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Northeastern Tropical Atlantic SST and Sahel Rainfall Variability

Atmospheric and Climate Sciences 2023年第4期13卷 431-454页

作者： Dahirou Wane abdou lahat dieng Coumba Niang Amadou T. Gaye Laboratoire de Physique de l’Atmosphère et de l’Océan Siméon Fongang Ecole Supérieure Polytechnique Université Cheikh Anta Diop de Dakar (LPAO-SF/ESP/UCAD) Dakar Senegal

The SST variability during the summer period in the northeastern tropical Atlantic region (NTA) is characterized by an alternation of warming/cooling which represents 87% of the total variability. The aim of this paper is to study the atmospheric responses as well as the precipitation associated with these oceanic conditions. Based on Reynolds’s SST from 1982 to 2019, a normalized Northern Tropical Atlantic index (NTAI) is computed into the region between 15° - 25°W;12° - 16°N and a composite analysis is then performed. It is shown that the NTAI is significantly correlated with the SST’s first principal component mode (PC1) in this region. Moreover, the composite of SST anomalies and atmospheric parameters exhibits a strong local ocean-atmosphere interaction which highly impacts the large-scale atmospheric circulation in West Africa, particularly in the western Sahel. An in-depth analysis shows that the atmospheric response to the warm (cold) SST is a cyclonic (anticyclonic) circulation in the lower layers near the West Africa Coast. This cyclonic (anticyclonic) circulation strengthens/reduces the moisture transport towards the continent in the low levels. In the middle layers of the atmosphere (500 hPa), the warm (cold) composite is associated with a decrease (increase) in the intensity of the African Easterly Jet (AEJ) whereas, in the upper atmosphere (200 hPa), the strengthening (weakening) of the Tropical Easterly Jet (TEJ) is observed. With regard to the composite precipitation field, a positive/negative SST anomaly is associated with significantly enhanced/reduced rainfall in the western Sahelian region. It is found that this relationship (correlation) increases as we are closer to the coasts.

关键词： SST-Rain Sahel Rainfall Senegal Rainfall Ocean-Atmosphere Interaction

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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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