troposphere of the tropics is analyzed in 23 years of daily averaged

high resolution reanalysis data. The 850 mb vorticity structures

(some of which may develop into tropical cyclones) can be divided into

elongated vorticity strips that we classify as Intertropical

Convergence Zones (ITCZs) and more localized maxima that we call

westward propagating disturbances (WPDs).

Using spectral methods we form a composite of such variability in

three regions: the tropical east to central Pacific, the tropical east

Atlantic/Africa, both north of the equator and in the summer half

year, and the east Pacific on both sides of the equator in boreal

spring when the double ITCZ is frequently observed. The analysis

shows the prevalence of ITCZ-type slowly propagating structures in the

Pacific in summer. By contrast, the Atlantic synoptic scale

variability is dominated by more localized disturbances (WPDs). The double ITCZ is particularly strong south of

the equator and is located at 10S, which is further poleward than

earlier studies have indicated. The northern branch is weak in

comparison and located at 5N. To quantify the variability of synoptic

scale vorticity structures on the seasonal and interannual time scale,

we use a Bayesian framework for tracking both types of disturbances

using a hidden-state representation. The analysis is currently

underway, but some early results from the tropical Pacific will be reported on at the conference.