Observations of Icing Conditions in Southern Ocean Clouds during SOCRATES

The recent Southern Ocean Cloud Radiation Aerosol Transport Experimental Study (SOCRATES) provided an extensive survey of supercooled liquid water conditions in Southern Ocean lower tropospheric clouds. The NSF/NCAR G-V (also known as HIAPER) aircraft was used for both in situ measurements of cloud and aerosol conditions and as a remote sensing platform for the High Spectral Resolution Lidar (HSRL) and the HIAPER Cloud Radar (HCR). The HCR is a W-band polarimetric Doppler radar providing information on reflectivity, radial velocity, and depolarization ratio. In situ instruments included a suite of imaging instruments, scattering instruments, and total water/liquid water instruments.

Icing conditions were encountered that included ice-free regions, mixed phase regions, and, importantly, supercooled large drops/drizzle regions, which are of particular concern for aviation safety. The HSRL was used to identify regions of supercooled water on the tops of clouds (but was rapidly attenuated by the cloud). Flights just above the tops of the clouds and below the base of the clouds provided the best radar view of the cloud structure, which often consisted of thin multi-layered clouds. After over-flights (or under-flights) of the clouds for remote sensing, the regions were sampled in situ by descending or ascending through the various layers and selecting layers for extended sampling at constant altitude in-cloud.

We present some examples of G-V data from the different icing conditions that were encountered, comparing the remote sensing view with the in situ measurements, with particular emphasis on the locations and meteorological conditions that exhibited supercooled large drops/drizzle.