Modeling, Simulation and Comparison Study of Cirrus Clouds ’ Ice Crystals

Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles ’ size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured by airborne instruments, specifically ice bullets. These can be found depending on the temperature and cloud altitude, isolated or in groups of two or more bullets, called bullet rosettes. The model of the bullet rosettes was developed using the parameters obtained by airborne measurements from the National Center for Atmospheric Research (NCAR). These measurements were done by Video Ice Particle Sampler (VIPS). This is an airborne instrument that flies inside cirrus clouds, and takes samples of the cirrus cloud particles sizes up to 5 µm in size. With these sample parameters we modeled the actual shape of the bullet rosettes using the software DDSCAT. This software allows us to create irregular models of particles using the Discrete Dipole Approximation method. With this model we are able to analyze the backscattering produced by the bullets rosettes model or reflectivity and compute the total volume backscattering coefficient expected from the cirrus clouds. Different models of ice crystals ’ size are compared, some assume constant ice density through out the bullet, while others used the density as a function of the dimension of the bullet