Hurricane Impact on Visibility

The goal of this work is to study the impacts of hurricanes on fog visibility (Vis) during the C-FOG (Coastal-Fog) project, which took place in Newfoundland, Canada from August 25 to October 06 2018. Coastal fog is usually dominated by advection processes but locally, both radiation and turbulent processes also play an important role in its life cycle. During the C-FOG project, at least 3 major hurricanes affected the project region to various degrees but only one of them, Leslie, is studied here. Hurricanes have cyclonic motions at low levels that bring moisture from warm ocean surfaces located at the lower latitudes of the Atlantic Ocean into higher latitudes. These cyclonic systems interact with northerly and north-westerly weather systems, and pressure gradients; therefore, their northern impact on fog processes is very complex. Local conditions such as warm Gulf Stream and cold Labrador currents also create a strong dynamical precursor for coastal fog formation and development. Results showed that Hurricane Leslie played a major role in creating low visibility (Vis) conditions at the northern latitudes where the C-FOG supersites were located. Vis variability is found to be very large and related to both radiative fluxes and turbulent fluxes, especially during the fog formation and dissipation stages. The estimated maxima of the droplet number concentration (Nd) and liquid water content (LWC) are at 80 cm^-3 and 0.2 g m^-3, respectively. The mean volume diameter-Nd relationship is found to be affected by LWC magnitude. Overall, it is concluded that hurricanes can play significant role for defining low Vis conditions over marine conditions for late summer.