Nowcasting aircraft icing conditions using GOES-derived cloud products

Since the winter of 1996-97 meteorologists at the National Center for Atmospheric Research (NCAR) have been providing short term forecasts (nowcasts) of icing conditions to flight engineers and pilots at the NASA Glenn Research Center. The forecasts are used to guide an instrumented research aircraft into icing conditions so that their characteristics, resulting ice accretion, and aircraft performance changes can be documented. The icing forecasts cover the 1 to 36-h time frame. Nowcasts are provided to the crew during the flight to direct the aircraft into and maintain exposure to the desired icing conditions.

The meteorologists use a variety of products to make the nowcasts. Fine-scale details are found in basic satellite fields (cloud top temperature, albedo, reflectance, etc.), radar reflectivity, pilot reports, and surface observations of cloud cover and precipitation. These products have been extremely useful in the determination of the presence or absence of supercooled liquid water (SLW) and ice crystals. In the past two years new tools developed at the NASA Langley Research Center have been available to assist in both the flight planning and directing of the aircraft in flight. These GOES-derived satellite products have proven to be of great value in refining the diagnoses of SLW content near cloud top, in particular. They have also appeared to be of some use for diagnosing the presence of larger droplets near cloud top.

The products are scheduled to be incorporated into the Current Icing Potential (CIP) algorithm, which was developed at NCAR and gives an hourly diagnosis of icing conditions across the CONUS. The forecasters experience with the GOES products supports these efforts. By examining the products in an operational setting the forecasters have been able to identify situations where the fields are most effective. This knowledge is useful for determining which fields should be integrated into CIP and for understanding when specific fields are likely to improve CIP results.

Cloud phase, liquid water path, and effective radius are the fields most used by the forecasters and are the best candidates for inclusion in CIP. In this paper, a typical flight day will be described, focusing on the use of the GOES-derived satellite products in both the planning and directing of the flight made on this day.