Southern Ocean Cloud Properties Derived From CAPRICORN and MARCUS Data

Abstract

While the region is known for deep midlatitude cyclones, it is the accompanying fields of marine boundary layer (MBL) clouds that seem to be critical to understanding the radiative energy balance of this region (Bodas-Salcedo et al., 2012, 2014, 2016, 2019). Inspired by Trenberth and Fasullo (2010), who showed a high bias in surface-absorbed solar energy by models, studies have increasingly focused on the ubiquity of supercooled liquid water in SO clouds. Simulations of these clouds too aggressively reduce cloud cover through ice phase precipitation processes (Frey & Kay, 2017; Vergara-Temprado et al., 2018). Recent modeling studies have mitigated this bias through various means and have shown the climate system's sensitivity to these SO MBL clouds (Kay et al., 2016; Tan et al., 2016). How the properties of liquid phase clouds-especially supercooled liquid phase clouds-vary across the SO remains an important topic. While the meteorology of the SO is predictable, variations in factors that control the local and regional aerosol properties differ considerably from regions north of the Antarctic Circumpolar Current (ACC) to the marginal seas along the Antarctic (Armour et al., 2016; Fossum et al., 2018). While seasonally varying sea surface temperatures and sea ice contribute to the cloud variability (Huang et al., 2016), the Antarctic Circumpolar Current essentially divides the SO into lower latitude temperate and high latitude oceans. Especially in the high latitude SO, seasonal biological productivity results in

Mixed‐Phase Clouds Over the Southern Ocean as Observed From Satellite and Surface Based Lidar and Radar

“…However, since we are considering cloudy environments, we can reasonably assume that the humidities in the sub cloud region are likely at least near ice saturation or ~80% with respect to water. This is in agreement with the radiosonde data that we have examined (Mace et al, 2021). For humidities in excess of 60% with respect to liquid, the depolarization ratio of sea salt aerosol is much less than 0.03 (Haareig et al, 2017;their Figure 12).…”

“…We only use MARCUS data collected between early January and March 2018 due to insufficient quality lidar data collected earlier. Mace and Protat (2018) and Mace et al (2021) describe the method used to identify MPC occurrence from the surface-based data. By examining warm layers where ice is not possible and ice-only layers, such as snow below cloud base, we identify the depolarization ratio threshold that separates ice hydrometeors from water droplets.…”

“…Observational studies of the absorbed shortwave bias over the SO have focused on the occurrence frequency of ice-phase precipitation (Bodas-Salcedo et al, 2016;Naud et al, 2014). Satellite data have provided the only broad observations of SO clouds in space and time, although recent shipborne studies have begun to fill in essential gaps (Fossum et al, 2018;Mace & Protat, 2018;Mace et al, 2021;Protat et al, 2017). In particular, the CALIPSO (Winker et al, 2009) and CloudSat (Stephens et al, 2008) satellites have significantly expanded our measurements that address SO cloud phase.…”

Mixed‐Phase Clouds and Precipitation in Southern Ocean Cyclones and Cloud Systems Observed Poleward of 64°S by Ship‐Based Cloud Radar and Lidar

“…MWACR data are calibrated by adding 4.5 dB to the reflectivity profiles provided by ARM. This value was deduced from evaluations of the MARCUS MWACR reflectivity against the calibrated W-band cloud radar onboard the CAPRICORN-II voyage over similar latitudes and times (Mace et al, 2021), and is consistent with the ARM cloud radar offsets identified by Kollias et al (2019). The MWACR was mounted on a stabilizing platform which helped ensure that it remained vertically pointing, although as we will detail below, the ship's heave, pitch, and roll during the three case studies was minimal.…”

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

“…Many field campaigns took place in the Southern Ocean to study cloud microphysical and radiative properties (McFarquhar et al, 2020). Mace, Protat, et al (2020) have shown that Southern Ocean clouds tend to be thicker with smaller and more numerous hydrometeors than other latitudes. With airborne measurements, Ahn et al (2017) showed that 38.5% of the clouds contained ice, mainly from mixed-phase clouds, and they suggested that these clouds were considered as ideal for the Hallet-Mossop secondary ice production process.…”