Local Meteorological and Large-Scale Weather Characteristics of Fog over the Grand Casablanca Region, Morocco

Abstract

Using a fog event approach, the local meteorological and synoptic characteristics of fogs that formed over the Grand Casablanca (GCB) region during a 9-yr period (2001–09) are investigated. A climatological study of fog, with emphasis on the fog temporal variability and spatial distribution, is carried out on the basis of hourly surface meteorological observations at two synoptic stations in the region. The fog events are classified into fog types, using an objective classification algorithm, and are characterized by their duration, intensity, and times of onset and dissipation. In addition, fog events are classified into two distinct categories (isolated and widespread) on the basis of their spatial extent. K-means cluster analysis is applied to the patterns of mean sea level pressure in ERA-Interim reanalyses at 0000 UTC to determine the synoptic circulation types associated with fog occurrence in the GCB region. Results show that the fog frequency at the inland suburban station is more recurrent than at the coastal urban station. The fog events are predominantly of the advection–radiation type, with a marked tendency of nighttime occurrence during the winter. The spatial distribution analysis points out the localized character of fog and reveals the possibility of different fog types occurring when fog is present near the two stations simultaneously. Furthermore, the interaction between local- and large-scale mechanisms suggests that advective processes associated with sea-breeze circulation during daytime, followed by radiative processes early in the night, often lead to fog formation over the GCB region.

Fog Spatial Distributions over the Central Namib Desert - An Isotope Approach

“…However, despite these limitations, this study demonstrated that besides advective fog, radiation and mixed fog occurred regularly in this section of the Namib Desert, at least during the observation period. Furthermore, stable isotope analysis of fog suggests co-occurrence of different types of fog during what appears as a single fog event over a large geographic area, similar to the observations of Bari et al (2016) in Morocco. This suggests that our current understanding of fog dominated ecosystems could be overly simplistic thus there is a need for further studies to understand spatial variability of fog types, their significance to ecohydrology and how shifts or changes might affect the composition of endemic flora and fauna in the future.…”

“…hours (Bari et al, 2016). However, although Volgefederberg showed an initial increase in specific humidity on the 16 th June 2016, by end of the daylight hours this had decreased and only increased during the night by 0.8 g kg -1 just before fog onset at 0:00 hrs (Fig.…”

“…Over the years, stable isotopes have been successfully applied to different fog studies and have shown that in some environments fog contributes to groundwater recharge Matthews, 1988, 1990;Scholl et al, 2002) and vegetation water use (Dawson, 1998;Limm et al, 2009;. Although the spatial variation of fog has been investigated at some sites (Tardif and Rasmussen, 2007;Bari et al, 2016), the classification methods are often based on subjective algorithms. As George (1951) points out that there will always be exceptions to classification based on meteorology or aviation forecasting.…”

Influence of Environmental Conditions on Forecasting of an Advection-Radiation Fog: A Case Study from the Casablanca Region, Morocco

“…Adverse visibility in foggy conditions often leads to serious accidents for air, road and marine traffic. Therefore, fog is a potentially disastrous weather phenomenon that is of widespread concern (e.g., Taylor, 1917;Musson-Genon, 1987;Duynkerke, 1991;Koracin et al, 2001;Bergot et al, 2005;Roquelaure et al, 2009) and has been studied extensively from different points of view (Gultepe et al, 2007): climatology studies (e.g., Tarif and Rasmussen, 2007;Bari et al, 2016), remote sensing studies (e.g., Cermak and Bendix, 2007), statistical forecasting (e.g., Hilliker and Fritsch, 1999;, and numerical modeling (e.g., Cuxart and Jiménez, 2012;Bergot et al, 2014.…”

“…It results from nighttime radiative cooling of moist air that has been advected over land from the ocean or from any large water body during the previous daylight hours (Ryznar, 1977). Bari et al (2016) have performed a climatological study in the Grand Casablanca region, Morocco. They show that advection-radiation fog is the most common fog type over this region.…”