The Research Of Meteorological Conditions And Objective Forecast Method Of Fog Occurring In Hebei

The MICAPS format surface observation data in the first format (the ground element mapping data) is used to get the time and space distribution of the fog and visibility in Hebei and weather conditions when the fog occurred. Use Stepwise decreasing and index of intussusceptions method to make objective prediction of fog in Hebei Province. The conclusions are as follows:1. The characteristics of fog in Hebei are that:(1) the fog’s happen and disappear temporal distribution in winter are both bimodal pattern in mountain and plain, happening between five and nine o’clock and disappearing between seven and eleven o’clock, while in summer are both singlet pattern, happening between four and seven o’clock and disappearing between six and nine o’clock, more than70%. The fog maintains shorter in summer than in winter and concentrates in fixed time.(2)The fog in mountain mainly happens from late summer to early winter, mostly in autumn, while the fog in plain mainly happens from late autumn to winter, mostly in December.(3)The fog can be affected by the topography, with obvious regional geographic characteristics. The fog days are more in plain than in mountain and continental plateau.(4) The fog days in Hebei increase anxiously, more in the1970s, decreasing in the1980s, increasing fast to a peak in the1990s, and decreasing after into the21st Century, but still more than early mid-1980s. The phase of stations in mountain synchronizes with in plain on the whole.2. The change of mean temperature and dew point temperature is relatively unanimous, increasing from January to July and reaching the most in July, decreasing from July to December and reaching the least in January. The mean dew point deficit changes little from January to September, between0.45and1, while it changes between2.5and3from October to December. The relative humidity is above90%from January to September, and is between80%and90%in other three months. The mean wind speed increases from January to April and decreases afterwards. The maximum value of mean visibility occurs in June. The mean visibility is under1km except May, June and July and under0.5km from January to March, October to December, up to the heavy fog standard. The surface pressure is between1020to1023hPa in Hebei plain on the day when the fog occurs, and pressure gradient is little, equating to uniform pressure field. Monthly variation of each meteorological element is relatively unanimous before the day when fog occurs. The large relative humidity, small wind speed, and poor visibility are to the benefit of the occurrence of fog on the following day.3. EOF method is used to analyze the time and space distribution of the fog in Hebei. It is found that occurrence of the fog in Hebei is more in plain than that in mountains from2000to2011. The fog occurred more in plain and less in mountains in six years during2000to2011(2001、2003、2004、2006、2007、2009), and the most occurred in2007. In other years(2000、2002、2005、2008、2010、2011), the fog occurred less in plain and more in mountains and the least occurred in east plain in2010.4. Index of intussusceptions method is a method when fog appears near the boundary layer while the time and space resolution ratio can’t reach the forecasting demand, uses the high and surface statistical results from1998to2006to make objective prediction of fog base on surface observation and numerical forecast products. The system enters prediction products of the following day’s fog twice every day from October2008, to provide an objective forecast method. It is found that the drop zone is right more or less in operational forecast.