New research looks at orbital factors in expansion and contraction of the intertropical convergence zone

Intertropical Convergence Zone [image credit: University of New Mexico]

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The sine wave shown in the paper (Fig. 1 reference F: ‘Comparison of PC2 (blue) with the difference between 30°N boreal solstice insolation and 30°S austral solstice insolation (orange)’) looks like the 21-kyr combined precession cycle, which isn’t mentioned here. However it does feature in an earlier paper (2015): ‘our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes.’
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The study focuses on the so-called Intertropical Convergence Zone (ITCZ), a low-pressure trough near the equator whose position and intensity changes seasonally with the position of the sun, says Bremen University @ Phys.org.

Trade winds from the northern and southern hemispheres meet here. This results in heavy cloud formation and heavy rainfall.

To analyze how the ITCZ has changed over the past 30,000 years, researchers use the stable oxygen isotope δ18O in calcareous deposits in cave systems on land and deposits of calcareous organisms on the ocean floor.

By releasing enormous amounts of water vapor and latent heat into the atmosphere, the position and strength of the ITCZ over the Indo-Pacific Warm Pool (IPWP) is of particular importance for global climate regulation.

While recent studies of the ITCZ have already fundamentally improved our understanding of the mechanism over the past millennia, Mohtadi and his colleagues used empirical orthogonal functional (EOF) analysis to examine the data in relation to precipitation in this and other regions.

The team was able to identify the main components for the size, strength and position of the ITCZ. They came to the conclusion that the inclination of the Earth’s axis and the eccentricity of the Earth’s orbit around the sun have significantly influenced the size of the ITCZ in the past.

Full article here.
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Study: Reconstruct the intertropical convergence zone over the Indo-Pacific Warm Pool with extended records and empirical orthogonal function – PNAS(2024).
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Image: Intertropical Convergence Zone [credit: University of New Mexico]