Aerosol‐Mediated Glaciation of Mixed‐Phase Clouds: Steady‐State Laboratory Measurements

Abstract

What concentration of ice‐nucleating particles is required to completely glaciate a typical atmospheric supercooled liquid cloud? This seemingly esoteric question has far reaching implications, as the ratio of liquid to ice in these clouds governs, for example, their influence on Earth's radiation budget and their precipitation efficiency. Microphysical properties of steady‐state mixed‐phase clouds formed in a laboratory convection chamber are observed using digital holography. It is observed that the ratio of ice to total water content of steady‐state mixed‐phase clouds is determined by the concentration of ice‐nucleating aerosol particles. Existing theory is adapted to show such clouds result from a balance between the thermodynamic forcing (i.e., the source of excess water vapor that is condensing to liquid and ice) and the number and size of particles that become ice (i.e., the ice integral radius). The measurements quantitatively support the Korolev‐Mazin conditions for existence of mixed‐phase clouds.

The Portable Ice Nucleation Experiment (PINE): a new online instrument for laboratory studies and automated long-term field observations of ice-nucleating particles

“…This underlines the importance of INPs for cloud radiative properties and precipitation formation, but it should be noted here that the cloud ice phase not only depends on the primary ice formation by INPs, but is also largely influenced by a cascade of secondary ice formation and interaction processes, in particular at temperatures above −15 • C (Field et al, 2016). Increased ice crystal concentrations can for example lead to rapid cloud glaciation and associated dissipation (Campbell and Shiobara, 2008;Paukert and Hoose, 2014), as also observed recently in a laboratory cloud chamber experiment (Desai et al, 2019).…”

“…Most of the previous INP measurements were only sensitive to immersion freezing INPs in the temperature range of mixed-phase clouds and were carried out at boundary layer field sites which were considered to be predominantly influenced by different aerosol types. Measurements in the free troposphere were either performed at high-altitude mountain stations (Boose et al, 2016a, b;DeMott et al, 2003a;Conen et al, 2015;Lacher et al, 2018a, b) or with aircraft-based measurements (Rogers et al, 2001;DeMott et al, 2003b;Prenni et al, 2009;Pratt et al, 2010;Eidhammer et al, 2010;Field et al, 2012), but most of them were also limited to measure immersion freezing INPs at higher temperatures. De-Mott et al (2003b) also measured the concentration of INPs active in the deposition mode at temperatures below −40 • C.…”

Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles

“…Within minutes they reach hundreds of micrometres in diameter, depleting liquid water through diffusional growth (Wegener-Bergeron-Findeisen process, WBF) and accretion of droplets (riming) as they grow and precipitate. In some situations the impact of INPs will be amplified through secondary ice production (SIP) where a range of mechanisms are thought to result in the production of additional ice crystals (Field et al, 2017). It should be borne in mind that these processes (SIP, WBF, riming) subsequent to ice nucleation are relatively poorly understood and need attention (Komurcu et al, 2014).…”

“…Modelling work suggests that at concentrations of ice crystals above about 1 L −1 there are dramatic reductions in liquid water, but smaller concentrations also deplete the liquid water path and reduce albedo (Vergara-Temprado et al, 2018;Stevens et al, 2018). However, the relationship between INP concentration and cloud glaciation is complex and governed by the WBF process (Desai et al, 2019). In some publications, CCN and INPs are collectively referred to as "cloudforming nuclei".…”

Aerosol-Cloud Interactions in Turbulent Clouds: A Combined Cloud Chamber and Theoretical Study

“…A study presented in Desai et al [75] explored this topic by creating a steady-state mixedphase cloud through continuous injection of cloud condensation nuclei and ice-nucleating particles at a controlled thermodynamic and turbulent condition. By controlling the relative fraction of ice nucleating particles, we achieve different degrees of the Wegener-Bergeron-Findeisen process, and the findings are consistent with the theoretical criteria of glaciation (Korolev [153]) within experimental uncertainties.…”