Detection of High Ice Water Content (HIWC) Conditions: Assessment of a Nowcasting Tool Using Data from the HAIC-HIWC International Field Campaign

Since the 1990s, it has been observed that commercial aircraft sometimes experience engine power-loss and related events while operating in the vicinity of deep convective clouds. Meteorological analyses of such events indicate that high concentrations of ice crystals present a potential hazard to aircraft. A database of ice crystal icing events, assembled by the Engine Harmonization Working Group, has provided guidance on the relevant meteorological predictors of high ice water content (HIWC) conditions and suggests quantitative ranges of each predictor associated with ice crystal icing.

Using information from prior ice crystal icing events, a real-time nowcasting tool for detecting HIWC conditions has been developed by the NCAR HIWC Product Development Team under FAA sponsorship. The Algorithm for Prediction of HIWC Areas (ALPHA) defines ranges of interest for a set of critical meteorological predictors of HIWC conditions. Input data from satellite, model, and radar products are blended using fuzzy logic methodology to yield an estimate of the likelihood of HIWC conditions in a given location. Currently, two separate regional implementations of ALPHA cover the continental United States and northern Australia, providing 3-dimensional estimates of HIWC likelihood over these geographic domains. Since the availability of research-quality data in clouds with HIWC conditions is limited, ALPHA development was based on a relatively small number of case studies of ice crystal icing events. However, objective verification and refinement of ALPHA's methods require a targeted data set characterizing the microphysical properties and dynamic processes in clouds associated with ice crystal icing.

The High Altitude Ice Crystal – High Ice Water Content (HAIC-HIWC) international field campaign was designed to enhance knowledge of ice crystal icing processes in deep convective clouds. Conducted in January-March 2014, Phase I of the HAIC-HIWC field campaign acquired aircraft, satellite, and radar observations of convective clouds near Darwin, Australia. The SAFIRE Falcon 20 aircraft, instrumented with cloud radar and an array of microphysical sensors, flew 23 research flights in monsoon-driven convection. Supporting data from ground-based radar and lightning networks, numerical weather model runs, and satellite overpasses were obtained in parallel. A variety of scientific and engineering objectives were addressed with this effort, including characterization of the microphysical and thermodynamic properties of convective core and near-core regions for research as well as regulatory purposes. The data set collected provides the best opportunity to date for statistically evaluating the performance of ALPHA. Results will enable continued development of an operational nowcasting tool that will support the aviation community in strategic and/or tactical planning for avoidance of ice crystal icing.

The presentation will describe ALPHA functionality in more detail, show examples of ALPHA products from the HAIC-HIWC field campaign, and discuss how specific measurements are being be used to assess ALPHA capabilities.