ITCZ-Fluctuations and Impact on Monsoon

ITCZ refers to the low-pressure region near the equator, from about 5° north and 5° south, where the northeast trade winds and southeast trade winds converge. This is also known as the Equatorial Convergence Zone or the Monsoon Trough.

Annual Fluctuations and Shifting of ITCZ

The location of the ITCZ varies throughout the year. While it remains near the equator, the ITCZ over land varies more in the north or south, than the ITCZ over the oceans, due to the variation in land temperatures. It can vary as much as 40° to 45° of latitude north or south of the equator based on the pattern of distribution of land and ocean.

The position of sun influences the movement of the thermal equator, shifting the belts of planetary winds and pressure systems to the north and to the south annually. Further, the directions of the planetary winds change according to the Coriolis effect imparted by Earth’s rotation. Variation in location of the ITCZ affects rainfall in the equatorial regions, as it is the region of low atmospheric pressure pulling the moisture laden winds and causing them to rise. This results in wet or dry seasons and even droughts, depending on the location of ITCZ.

The significance of ITCZ for India is its contribution to the Indian monsoon. In July when ITCZ is located in the north, it creates the Monsoon Trough. This encourages the development of thermal low over the North and Northwest India. Due to this shift of ITCZ, the trade winds of the southern hemisphere cross the equator between 40oE and 60oE longitudes and start blowing from southwest to northeast due to the Coriolis force. It becomes the Southwest monsoon.

In winter, the ITCZ moves southward, and so the reversal of winds, from northeast to south and southwest, takes place thus leading to the Northeast monsoon. The amount and intensity of rainfall follows the movement of the ITCZ, as the regions lying along its location are regions of high rainfall. Therefore, the location and variations in the ITCZ influence the global circulation systems that, in turn, determine the weather patterns and precipitation across regions.

By: ABHISHEK KUMAR GARG