Fig. (2) Schematic cross section approximately along latitude 15 degrees north from the western Sahara to the Atlantic Ocean, showing the Saharan Air Layer (SAL) moving from the desert over the cooler marine boundary layer where it appears as an elevated mixed layer. Clouds form at the top of the marine boundary layer (stratocumulus) and at the top of the SAL (alto cumulus castellatus) are indicated; (based on a figure by Cuesta et al. [18]).