Home – Home – Jornals – Atmospheric and Oceanic Optics 2017 number 7

The study of cirrus clouds, which significantly affect the climate, is carried out using lidars. Interpretation of the lidar data is based on the direct solution of the problem of light scattering by particles of crystal clouds. Optical characteristics of perfect ice hexagonal columns, obtained previously, poorly agree with the lidar observation results. The work describes calculations of the optical characteristics of irregular hexagonal ice columns, which are in a good agreement with the experimental results. The calculations for particles with deformation of a dihedral angle of 90° are presented. It is shown that the logarithm of the scattering matrix can be well linearly approximated by the logarithm of the particle size. This can significantly speed up the calculations of the optical characteristics of clouds. It is ascertained that the optical characteristics are in a good agreement with the lidar observation results throughout the entire range of sizes calculated even at deformation angles of a few degrees.

The study shows the results of retrieving the fraction of quazi-horizontally oriented ice plates in a cirrus cloud of randomly oriented ice columns from the data of simultaneously sounding Raman lidar and ceilometer. It is show that in the case of absence of a layer of quasi-horizontally oriented particles the perpendicular and parallel components of the backscatter coefficient of vertically oriented Raman lidar coincide up to a constant factor with the backscatter coefficient of 5° inclined ceilometer. If quazi-horizontally oriented plates appear in a cloud, the fraction of the plates and the flutter angle can be retrieved from the difference of the backscattering coefficient profiles with help of the extinction coefficient profile.

Analytical equations are derived for the useful signal reflected from the rough surface of an object and the noise signal scattered (in the single-scattering approximation) by aerosol, which is between the transmitting-receiving system and the object, in the approximation of Gaussian distributions of the field of a partially coherent laser beam, coefficient of diffusion reflection from the object, phase scattering function of the atmosphere, and the receiving aperture transmission function. The ratio of these signals is calculated as a function of the distance to the object.

A technique is suggested for the joint consideration of turbulent (refraction) and aerosol (scattering) distortions when imaging laser illuminated objects. The technique is based on the joint solution of the parabolic equation and the radiation transfer equation by the split-step method. Turbulent distortions are simulated with the common phase screen method. The aerosol scattering simulation is based on the division of the object-observer distance to a certain number of statistically independent scattering layers, for each of which coherent (for forward scattering) and incoherent (for forward and back scattering) components of the scattered field are formed in the single-scattering approximation. The results of simulation of coherent and incoherent images of a laser radiation illuminated object are presented.

Results of the analysis of the mean intensity, intensity fluctuations, and regular and random wandering of optical beams propagating through the high-density area, which is formed due to subsonic airflow about a turret, in a turbulent atmosphere, are described. It is shown that the presence of perturbations around the turret caused by aircraft subsonic movements has a little impact on beam parameter. Quantitative data, which illustrate changes in the beam parameters along paths of different geometry versus turbulent conditions of light propagation, are presented and discussed.

Results of the analysis of microphysical characteristics obtained from the data of nighttime Raman lidar measurements in Tomsk (56N, 85E) in 2013 within the CIS-LiNet project (lidar networks in CIS countries) are presented. Theoretical aspects of the retrieval of the particle size distribution function at the preset refractive index are considered. It is shown that the coarse fraction is retrieved ambiguously. Parabolic approximation of the mean size of coarse particles, R_coarse, is suggested, which allows calculation of the size distribution function determine for particles of up to 3 mm in size. It is shown that when estimating the parameters under study together, the retrieved refractive index is non-linearly related with the optical coefficients and the distribution function, which leads to appearance of different, including false values of the_{refractive index. The parameters are assessed for the boundary air layer and middle troposphere.}

Application of bionic methods, such as neural networks and genetic algorithms, to solution of the inverse problem of CO₂ relative concentration determination from stratospheric airship signals is considered. The backscattered and reflected from the surface signals at wavelengths near 1572 nm are used for the measurements. The errors of the standard DIAL approach and DIAL-IDPA technology are compared. For the lidar with specification described, the mean error of algorithms developed is lower than 1 ppm. The genetic algorithm used is based on the minimization of the difference between the model signal and the signal received. Application of neural networks is based on their training on the examples of the simulated signals (reflected and scattered) and the altitude distribution of the gas concentration.

An OPO-based laser system is presented, which is a part of a differential absorption lidar and provides for tunable generation of nanosecond pulses in the 3-4 mm spectral range. The DIAL-DOAS technique for lidar measurements of atmospheric gases is developed and tested in numerical simulation with the aim of estimating the lidar capabilities of sensing atmospheric trace gases. The simulation results of lidar measurements of atmospheric trace gases in the 3-4 mm range are described.

Data on the variability of vertical and temporal aerosol structures in the stratosphere over Tomsk received during experiments at the lidar station for high-altitude atmosphere sounding of Institute of Atmospheric Optics SB RAS carried out in 2011-2015 are described. As in the previous studies, the emphasis is placed on disturbances of the aerosol components in the stratosphere due to volcanic eruptions and on identification of peculiarities in the intra-annual variability of the stratospheric aerosol content. A feature of that period, except for the second half of 2011 (the appearance of eruptive layers from the Grimsvotn volcano eruption over Tomsk), was near absence of volcanic activity, which leads to the formation of stratospheric aerosol and its transfer toward Tomsk; this allows the study of the behavior of the vertical structure of the background aerosol in the stratosphere during the five years. The analysis of the lidar data shows a steady trend of aerosol filling of the lower stratosphere during cold seasons, with the aerosol content maximum in December-January, and near absence in warm seasons throughout the stratosphere.

The high-resolution analysis of the ro-vibrational IR spectrum of the absorption bending bands n₂ + n₄ (F₁) and n₂ + n₄ (F₂) of the ²⁸SiH₄ molecule is performed with the SPHETOM software package. About 618 experimental transitions are assigned to n₂ + n₄ (F₁) and n₂ + n₄ (F₂) bands with J^max = 8. Rotational, centrifugal distortion, tetrahedral splitting, and resonance interaction parameters for these vibrational bands are determined from the weighted fit of experimental line positions. The obtained set of parameters reproduces the initial experimental data with the accuracy closed to experimental uncertainties, d_rms = 8 × 10^-4 cm^-1.

A method for parameterizations of the absorption of UV radiation by atmospheric ozone is described. Parameterizations are proposed for computer modeling of tropospheric fluxes of UV-A and UV-B radiation and modified fluxes of biologically active UV radiation in medical applications (for the analysis of vitamin D formation and risk of erythema, cancer, and cataracts). The parameterizations allow solution of the UV radiation transfer equations at the only effective spectral point to obtain integral fluxes in the 280-400 nm range (taking into account the spectral factors characterizing biological effects). When using the parameterizations, the characteristic errors in the calculations of the fluxes in the clear and cloudy troposphere are ~ 3-5%. The use of these parameterizations is relevant for fast radiation models, for example for on-line modeling of UV radiation fluxes for medical purposes. This method can be used to improve the accuracy of radiation codes in general atmospheric circulation models, radiation-chemical models, etc.