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Study of Boundary Layer Height over West Africa

Journal of Geoscience and Environment Protection 2019年第11期7卷 179-194页

作者： semou ndao Djiondo Ngongang Rinelle Daouda Badiane Andre Lenouo Saidou Moustapha Sall LPAO-SF ESP-University Cheikh Anta DiopDakarSenegal Department of Physics Faculty of ScienceUniversity of DoualaDoualaCameroon

Monthly means of boundary layer height (BLH) over West Africa are presented based on 36 years (1979-2014) of six-hourly ERA-Interim reanalysis. In this region, we found that there is a link between the West Africa Monsoon (WAM) and the monthly means of BLH in the summer. The trend and empirical orthogonal function (EOF) of BLH are presented, including the mid July variability of BLH with the precipitation. The dominant EOF of BLH accounts for around 42% of the variance with slightly large amplitude in the north while relatively small in the equatorial band. The second EOF which accounts for 16.4%, describes a longitudinal contrast with a zonal gradient. The relationship between BLH and precipitation is found using the canonical correlation analysis (CCA). Significant trends of the first and second pairs of BLH with precipitation are shown. The first and second CCA pair has a correlation of 68% and 60% with 12.2 and 10.8 degrees of freedom respectively. The critical correlation coefficients at the 95% level are 0.21 and 0.65 for the first and second CCA pairs respectively. This first CCA pair mostly determines the arid and semi-arid areas where the rate of explained regional variance is about 78% in the arid area and 73% in the semi-arid area. For the second pair of CCA, the rate of explained regional variance is more than 60% in the Guinea coast and wet equatorial area.

关键词： Boundary Layer Height West Africa Monsoon Inter Tropical Convergence Zone CCA

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Case Study of Coastal Fog Events in Senegal Using LIDAR Ceilometer

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Journal of Atmospheric Science Research 2023年第4期6卷 64-76页

作者： semou ndao Cheikh Modou Noreyni Fall Luis Duran Assie Regina Djiguene Diatta Abdou lahat Dieng Badara Sane Amadou Thierno Gaye Laboratory of Physics of the Atmosphere and Ocean-Siméon Fongang(LPAO-SF) Higher Polytechnic SchoolUniversity Cheikh Anta Diop(UCAD)PO BOX 5085DakarSenegal Department of Earth Physics and Astrophysics Complutense University of MadridMadrid28040Spain Meteorological Operation Service Representation of the Agency for the Safety of Air Navigation in Africa and Madagascar(ASECNA)in SenegalPO BOX 3144DakarSenegal Laboratory of Oceanography and Climate Experiments and Numerical Approaches(LOCEAN)Sorbonne University(SU)Paris75006France

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,*** 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 *** 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 *** April 30 event characterized by a good vertical extension from the surface up to 300 m above sea level,was triggered just after 2 *** lasted around 3 *** results showed that a decrease in temperature,accompanied by an increase in humidity and light wind,is favorable for the triggering and persistence of *** Level Pressure(SLP)anomaly fields show two distinct *** 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 *** 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 *** 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.

关键词： Coastal fog LIDAR Ceilometer Sea level pressure Relative humidity Temperature

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