Monte Carlo simulations of the extinction rate of densely packed spheres with clustered and non-clustered geometries

摘要

The attempt to characterize physical media such as snow has led to the development of discrete particle models, in which aggregations of particles are embedded in a background media. The authors use such a model to drive Monte Carlo simulations and compute electromagnetic extinction rates, taking into account interactions between the particles. Although the particles can be modeled with any shape, spheres are more easily handled computationally and can be close to actual grain shapes. Results have previously been presented for Monte Carlo simulations of densely distributed spheres for fractional volumes up to 25% and a size parameter of ka=0.2. The authors now produce extinction rates for higher fractional volumes and include the effects of both the electric and magnetic dipole. The result is obtained from an interative solution of Maxwell's multiple scattering equations. Extinction rates are also calculated for aggregations of particles that exhibit surface adhesion and fractal properties. Sticky particles form clusters than can more realistically simulate the structure of geophysical media. The placement of these sticky particles for a Monte Carlo simulation is described. The extinction rates from the Monte Carlo simulations are compared with the quasi-crystalline approximation with coherent potential (QCA-CP), for sticky and non-sticky particles. The result of this comparison shows that the Monte Carlo simulations agree well with QCA-CP for the non-sticky particles, and that the sticky particles exhibit greater extinction than the non-sticky.