Primary Discussion on the Characteristics and Forecasting Methods of Dense Fog in Xuzhou City

[Objective] The study aimed to discuss the characteristics and forecasting methods of dense fog in Xuzhou City. [Method] Based on the data of dense fog in Xuzhou City from 1960 to 2009, the characteristics and forming conditions of dense fog in the region were analyzed, and then its forecasting methods were introduced, finally corresponding disaster prevention measures were put forward. [ Result] Dense fog might ap- pear in each season, its frequency of occurrence was the highest in December, namely 16.4% ; it was the lowest in June （2.2%）, and the fog las- ted for a short time and was thin. Heavy fog occurred more frequently in winter half year than summer half year, and the frequency of occurrence from October to next February was about 66.7%. In addition, dense fog mostly generated from late midnight to morning, while it appeared less in the afternoon. It shows that dense fog in Xuzhou City is mainly radiation fog instead of advection fog, but the two kinds of fog appeared simultane- ously sometimes. [ Conclusion] The research could provide scientific forecasting methods for the precise prediction of dense fog in Xuzhou City.

Early Warning Role of Data from Automatic Stations in Forecast of Dense Fog

Based on observation data from automatic stations in Lianyungang, visibility and weather situation of dense fog leading to a traffic accident in Lianyungang on April 15, 2012 were analyzed firstly, and then changes of meteorological factors related to fog appearance and disappearance, such as wind speed, temperature and relative humidity, were discussed. The results showed that wind speed was below 2 m/s when fog occurred, and wind velocity reduced obviously before visibility deceased, appearing a trough. Fog appeared when temperature was neady the minimum, and there was no great change in wind speed, but visibility went up gradually after temperature rose. The longer the duration of the minimum temperature, the longer the duration of the minimum visibility. Moreover, visibility would become low after temperature rose.

The 3D-Var Data Assimilation Experiments on a Dense Fog Event over the Central Plain of China

Nonhydrostatic mesoscale WRF and its 3D-Var system are used to study a dense fog event occurring in 13-14 January 2006. Three different observation data sets including GTS （Global Telecommunication System）, AMDAR （Aircraft Meteorological Data Relay） data, and 9210 data are assimilated into the initial analysis fields in experiments. Experiments with three different assimilation time intervals （1, 3, and 6 h） are also carried out. Three experiments with different data sets have all modified the temperature and humidity field of initial fields, and therefore show an obvious positive effect on fog simulation. Further study indicates that the humidity and stability of boundary layer are improved obviously in assimilation experiments, although different data sets make different contribution to the analysis fields. The multi-time assimilation cycle experiments show that the analysis increment in experiment with l-h interval is more realistic than that with 3- and 6-h intervals.

On the Evolution and Structure of a Radiation Fog Event in Nanjing

An extremely dense radiation fog event during 10-11 December 2007 was studied to understand its macro-micro-physics in relation to dynamic and thermodynamic structures of the boundary layer, as well as its structural evolution in conjunction with the air-surface exchange of heat and water vapor. The findings are as follows. The extreme radiation fog process was divisible into formation, development, mature, and dissipation phases, depending on microstructure and visibility. This fog event was marked by rapid evolution that occurred after sunrise, when enhanced surface evaporation and cold air intrusion led to a three order of magnitude increase in liquid water content （LWC） in just 20 minutes. The maximum droplet diameter （MDD） increased four-fold during the same period. The fog structure was two-layered, with the top of both the surface-layer and upper-layer components characterized by strong temperature and humidity inversions, and low-level jets existed in the boundary layer above each fog layer. Turbulence intensity, turbulent kinetic energy, and friction velocity differed remarkably from phase to phase： these features increased gradually before the fog formation and decreased during the development phase; during the mature and dissipation phases these characteristics increased and then decreased again. In the development and mature stages, the mean kinetic energy of the lower-level winds decreased pronouncedly, both in the horizontal and vertical directions.

Analysis of Climatic Characteristics of Fog and Haze Weather in Shaoyang in the Past 60 Years and Its Forecast

Based on conventional observation data and NCEP reanalysis data at 10 national basic stations and reference stations of Shaoyang City during 1951-2014,300 cases of typical regional dense fog process appeared in the history were selected. From meteorological factors and weather situation,temporal-spatial distribution characteristics and trend change characteristics of dense fog in Shaoyang were analyzed. The results showed that（ 1） temporal-spatial distribution of dense fog in Shaoyang region was uneven,and interannual variability of fog days had large volatility and bad periodicity; dense fog days in Shaoyang region was obviously more in winter half year and less in summer half year. Dense fog was the most in November and the least in July. Dense fog mostly concentrated during 03： 00-09： 00; appearance time mostly concentrated during 05： 00-07： 30,and dissipation time mostly appeared after 08： 30. Dense fog appeared early and dissipated late in winter half year,and vice verse in summer half year.（ 2） Seen from meteorological factors,ground and 850 h Pa of wind velocity was generally 0-3 m/s,which was all small. Moreover,there existed temperature inversion from ground to 850 h Pa. Relative humidity on dense fog day was larger,and precipitation or cloudy day mostly appeared in prior day.（ 3） There were four kinds of ground weather situation forming dense fog： uniform pressure field type,cold and high pressure bottom type,cold and high pressure rear type,frontal type. Based on grasping change characteristics,rule and formation reason of dense fog,some forecast focus was found.