Long term in-situ measurement of fog at a mountainous site and the new visibility parameterization of fog and light precipitation

Fog is considered as a hazardous weather event due to visibility degradation. Observation and forecast are therefore important to understand the nature of fog better and to make better forecast model and eventually contribute to preventing fatal fog-related accidents. In this study we present the data from long-term microphysical measurement of fog, cloud, and precipitation with Fog Monitor (FM-120) and Meteorological Particle Spectrometer (MPS). In total 110 fog/cloud cases were observed between July 2015 and September 2016 at the Cloud Physics Observation Site (CPOS), located at a mountainous region in Korea. Observed fog/cloud exhibited many stages; newly generating, developing, dissipating stage. Based on the analysis of observation data, we introduce a new visibility parameterization method utilizing effective diameter (DE) of fog spectra along with liquid water content (LWC) and droplet number concentration (N_D). Compared to the previously developed visibility parameterization methods, the new method demonstrated improvement for the cases with the presence of large drops. Also found is that visibility values obtained from direct Mie calculation were more inaccurate than the parameterized visibility when large drops were present because of the complex nature of scattering. Details of the interesting features of measurement and new visibility parameterization will be presented at the conference.