Analyzing the Thermodynamic Phase Partitioning of Mixed Phase Clouds Over the Southern Ocean Using Passive Satellite Observations

Abstract

The thermodynamic phase transition of clouds is still not well understood, therefore, the partitioning of ice and liquid in mixed phase clouds is often misrepresented in numerical models. We use 12 years of cloud observations from the geostationary Spinning Enhanced Visible and InfraRed Imager over the Southern Ocean to detect clouds which contain both liquid and ice pixels at their tops and we retrieve microphysical and radiative properties in each cloud object. The results show that large cloud droplet effective radius coincides with high ice fraction and high ice optical thickness for cloud top temperatures higher than −8 °C. We also found that the density of ice pixel clusters increases with the cloud ice fraction, for ice fraction lower than 0.5, suggesting a multiplication of ice pockets in line with previous studies, particularly efficient for clouds with high perimeter fractal dimension.

Characterization of the Spatial Distribution of the Thermodynamic Phase Within Mixed‐Phase Clouds Using Satellite Observations

“…In particular, Coopman et al. (2021) showed that liquid cloud droplet effective radius at cloud‐top is correlated with cloud ice fraction but does not impact the density of ice pockets within mixed‐phase clouds.…”

“…Clouds continue to be poorly represented in Global Climate Models (GCMs) (Vignesh et al., 2020). One particular cloud type that GCMs continue to struggle to represent are mixed‐phase clouds that exist at temperatures between −38 and 0°C which are particularly ubiquitous in the Arctic and Southern Ocean (Coopman et al., 2021; Korolev et al., 2017; Listowski et al., 2019; Matus & L’Ecuyer, 2017; Mioche et al., 2015; Nomokonova et al., 2019; Shupe, 2011; Shupe et al., 2006; Wang et al., 2003; Zhao & Wang, 2010). Large‐scale forcing, dynamics, surface conditions, and microphysical, radiative, and turbulent processes all contribute to the life cycle of mixed‐phase clouds (Morrison et al., 2011).…”

Another Piece of Evidence for Important but Uncertain Ice Multiplication Processes

“…These include the rime splintering process (also Hallett‐Mossop process, Hallett & Mossop, 1974), droplet shattering upon freezing, collisional breakup of ice particles and several more. Some indications on dominant processes in certain situation can be derived from indirect evidence, such as the temperature ranges of the observed ice enhancement or the correlation with large droplet sizes (Coopman et al., 2021; Lasher‐Trapp et al., 2016; Luke et al., 2021). In contrast to primary ice formation, there are relatively few recent efforts to study ice multiplication in the laboratory.…”

Cloud Top Thermodynamic Phase from Synergistic Lidar-Radar Cloud Products from Polar Orbiting Satellites: Implications for Observations from Geostationary Satellites

“…The thermodynamic phase transition of clouds is still not well understood, often leading to inaccurate representations of the distribution of ice and liquid in numerical models [10,13,16,17]. Mixed-phase clouds in particular are often poorly represented in global models as they tend to oversimplify the intricate microphysical processes that govern the transition between liquid and ice phases [4,10,18].…”

“…Constraining the phase transition mechanisms is particularly challenging since the physics and dynamics of mixed-phase clouds are nonlinear [10,19]. Numerous studies have also demonstrated the influence of cloud phase in climate sensitivity in general circulation models [16,[20][21][22]. The phase partitioning of clouds and their parameterization are therefore of particular interest.…”