Comparison of Airborne In Situ Icing Observations to Icing Algorithm Output and Aviation Forecasts in the Southern Ocean

In 2018 the international Southern Ocean Cloud, Radiation, and Aerosol Transport Experimental Study (SOCRATES) project used the NSF/NCAR Gulfstream V research aircraft to collect atmospheric observations in the remote, pristine environment between Australia and Antarctica. One of the goals of the project was to characterize the icing environment in this region using cloud microphysics instrumentation. During the fifteen research flights clouds containing supercooled liquid water (SLW) and supercooled large drops (SLD) were sampled. These observations are used to identify flight segments where airframe icing occurred. Those segments are compared with output from the Forecast Icing Potential (FIP) algorithm developed at NCAR, as well as with official forecasts from the Australian Bureau of Meteorology’s (BoM) National Operations Center (NOC).

FIP runs using output from the Australian Community Climate and Earth-System Simulator (ACCESS) model are analyzed for a variety of forecast lead times valid during the research flights. The regional ACCESS-R is available over the project domain and has a horizontal resolution of approximately 12 km. Differences in the fields available between ACCESS and the typical model that the FIP runs on required some modifications and tuning of the algorithm. Cross sections and flight level plots are compared with icing observations from the research aircraft and statistics calculated to evaluate the skill of the algorithm in this part of the world.

As part of its duties the NOC issues icing forecasts and Significant Meteorological Information advisories (SIGMETs) for Australia and the ocean areas surrounding it. During SOCRATES they also issued forecasts and advisories for the flight domain to provide information for safe flight operations. Observations to validate these forecasts are difficult to obtain in this part of the world, so the SOCRATES dataset provides a unique opportunity to compare the products issued by the NOC to the observed conditions.