Antarctic Cloud Macrophysical, Thermodynamic Phase, and Atmospheric Inversion Coupling Properties at McMurdo Station: I. Principal Data Processing and Climatology

Abstract

Polar cloud radiative forcing plays a crucial role in the determination of the surface and atmospheric energy balance through processes which are not yet fully understood. While there is a broad and fairly complete database of cloud measurements from several Arctic sites and field campaigns through the past two decades, the recent one‐year long U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE) field campaign at McMurdo Station has provided a hitherto unmatched multiple‐instrument set of ground‐based Antarctic cloud measurements. These observations are processed and used to derive the main cloud and liquid containing layer properties: occurrence fraction, cloud persistence and boundaries, and configuration relative to temperature and moisture inversions. The results are compared to previous Arctic observations. It is concluded that clouds and liquid‐bearing layers over McMurdo Station are essentially less prevalent and persistent than their Arctic counterparts. However, they typically have higher bases and show a weaker temperature dependence than in the Arctic, suggesting a more “pristine” Antarctic atmosphere. In addition, the clouds (including both water phases) typically extend toward relatively lower altitudes, and their relation to inversions near cloud top is often similar to those observed in the Arctic.

Persistent Supercooled Drizzle at Temperatures Below −25 °C Observed at McMurdo Station, Antarctica

“…While specular reflection by plate ice crystals may induce similar low LDR values (see Appendix in Silber, Verlinde, Eloranta, Flynn, & Flynn, ), the cloud layer temperatures ( T ; Figure h, left panel) were well below the plate crystal growth regime (Bailey & Hallett, ). Aerosol particles and cloud droplets may also produce low LDR, but the measured β p values are too high and low for aerosol particles and cloud droplets, respectively (e.g., Silber, Verlinde, Eloranta, & Cadeddu, , Figure ). Moreover, the temporal variability of these β p ‐LDR features is significantly patchier than that of a typical liquid‐bearing cloud layer.…”

Antarctic Cloud Macrophysical, Thermodynamic Phase, and Atmospheric Inversion Coupling Properties at McMurdo Station—Part II: Radiative Impact During Different Synoptic Regimes

“…The CRF LW value consistency is in agreement with the results from Summit, Greenland, reported by Miller et al (). The higher CRF LW values for the same LWP range in the Summit study might be related to the lower cloud base AGL measured at Summit in comparison with McMurdo Station (e.g., Shupe et al, ; Silber, Verlinde, Eloranta, & Cadeddu, ).…”

“…The hydrometeor properties from 1 January to 31 December 2016 at McMurdo are derived, following the methodology given in Part I of this series of papers (Silber, Verlinde, Eloranta, & Cadeddu, 2018). In brief, high spectral resolution lidar (HSRL; Eloranta, 2005) data are combined with Ka-Band ARM Zenith Radar (KAZR; Widener et al, 2012) data to generate hourly hydrometeor-bearing air-volume (hereafter referred to as cloud) masks.…”

“…Ice water path (IWP) values are estimated (for qualitative purposes) by using the KAZR reflectivity and (linearly interpolated) sounding temperature measurements, applying the Hogan et al (2006) ice water content retrieval method and integrating the results over the cloud profile. Liquid water path (LWP) information (available after 1 February 2016; 88% complete relative to the full data set) is extracted from the two-channel microwave radiometer (MWR; Morris, 2006) measurements (e.g., Fielding et al, 2015;Nicolas et al, 2017;Silber, Verlinde, Eloranta, & Cadeddu, 2018), with a typical uncertainty of~25 g/m 2 (Cadeddu et al, 2007;Turner, Clough, et al, 2007;Westwater et al, 2001). This parameter is used in combination with the HSRL to determine the total LBCL occurrence fraction (see Silber, Verlinde, Eloranta, & Cadeddu, 2018).…”

“…Liquid water path (LWP) information (available after 1 February 2016; 88% complete relative to the full data set) is extracted from the two-channel microwave radiometer (MWR; Morris, 2006) measurements (e.g., Fielding et al, 2015;Nicolas et al, 2017;Silber, Verlinde, Eloranta, & Cadeddu, 2018), with a typical uncertainty of~25 g/m 2 (Cadeddu et al, 2007;Turner, Clough, et al, 2007;Westwater et al, 2001). This parameter is used in combination with the HSRL to determine the total LBCL occurrence fraction (see Silber, Verlinde, Eloranta, & Cadeddu, 2018). A G-Band Vapor Radiometer Profiler (GVRP; Cadeddu, 2010), which produces (in combination with the MWR measurements) a LWP product with an uncertainty as low as~10 g/m 2 (Cadeddu et al, 2009), was also operated at McMurdo Station from mid-June until the end of the AWARE campaign.…”