The structure of turbulence and mixed-phase cloud microphysics in a highly supercooled altocumulus cloud

Abstract

Abstract. Observations of vertically resolved turbulence and cloud microphysics in a mixed-phase altocumulus cloud are presented using in situ measurements from an instrumented aircraft. The turbulence spectrum is observed to have an increasingly negative skewness with distance below cloud top, suggesting that long-wave radiative cooling from the liquid cloud layer is an important source of turbulence kinetic energy. Turbulence measurements are presented from both the liquid cloud layer and ice virga below. Vertical profiles of both bulk and microphysical liquid and ice cloud properties indicate that ice is produced within the liquid layer cloud at a temperature of −30 ∘C. These high-resolution in situ measurements support previous remotely sensed observations from both ground-based and space-borne instruments and could be used to evaluate numerical model simulations of altocumulus clouds at spatial scales from eddy-resolving models to global numerical weather prediction models and climate simulations.

Development of aerosol activation in the double-moment Unified Model and evaluation with CLARIFY measurements

“…The derived in-cloud relative humidity is therefore set to 100 % in this work. Zonal, meridional and vertical wind components were derived from the five-port turbulence probe located on the aircraft radome (Petersen and Renfrew, 2009;Barrett et al, 2020). On the transit at 5180 m altitude from Ascension Island to the cloud, the mean vertical velocity was −0.010 m s −1 .…”

“…Aerosol data were only used when in cloudand precipitation-free air. We determined this using the standard deviation of raw power on the Nevzorov total water content probe (Korolev et al, 2013), where a power greater than 3.0 mW (∼ 1.5 × 10 −4 g m −3 ) indicates cloud conditions, following Barrett et al (2020). An additional safety window of 5 s (∼ 500 m) either side of positively identified cloud was applied to account for diffuse cloud edges and imperfect temporal and spatial synchronisation between probes and data recording systems.…”

Nonturbulent Liquid‐Bearing Polar Clouds: Observed Frequency of Occurrence and Simulated Sensitivity to Gravity Waves

“…Previous studies examined GW influence on ice nucleation in cirrus (e.g., Haag & Kärcher, 2004; Jensen et al, 2016), midlatitude altocumulus formation (e.g., Ansmann et al, 2005; Barrett et al, 2020; Hogan et al, 2003), wave‐cloud processes (e.g., Cotton & Field, 2002; Field et al, 2012), and the evolution of marine stratocumulus (e.g., Allen et al, 2013; Connolly et al, 2013; Jiang & Wang, 2012). However, the impact of GWs on polar LBC development has not appeared in the literature to our knowledge, despite the intense and prevalent nature of GW‐induced fluctuations over polar regions (e.g., Podglajen et al, 2016).…”

Exploring the Cloud Top Phase Partitioning in Different Cloud Types Using Active and Passive Satellite Sensors

“…Several studies have shown that mixed-phase clouds occur irrespective of the season, can be found in diverse locations, and can be associated with various cloud types (Korolev et al, 2017). Observations of mixed-phase clouds include active (e.g., Zhang et al, 2010;Tan et al, 2014;Cesana & Storelvmo, 2017) and passive satellite (e.g., Coopman et al, 2019;Noh et al, 2019;Tan et al, 2019), airborne in situ (e.g., Korolev, 2008;Costa et al, 2017;Barrett et al, 2020), ground-based (e.g., Henneberger et al, 2013;Yu et al, 2014;Gierens et al, 2020) and aircraft-based remote sensing measurements (e.g., Wang et al, 2012;Plummer et al, 2014). In Tan et al (2014), in particular, mixed-phase clouds have been studied statistically in terms of supercooled cloud fraction, defined as the ratio of the in-cloud frequency of supercooled liquid pixels to the total frequency of supercooled liquid and ice pixels within 2 • latitude by 5 • longitude grid boxes, at several isotherms between -10 • C and -30 • C, distinguishing cases in the Northern Hemisphere (NH) and in the Southern Hemisphere (SH), as well as cases over ocean and over land.…”

“…Several studies have shown that mixed‐phase clouds occur irrespective of the season, can be found in diverse locations, and can be associated with various cloud types (Korolev et al., 2017). Observations of mixed‐phase clouds include active (e.g., Cesana & Storelvmo, 2017; Tan et al., 2014; Zhang et al., 2010) and passive satellite (e.g., Coopman et al., 2019; Noh et al., 2019; Tan et al., 2019), airborne in situ (e.g., Barrett et al., 2020; Costa et al., 2017; Korolev, 2008), ground‐based (e.g., Gierens et al., 2020; Henneberger et al., 2013; Yu et al., 2014) and aircraft‐based remote sensing measurements (e.g., Plummer et al., 2014; Wang et al., 2012). In Tan et al.…”