ITCZ is the rising branch of the Hadley circulation, marked by low-level convergence, deep convection, and precipitation. Its importance for the climate system can hardly be exaggerated. The ITCZ plays a central role in the global circulation system and around 1/3 of the global precipitation falls within the latitudinal band associated with the ITCZ. While the ITCZ is expected to change in a warming climate, our confidence in the ability of climate model to correctly represent this trend is limited as climate models have struggled for decades to correctly represent the ITCZ. Due to this central role, the ITCZ has, of course, already been studied intensely and the classic picture that arises is that of a continuous band of precipitating clouds spanning from east to west. However, the figure below shows the day-to-day variability of the ITCZ revealing a more chaotic picture with significant changes in cloud amount and organisation from one day to the next.

The day-to-day variability of the ITCZ

Fig. 5 Snapshots from VIIRS (NOAA-20) from the 1st of July 2021 until the 15th of July 2021 in the East Atlantic (26°W to 20°W, 0° to 14°N).#

Such deviations from the mean picture of the ITCZ have already been observed during the GATE campaign about 50 years ago and is nicely stated in a paper by Frank (1983):

With the introduction of meteorological satellites two decades ago, it became clear that long east-west oriented lindes of maximum cloudiness occur in the mean. However, the lines of maximum mean cloudiness consist only of preferred locations for a variety of complex convective phenomena. At any given time and place along the zonal band containing the ITCZ, there may be deep convective clouds organized into a number of mesoscale patterns or no clouds at all.

(add a short intro to GATE and link to a separate section page)

The inner life of the ITCZ#

The doldrums#