Validation of a theory for ice formation in freezing drizzle events

The causes of in-flight aircraft icing are still not completely understood . The prediction models of when icing will occur are being improved to reflect the knowledge gained about the causes of in-flight icing. The factors identified, up to this point, are the liquid water content of the clouds, the air temperature in the clouds, and the presence of large supercooled water droplets. It is important to understand not only these factors but the types of icing they will cause. The current standard model predicts broad areas of icing and has a high false alarm rate. An area where current modeling efforts are inadequate are for freezing drizzle events and how such conditions affect ice formation, especially for aircraft icing.

This purpose of this project is to examine actual weather conditions associated with freezing drizzle events. This study is based on a theory by Alexei Korolev and George Isaac, which states that freezing drizzle events coincide with large supercooled liquid droplets (D> 75 µm) at the cloud tops. To determine the validity of this theory, freezing drizzle events from January 2004 to May 2005 were compared with satellite images of cloud top droplet size. This poster presents results from the study to determine how well it validates the theory for ice formation as postulated by Korolev and Isaac.