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 airworthiness 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， geostationary satellite observations， ERA5 reanalysis data， and sounding data collected during a non-precipitating stratiform 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 environmental data with airworthiness requirements was further evaluated.The results show that： （1） Under the combined 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 inversion 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 inversion 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 upper part of the cloud layer are relatively consistent.Small cloud droplets below 50 μm exhibit a bimodal distribution， 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 factors： 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 remained 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.

This study conducts a comprehensive risk assessment of meteorological safety for aviation operations in Yunnan Province.Leveraging meticulously curated observational data from 124 county-level meteorological stations across the province， encompassing measurements of low clouds and reduced visibility， rainfall， strong winds， icing， and thunderstorms， the research delves into the primary meteorological elements influencing aviation safety during takeoff and landing in various regions of Yunnan.Employing a fuzzy comprehensive evaluation method and Arcgis spatial analysis tools， a zoning map is developed to delineate the levels of aviation weather safety risk in Yunnan Province.The analysis yields the following significant findings： （1） Regionally， the primary meteorological factors influencing aviation safety in Yunnan encompass icing in the northwest， rainfall and strong winds in the west， low clouds and reduced visibility， as well as rainfall and thunderstorms in the southwest.Furthermore， prevalent meteorological challenges include low clouds and reduced visibility along with rainfall in the southeast， while rainfall predominates in the southern part of the east.Overall conditions demonstrate relative favorability without significant influencing factors observed in other parts of northeastern， central and most of eastern Yunnan.（2） When assessing aviation operation meteorological safety days and dangerous days across different regions within Yunnan province， it is evident that meteorological conditions for aviation operations generally exhibit favorability across most areas.Relatively poorer meteorological conditions are primarily concentrated in specific areas such as the northwest， the southern edge of the west， the southwestern edge of the southwest， the southern edge of the southeast， the southern part of the east etc.（3） In terms of comprehensive assessment regarding meteorological risk associated with aviation operations within various regions across Yunnan province， a majority fall into safe or very safe categories.The relatively dangerous or very dangerous grades are only found to be distributed within specific areas such as central Diqing Prefecture in the northwest， the southwestern part of Lincang City in the southwest， Xishuangbanna Dai Autonomous Prefecture etc.Overall assessment indicates a favorable level for comprehensive meteorological risk associated with aviation operations throughout Yunnan province.

In order to investigate the four key meteorological factors affecting aviation safety and their regional variations in Yunnan， research employed daily and hourly ground observation data from 125 meteorological stations across Yunnan from 2010 to 2021， as well as airport ground observation data from Tengchong Tuofeng Airport during 2013 -2019.Initially， an analysis was conducted on the primary seasonal variations of key meteorological elements in Yunnan.Subsequently， a spatiotemporal evolution analysis was performed for short-duration heavy precipitation and strong wind events during typical seasons at 15 airports.Furthermore， select observational data from typical plateau mountain airports-Tengchong Tuofeng Airport， and compare it with observation data from the Tengchong meteorological station.Analyze the annual frequency of short-duration heavy precipitation events during summer and the daily occurrence periods of spring strong wind events.Ultimately， a complex interrelation analysis among the four categories of meteorological elements was undertaken， followed by an exploration of the spatial distribution patterns of safe and dangerous aviation days in the Yunnan region.The findings revealed the following outcomes： （1） Short-duration heavy precipitation was most pronounced during summer， with areas spanning from Baoshan through Lincang to Puer experiencing heightened occurrences.Spring was characterized by prominent strong wind occurrences， particularly in Ninglang and Kunming， both exhibiting an increasing trend in the frequency of windy days.Notably significant was the occurrence of low visibility during autumn， predominantly observed in the southwestern region of Yunnan， encompassing Lincang， Cangyuan， Puer， and Xishuangbanna， with an escalating tendency.The spatial distribution of low clouds remained relatively similar across all seasons， with higher occurrence frequencies and distribution areas noted during summer and autumn， as opposed to winter and spring.（2） The occurrence of short-duration heavy precipitation events in summer exhibited a distinct positive correlation with precipitation amount， and the timing of occurrences aligned well with the primary operational periods of the airports.Variances in springtime strong wind events were noticeable among airports， predominantly transpiring between 14:00 and 23:00 （Beijing time）.（3） The localized nature of weather systems results in frequency disparities in weather phenomena occurring at airport locations compared to their surrounding areas， while maintaining a correlation in their patterns of variability.（4） Notably elevated were the average numbers of safe aviation days in the northern region along the Dali-Kunming alignment， compared to the southern areas of Yunnan.The majority of Yunnan's locales exhibited a declining trend in safe aviation days， whereas dangerous days were concentrated along the eastern vicinity of Puer to the western border of Wenshan， presenting an increasing trend along the Diqing-Lijiang-Kunming westward direction.

