Scattering Phase Function of Bullet Rosette Ice Crystals

Abstract Ice crystals in cirrus frequently exhibit the shape of a bullet rosette composed of multiple bullets that radiate from a junction center. The scattering phase function of these ice crystals, pertinent to the radiation budget of cirrus, may differ from the one obtained for ice crystals with a simple geometrical shape. In this paper, the authors studied the sensitivity of the scattering phase function of a bullet rosette to its geometrical characteristics: the shape, aspect ratio, and spatial orientation. In doing so, they defined first an idealized bullet rosette according to the current knowledge of the crystalline structure and nucleation process of bullet rosettes. The scattering phase function was computed with a ray-tracing method. The scattering phase function of a bullet rosette varies with its shape, and the lateral and backward scattering tends to increase with the number of bullets/bullet rosettes. This is due to the interaction of light scattered by a bullet with its adjacent bullets. T...