Improved Formulation of Snow Fragmentation during Collision with Hail/ Graupel based on Field Observation at Jungfraujoch

Secondary Ice Production (SIP) has been ascribed to the formation of new ice particles from preexisting ones. Fragmentation of ice particles during collision is one among the known SIP processes. Some of the studies have used theoretical formulation of this SIP processes in the cloud micro-physics scheme of numerical atmospheric models. However, there has been a lack of observational data for better understanding of the SIP process. This study reports fragmentation of naturally falling snow  during their collision with graupel/hail particles based on the observation at Jungfraujoch, a mountain pass in the Alps located about 3.4 km above mean sea level. The study used a  specially designed portable chamber to observe the fragmentation of snow particles outdoor. Based on the observational study, we optimised the theoretical formulation for the prediction of number of fragments arising from the collision between non-dendritic snow and hail/graupel. The observations show an average number of fragments per collision of about 5. The study improved the prediction of SIP through fragmentation compared to our original theoretical formulation, for snow in the non-dendritic regime of temperatures less than -17⁰C.