Page 130 - 《高原气象》2025年第5期

高 原 气 象 44 卷
1248

Aircraft Observations of Non-Precipitating Stratiform Cloud Icing

Environments in Northwest China： A Winter Case Study

1
2， 3
WANG Zelin ， CAI Zhaoxin ， WU Junhui ， ZHOU Xu 3， 4
1
（1. Chinese Flight Test Establishment， Xi’an 710089， Shaanxi， China；
2. Meteorological Disaster Defense Technology Center of Shanxi Province， Taiyuan 030002， Shanxi， China；
3. CMA Weather Modification Center（WMC）， Beijing 100081， China；
4. CMA Cloud-Precipitation Physics and Weather Modification Key Laboratory （CPML）， Beijing 100081， China）

Abstract： Aircraft icing is a high-impact weather phenomenon that poses a serious threat to aviation safety while
also offering valuable opportunities for flight testing under complex meteorological conditions. Verification flight
tests of civil aircraft in stratiform cloud icing environments are critical for airworthiness certification. A deeper
understanding of the cloud microphysical characteristics in such conditions is essential to support the airworthi‐
ness certification of domestic civil aircraft. To investigate the cloud microphysical properties and airworthiness
compliance of icing environments in Northwest China， this study analyzes in situ aircraft measurements， geosta‐
tionary satellite observations， ERA5 reanalysis data， and sounding data collected during a non-precipitating strat‐
iform cloud icing experiment over eastern Shaanxi Province on 8 December 2021. The synoptic background，
cloud microphysical characteristics， and icing intensity were examined， and the compliance of the observed envi‐
ronmental data with airworthiness requirements was further evaluated. The results show that： （1） Under the com‐
bined influence of a 500 hPa upper-level trough， a 700 hPa shear line， and a surface cold high-pressure system，
southwesterly warm and moist airflow generated extensive stratiform clouds in eastern Northwest China. An in‐
version layer at the cloud top facilitated the accumulation of supercooled liquid water.（2） The stratiform clouds
were distributed between 2. 8 km and 4. 2 km in altitude， with temperatures ranging from -4 °C to -11 °C. An in‐
version layer approximately 100 m thick existed at the cloud top. The liquid water content （LWC） increased with
altitude， from about 0. 1 g·m⁻³ near the cloud base to a maximum of 0. 39 g·m⁻³ at the bottom of the inversion
layer near the cloud top. At 3. 7~4. 2 km and 3. 0~3. 3 km， small cloud droplets （10~15 μm） and larger particles
（50~75 μm） dominated， with elevated LWC， median volume diameter （MVD）， and spectral width of small
cloud droplets. In contrast， at 3. 3~3. 7 km， droplets were primarily 5~10 μm， with peak number concentrations
but lower MVD.（3） The distribution trends of the average particle spectra across different height layers in the up‐
per part of the cloud layer are relatively consistent. Small cloud droplets below 50 μm exhibit a bimodal distribu‐
tion， while larger cloud particles above 50 μm display a unimodal distribution. The “Khrgian-Mazin” distribution
fits the small droplet portion well. The region of high LWC near the cloud top correlates well with several fac‐
tors： higher albedo （38%~44%）， smaller cloud effective radius （7~12 μm）， warmer cloud tops （> -15 °C），
and high optical thickness （40%~100） from the Himawari-8 satellite data. These satellite products are valuable
for identifying the icing environment of single-layer stratiform clouds.（4） During three horizontal flight legs at
different altitudes， the aircraft primarily encountered moderate icing. Temperature， droplet MVD， and LWC re‐
mained horizontally stable. The cumulative average LWC reached 40%~60% of the certification envelope value
at -10 °C， with all icing conditions falling within the envelope. Overall， the microphysical characteristics of this
non-precipitating stratiform cloud icing case met the environmental requirements for airworthiness certification
flight testing， with particularly favorable conditions observed within the inversion layer beneath the cloud top.
Key words： non-precipitating stratiform cloud； aircraft observation； icing environment； cloud microphysical
characteristic