities under excitable conditions. Gas-phase coupling is shown to either synchronize the oscillations or to yield turbulence and standing structures. The latter findings are closely related to clustering in networks of coupled oscillators and indicate a dominance of the global gas-phase coupling over local coupling via surface diffusion. In the excitable regime wave instabilities in one and two dimensions have been discovered. In one dimension, pulses become unstable due to a vanishing of the refractory zone. In two dimensions, turbulence can also emerge due to spiral breakup, which results from a violation of the dispersion relation.     

A model of the atmosphere above a sunspot from radio observations

The results of VLA observations of an unusual source of microwave radiation, associated with the sunspot NOAA 7789 on October, 15, 1994, are presented. The fine structure of the source, which is a ring structure in intensity and polarization at frequencies 4.5 and 8.0 GHz, is discussed. It is shown that the features observed can be explained by a thermal cyclotron mechanism if the magnetic field is approximated by a vertical dipole buried under the photosphere, but the spatial distributions of kinetic temperature and electron density in the atmosphere above the sunspot differ considerably from the standard model. A two-dimensional source model (the dependences of the parameters on the height and distance from the center of the sunspot), which fits the observations at the above frequencies, is evolved. The principal physical result is that the data observed are explainable by the presence of an unexpectedly dense cool plasma in the atmosphere over the center of the umbra.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 3, pp. 372–389, March, 1996.The authors are grateful to V. V. Zheleznyakov for useful discussions and remarks. The work was partly supported by the Russian Foundation for Fundamental Research (Grant No. 95-02-04272-a).     

Study of response of scintillation detector based on BaF2 crystals and nanoceramics

Fast and slow components of responses of scintillation detectors based on BaF₂ crystals and nanoceramics with various activators are studied by the registration of annihilation gamma-quanta with an energy of 511 keV. A comparative analysis of the obtained results for the determination of promising scintillators for the development of detectors with high time and pulse height resolution is carried out.     

Effects of target fragmentation on evaluation of LET spectra from space radiations: implications for space radiation protection studies

We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the HZETRN/BRYNTRN computer code. The emphasis of our calculations is on the analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvements in the HZETRN/BRYNTRN radiation transport computer code are described. Calculations show that at large values of LET (> 100 keV/μm) the LET spectra seen in free space and low earth orbit (LEO) are dominated by target fragments and not the primary nuclei. Although the evaluation of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are dominated by the target fragments. Finally, we discuss the situation for interplanetary exposures to galactic cosmic rays and show that current radiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths (> 10 g/cm² of Al) is greatly modified by target fragments. These results suggest that studies of track structure and biological response of space radiation should place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons.     

平流层中部垂直运动年循环异常的模拟研究

利用NCAR提供的包含化学、辐射、动力相互作用的二维模式(SOCRATES)进行模拟试验，进一步探讨年循环年际异常的可能成因.模拟结果的分析表明臭氧高值中心相对于赤道准两年移动是年循环的年际异常的一个重要原因.当臭氧高值区离开赤道偏向夏半球时，夏半球的平流层中部将吸收更多的太阳短波辐射，而冬半球的则相反，因此更大的短波加热率将增大夏半球平流层中部的上升运动，导致年循环的增强；相反地，臭氧高值中心接近赤道时则导致了相对较弱的年循环. 关键词： 臭氧 甲烷 年循环 准两年变率     

Transport of waves in disordered waveguides: A potential model

We study the statistical properties of wave transport in a disordered waveguide. We first derive the properties of a “building block” (BB) of length δL starting from a potential model consisting of thin potential slices. We then find a diffusion equation—in the space of transfer matrices that describe our system—which governs the evolution with the length L of the disordered waveguide of the transport properties of interest. The latter depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. We have developed a numerical simulation in which the universal statistical properties of the BB found analytically are first implemented numerically, and then the various BBs are combined to construct the full waveguide. The reported results thus obtained are in good agreement with microscopic calculations, for both bulk and surface disorder.     

Energy spectra of the ocean's internal wave field: theory and observations

The high-frequency limit of the Garrett and Munk spectrum of internal waves in the ocean and the observed deviations from it are shown to form a pattern consistent with the predictions of wave turbulence theory. In particular, the high-frequency limit of the Garrett and Munk spectrum constitutes an exact steady-state solution of the corresponding kinetic equation.