Numerical modeling of polarized radiation transfer in spatially inhomogeneous clouds and precipitation.

The report systematizes the results of numerical studies of polarized electromagnetic radiation transfer in clouds and precipitation conducted by the authors.
Various theoretical and applied problems were investigated within the framework of a unified computational approach. The basis of the approach to the study adopted by the authors is a finite-difference scheme for the vector equation of radiation transfer with counter differences, implemented by the authors for one-dimensional, two-dimensional and three-dimensional problems. The calculations were implemented on high-performance supercomputer parallel cluster equipment of the Chebyshev, Lomonosov and Lomonosov-2 complexes of the Moscow State University Research Computing Center. Due to the highly efficient use of parallel computing technology, a significant increase in the performance of calculations was achieved.
The authors studied in most detail the problems of transfer of thermal radio radiation of the microwave range in cumulus clouds and rainfall, which have a predominant orientation of non-spherical falling raindrops and, as a consequence, anisotropy of electromagnetic radiation scattering. Calculations were performed for the models of a homogeneous plane-parallel rain layer and three-dimensional cubic rain cells for different values ​​of rainfall intensity (1-100 mm/h) and several microwave radiation wavelengths (3, 8, 15 and 22 mm) corresponding to the operating ranges of microwave radiometric and radar equipment. Based on the calculation results, a relationship was shown between the intensity and polarization of the observed radiation and the intensity of precipitation. As follows from the results obtained, observation and analysis of the intensity and polarization of thermal radio emission of rainfall at several wavelengths simultaneously allows identifying rainfall cells in the atmosphere and estimating the intensity of their fall. The effects associated with the tilt of the axes of falling non-spherical raindrops were also investigated. It was shown that the assumption of the tilt of the axes of raindrops makes it possible to generally explain the observed patterns in the behavior of the third Stokes parameter U. In addition, the dependence of the intensity and polarization of the observed radiation on the properties of the underlying surface was investigated, including in the presence of partial Lambertian reflection.
 
In addition, the propagation of laser radiation pulses of different polarization in thin cloud layers was studied. Various schemes for probing cloud layers with different probing directions were studied, including horizontal probing from aircraft. The revealed patterns, in turn, made it possible to formulate the criteria for the manifestation of the observed scattering effects and to indicate the possibilities of solving the inverse problem, i.e. estimating the thickness of the scattering layer of the medium and its microphysical parameters.
The study was carried out within the framework of the state assignment of Lomonosov Moscow State University. The work was carried out using the equipment of the Center for Shared Use of Ultra-High-Performance Computing Resources of Lomonosov Moscow State University.