Failed cyclogenesis of a mesoscale convective system near Cape Verde: The role of the Saharan trade wind layer among other inhibiting factors observed during the CADDIWA field campaign

Abstract. The role of the Saharan air layer in Cape Verde cyclogenesis remains uncertain. Here, we investigate the inhibiting factors leading to the failed cyclogenesis of the mesoscale convective system (MCS) Pierre Henri (PH) observed during two flights of the CADDIWA campaign. We use CADDIWA data and a convection-permitting simulation run with the Meso-NH model. We show that the African easterly wave in which PH is embedded forms a marsupial pouch that keeps the SAL away from PH. On the contrary, a dusty, dry and warm air layer between 0.8 and 2 km altitude, called Saharan trade wind layer (STWL), penetrates into PH convective core, increasing the convective inhibition (CIN) area, and contributing up to 40 % of the CIN area during the MCS mature phase. The cold pools produced by convection also increase the CIN area, and contribute up to 50 % of this area after the MCS intense phase. Upper tropospheric (UT) dry air, with relative humidity below 15 % between 7 and 11 km altitude, gradually penetrates into the 150 km circle around PH, reaching 18 % of the area during its dissipation phase, preventing the MCS anvil expansion. The inhibiting roles of the STWL, cold pools, and UT dry air in leading the cyclogenesis to fail provide new insights into the complex dynamics of cyclogenesis in the Cape Verde region and challenge the existing model of the SAL.