A group of Taiwanese researchers said they have found that variations in the Earth’s axial tilt could influence the migration of tropical rain belts and monsoon systems, which could result in extreme weather events, adding that their findings might allow them to predict weather patterns.
A team led by National Taiwan University geology professor Shen Chuan-chou (沈川洲) studied the relationship between the movement of the western Pacific Intertropical Convergence Zone (ITCZ) — a weather system that encompasses the planet’s heaviest rain belt, which migrates meridionally with the seasonal angle of the sun — and changes in the Earth’s axial tilt and the shape of its orbit.
A small displacement in the position of the ITCZ can cause dramatic changes in hydrology and the frequency of extreme weather events, such as droughts, floods and tropical cyclones, Shen said, adding that the collapse of the Mayan civilization and several Chinese dynasties have been attributed to persistent droughts associated with ITCZ migrations.
The team collected marine sedimentary sequence off the eastern coast of Papua New Guinea to reconstruct a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferring that the migration of the ITCZ is heavily conditioned by the Earth’s axial tilt, Shen said.
The axial tilt is the angle between the Earth’s rotational and orbital axes, oscillating between 22.1o and 24.5o on a 41,000-year cycle, and is currently at 23.44o and decreasing.
When the axial tilt is high, high-altitude areas in the north hemisphere receive less sunlight, causing the establishment of a strong Siberian high-pressure structure and East Asian winter monsoon system, resulting in the southward shift of the ITCZ rain belt to the southernmost position in boreal winter to increase precipitation in northern Australia, Shen said.
When the axial tilt is low, the north hemisphere receives more sunlight and northerly winds are not as strong, resulting is weaker cross-equatorial movement of the ITCZ, causing the rain belt to stay in the north, with northern Australia receiving less rainfall while Papua New Guinea experiences enormous precipitation, he said.
The current build-up of atmospheric greenhouse gases has the potential to affect the future position of the ITCZ and weather patterns, and the research could enable the understanding of long-term natural variability for predicting future ITCZ migration, he said.
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