On February 19-22， 2022， Yunnan province， located on the low latitude plateau， experienced a large-scale cooling， rainfall and snow weather process， leading to the cancellation， delay， and return of multiple flights at eight airports.Focusing on this high-impact weather， this paper employs rain gauge data， ERA5 reanalysis data， and wind profile radar data to investigate the circulation causes， features of the cold front activity， and their impacts on aviation.The results show that： （1） This low-temperature rain and snow weather was a large-scale cold surge process that happened under the joint influence of a cold front and the southern branch trough.Before February 21， mainly affected by the cold front， the temperature dropped sharply with mild precipitation.The primary impact on aviation was aircraft turbulence caused by strong wind shear and unstable stratification.Subsequently， with the westward of the southern branch trough， precipitation increased， and the adverse weathers， such as airport snow cover， low-level clouds， thunderstorms， and wind shear， imposed a significant impact on flights.（2） The main body of the cold front regime was located below 700 hPa.When the cold surge out broke， the cold air leading by low-level easterly winds rushed westward with a nose-shaped forehead.The strength and thickness of the low-level easterly winds correspond well with those of the cold air mass； the warm westerly wind in front of the front climbs along the front， forming a inversion layer over the cold air mass.（3） When the front strongly developed and moved westward， the high value belts of the frontogenesis function at 800 hPa could well indicate the position and intensity of the front lines.The convergence of easterly behind the front and warm westerly before the front caused a significant updraft over the frontogenesis area.Meanwhile， the Richardson numbers （R_i ） were small in the areas where the vertical temperature gradient was large below 650 hPa before the front and in the near-surface layer behind the front， suggesting the potential turbulence regions.（4） Wind profile radar data indicated that during the maintenance period of low-level easterly winds， the strengthening of westerly winds above 2 km had a certain indicative significance for precipitation.When the low-level easterly winds weakened and disappeared， the process ended.

During March 23 and March 26， 2020， an area along the international route from Kunming， Yunnan to Vientiane， Laos experienced severe weather conditions including hail， thunderstorm winds， and heavy precipitation.A severe convective weather process was simulated using the mesoscale numerical model WRFV4.2 （Weather Research and Forecasting Model） and FNL （Final Operational Global Analysis） data from the National Centers for Environmental Prediction （NCEP）.Hourly weather station data from the China Meteorological Administration was used to check the reliability of the simulation.Furthermore， a diagnostic analysis of various physical quantities output from the WRF model was performed to provide an aviation safety reference for the Kunming-Laos Vientiane route in Yunnan.The results show that： （1） the WRF model can better simulate temperature and precipitable water， but the simulated values of the near-surface wind field are large during the daytime.（2） The simulated output physical quantity field of the simulation can indicate the time and location of severe convective weather， which has certain spatial and temporal forecasting and warning functions and can be used to judge the impact of severe convective weather on flight and the degree of impact according to it.（3） The severe convection was mainly caused by the eastward movement of the Southern Branch Trough， with dry and cold air in the upper levels superimposed on the warm and moist air forming an unstable structure， triggered by the surface convergence lines.Convective available potential energy （CAPE） in the route area is large， and the water vapor conditions are abundant-the rising motion and sinking motion alternate below 9 km altitude， which can cause turbulence during flights.Additionally， the 0 ℃ layer is located at an altitude of about 3 km， which can cause ice to form on the airframe or encounter hail weather， causing a certain impact on flight safety.

Low-level wind shear significantly impacts aviation safety and operational efficiency.Zhongchuan Airport， located in a mountainous inland region， experiences the influence of complex terrain and weather systems.Wind shear is frequently observed during the summer season.This study analyzes the spatial and temporal characteristics of low-level wind shear events at Zhongchuan Airport using aircraft reports spanning from 2009 to 2018.During the observation period from May 2016 to November 2017， a total of 18 low-level wind shear events were confirmed through aircraft verification.Two methods， namely the fixed and adaptive window methods， were compared to identify wind shear events using LIDAR data from the Windcube 400s-at instrument.The study also explored the continuous evolution and spatial characteristics of the three-dimensional wind shear structure.The results indicate that the frequency of low-level wind shear events has increased at a faster rate compared to the flight volume at Zhongchuan Airport over the past ten years.The peak months for low-level wind shear events at Zhongchuan Airport are April-July and August-October， influenced by local weather patterns.The peak months for low-level wind shear events at Zhongchuan Airport are April-July and August-October， influenced by local weather patterns.Wind shear induced by convective weather occurs in the weak or non-echo region surrounding the convective cloud， resulting from the convergence of updrafts and downdrafts outside the cloud， or the formation of a gust front following the downdraft's contact with the ground.The wind shear factor is correlated with the intensity of radar echoes.Compared to the fixed window method， the adaptive window method had a larger recognition range due to the different data sets included in the recognition window.Therefore， the adaptive window method was found to be more suitable for studying the three-dimensional evolution of wind shear structures.Therefore， the adaptive window method is better suited for studying the evolution of the three-dimensional wind shear structure.The wind shear in the vicinity of Zhongchuan Airport is characterized by a low spatial distribution， small horizontal scale， and short duration， primarily concentrated in the small-scale and γ mesoscale.In other words， the wind shear events occurred at relatively low altitudes， with horizontal scales mostly ranging between 1000~1500 m and 2000~2600 m， lasting less than 20 minutes.Furthermore， 40.5% of the wind shear events were attributed to the movement of the wind， primarily influenced by the background wind.The findings of this study contribute to a better understanding of the characteristics of wind shear， offering valuable insights for the identification， mechanisms， forecasting， and early warning of low-level wind shear events at Zhongchuan Airport.

