The calm but variable inner life of the Atlantic ITCZ: the relationship between ITCZ, doldrums, and surface convergence revisited

Julia Windmiller (Max Planck Institut for Meteorology)

Séminaire du LMD à l’ENS.


Date de début 28/03/2024 11:00
Date de fin 28/03/2024
Organisateur LMD
Lieu ENS – salle Claude Froidevaux – E314 • 24, rue Lhomond 75005 PARIS


The Intertropical Convergence Zone (ITCZ) is a central component of the atmospheric general circulation, traditionally described as a region of mean surface convergence and high mean precipitation. This region of mean convergence has also been associated with the doldrums – a region of low wind speeds known to sailors for centuries.

This description neglects the substantial day-to-day variation in the ITCZ. Combining observational data with reanalysis data we revisit the relationship between the ITCZ, the doldrums, and surface convergence in an instantaneous way.

We show that the ITCZ can be best described as a meridionally extended region with enhanced surface convergence at the edges. We observe distinctive patterns in the ITCZ structure during summer and winter. Summer shows a pronounced asymmetry, with a speed convergence line marking the southern edge and a confluence line marking the northern edge, while winter shows a more symmetric pattern.

By analyzing the frequency distribution of low wind speed events, we show that the doldrums are largely confined to within the ITCZ. While the region between the edges is a region of high mean precipitation, low wind speed events occur within the ITCZ in the absence of precipitation. Based on these results, we hypothesize that low wind speed events occur in regions of local descent rather than ascent.

Informations supplémentaires

École normale supérieure
24 rue Lhomond – aile Erasme
salle Claude Froidevaux – E314