Vol 29, No 3 (2016)

The vibrational-rotational energy levels of the first and second triads and the first and second hexads of the D₂¹⁸O, HD¹⁸O, D₂¹⁷O, and HD¹⁷O molecules are simulated on the basis of the Watson-type Hamiltonian and the rotation operator written in terms of the Padé–Borel approximants. Rotational, centrifugal distortion, and resonance constants and mixing coefficients of the resulting wave functions are found by the least squares method. The resonance interactions are analyzed. The predictive capability of the effective Hamiltonian parameters found is examined for the long extrapolated rotational quantum numbers.

The structure of air turbulent motions inside closed volumes (without exchange of material through the boundary) over inhomogeneously heated underlying surfaces is studied by the numerical solution of boundary problems for hydrodynamics equations (Navier–Stokes). Large solitary vortices (coherent structures, topological solitons) are observed over inhomogeneously heated surfaces. The number of vortices and their internal structure depend on the form and size of heated inhomogenities. In the case of simple forms of heating (homogeneous heating, a round heated spot), a coherent turbulence induced by the decay of coherent vortices is observed inside a closed volume. For complex forms of heating (thermal diversity), the toroidal vortices are noticeably deformed. The vortices can be extended along the surface and have spiral (helix) streamlines. The vortices are noticeably mixed during the evolution, which results in a Kolmogorov (incoherent) turbulence. Experimental data received earlier inside dome rooms of astronomical telescopes confirm our numerical simulation.

The technique for solving the problem of light backscattering by the physical optics method is considered. Recommendations on carrying out a preliminary estimation of the contribution of geometrical optics beams are given to reduce the list of beams that are necessary for the calculation by a factor of hundreds. The presented empirical estimating formulas and recommendations on choosing the optimum step of numerical integration make it possible to considerably reduce the resource intensity of the physical optics method for specified microphysical models of hexagonal crystalline particles. The obtained results of solving the light scattering problem are freely available in the form of a databank of Mueller matrices.

Microwave (MW) radiometers are widely used for monitoring the precipitable water vapor (PWV), which is a key greenhouse gas in the Earth’s atmosphere. Different measurement campaigns are carried out to estimate the accuracy of MW measurements of PWV. In this work, we compare the results of PWV measurements performed with a ground-based MW radiometer RPG-HATPRO at the Peterhof station of Saint Petersburg State University with radiosounding data from the Voyeykovo station. More than 850 measurements (at the day and nighttime) in the period from March 13, 2013, to May 31, 2014, are included in the comparison. It is shown that the discrepancy of PWV values measured with both methods is caused by the errors of the methods and by the spatial inhomogeneity of the PWV field. The discrepancy can attain tens of percent, which is to be taken into account in the intercomparison and validation of different methods for PWV retrieval. Exclusion of the cases with strong spatial inhomogeneity allowed reducing the mean deviations between MW and radiosounding measurements to 3–4% and the standard deviations between two sets of measurements to 12–14%.

A technique is considered for retrieving the spatial distributions of respirable fractions of aerosol in the lower atmosphere on the basis of multifrequency lidar sounding data without the use of additional aerosol optical and microphysical parameters along a sounding path. For this purpose, it is suggested to replace the spectral values of the aerosol extinction coefficient involved in lidar equations with the linearly independent parameters of their approximation, and retrieve the spatial distributions of these parameters from the numerical solution of the set of equations composed of all wavelength-time lidar signal samples. As a result, the number of unknowns in the set of equations to be solved is significantly reduced, and its matrix becomes overdetermined, which can be used for selection of physically reasonable values of the aerosol backscattering phase function at the lidar operating wavelengths. An assumption that there are two segments at the sounding path with similar aerosol extinction coefficient profiles is used to determine the lidar calibration constants. An algorithm is suggested for the search for these segments by the wavelength-time structure of a lidar signal. The inverse problem of aerosol light scattering is solved on the basis of stable regression relations between the concentrations of respirable aerosol fractions and approximation parameters of the aerosol extinction spectrum. The stability of the technique developed to the calibration errors and spatial variations in the aerosol backscattering phase function is shown in numerical experiments on laser sounding of aerosol.

The status of ground-based microwave radiometry in view of determining the air temperature and moisture profiles, atmospheric water vapor, liquid water in clouds, and rainfall intensity is discussed. Approaches to the solution of inverse problems of microwave radiometry of the atmosphere are described, as well as results of experimental studies of atmospheric water vapor and liquid water in clouds with a dual-frequency radiometer. Promising directions in the practical use of microwave radiometry of the atmosphere are formulated.