Single-scattering characteristics of melting ice crystal particles in the millimeter-wave band

The melting process of ice crystal particles has a significant effect on weather forecasting and global climate. Millimeter waveband is an excellent frequency range for exploring the optical characteristics of ice crystal particles. In this study, a new nonspherical and inhomogeneous ice crystal particle model is built based on the melting process of ice crystal particles. The single-scattering characteristics of ice crystal particles with different frequencies, sizes, shapes and ice crystal content (ICC) are investigated using the discrete dipole approximation (DDA) method. The results show that the single-scattering characteristics of ice crystal particles are closely related to the equivalent radius, frequency, morphology and mixing state. The single-scattering properties of the particles change regularly with the melting process of the ice crystal particles. Specifically, in the early stage of the ice crystal particle melting process, the single-scattering characteristics of ice crystal particles change significantly. With further melting, the change in the single-scattering characteristics of ice crystal particles gradually slows down when the ICC is less than 0.5. The results also show that in the early stage of the melting process, the shape of the ice crystal particles has a huge influence on the single-scattering characteristics of the particles, and in the late stage of the melting process, the single-scattering characteristics of the ice crystal particles are basically independent of the morphology of the ice crystal nuclei. This means that the influence of the morphology of the ice crystal nuclei needs to be considered in phases when simulating the scattering characteristics of the melting ice crystal particles. In summary, the results of this study should improve our understanding of the effect of size parameter, morphology and mixing state on the millimeter-wave scattering characteristics of ice clouds during the melting process and provide a reference for the remote sensing inversion of ice cloud microphysical characteristics.