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Abstract

Cirrus clouds play a significant role in the Earth's global radiative budget. The radiative effect of cirrus clouds depends on the aspherical ice crystal composition present within, making a proper understanding of ice crystal single scattering properties crucial for accurate climatological modeling and forecasting. One of the most relevant cirrus ice crystal habits is a polycrystalline bullet rosette, where individual bullets are radiating from the same nucleation point. Comprehensive studies on the dependencies of ice crystal habit formation have shown that bullet rosettes grow at a range of ice supersaturations with temperatures below -40 °C; environmental conditions frequently found within high altitude cirrus clouds. Here, single scattering properties of atmospheric bullet rosettes were investigated using correlated high resolution in-situ stereo-images of individual bullet rosettes and their angular scattering functions measured by the airborne Particle Habit Imaging Polar Scattering (PHIPS-HALO) cloud probe during the CIRRUS-HL airborne campaign. The microphysical properties of individual bullet rosettes, such as their maximum dimensions, crystal complexity, and number of bullets per rosette, were analyzed and associated with environmental conditions and their measured angular light scattering functions and resulting asymmetry parameter and complexity parameter. Results show that the asymmetry parameters of atmospheric bullet rosettes are lower than what is expected by theoretical studies assuming smooth surfaces on solid and hollow bullet rosettes.