Importance of Secondary Ice Production to Ice Formation and Phase of
High-Latitude Mixed-Phase Clouds during SOCRATES and MARCUS
Abstract
Measured ice number concentrations are often much higher than the number
concentrations of ice nucleating particles (INPs) in moderately cold
mixed-phase clouds, suggesting the potential importance of secondary ice
nucleation (SIP). However, the occurrence frequency and importance of
SIP relative to primary ice nucleation for ice formation and mixed-phase
cloud properties are largely unknown. Representing the SIP processes in
weather and climate models is equally challenging. In this study, we
present a process-level understanding of SIP in high-latitude
mixed-phase clouds based on integrated model-observational analyses of
the NSF SOCRATES aircraft and DOE ARM MARCUS ship-borne data. We run the
Community Earth System Model version 2 (CESM2) nudged towards the MERRA2
Reanalysis and output the modeled clouds and aerosols along the aircraft
flight and ship tracks for direct model-observation comparisons. We
found that CESM2 with a physical representation of SIP processes (e.g.,
ice-ice collisional break-up, droplet shattering during rain freezing)
better capture the observed ice crystal number concentrations (ICNCs)
and cloud properties. SIP often dominants the ice formation in the
moderately cold mixed-phase clouds, and transforms ~30%
of pure liquid-phase clouds simulated in the model into mixed-phase
clouds. We also compare modeled ice enhancement ratio due to SIP to ICNC
and INP number concentrations observed during SOCRATES and MARCUS.