Simulating scattering properties of nonspherical aerosol particles using multiresolution timedomain method

Abstract

Scattering process of aerosol particles plays an important role in atmospheric radiative transfer since it can modify the transmission, reflection and absorption ability of atmospheric system. Owning to the uncertainty of aerosol particles' scattering properties, which results from their complicated geometries and inhomogeneous compositions, there still exists a considerable uncertainty in the radiative transfer numerical simulation, and simulating the scattering properties of aerosol with irregular shapes has become a hotspot in meteorological study. To this end, a new aerosol scattering model is developed based on multi-resolution time-domain (MRTD), by which the scattering processes of nonspherical and inhomogeneous particles can be simulated. In this model, the near electromagnetic field is calculated by MRTD technique. Considering the particularity of aerosol medium, a transformation technique from near field to far field is derived based on volume integration method, and then the scattering amplitude matrix and Meller matrix can be calculated by the obtained far electric field as well. The models for particle extinction and absorption cross section are derived from Maxwell's curl equations in the frequency domain, by which the integration scattering properties can be simulated accurately. The MRTD scattering model is validated by comparing with Mie theory and T matrix method for spherical particle, ellipsoidal particle and cylindrical particle, and the influence of grid size on the simulation accuracy is analyzed subsequently. In the last part, the efficiency of the MRTD scattering model is quantitatively discussed. The simulation results show that the relative errors of scattering phase function simulated by our model are less than 8%, and the errors in forward scattering direction are much smaller, which are less than 4%. The precisions for extinction and absorption efficiency are much higher than the results from the scattering phase function, and the relative errors can reduce to 0.1% for particles with their radii comparable to the wavelength of incident light. The gird size has a significant influence on model precision; to achieve the same accuracy, the grid size first increases with increasing particle radius, and then decreases as a function of particle size for particles with size parameter less than 20. In the next step, we will try to establish the scattering property database of nonspherical particles based on the MRTD scattering model developed here.