Coupling the FASST Land Surface Model with WRF-ARW for Low-level Icing Forecasts in Complex Terrain

Icing poses as a severe hazard to aircraft safety with human lives and financial resources hanging in the balance, when the decision to ground a flight must be made. Ice accretion not only occurs on the ground and major aircraft components such as propellers, windshield, and wings, but also occurs on antennas, vents, intakes, and cowlings, which also aid in the ability of the aircraft to fly safely. Forecasting conditions where ice may pose these types of hazards is a crucial element in assuring safety as well as aiding research efforts. Complex terrain, in particular, poses difficulty in creating accurate and robust forecasts, because of the many processes occurring between the land and atmosphere in the unique alpine environment.

The Weather Research and Forecast (WRF) model Advanced Research WRF (WRF-ARW) is a collaboratively created, flexible model designed to run on distributed computing systems for a variety of applications, including forecasting research. Among the many physics packages included in the WRF-ARW is land-surface modeling options. Land-surface models provide output data on surface heat and moisture fluxes given radiation, precipitation, and surface properties (such as soil type) as input. The purpose of this type of output is to provide lower-boundary condition for use in the planetary boundary layer schemes.

The Fast All-Season Soil STrength (FASST) land-surface model was developed by the U.S. Army Cold Regions Research and Engineering Laboratory in Hanover, New Hampshire. Originally, FASST was intended for military purposes of providing information to mobility and sensor performance algorithms, but has since been utilized in civilian applications and research. Designed to use both meteorological and terrain data, the model calculates heat and moisture within the surface layer as well as the exchange of these parameters between the soil, surface elements, and atmosphere.

Focusing on the Presidential Mountain Range of New Hampshire under the NASA EPSCoR Icing Assessments in Cold and Alpine Environments project, one of the main goals is to create a customized, high resolution model to predict and assess ice accretion in complex terrain. The purpose of this research is to couple the FASST land-surface model with the WRF to improve low-level icing forecasts in complex terrain. The coupled system is anticipated to improve icing forecasts produced by the WRF-ARW because of FASST's sophisticated approach to handling processes such as meltwater, freezing, and thawing which affect the water and energy budget.