Integration of advanced satellite cloud products into an icing aircraft icing nowcasting system

Operational products used by the U.S. Federal Aviation Administration provide nowcast and short-term forecast estimates of the potential for the presence of supercooled liquid water and supercooled large droplets. The Current Icing Potential (CIP) system employs basic satellite-derived information, including a cloud mask and cloud top temperature estimates, together with multiple other data sources to produce a gridded, three-dimensional, hourly depiction of icing potential.

Advanced satellite-derived cloud products developed at the NASA Langley Research Center (LaRC) provide a more detailed description of cloud properties (primarily at cloud top) compared to the basic satellite-derived information used currently in CIP. Several of the LaRC products are related to icing potential. This paper describes the process of integrating these advanced cloud products into CIP and understanding the conditions under which satellite-derived cloud products will improve the detection of potential icing conditions.

Cloud phase, liquid water path, and droplet effective radius as estimated by the LaRC algorithms are thought to be good candidates for improving CIP results. Anecdotal evidence provided by the use of LaRC cloud products as a short-term forecasting tool during icing field programs indicates that these satellite-derived fields are indeed useful for discerning the existence of supercooled liquid water and ice crystals. By examining these products in an operational setting, forecasters have been able to identify situations where specific fields are most effective.

Objective assessment of LaRC cloud products is being conducted prior to integration. Case studies using research aircraft data to evaluate specific satellite-derived fields have been analyzed. Tests of both CIP and LaRC products against pilot reports of icing incidence are providing information about the current skill of each. Preliminary results coupled with forecaster experience suggest that phase estimates are typically accurate, and higher effective radius estimates tend to correlate positively with in situ observations of larger drops. LWP estimates compare well with independent observations, particularly at LWP values below 300 g m^-2. Cases where the LaRC cloud products exhibit uniform values of phase, LWP, and effective radius over a large area tend to be more accurate than cases with high spatial variability.

Initial integration of LaRC products targets the experimental high-resolution CIP algorithm. This version of CIP features enhanced spatial resolution of 5 km or less and temporal resolution of 15-30 minutes. Satellite data are essential for achieving these improved resolutions. First attempts to utilize the LaRC cloud products for enhancement of CIP output incorporate the cloud phase and LWP products to adjust the CIP icing severity index within the uppermost cloud layer. In a case with a fairly uniform, single layer, liquid phase cloud over the Great Lakes region, combining the satellite-derived phase and LWP values with other data sources used in CIP produced an icing severity index field consistent with pilot reports in the area. Additional examples demonstrating the impact of LaRC cloud products on CIP regional diagnoses will be presented at the conference.