S138 Heat Wave occurrences over Senegal during Spring :Regionalization and Synoptic Patterns.

Sunday, 6 January 2019
Hall 4 (Phoenix Convention Center - West and North Buildings)
Marie Jeanne G. Sambou, Université Cheikh Anta Diop/LPAO-SF, Dakar, Senegal; and S. Janicot, B. Pohl, D. Badiane, A. L. DIENG, and A. T. Gaye

The coastal situation of Senegal modifies its heat waves (HW). Based on twelve stations of the Global Summary of the Day (GSOD) database (1979-2014), HW are defined in the spring (March-April-May, the hottest season in Senegal) for each station as the daily
maximum temperature (Tx), minimum temperature (Tn), or average apparent temperature of the day (AT), exceeding the corresponding 95% mobile percentile for at least three consecutive days. A hierarchical classification is performed on these 12 stations based on simultaneous occurrences of daily temperature peaks over their 95% mobile percentile. Three homogeneous zones of 4 stations each are identified (Zone #1, #2 and #3, located from west to east on Senegal). Atmospheric circulation associated with HW is assessed through composites of ERA-Interim deseasonalized anomalies, with the start date of each HW in each zone used as a reference. One main pattern controls the presence of HW in Senegal, consisting in positive pressure anomalies centered around the strait of Gibraltar, promoting easterly to northeasterly wind anomalies. This causes higher temperatures in the three zones of Senegal, and lower temperatures and drier air over the central Sahel. From Zone #1 to Zone #3, the corresponding pattern is also shifted to the east. The amplitude of this pattern is larger hinterland and weaker in the coastal zone. "Dry" and "wet" HW are next differentiated, the "dry" HW being more specific to Tx-HW and the “wet” HW to Tn-HW, corroborating and complementing previous work over the Sahel.
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