Using the 2013-2018 hourly meteorological observation data of Shuangliu International Airport's， ECMWF ERA-interim and ERA5 reanalysis data， MICAPS conventional meteorological observation data and airport Doppler weather radar product data， the spatiotemporal characteristics and features in four types of thunderstorm weather at Shuangliu Airport are analyzed.The results show that the 77.03% of thunderstorms at Shuangliu Airport were accompanied by precipitation during 2013 and 2018.The occurrence of thunderstorm in summer （June， July and August） is more than half of that of the whole year， which is featured with "more night thunder and less day thunder".82.7% of the thunderstorms have a duration within 3 hours and the thunderstorms are most active over the east of the airport.The thunderstorms occured at Shuangliu Airport are divided into four types， cold advection forced， warm advection forced， baroclinic frontogenesis and weak advection， according to different baroclinic frontogenesis and thermal conditions of the environmental field.The northwest cold air in the upper level plays a crutial role in the occurrence of cold advection forced thunderstorms.When this type of thunderstorm occurs， Shuangliu Airport is mostly located behind the 500 hPa trough， and the wind rotates counterclockwise with height from the middle to the upper troposphere.The atmosphere exhibited strong unstable energy， thus this type of thunderstorms are often accompanied by thunderstorm gale， hail， and short-time heavy rainfall.The associated radar echo of precipitation shows combined features from cumuliform clouds and stratiform clouds.In contrast， the strong warm and humid southerly is more important in the warm advection forced thunderstorm.Shuangliu Airport is often located in front of the 500 hPa trough and wind tends to rotate clockwise with height in this type of thunderstorm.Although the unstable energy of the atmosphere is relatively weak， the thunderstorm can still induce short-time heavy rainfall as the atmosphere is generally moist.The radar echo of precipitation is mainly featured with the stratiform clouds.Baroclinic frontogenesis type of thunderstorms occur in the background of strong intersection of cold and warm air in the middle and lower troposphere where the function of frontogenesis is significant.The atmospheric baroclinicity is strong and the dynamic condition is good during this thunderstorm.Strong convection occures along with various synoptic processes.The realated radar echo shows a radar bow-shaped echo band near the Shuangliu Airport that is arranged laterally by many thunderstorm cells in the northeast-southwest direction.Weak advection thunderstorms often occur under the weak baroclinic condition.During this thunderstorm， the atmosphere is approximately quasi-barotropic with a small frontogenesis function and the temperature advection is insignificant.The horizontal distribution of atmospheric water vapor is relatively uniform.The air at the near-surface is characterized by high temperature and high humidity， and unstable energy is accumulated at the lower level.Once triggered by somehow mechanisms， the thundershower and gusty winds will be generated after overcoming convective instability.The map of radar echo is shown with many echoes in small range and weak intensity scattering around the Shuangliu Airport and have no obvious typical characteristics.

In order to improve the prediction and early waning ability of the wind shear over Xining Airport.ERA-Interim reanalysis data， airport automatic meteorological observation station data， wind profile radar data and laser wind radar data was used in this paper， and analyzed the process of low altitude wind shear caused by micro-downburst in Xining Airport on 26 April 2018， comprehensively.The results showed the low-level wind shear occurred in Xining Airport Runway 11， which was a horizontal wind shear during the sudden change of wind speed.Before the occurrence of low-level wind shear， the study area was in the front of the transverse trough， mainly was controled by northwest air flow； The sky over Xining Airport was cloudy with low convective clouds， the condition of surface humidity was good（t-td≤4 ℃）； The middle layer contains dry air， which was conducive to the development of convective activities.The wind profile radar showed that there was a strong sinking motion at the time of landing， and appeared low-level precipitation in addition to， there was strong turbulence over 1000 m when 10~20 min before low-level wind shear process.The laser wind radar indicated at 13:25（Beijing Time， after the same）， a cyclonic vortex appeared at the landing track line 4.05 km away from the runway entrance and 475 m high， which was the early signal of low-level wind shear.A micro-downburst and thunderstorm high pressure are formed at 13:29-13:30， as well as a moderate divergence 441 m away from the runway entrance， 81 m high which induces horizontal wind shear and leads to low altitude missed approach of the aircraft.The research results of this paper provided a certain reference for understanding the information of the convection system by using the multi-source detection data， and it is important to guide significance for the prediction and early warning of the wind shear over the airport， and provide scientific and technological support for the timely response measures of the aircraft in the wind shear.