Low Altitude UAS Icing Study with Cloud Model 1

Icing clouds have resulted in significant loss of aircraft performance due the severity of ice accumulation. Unmanned aircraft systems (UAS) may provide an effective and safe platform for advanced weather surveillance and atmospheric data collection. In order to plan flight testing procedure and estimate the parameters of icing conditions, the Cloud Map 1 program will be used to identify possible icing regions in the lower boundary layer.

CM1, a three-dimensional, non-hydrostatic, non-linear, time-dependent numerical model designed for idealized studies of atmospheric phenomena was used to generate the data used in the evaluations. The latest available version of CM1 was used -- revision 18.3 -- for these simulations. Standard cases for a supercell and squall line were utilized to provide data for the OSSEs using the 1/4 circle and 1-km weak-shear case, respectively. Simulations were performed on the Oklahoma State University High Performance Computing Center {\em Cowboy} supercomputer. Cowboy consists of 252 standard compute nodes, each with dual Intel Xeon E5-2620 Sandy Bridge hex core 2.0 GHz CPUs, with 32 GB of 1333 MHz RAM and two fat nodes each with 256 GB RAM and an NVIDIA Tesla C2075 card. Cowboys' aggregate peak speed is 48.8 TFLOPs, with 3048 cores and 8576 GB of RAM. Simulations were run on a single node.

For the supercell simulations, the grid spacing is 1 km in the horizontal and 500-m in the vertical, with resolutions sufficient to resolve storm-scale features, such as the mid-level updraft structure and low-level mesocyclogenesis, but are not generally considered sufficient to accurately represent tornadogenesis. The domain is 120 km by 120 km by 17.5 km, with each simulation extending out through 2 hours. Composite reflectivity near the start and end of the simulaiton is shown in Fig.~\ref{f:cm1} (shown in dBZ). Following the approach of Keeler and Houston, UAS are placed within the simulation domain at specific locations and times to provide the OSSE data, in this case for LEWICE. Notional aircraft with representative paths for a fixed wing (OSU MARIA) and a rotary wing (3DR Solo) are shown with potential representative mission profiles for each.

Simulations will explore weather systems likely to create icing hazards at low altitude (under 1500m AGL). This will contribute to further efforts in an icing flight campaign and an airfoil icing study.