Marine Fog Research During Fatima Field Campaigns

The goal of this work is to provide comparisons of marine fog microphysical and dynamical observations that play a significant role for fog life cycle during fog and turbulence in marine atmosphere (FATIMA) project. The FATIMA took place in two locations: 1) Eastern Canada, Grand Bank (GB) region and 2) Republic of Korea (ROK), Yellow Sea (YS) region. GB observations during July 2022 were collected by Canadian Atlantic Condor R/V and various meteorological supersites located in the Sable Island off the Nova Scotia. YS observations from June 15 to July 10, 2023 were collected mainly by the Korean Annuri R/V and GISANG-1 as well as King Air off the western ROK and nearby the three ocean observing sites. To study large-scale weather systems effects on marine fog microphysics, global reanalysis information as well as modeling studies for which synoptic forecasts, NWP (Numerical Weather Prediction) models (e.g., COAMPS: Coupled Ocean Atmosphere Mesoscale Prediction System) were used.

Measurements collected by the in-situ instruments represent marine fog droplet spectra from various instruments, including FM120, CDP, BCP, FD70, OPC-N3 microphysical (MP) instruments that provide particle size range from 0.3 µm up to 1 cm size range. These were used for the calculation of liquid water content (LWC), droplet number concentration (Nd), mean volume diameter (MVD) as well as precipitation rate (PR), and also for droplet settling rates (SR). In addition, SW and IR radiative fluxes and 3D wind speed at 24 Hz were also measured. All these measurements are considered in the derivation of visibility (Vis) from the visible extinction coefficient, and direct measurements of Vis from Vaisala PWD and FD70 instruments were also obtained. Vertical profiles of fog related measurements at 2, 5, 8, and 10 m levels of the turbulence towers were also provided at the surface observing sites. The tethered balloon systems (TBS), unmanned aerial vehicles (UAS) as well as remote sensing based profiles of meteorological parameters also provided extensive physical and dynamical information for the marine boundary layer.

Results suggested that MP and turbulence characteristics of marine fog events for both field campaigns (GB and YS) were found significantly different, and these can affect the Vis predictions based on the statistical analysis. Advection and mixing, as well as ocean upwelling processes are found to be main processes affecting fog life cycle and fog microphysics. It is also suggested that differences between observed Vis and Vis from MP measurements can be significant and that need to be improved in the studies of fog life cycle and its prediction. Overall, it is concluded that Na and Nd relationships need to be improved and MP parameterizations should be carefully obtained for specific climatic regions. Turbulence and eddy dissipation rates together with advective processes can play significant role for marine fog cycle, especially during pre- and post-conditions rather that mature stages. In the presentation, measurement issues, MP parameterizations, turbulence and cloud condensation nuclei (CCN) impact on Nd will be evaluated and challenges faced during the study will be provided.

This work was funded by the Grant N00014-21-1-2296 (Fatima Multidisciplinary University Research Initiative) of the USA Office of Naval Research, administered by the Marine Meteorology and Space Program.