Ice Multiplication by Breakup in Ice–Ice Collisions. Part II: Numerical Simulations

• Published in: Journal of the atmospheric sciences Vol. 74; no. 9; pp. 2789 - 2811
• Main Authors: 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.
• Format: Journal Article
• Language: English
• Published: United States American Meteorological Society 01.09.2017
• Subjects: Cloud microphysics; Clouds; Earth and Related Environmental Sciences; Geovetenskap och miljövetenskap; Hail; Ice particles; Meteorologi och atmosfärforskning; Meteorology and Atmospheric Sciences; Natural Sciences; Naturvetenskap
• ISSN: 0022-4928; 1520-0469
• DOI: 10.1175/JAS-D-16-0223.1

Abstract 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%.