Abstract:
Aircraft icing poses a serious threat to flight safety. To better understand the meteorological conditions and cloud microphysical characteristics of aircraft icing, and to find the relationship between icing and the threshold of macro meteorological conditions, this study used aircraft observation data, combined with radar and ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts, to analyze the weather conditions and cloud microphysical processes of a severe aircraft icing event in central and eastern Henan Province on December 10, 2018. The intensity of the icing event was also assessed. This icing event was caused by the combined effects of an upper-level trough, low-level shear, and surface cold high pressure. Warm and moist air at low levels flowing towards Henan ascended along the cold high pressure, forming an inversion layer with warm air above and cold air below, which facilitated the accumulation of liquid water in the region. The icing area was rich in liquid water content but had low ice water content, liquid water content is significantly higher between the altitudes of 550 to 750hPa compared to other altitudes. The aircraft observation data is relatively consistent with the results of ERA5 reanalysis data, the severe icing area was at an altitude of 3630m, with cloud temperatures between -8.2 and -6.8°C, relative humidity between 87% and 92%, an average cloud droplet concentration of 499.9cm-3, and a maximum liquid water content of up to 0.87g/m3. In this area, large and small supercooled liquid droplets coexisted, with virtually no ice crystal particles. Calculations showed that the thresholds for light, moderate, and severe aircraft icing in areas rich in liquid water content were 0.05g/m3, 0.20g/m3, and 0.58g/m3, respectively. Under conditions where the inversion layer strength was 1.93°C/100hPa, vertical motion speed ranged from -0.25 to 0.2Pa/s, and horizontal convergence intensity was -3.73kg/(m2s), the probability of icing intensity reaching moderate or above was 77%.