Icing condition probabilities (ICPs) are the probability of encountering conditions known to lead to in-flight aircraft icing. ICPs provide reseachers and planners as well as pilots an analysis of the atmosphere not presented before. ICPs are dependent on temperature, relative humidity, and stability, and for this study are calculated by using an automated aircraft icing forecast algorithm developed by NCAR RAP. Thirty years of radiosonde data from over 100 upper-air stations across North America are used to identify monthly ICPs for different pressure levels, and the ICPs are compared to monthly mean temperatures and relative humidities to recognize similar patterns.
In winter at 85 kPa, monthly ICPs range from 0.00 over Mexico and the Caribbean Sea to 0.50 over the Aleutian Islands. ICPs decrease with height in winter, becoming 0.00 at levels above 50 kPa over all of North America because any clouds at these levels are considered glaciated by the algorithm and do not represent an icing hazard. Summer month ICPs at 85 kPa are negligible over most of North America due to temperatures above 0 degrees Celsius, although summer 85 kPa ICPs do reach 0.30 over the Canadian Archipelago. The highest probabilities are found southward with increases in height during the summer, becoming 0.20 over the Caribbean Sea at 50 kPa. Generally, overall highest ICPs are found near the surface over the north Pacific and the north Atlantic coasts in winter and spring. Comparing ICP distribution to previous climate studies of cloud cover, icing mishaps, and potential icing confirms the validity of this approach to analyzing the temporal and spatial patterns of conditions known to lead to aircraft icing.
The 8th Conference on Aviation, Range, and Aerospace Meteorology