A Freezing Fog/Drizzle Event during the FRAM-S Project 2011-38-0028

The objective of this work is to better understand freezing fog/drizzle conditions using observations collected during the Fog Remote Sensing and Modeling project (FRAM-S) that took place at St. John's International Airport, St. John's, NL, Canada. This location was ~1 km away from the Atlantic Ocean coast. During the project, the following measurements at one minute resolution were collected: precipitation rate (PR) and amount, fog/drizzle microphysics, 3D wind speed (Uh) and turbulence (Uh'), visibility (Vis), IR and SW radiative fluxes, temperature (T) and relative humidity (RH), and aerosol observations. The reflectivity and microphysical parameters obtained from the Metek Inc. MRR (Microwave Rain Radar) were also used in the analysis. The measurements were then used to obtain freezing fog/drizzle microphysical characteristics and their relation to visibility.

The ground-based CIP (Cloud Imaging Probe) measurements of freezing fog/drizzle particles together with hydrometeor measurements obtained from disdrometers have been used in the analysis. During FRAM-S, ice accumulation over the surfaces was more than 2 cm on 26 March 2009 and this affected some of the various sensors but the major instruments worked properly to get freezing fog/drizzle conditions. The results suggested that better prediction techniques for freezing fog/drizzle events are needed for marine environment applications. Particle microphysical measurements play a crucial role for developing better nowcasting/forecasting techniques.