Simulations and Observations Implicating Mesoscale Gravity Waves in Producing an Environment which is Conducive to Aircraft Icing

An in-depth analysis of the dynamical and microphysical processes responsible for the ATR72 plane crash near Roselawn, Indiana is presented. Observed surface and upper air data, satellite data, and numerical simulations using MASS version 5.12 at 44, 20, and 10 km resolutions are used to assess the atmospheric conditions present at the time of the crash. Preliminary results from the 10 km simulation indicate that high icing potential existed at the altitude of the crash and near the time of the accident. The mesoscale numerical simulations suggest that a ducted, large-amplitude, hydrostatic, propagating, internal gravity wave was the key organizing mechanism for an icing environment. This wave is diagnosed from model cross-sections which indicate a region of descent around 400mb coupled with a region of ascent around 650mb propagating through the area surrounding Roselawn, Indiana from west-southwest to east-northeast. Such a wave is likely to have produced three key signals necessary for icing: 1) descent aloft resulting in the removal of frozen hydrometeors 2) ascent within the lower-middle troposphere resulting in production of substantial cloud water, some of which is supercooled, and 3) relatively strong vertical wind shear near the wave duct enhancing turbulent mixing aiding the collision-coalescence droplet growth process. The gravity waves evident in the simulation, will be verified against satellite, radar, wind profiler, and surface microbarogram observations.