Impacts of secondary ice production on arctic mixed-phase clouds during M-PACE
Liu, Xiaohong — Texas A&M University
Area of research:
Mixed-phase stratus clouds in the Arctic are long-lived and have a large impact on the surface radiation budget. Ice crystals play a key role in the cloud phase and thus determine the optical properties of these clouds. However, how ice crystals are produced in these clouds is still unknown. In this study, we quantify the contribution of secondary ice production (SIP) to the formation of ice in the arctic mixed-phase clouds observed during the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility Mixed-Phase Arctic Cloud Experiment (M-PACE). We represent different SIP mechanisms (i.e., frozen raindrop shattering, ice–ice collisional breakup, and rime splintering) in a global climate model (CESM2) and evaluate the CESM2-simulated clouds against the M-PACE observations.
We find that the SIP is the dominant source of ice crystals near the cloud base in the single-layer mixed-phase clouds observed in M-PACE, with the maximum enhancement in ice crystal number concentrations by up to 4 orders of magnitude in moderately supercooled clouds (~ −10 °C). The model with SIP improves the occurrence and phase partitioning of mixed-phase clouds, reverses the vertical distribution pattern of ice number concentrations, and provides better agreement with the M-PACE observations.
This study indicates that SIP contributes 85% to the total ice formation during the single-layer mixed-phase cloud period in M-PACE. The model biases of underestimation of mixed-phase cloud occurrence are reduced after considering the SIP processes. The mixed-phase cloud occurrence is increased from 26.9% to 58.8%, much closer to 62.7% in the observation. The findings of this study highlight the importance of considering SIP in global climate models.