What causes the shift in the ITCZ and global circulation throughout the year?

The shift in the Intertropical Convergence Zone (ITCZ) and global circulation patterns throughout the year is primarily influenced by Earth's axial tilt and the distribution of incoming solar radiation. As the Earth orbits the Sun, different regions receive varying amounts of sunlight due to this tilt. This variation causes seasonal changes in temperature and atmospheric pressure, which in turn affect the position of the ITCZ.

The ITCZ itself is characterized by the convergence of trade winds from both hemispheres, where warm, moist air rises, leading to cloud formation and precipitation. During different times of the year, the ITCZ migrates north and south, following the sun's zenith point. For example, it moves northward during the northern hemisphere summer when sunlight is more direct over that area, and moves southward during the southern hemisphere summer.

This axial tilt and its consequent impact on solar radiation are fundamental in driving seasonal climate variations and consequently dictate global circulation patterns, such as the monsoon seasons in tropical regions and the trade winds in subtropical latitudes. Other factors, while influential in specific contexts, do not account for the large-scale, cyclical nature of these shifts as effectively as axial tilt and solar radiation do.