Comprehensive Observation of the Cloud Macro- and Microstructures of a Rare Aircraft Icing Case in Henan Province

The strongest aircraft icing was observed by the Henan Weather Modification Center in the history of their precipitation enhancement operation using an aircraft in Henan Province on 10 December 2018. The strong icing took place at a height of 3600 m (−7.9°C–−12.9°C), with the thickness of the icing in the nose and wings reaching 16.2 cm. The macro- and microstructures of the cloud were examined in detail using the airborne DMT observation combined with FY4A satellite retrieval cloud parameters and radar observations. The strong ice accretion area was located in front of the 700-hPa shear line, and water vapor was transported continuously by the southwest jet stream. The deep inversion layer offered conditions conducive to accumulating water vapor and liquid water. In the area with strong icing, the cloud top height was approximately 4000–5000 m, the cloud top temperature was −15°C–−20°C, and the cloud optical thickness was more than 30. The FY4A cloud top phase production was in good agreement with the airborne observations, which has certain indication significance for identifying the areas with supercooled water that are prone to ice accumulation. During the strong icing period, liquid water content is abundant in the cloud, and the maximum liquid water content reaches up to 0.818 g m⁻³. The presence of numerous spherical supercooled droplets and large supercooled droplets with a radius >50 μm are important reasons for the ice accumulation. Due to the lack of ice crystal particles with scales surpassing the millimeter scale in the area of strong ice accumulation, the S-band weather radar echo is weak, even considerably lower than that in non-icing areas. When using weather radar for monitoring the evolution of weather process and conditions of flight safety, certain limitations in estimating of the ice accretion intensity when only the echo intensity is used should be considered.