Change Analysis Of Low Visibility Weather In Sichuan Basin And Its Impact On Airport Operation

Low visibility weather caused by fog has an important impact on the normal operation of airport flights.In this paper,using the methods of weather diagnostic analysis and mesoscale WRF numerical simulation,visibility data from surface meteorological observations and FNL reanalysis data are used.According to the heavy fog weather under the special topographic conditions of Sichuan Basin,starting from the perspective of mountain-valley wind between Plateau and basin.The influence of local mountain-valley wind circulation on the diurnal variation of heavy fog in Sichuan Basin on December 22,2016 was investigated.The possible mechanism of the heavy dense fog event and the influence of heavy fog on airport operation are analyzed.The following conclusions are drawn:1)The fog began to form at 1800 UTC on 21 December 2016 and dissipated at 0600 UTC on 22 December 2016.This heavy fog event was influenced by the southwest of low pressure with a weak horizontal pressure gradient and higher relative humidity and showed typical diurnal variation characteristics.2)The Weather Research and Forecasting model was able to partially reproduce the main features of this fog event.The simulated horizontal visibility and liquid water content were used to characterize the fog.Although the simulated horizontal visibility and liquid water content are both less than the actual observed values,the diurnal variation of them is consistent with the actual observation.The Weather Research and Forecasting model can simulate the diurnal variation in the local mountain to basin winds caused by the topography around the Sichuan Basin.The velocity of the simulated upslope airflow is obviously higher than that of the downslope airflow.The downhill wind with higher relative humidity is conducive to the formation of fog after cooling,while the stronger uphill wind and lower relative humidity are conducive to the dissipation of fog.3)The mountain to basin winds had an important role in the diurnal variation of the fog event.The positive feedback mechanism between the fog and mountain to basin winds wasgood for the formation and maintain of the fog during the night.During the day,the mountain to basin wind displayed a transition from downslope flows to upslope flows.Water vapor evaporated easily from the warm,strong upslope winds,which resulted in the dissipation of fog during the day.The topography surrounding the Sichuan Basin favored the lifting and condensation of air parcels in the lower troposphere as a result of the lower height of the lifting condensation level.4)The winter fog in Sichuan Basin is mainly radiation fog,which is seriously affected by topography.Once the fog begins to form at night,it will inevitably affect the operation of airport flights the next day.In case of heavy fog weather,the meteorological department should make an accurate forecast.Conditional airport can also adopt artificial fog elimination method to disperse the fog over the airport and improve the meteorological conditions of the aircraft during take-off and landing,so as to ensure the normal take-off and landing of aircraft.