Analysis Of Meteorological Conditions Of Aircraft Icing Events At The Diwopu Airport In Urumqi And Their Case Simulations

Aircraft icing poses a serious security threat to aviation flight.It makes the aerodynamic performance of the aircraft worsen,the lift reduced,the resistance increased,and affects the stability and maneuverability of the aircraft,which is easy to cause aircraft crash.In order to ascertain the occurrence characteristics and atmospheric backgrounds of icing of civil aviation aircraft taking off and landing at an airport,to accurately forecast the meteorological conditions of its occurrence,and to provide decision-making suggestions for disaster prevention and avoidance in time.In this paper,the characteristics of aircraft icing were analyzed based on the voice reports from 20 cases of aircraft icing provided by the civil aviation airliners taken off and landed at the Diwopu Airport in 2018,combined with the meteorological reanalyzed data from the National Center of Environmental Predicting(NCEP)in USA which covered the each icing event.Consequently the atmospheric circulation situations of these icing processes were classified,the three typical ice accretion cases with the high probabilities of icing were selected.The high-resolution numerical simulations of the atmospheric backgrounds were carried out by using the Weather Research and Forecast Model(WRF),and the meteorological conditions of these ice accretion processes were diagnosed and analyzed.The most serious ice accretion process was screened out from 20 cases and the WRF model was used to carry out the numerical simulation.According to the atmospheric physical quantity field output by the model,the main atmospheric physical backgrounds of this icing process were discussed.It has important reference value to investigate the pattern of aircraft icing and its formation mechanism,the prediction and early warning of icing potential conditions and the meteorological guarantee of civil aviation flight safety.The main conclusions of this study were as follows:(1)The analysis on the occurrence characteristics of ice accretion showed that: in 2018,the ice accretion of civil aviation airliner taken off and landed at the Diwopu Airport had obvious seasonal characteristics that 70% of the ice accretion processes occurred in spring and autumn,and the flight heights at the time of ice accretion were 2000-9000 m.There were five types of atmospheric circulation situation that led to aircraft icing such as the westerlytrough type,the cold front type,the Central Asia vortex type,the jet type and the convective cloud type.Among them,the westerly trough type accounted for 45% of all ice accretion processes,the cold front type accounted for 20%,and the Central Asia vortex type accounted for 15%.The probabilities of occurrence of jet type and convective cloud type were less than12%,and the combination of them accounted for 20%.(2)Simulations on the ice accretion index of various weather types indicated that the average strength of the jet icing types was as high as 80.02 and it was easy to produce heavy icing,the average icing intensity indices of the westerly trough types,the cold front types and the convective cloud types were 66.67,72.56 and 70.13 respectively and these were easy to produce moderate icing,the average ice accretion intensity of the Central Asia vortex types was 41.63 and it was easy to produce light icing.(3)The atmospheric background simulations on the processes of three main icing weather types with the high probabilities displayed that the icing processes of the westerly trough type were mainly affected by the atmospheric thermal conditions,the effect of the water vapor conditions was the greatest in the occurring processes of the cold front type icing,and the atmospheric dynamic conditions had the most obvious influence on the icing process of Central Asia vortex type.The icing layer height of cold front type was highest and it situated in between 4-8km,the cloud water content was more than 0.04g/kg.The icing layer height of the westerly trough type and the Central Asia vortex type were low and changed from 1km to 5km,their cloud water content were more than 0.1g/kg.The super-cooled water distribution areas of the three types were relatively continuous.The cloud top temperature of the cold front type was below-30?,while that of westerly trough type and Central Asia vortex type were above-20?.(4)After analyzing the atmospheric physical backgrounds of the most serious ice accretion process(the maximum ice accretion index is over 80.0)in 20 icing cases,it was found that the temperature and humidity conditions before taking-off,in the early and middle flight process were very conducive to the generation of aircraft ice accretion,among which the lower layer temperature was-12 ?-Between 2?,the relative humidity in the lower layerwas more than 90%,the vapor in the middle and upper layers was about 50%,and the cloud top temperature was below-30? when ice accretion occurs.The cloud thermal conditions in the middle and lower layers were conducive to the formation of super-cooled water droplets.The cloud water content changed from 0.50 to 0.60g/kg in the early and later flight periods on the flight altitudes and it was very conducive to the formation of ice accretion.