The African Easterly Jet (AEJ) is part of a climatic system which is of critical importance to African and global weather and climate, but is poorly observed and not well represented in model analyses. For the JET2000 project the Met Office Met Research flight (MRF) aircraft performed four flights, involving transects along and across the jet and the baroclinic zone, to make observations of unprecedented resolution for this part of the world. 110 dropsondes were dropped along the fight path. The data includes detailed synoptic observations of the basic state over mainland West Africa, and detailed synoptic observations of the African Easterly Waves (AEW) over mainland tropical West Africa.