Numerical study of a coastal fog event over Casablanca, Morocco

Abstract

This numerical study focuses on a dense fog event that occurred during the night of 21-22 January 2008 in the Grand Casablanca region, on the northwestern coast of Morocco. This fog event, which lasted for 15 h, is simulated by the mesoscale non-hydrostatic model Meso-NH and analyzed using conventional meteorological observations from two synoptic stations of the region, Meteosat Second Generation (MSG) satellite imagery and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis. Results demonstrate that this fog event included the formation of radiation fog over a continental zone and its extension to the coastal zone through the lowering of low-stratus clouds, which is in agreement with observations and is captured well by the Meso-NH model. Sensitivity experiments show that coastal fog prediction improves with improved sea-surface temperature. Model skill also depends on the adjustment of microphysical parameters when a single-moment microphysical scheme is used, and on reliable initial conditions.

Estimating fog-top height through near-surface micrometeorological measurements

“…1 In any case, fog is defined as a visibility threshold 2 (surface horizontal visibility <1000 m, (DOC/NOAA, 3 1995)), but unfortunately, only a few works have the 4 opportunity of using visibilimeters deployed at differ-5 ent heights to determine the fog top (e.g., Guedalia and 6 Bergot, 1994). 7 In this work, on the one hand we have found a clear 8 linear correlation between surface turbulence and fog-9 top height. Thus, regression equations are derived re-10 lating friction velocity and buoyancy flux at surface 11 with fog thickness data.…”

“…This method is based on the turbu-3 lent homogenization of well-mixed fog, which makes 4 the potential temperature converge to approximately the 5 same value at the heights where the fog layer is present.6 Thus, fog-top height is defined as the maximum height 7 (z) where |∆θ| = θ 2m −θ z is lower than 1.2°C. It is shown8 how this method offers satisfactory results for deep fog 9…”

“…In this section, we show how surface turbulent pa-32 rameters calculated from sonic anemometer measure-33 ments can provide satisfactory estimations of the fog-34 top height. 36 Firstly, surface friction velocity (u * ) values are cal-37 culated from high frequency measurements of sonic 38 anemometers (Eq.1) at both sites: Figure 1 for differences between sites) and it is assigned 8 to the midpoint between the maximum height where the 9 visibility is <1000 m and the height of the next visi-10 bilimeter up in the tower (where visibility is >1000m).…”

Machine-learning regression applied to diagnose horizontal visibility from mesoscale NWP model forecasts

“…For example, a dense advection-radiation fog that occurred in December 2013 led to several vehicle collisions and loss of life on a highway of the Grand Casablanca region, Morocco [4]. For air traffic, a dense fog event (visibility below 200 m) obliged the diversion of 21 aircrafts in 2008, which were supposed to land at Mohamed V international airport, Casablanca, Morocco, to other national airports [5]. Such flight diversion results in a considerable cost to airlines (e.g.…”

Forecasting radiation fog at climatologically contrasting sites: evaluation of statistical methods and WRF

“…Katata et al, 2011) or increasing resolution (Boutle et al, 2015). Apart from this, NWP models also have issues associated with the role of initial conditions (Rémy et al, 2012;Bari et al, 2015) and the use of appropriate vertical (Tardif, 2007) and horizontal (Tang et al, 2009) resolutions. Some of these fog modelling problems have been investigated with the Weather Research and Forecasting (WRF) model, which allows the use of different combinations of physical options, domain configuration or the application of data assimilation.…”