Observed structure and propagation characteristics of tropical summertime synoptic scale disturbances

Regions of enhanced variability in relative vorticity at 850 mb are identified in the western Pacific, eastern Pacific, Bay of Bengal/northern India and eastern Atlantic/western Africa sectors. Dominant spectral peaks with time scales ranging from 3 to 8 days are noted in the power spectra for these locations. Whereas considerable similarities are noted among disturbances occurring over various active maritime sites, the perturbations over central and western Africa exhibit structural characteristics that are unique to that region. Specifically, two propagation tracks are identified in the African sector. The northern track along southern Sahara consists mostly of eddies commonly found over arid zones, with ascent of warm and dry air over surface troughs. The southern track is collocated with the climatological rainfall maximum at about 10°N, and is associated with moist convective systems. -from Authors