The JET2000 experiment took place in the last week of August 2000 in West Africa. Four flights with dropsondes (0.5-1 degree of resolution), involving transects along and across the African Easterly Jet (AEJ) and the baroclinic zone were made. The AEJ, whose existence is due to the strong meridional surface temperature gradient over West Africa, is crucial both for generating synoptic-scale African easterly waves (AEWs) and organizing long-lived mesoscale convective systems (MCSs).

The JET2000 experiment provides a high resolution dataset allowing analysis of the meteorological features of the West African monsoon and their interactions on synoptic and diurnal time-scales. The flights observed an AEJ stronger and southward (20 m/s at 10 N) of climatological observations (15 m/s at 15N). Farther north in the Sahel, there is evidence of a dry spell which may be consistent with a dry intrusion of mid-level air from the Sahara. Observations made at 2 - 24 hour times after the passages of different MCSs revealed a strong impact of organized convection on the AEJ structure. The low-level observations present significant mesoscale structures with a strong baroclinic zone around 16 N which may be related to land-surface properties.

The ability of NWP models to analyse and forecast the features of the West African Monsoon region is also investigated, using the Unified Model of The Met Office and the ECMWF model. Preliminary results show that both models' analyses (without JET2000 extra data) appear to represent the AEJ well. However, the 5-day forecasts exhibit structures significantly different to the observations and climatology. The presentation will explore the significance of different data sources in generating a good analysis from a poor forecast over west Africa.