Abstract
A discrepancy of up to 5 orders of magnitude between ice crystal and ice nucleating particle (INP) number concentrations was found in the measurements, indicating the potential important role of secondary ice production (SIP) in the clouds. However, the relative importance and interactions between primary and SIP processes remain unexplored. In this study, we implement five different ice nucleation schemes as well as physical representations of SIP processes (i.e., droplet shattering during rain freezing, ice-ice collisional break-up, and rime splintering) in the Community Earth System Model version 2 (CESM2). We run CESM2 in the single column mode for model comparisons with the DOE Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment (M-PACE) observations. We find that the model experiments with aerosol-aware ice nucleation schemes and SIP processes yield the best simulation results for the M-PACE single-layer mixed-phase clouds. We further investigate the relative importance of ice nucleation and SIP to ice number and cloud phase as well as interactions between ice nucleation and SIP in the M-PACE single-layer mixed-phase clouds. Our results show that SIP contributes 80 % to the total ice formation and transforms ~ 30 % of pure liquid-phase clouds simulated in the model experiments without considering SIP into mixed-phase clouds. We find that SIP is not only a result of ice crystals produced from ice nucleation, but also competes with the ice nucleation. Conversely, strong ice nucleation also suppresses SIP by glaciating mixed-phase clouds.
Highlights
Ice crystals significantly impact microphysical and radiative properties of mixedphase clouds (Korolev and Isaac 2003; Korolev et al, 2017; Morrison et al, 2012), which further impact the Earth’s energy budgets
secondary ice production (SIP) processes have a varied impact on modeled liquid water path (LWP) and ice water path (IWP), depending on ice nucleation
In the experiments with the classical nucleation theory (CNT), N12, and D15 ice nucleation schemes, simulated IWP is enhanced and LWP is reduced after considering the SIP
Summary
Ice crystals significantly impact microphysical and radiative properties of mixedphase clouds (Korolev and Isaac 2003; Korolev et al, 2017; Morrison et al, 2012), which further impact the Earth’s energy budgets. Ice particles in mixed-phase clouds with temperatures between about -38 °C and 0 °C can be formed via heterogeneous ice nucleation on ice nucleating particles (INPs) or arisen through secondary ice production (SIP) (Kanji et al, 2017; Field et al, 2017). Dust is generally considered as the most effective INPs for heterogeneous ice nucleation at temperatures below about -15 °C (Hoose et al, 2008; Atkinson et al, 2013; Kanji et al, 2017). SIP processes generate additional ice crystals, often involving the primary ice. Several SIP mechanisms have been suggested: rime splintering ( known as the Hallett–Mossop (HM) process), droplet shattering during rain freezing (FR), iceice collisional break-up (IIC), and fragmentation during the sublimation of ice bridge (Field et al, 2017; Korolev et al, 2020). Other microphysical processes such as rain formation and ice growth are important for mixed-phase cloud properties
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