Search Results

A large database is being created from icing flight programs completed by aircraft manufacturers for certification and by the NASA-Glenn Research Center for basic research. Although not yet complete, this database already provides an excellent opportunity to study aircraft icing conditions sampled in a wide variety of environments across eastern Canada and most of the United States, including Alaska. In this study, the focus is a comparison of conditions found within boundary-layer stratocumulus icing clouds over the Great Lakes, Pacific Northwest and Alaskan Interior. The clouds will be characterized in terms of temperature, liquid water content, median volumetric diameter, and drop concentration. Critical factors driving these parameters will be discussed.

In the continental United States east of the Rocky Mountains cold fronts are quite common in wintertime due to the many cyclones moving through this region, and icing conditions in the vicinity of cold fronts are a major contributor to the overall occurrence of icing in the atmosphere. The conditions examined in this study will be those behind the cold front. Icing there is often found in stratocumulus clouds that form due to destabilization of the boundary layer through cold air advection and an inversion formed by subsidence aloft which caps their growth. Moist adiabatic lapse rates, small drop sizes, high drop concentrations, and moderate to high liquid water contents depending on the cloud depth often characterize these clouds.

The Current Icing Product (CIP) provides an hourly diagnosis of the severity of icing occurring based on multiple data sources. Pilot reports (PIREPs) and surface observations (METARs), as well as satellite, numerical weather prediction (NWP) model, radar, and lightning data are all utilized within the algorithm. The accurate identification of cloud base is a large factor in the algorithm's determination of icing severity. Current methods employ the METAR observation of ceiling to identify the cloud base over a specified area within the CIP domain. The temperature from the Rapid Update Cycle (RUC) NWP model at the height of the observed METAR ceiling can be utilized as a proxy for the amount of condensate in the cloud. The likelihood of a large amount of condensate in the identified cloud increases with increasing cloud base temperature. As the amount of liquid water diagnosed by CIP severity increases, so does the estimated icing severity.

A theoretically based algorithm to derive super-cooled liquid water (SLW) cloud macrophysical and microphysical properties is applied to operational satellite data and compared to pilot reports (PIREPS – from commercial and private aircraft) of icing and to in-situ measurements collected from a NASA icing research aircraft. The method has been shown to correctly identify the existence of SLW provided there are no higher-level ice crystal clouds (i.e. cirrus) above the SLW deck. The satellite-derived SLW cloud properties, particularly the cloud temperature, optical thickness or water path and water droplet size, show good qualitative correspondence with aircraft observations and icing intensity reports. Preliminary efforts to quantify the relationship between the satellite retrievals, PIREPS and aircraft measurements are reported here. The goal is to determine the extent to which the satellite-derived cloud parameters can be used to improve icing diagnoses and forecasts.