Study On Synoptic Climatolog Characteristics And Forecast Methods Of Fog In Enshi Mountainous Region

Enshi Mountain is a foggy area, in which the unique geographical environment leads the regional characteritics of fog different from the fog of plains and hilly areas.Based on the data including the original meteorological observational data from 1971 to 2007 in 8 counties of Enshi of Hubei Prpvince and the synoptic data as well as the numerical simulation products, the effects of the geological evironment on the fog,the climate and synoptic background of the fog and meteorological features of the mountain area fog etc are studied by using the methods such as the relative analysis, clustering method, the Fisher criterion, x2 test methods,and the perfact prediction (PP) method, etc. A series of the oprational forcasting methods and prediction system is established. The major results are as follows:(1) The fog distribution,which presented in a belt-ship along NNE-SSW direction,in Enshi has a clear local change,which is caused by elevation and topograph differences. The average fog days,which is distingushed changed with seasons and locations, in mid part of Enshi is about 63.7 per year.(2) The statistics features and synoptic background of the heavy fogs in Enshi are distigushed.According to the observations,three types of fogs can be found in Enshi area.The surface background systems has 6 types:the high pressure,the rear part of high pressure, the low pressure, the cold front,the uniform pressure field,and the col pressure field;the 500hPa background has 5 types:the high pressure ridge,soputh-west airflow,straght westly flow, low pressure voetex warm shear,and south-east flow; the 700hPa and 850hPa background have also 5 types:the high pressure ridge,south-west airflow,cold type shear flow, low pressure voetex warm shear,and south-east flow etc.(3) The biger difference of day-night temperature is a critical condition favourable to form radiation fog and thicker moist layer favouable to form advection fog. The 700hPa wind is a good indicator.The south wind indicats the warm advection for advection fog day with a 66% frequency and 52% for radiation fog days.For all types of fogs the low levvel 850hPa wind less than 6m/s and disturbance is very weak. (4) According to the analysis of the radar wind profile features, we can discovery the features to indicate the dissipearing of the fog. And the phenomena that the particls spread upward will indicate the heavy fog will be terminated.(5) A set of the prediction methods of fog is established.30 forasting models of fog for different seasons and different types of fog and different geographic environment area respectively. The tests showed that forecasating resoults are quite good with the average accuracy above 60%,lesser omit forecastings but relatively more null (vacancy) forecastings,so that the indicators to eliminate the vacancy forecastings are needed for opperational services.This study filled a gap in research of the local fog in Enshi area. The achivements will helpfull for increasing the ability of fog forecating and to serve the society better.