Boundary Layer Parameterizations to Simulate Fog Over Atlantic Canada Waters

Abstract

Abstract In this study, a series of fog events that occurred near Halifax, Canada, during 20 June to 31 July 2016 are investigated using the Weather Research and Forecasting Model Version 3.8.1 (WRF), in comparison with in situ and satellite remotely sensed observations from the Moderate Resolution Imaging Spectroradiometer. We evaluate five planetary boundary layer (PBL) schemes available in WRF. Results show that these five PBL schemes lead to overestimates in liquid water content, especially the nonlocal schemes, and that they are biased early, in terms of the predicting the onset of fog, and late, in terms of fog dissipation, although their spatial patterns of fog are in good agreement with those suggested by Moderate Resolution Imaging Spectroradiometer imagery. The Kunkel equation is used to calculate visibility, based on WRF modeling of liquid water content. Comparisons with observed visibility show that this methodology sometimes fails to predict fog dissipation. We present a modification of this formulation for visibility that shows improved agreement with observations and more accurate fog dissipation. Continued improvements in the PBL scheme and visibility parameterization are needed for more accurate fog prediction.

Keywords

• Fog modelling
• Boundary layer schemes
• Visibility equation
• WRF