Exploring the Role of Fragmentation of Ice Particles by Combining Super-Particle Modeling, Laboratory Studies, and Polarimetric Radar Observations (Invited Presentation)

Ice microphysical processes (IMP) still belong to the least understood cloud and precipitation processes. This hampers our ability to correctly model them in numerical weather prediction models. Especially secondary ice processes (SIP) remain among the least studied IMP, even though in-situ and remote sensing observations have measured large discrepancies between ice particle number concentration (IPNC) and the number of available ice nucleating particles (INP). Recent studies have found an increase of IPNC alongside enhanced aggregation at temperatures warmer than -20°C. Ice-ice collisional fragmentation is one possible SIP that might explain the observed increase in IPNC. In this contribution, we combine zenith triple-frequency (X, Ka, W-band) and slant-viewing W-band spectral polarimetric radar observations with Monte-Carlo Lagrangian particle modeling and laboratory studies to explore ice-ice collisional fragmentation. While the combination of polarimetric and triple-frequency radar observations is a powerful tool which can provide information about the shape, size and concentration of ice particles, radars only observe the impact of IMP on the observed particle distribution, not the IMP themselves. The Lagrangian super-particle model McSnow allows us to describe IMP on the detailed particle level. Recently, a habit prediction scheme which simulates the evolution of ice crystal shape and density has been implemented. Ice habit, particle size, density and fall velocity are core information for radar forward simulations, facilitating the comparison with radar observations and allowing to link the radar observations to specific ice microphysical processes. Initial laboratory studies on ice-ice collisional fragmentation allowed us to implement a new fragmentation scheme in McSnow. To make full use of the rich information content of the McSnow simulations, a new radar forward operator has been developed. The forward operator is based on DDA calculations of more than 1000 ice crystals with varying habits, as well as approximately 500 aggregates with varying degrees of riming. The simulations with the new fragmentation scheme suggest that the increase in ice particle number concentration especially in the dendritic growth regime might be linked to fragmentation. However, further laboratory studies are needed in order to constrain the fragmentation scheme and help answer the question whether fragmentation is an important SIP that can explain the discrepancy between observed IPNC and available INP.