Phase Characterization of Southern Ocean Clouds using HIAPER Cloud Radar (HCR) and High Spectral Resolution Lidar (HSRL) Observations: results from SOCRATES
Abstract
From 15 January to 24 February 2018, the NSF/NCAR Gulfstream-V flew over the Southern Ocean to observe fine scale features and structures of clouds as part of SOCRATES. The aircraft sampled low-level boundary layer mixed-phase clouds in the cold sector of Southern Ocean cyclones. Climate models often underestimate shortwave radiation reflected by near surface cloud cover during the Austral summer due to difficulties in representing mixed-phase and supercooled liquid water (SLW). Understanding these cloud properties is critical to accurately simulating them.
Each flight during the campaign consisted of an initial high-altitude flight leg between Tasmania and 60° south, after which the aircraft descended to make in situ measurements. During the high-altitude flight legs, the HCR and HSRL were pointed at nadir and were able to remotely sense cloud properties and cloud top phase. During twelve of the high-altitude flight legs, dropsondes were deployed to sample the thermodynamic environment present. Thermodynamic fields measured by the dropsondes were overlaid on the radar and lidar cross sections. An algorithm was developed to characterize cloud top phase and ice particle production as a function of cloud top temperature. Cloud tops were classified as containing SLW if they had low particle linear depolarization ratios and a high backscatter coefficient and ice if a high linear depolarization ratio was present. Many SLW topped clouds had plumes of precipitation falling from the cloud top. These plumes were determined to be ice phase if the precipitation fell through the 0° C isotherm and a definitive bright band and/or a distinct jump in particle fall velocity was present. Deliquesced sea salt and other aerosols were also detected in cloud free regions using the HSRL. Results indicate that nearly all clouds sampled during SOCRATES had SLW containing cloud tops. Most cloud tops had temperatures between -10° C and 0° C supporting the existence of SLW and mixed-phase cloud processes. Of the clouds sampled, approximately one in fifteen had a definitive bright band present. Ice production at relatively warm environmental temperatures was also occurring indicated by a definitive bright band even when cloud top temperatures were as warm as -2° C. The sources of these radar, lidar, and thermodynamic observations will be discussed.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A11J2903R
- Keywords:
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- 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0321 Cloud/radiation interaction;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3349 Polar meteorology;
- ATMOSPHERIC PROCESSES