Research On Forecast Method Of Fog Around The Bohai Sea Coastal Areas

Fog is a kind of common disastrous weather phenomenon, which causes enormous economic losses to industrial and agricultural production, transportation and electrical equipment. As one of the developed areas in our country, the Areas around the Bohai with well-developed transportation and dense population are often affected by fog weather. By using the conventional observation data from 2001 to 2014 around the Bohai Sea Coastal Areas, the spatial and temporal distribution and the climatic character of the fog around the Bohai Sea Coastal Areas have been systematically studied. Based on the reanalysis of geopotential height and wind speed data from National Centers for Environmental Prediction, the synoptic situations at both high and low altitude during the process of fog were concluded by taking use of the principles and methods of synoptic meteorology. According to the character of the ridges and troughs, high and low pressure center, the automatic synoptic type discrimination system is designed. The synoptic situations at both high and low altitude can be judged and classified day by day, thus the samples conductive to the formation of fog can be determined. According to the formation conditions of the fog, forecast factors can be filtrated. Apply the diagnostic analyses of physical quantity to the automatic discrimination samples of synoptic situation. Establish two forecast systems respectively by using the PP method and MOS method. Carry out the inspection by the method of history matching and trial forecast. The main results are as follows:(1) By analyzing the spatial and temporal distribution character of the fog around the Bohai Sea Coastal Areas, it turns out that the fog occurs more frequently in the south of Beijing-Tianjin-Hebei region, the northwest of Shandong province, the central region of Liaoning province, while the fog occurs less frequently in the north of Beijing, the north of Hebei province, the west of Liaoning province and the Inner Mongolia adjacent to Hebei province and Liaoning province. The regional fog weather around the Bohai Sea Coastal Areas occurs 63 times from 2001 to 2013. The yearly changes of the occurrence frequency of fog are fluctuations and show an decreasing trend. Fog appears mainly from January to April and from September to December while fog does not appear in the other months. Fog occurs most frequently around 8:00 in a day and occurs in a very low frequency in the other times during the day.(2) By generalizing and summarizing the characters of the synoptic situations at both high and low altitude around the Bohai Sea Coastal Areas, it turns out that there are three types of 500 hPa synoptic situations when the regional fog occurs, which are low trough, high pressure ridge and zonal flow, and there are four patterns of the surface synoptic situations, which are the front of high pressure, frontal cyclone, weak high pressure and uniform pressure field. By taking use of the identification theories of ridges and troughs, high and low pressure centers, and geopotential height variance, the automatic synoptic situations at high and low altitude discrimination system is designed. There are 3149 days in total from 2001 to 2013, after the automatic synoptic situations discrimination, 483 days left, 84.7% of them are eliminated. Among the 63 regional foggy days, each of the high and low altitude has an omission. The forecasting accuracy of synoptic situations discrimination system is 12.6%.(3) After physical diagnosis during the forming of the fog and repeated trials, the dew point of the surface temperature((T-Td)2m), surface wind speed(W10), temperature difference between 925 hPa and 850hPa(VT9-8=T925-T850), M index are selected as typical predictors of fog.(4) Establish the fog forecasting system by the PP method. Establish the statistical relation of threshold value of the 4 predictors by using the historical data of the regional fog meteorological stations from 2001 to 2013. The TS score of the regional fog simulation forecasting from 2001 to 2013 can be 51.7%. It can also make an accurate forecast of the Spatial Range of the fog. The forecast in 2014 is conducted and tested by using the threshold value of predictors confirmed by the historical data from the meteorological stations. In comparison with to the actual situations that fog occurs 9 times, the successful forecast happens 6 times, failure forecast happens 3 times and empty forecast happens 3 times. The TS score is 50%. It can also make an accurate forecast of the special scale of the fog. Because of the difference between the T639 Numerical Forecast Product and the data from the meteorological stations, it is unsuccessful to forecast the regional fog around the Bohai Sea Coastal Areas by taking use of the PP method.(5) Establish the fog forecasting system by the MOS method. Establish the statistical relation of threshold value of the 4 predictors by using the historical data of T639 from 2010 to 2013. The TS score of the regional fog simulation forecasting from 2010 to 2013 can be 50.0%、53.3% and 42.1% in each of the future 3 days. It can also make an accurate forecast of the Spatial Range of the fog. The forecast in 2014 is conducted and tested by using the MOS method. In comparison with to the actual situations that fog occurs 9 times for the next day, the successful forecast happens 6 times, empty forecast happens 8 times and failure forecast happens 3 times. The final TS score is 35.3%. It can make a 5 successful forecast while 4 failure forecast for the future 2 days and 3 days. The TS score for the future 2 days and 3 days respectively are 25.0% and 26.3%. After practice and test, the fog forecasting system established by the MOS method can be provided as a reference for the forecast of the fog around the Bohai Sea Coastal Areas.