Surface deposition of marine fog and its treatment in WRF model

Introduction

I have been doing research on marine fog based on the “Surface deposition of marine fog and its treatment in the Weather Research and Forecasting (WRF) model” paper. Much research has been done on fog occurrence, but the models have always been overestimating the cloud droplets leading to denser fog than observations. So, the paper focused on how the fog droplets interacted with the ocean surface. It was done so by parametrizing the process involving the interaction of fog droplets and the water surface, that is, adding another deposition velocity and a new variable z0c which is the roughness length for water droplets. I used the WRF single-column model (WRF-SCM) to analyze the marine fog near Sable Island.

I set up the WRF model for the ideal case and compiled it to the single column (em_scm_xy). Then, I did all the modifications such as adding the gravitation settling and z0c in the boundary layer modules and the registry. Then I edited the namelist.input to run for four days from the 15th of August 2018 to the 19th and made all the necessary adjustments. I was able to get the result that was in Figure 1 and Figure 2 of the paper. Once I was able to reproduce the results, I started incorporating radiation schemes in the namelist as no radiation schemes were added for the results in the paper. I found out that the best option for longwave radiation would be either RRTMG ( Rapid Radiative Transfer Model for GCMs) or RRTMG-k; for shortwave, it would be either RRTMG-k or Dudhia [1]. The details of the modifications are provided on the GitHub page.

The plot in Figure 1 of the paper was replicated using the WRF-SCM. Qc plot against height was plotted with 6hr of radiative cooling at 3 K/hr. MYNN boundary layer scheme was used using the direct approach method to add z0c= 0.01 m and for the microphysics scheme, Thompson. In the paper, no radiation scheme was used to simplify the interpretation of the results provided. The input sounding has a potential temperature of 300 K at the surface, increasing with height at a rate of 4 K/km. The initial relative humidity was 100 % at the surface, dropping to 0 % at 6 km. The wind profile was established with a long, no cooling run and has geostrophic wind components, (U, V), of (20,0) m/s.

Figure 1a) No radiation scheme

Figure 1b) LW and SW RRTMG

Figure 1c) LW RRTMG and SW Dudhia

Fog forms due to radiative cooling as is seen in Figure 1a), as after 6 hrs on the 15th, fog starts to develop.

References

1. Vivek Kumar Singh, Manju Mohan, Shweta Bhati, “Evaluation of different parameterization schemes in the WRF model for assessment of meteorological conditions over an industrial region in South‑East India”, Theoretical and Applied Climatology, 24 Sept. 2022, 150:1045-1066.