Case Study of Coastal Fog Events in Senegal Using LIDAR Ceilometer

Source:
By:Semou Ndao, Cheikh Modou Noreyni Fall, Luis Durán, Assie Regina Djiguene Diatta, Abdou lahat Dieng, Badara Sane, Amadou Thierno Gaye

DOI: https://doi.org/10.30564/jasr.v6i4.5943

Abstract:

This study aims to examine the atmospheric conditions characterising fog phenomena on the Senegalese coast focusing on two specific instances that occurred on April 3 and April 30, 2023. These events were detected by the LIDAR Ceilometer installed at LPAOSF/ESP/UCAD and confirmed on the METARs of the meteorological stations at Dakar and Diass airports. The LIDAR's backscatter signal showed that the fog of April 3 started around midnight with a vertical extension at 100 m altitude and dissipated around 10 a.m. The April 30 event characterized by a good vertical extension from the surface up to 300 m above sea level, was triggered just after 2 a.m. and lasted around 3 hours. The results showed that a decrease in temperature, accompanied by an increase in humidity and light wind, is favorable for the triggering and persistence of fog. Sea Level Pressure (SLP) anomaly fields show two distinct configurations. The April 3 event was characterized by a zonal dipole of SLP anomalies between the Sahara and the northern Senegalese coast, while the April 30 event was characterized by a meridional dipole between the Sahara and the Gulf of Guinea area as far as the equatorial Atlantic. A weakening of the pressure around the study area was observed in both cases, allowing moisture advection to favor the onset of fog. The hovmoller diagrams of relative humidity and wind show that a good vertical extension of humidity associated with a westerly wind in the lower layers plays an important role in the formation and persistence of fog. The presence of dry air associated with a weak easterly wind in the middle layers could explain the low vertical extension of the fog on April 3. A strong wind in the lower layers would be responsible for the premature dissipation of the April 30 fog.

References:

