Ice Multiplication by Breakup in Ice-Ice Collisions. Part II: Numerical Simulations
Phillips, Vaughan T. J. ; Yano, Jun-Ichi ; Formenton, Marco ; Ilotoviz, Eyal ; Kanawade, Vijay ; Kudzotsa, Innocent ; Sun, Jiming ; Bansemer, Aaron ; Detwiler, Andrew G. ; Khain, Alexander ; Tessendorf, Sarah A.
In Part I of this two-part paper, a formulation was developed to treat fragmentation in ice-ice collisions. In the present Part II, the formulation is implemented in two microphysically advanced cloud models simulating a convective line observed over the U.S. high plains. One model is 2D with a spectral bin microphysics scheme. The other has a hybrid bin-two-moment bulk microphysics scheme in 3D. The case consists of cumulonimbus cells with cold cloud bases (near 0°C) in a dry troposphere.Only with breakup included in the simulation are aircraft observations of particles with maximum dimensions >0.2 mm in the storm adequately predicted by both models. In fact, breakup in ice-ice collisions is by far the most prolific process of ice initiation in the simulated clouds (95%-98% of all nonhomogeneous ice), apart from homogeneous freezing of droplets. Inclusion of breakup in the cloud-resolving model (CRM) simulations increased, by between about one and two orders of magnitude, the average concentration of ice between about 0° and -30°C. Most of the breakup is due to collisions of snow with graupel/hail. It is broadly consistent with the theoretical result in Part I about an explosive tendency for ice multiplication.Breakup in collisions of snow (crystals >~1 mm and aggregates) with denser graupel/hail was the main pathway for collisional breakup and initiated about 60%-90% of all ice particles not from homogeneous freezing, in the simulations by both models. Breakup is predicted to reduce accumulated surface precipitation in the simulated storm by about 20%-40%.
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