Monday, 9 July 2018
Regency A/B/C (Hyatt Regency Vancouver)
Arctic mixed-phase clouds (AMCs) play an important role in the energy balance in the Arctic region. However, many processes occurring in the AMCs have not been well understood. In particular, previous studies found that when using prognostic formulations for ice-nucleating particles (INPs), the INPs were rapidly depleted and the simulated ice water path was much smaller than observation. Here, we developed a parameterization for ice formation based on the classical nucleation theory, and then implemented the parameterization into the large-eddy simulation (LES) model and the Weather Research and Forecasting (WRF) model. Our results showed that when all INPs had the same efficiency, the ice formation did not persist throughout the simulation. Specifically, when all INPs had a high efficiency, ice formation occurred at the beginning of the simulation but stopped very soon. When all INPs had a low efficiency, ice did not form at the beginning of the simulation but formed several hours later when the temperature became lower. Results also showed that when the INPs had an efficiency spectrum, the ice formation persisted throughout the simulation. In this situation, as the high-efficiency INPs were depleted, the low-efficiency INPs gradually nucleated more ice crystals because the cloud top longwave cooling kept decreasing the temperature of the cloud.
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