[1] Fog [Internet]. World Meteorological Organization [cited 2022 Jul 4]. Available from: https://cloudatlas.wmo.int/en/fog.html [2] Baguskas, S.A., Clemesha, R.E., Loik, M.E., 2018. Coastal low cloudiness and fog enhance crop water use efficiency in a California agricultural system. Agricultural and Forest Meteorology. 252, 109-120. DOI: https://doi.org/10.1016/j.agrformet.2018.01.015 [3] Fall, C.M.N., Lavaysse, C., Kerdiles, H., et al., 2021. Performance of dry and wet spells combined with remote sensing indicators for crop yield prediction in Senegal. Climate Risk Management. 33, 100331. DOI: https://doi.org/10.1016/j.crm.2021.100331 [4] Boudala, F.S., Wu, D., Isaac, G.A., et al., 2022. Seasonal and microphysical characteristics of fog at a northern airport in Alberta, Canada. Remote Sensing. 14(19), 4865. DOI: https://doi.org/10.3390/rs14194865 [5] Zimmer, A., 1930. ‘Le brouillard mortel de la vallée de la Meuse': Décembre 1930-Naturalisation de la catastrophe (French) ['Deadly fog of Meuse' s valley' (December 1930). Naturalization of the disaster]. Débordements industriels: Environnement, territoire et conflit, edited by Thomas Le Roux and Michel Letté. 115-134. [6] Gultepe, I., Milbrandt, J.A., Zhou, B., 2017. Marine fog: A review on microphysics and visibility prediction. Marine fog: Challenges and advancements in observations, modeling, and forecasting. Springer: Cham. pp. 345-394. [7] Kim, C.K., Yum, S.S., 2010. Local meteorological and synoptic characteristics of fogs formed over Incheon international airport in the west coast of Korea. Advances in Atmospheric Sciences. 27, 761-776. [8] Fu, G., Li, P., Crompton, J.G., et al., 2010. An observational and modeling study of a sea fog event over the Yellow Sea on 1 August 2003. Meteorology and Atmospheric Physics. 107,149-159. [9] Heo, K.Y., Ha, K.J., Mahrt, L., et al., 2010. Comparison of advection and steam fogs: From direct observation over the sea. Atmospheric Research. 98(2-4), 426-437. [10]Wagh, S., Krishnamurthy, R., Wainwright, C., et al., 2021. Study of stratus-lowering marine-fog events observed during C-FOG. Boundary-Layer Meteorology. 181, 317-344. DOI: https://doi.org/10.1007/s10546-021-00670-w [11] Ryznar, E., 1977. Advection-radiation fog near Lake Michigan. Atmospheric Environment. 11(5), 427-430. [12]Fernando, H.J., Gultepe, I., Dorman, C., et al., 2021. C-FOG: Life of coastal fog. Bulletin of the American Meteorological Society. 102(2), E244-E272. DOI: https://doi.org/10.1175/BAMS-D-19-0070.1 [13]Dione, C., Haeffelin, M., Burnet, F., et al., 2023. Role of thermodynamic and turbulence processes on the fog life cycle during SOFOF3D experiment. Atmospheric Chemistry and Physics Discussions. DOI: https://doi.org/10.5194/egusphere-2023-1224 [14]Fernando, H.J., Gultepe, I., Dorman, C., et al., 2020. C-FOG: Life of coastal fog. Bulletin of the American Meteorological Society. 1(aop), 1-53. [15]Bardoel, S.L., Horna Muñoz, D.V., Grachev, A.A., et al., 2021. Fog formation related to gravity currents interacting with coastal topography. Boundary-Layer Meteorology. 181(2-3), 499-521. DOI: https://doi.org/10.1007/s10546-021-00638-w [16]Choi, H., Speer, M.S., 2006. The influence of synoptic‐mesoscale winds and sea surface temperature distribution on fog formation near the Korean western peninsula. Meteorological Applications: A Journal of Forecasting, Practical Applications, Training Techniques and Modelling. 13(4), 347-360. [17]Findlater, J., Roach, W.T., McHugh, B.C., 1989. The haar of north‐east Scotland. Quarterly Journal of the Royal Meteorological Society. 115(487), 581-608. [18]Ballard, S.P., Golding, B.W., Smith, R.N.B., 1991. Mesoscale model experimental forecasts of the Haar of northeast Scotland. Monthly Weather Review. 119(9), 2107-2123. [19]Pilié, R.J., Mack, E.J., Kocmond, W.C., et al., 1975. The life cycle of valley fog. Part I: Micrometeorological characteristics. Journal of Applied Meteorology and Climatology. 14(3), 347-363. [20]Leipper, D.F., 1994. Fog on the US west coast: A review. Bulletin of the American Meteorological Society. 75(2), 229-240. [21]Lewis, J.M., Koracin, D., Rabin, R., et al., 2003. Sea fog off the California coast: Viewed in the context of transient weather systems. Journal of Geophysical Research: Atmospheres. 108(D15). [22]Wong, W.K., Lai, E.S., 2010. Numerical simulation of fog using non-hydrostatic NWP model with third-order turbulence closure. Journal of Hydro-environment Research. 4(2), 131-141. [23]Diao, X., 1996. Main features of sea fog on Qingdao and its neighbouring sea areas. Marine Science Bulletin-Tianjin. 15, 87-91. [24]Zhou, B., Du, J., 2010. Fog prediction from a multimodel mesoscale ensemble prediction system. Weather and Forecasting. 25(1), 303-322. [25]Tsaknakis, G., Papayannis, A., Kokkalis, P., et al., 2011. Inter-comparison of lidar and ceilometer retrievals for aerosol and Planetary Boundary Layer profiling over Athens, Greece. Atmospheric Measurement Techniques. 4(6), 1261-1273. DOI: https://doi.org/10.5194/amt-4-1261-2011 [26]Guerrero-Rascado, J.L., Costa, M.J., Bortoli, D., et al., 2010. Infrared lidar overlap function: An experimental determination. Optics Express. 18(19), 20350-20369. DOI: https://doi.org/10.1364/OE.18.020350 [27]Senghor, H., Machu, É., Durán, L., et al., 2020. Seasonal behavior of aerosol vertical concentration in Dakar and role played by the sea-breeze. Open Journal of Air Pollution. 7(9), 11-26. DOI: https://doi.org/10.4236/ojap.2020.91002 [28]Hersbach, H., Dee, D., 2016. ERA5 Reanalysis is in Production [Internet]. ECMWF. Available from: https://www.ecmwf.int/en/newsletter/147/news/era5-reanalysis-production [29]Lawrence, M.G., 2005. The relationship between relative humidity and the dewpoint temperature in moist air: A simple conversion and applications. Bulletin of the American Meteorological Society. 86(2), 225-234. [30]Wang, H., Long, L., Kumar, A., et al., 2014. How well do global climate models simulate the variability of Atlantic tropical cyclones associated with ENSO? Journal of Climate. 27(15), 5673-5692. DOI: https://doi.org/10.1175/JCLI-D-13-00625.1 [31]Gultepe, I., Tardif, R., Michaelides, S.C., et al., 2007. Fog research: A review of past achievements and future perspectives. Pure and Applied Geophysics. 164, 1121-1159. [32]Miller, B.I., 1958. On the maximum intensity of hurricanes. Journal of Atmospheric Sciences. 15(2), 184-195. [33]Saucier, W.J., 1955. Principles of meteorological analysis. University of Chicago Press: Chicago.