Improved Visibility Diagnostic Scheme Based on Fog Microphysical Observation

To enhance the accuracy of fog visibility forecasts, a new fog visibility diagnostic scheme was established and tested using observational data on fog microphysics. The data were collected from April to July 2008, May to August 2009, and May to September 2011 at the Bright Summit of Mount Huangshan and from January to March 2009 in Enshi, Hubei. First, existing visibility diagnostic schemes were compared, confirming the importance of considering liquid water content as well as droplet number concentration in such schemes. Second, the study found that the coefficients used in previous diagnostic schemes—generally treated as constants—are closely related to microphysics. The relationships between the fitting coefficients and the droplet number concentration were established using half of the data about Mount Huangshan for 2008; thus, the visibility diagnostic schemes were improved. The effectiveness of the new scheme was verified using independent data, which included the other half of the data about Mount Huangshan for 2008 and the entire dataset for 2009 and 2011. Additionally, data on Enshi, Hubei, for 2009 were included in the verification process.