Study on shortwave radiative transfer characteristics in polydisperse aerosols in a clear sky

The shortwave radiative transfer is a key factor in the utilization of solar energy and the balance in the earth's radiation budget, and need accurate calculations in research. In clear sky, aerosol is the main medium that interacts with the shortwave radiative transfer, and the accuracy of radiative transfer simulation will be affected by the polydispersity of aerosols. In this paper, a new program of Monte-Carlo ray-tracing (MCRT) is written to simulate the radiative transfer of polydisperse aerosols. The new method of dividing regions with different particle sizes in this paper is used to improve the calculation accuracy, and the scattering process of photons in polydisperse aerosols can be tracked. The difference between the new method and the traditional method (radiative transfer calculation using the average parameters in the particle system) is calculated. The effects of different input parameters on the photon radiative transfer and the order of scattering are studied. The results show that the absorptivity of the new method at different wavelengths is 3.727 % higher on average than the other one, and at the different imaginary part of the complex refractive index (n +/- ki) is first greater than the traditional method and then less than it, the intersection of the two curves is ki = 0.008 (absorptivity = 0.48), there is a significant difference between the two methods. The transmissivity curve has an extreme value with the change of wavelength and complex refractive index, and the extreme point is at lambda = 3.75 mu m and ki = 0.1. Meanwhile, the order of scattering of Photon radiative transfer under the influence of AOD has a normal distribution characteristic, and the AOD corresponding to the peak of normal distribution increases with the order of scattering, but the peak value decreases.