Boundary Layer and Microphysical Characteristics of Marine Fog- Mist Transitions.

Abstract:

The goal of this study is to evaluate microphysical conditions of transitions between coastal fog and mist. Onshore measurements of aerosol and fog/cloud physical properties collected during an intense 45-day field campaign, C-FOG (Toward Improving Coastal Fog Prediction), conducted near Newfoundland and Halifax, Canada are presented for a cold-front marine fog case. This Intensive Operational Period (IOP) occurred from 28 to 30 September 2018, near the coast of Newfoundland. Satellite image analysis allowed monitoring of large-scale weather systems during the IOP. The ground-based in-situ instruments at the Battery supersite measured droplet spectra (fog monitor) as well as various boundary layer physical and dynamical at various levels along a 15 m meteorological tower. Radiosondes were launched during fog events at 3-hr periods. A profiling microwave radiometer provided information related to RH and T on the arrival of a cold front. A pronounced layer of cold and moist air layer with RH ~ 90% and < 10 ^oC, respectively, formed up to 900 m AGL. During IOP, mist-fog-mist transitions were observed with the most prolonged fog spell being 12 hours on 29 September 0000 to 1200 UTC. Fog microphysical observations show a monomodal drop-size distribution, attributed to aerosol-laden airmasses came from northeast Canada. The fog layer was usually turbulent and unstable, and its erosion due to SW heating and mixing led to a stratus deck formation. Overall, frontal fog conditions led to coastal marine fog formation and precipitation that affected visibility.

This research is funded by the Office of Naval Research Award # N00014-18-1-2472 entitled: Toward Improving Coastal Fog Prediction (C-FOG).