Observational Research On Supercooled Fog Microstructure And Icing Accumulation Mechanism In Lushan

Fog monitor, hotplate total precipitation sensor, weather identifier and visibility sensor, aerodynamic diameter spectrometer, ultrasonic wind speed meter, ice gradient observation frame and automated weather station with 7 factors were laid in the observation field of Lushan Meteorological Bureau of Jiangxi Province, four icing processes were observed, icing process from 20 to 25 Jan 2016 was mainly analyzed.The duration, frequency and spectrum distribution of fog were analyzed. The effects of rain, snow and supercooled fog on the growth of ice were studied. The ice growth and meteorological conditions of two heights (10m, 1.5m) were compared and analyzed to reveal the mechanism of ice formation. And the ice thickness was simulated and discussed. The main conclusions are as follows:Cold wave is the background of this ice process,ice accumulates when the whole layer of the atmosphere is below zero without warm layer. There are 227 fog groups, of which fog groups with duration less than 10 minutes and more than 10 minutes account for 90.7% and 9.3%, and of which the average time interval between formation and disappearing is 9.6 minutes. The fog droplet number concentration in 2 ～ 15μm and 30 ～50μm increase during rainfall, and decrease in 2～27μm during snow.Ice grows rapidly (1.3 mm·h-1) in freezing rain stage but slowly (0.1mm·h-1) in dry snow stage. Intensive appearance of supercooled fog,the lower temperature(-7.8℃ on average) and the increase of the wind speed (4.2m·s-1 on average)increase the growth rate of ice in the process of dry snow (0.5mm·h-1).The maximum ice thickness at heights of 10m and 1.5m are 20.7mm and 1.2mm,and duration are 102h and 61 h,respectively. The density of ice at the height of 10m is less than that of ice at the height of 1.5m. Ice accumulation rate at a height of 10m is closely related with precipitation rate and fog droplet microphysical characteristics.Ice thickness at a height of 1.5m is sensitive to changes in temperature and relative humidity during the day,and the diurnal variation is obvious. The difference between temperature and wind speed are the main reasons for the difference of ice thickness,duration, density and growth mechanism at two heights, which indicates that the thickness, duration, density and growth mechanism are closely related to heights.The ice thickness is simulated by the model of freezing rain, supercooled fog and wet snow ice loads. Ice thickness increase to 0.8mm and 0.12mm under the influence of freezing rain and supercooled fog, respectively. Freezing rain and supercooled fog’s contribution on ice are smaller. The sensitivity test is carried out to select the sticking efficiency. Simulation results of wet snow accretion model can better reflect the accumulation of ice thickness when sticking efficiency is 0.1/ U.