ITCZ – Intertropical Convergence Zone

Intertropical Convergence Zone (ITCZ)

AUTHOR: Patrick Bodzak

13.01.2023

I will start by confirming that, yes, this is an article about the weather. I am new to Costa Rica and was given the opportunity to write an article for Ballena Tales. I considered a few topics before arriving at this obvious small-talk starter!

We all know that many tropical areas experience only slight annual temperature variation and very dramatic rainfall changes – often dividing their year into summer (dry season) and winter (wet season). Costa Rica is no exception, and the last few weeks fully demonstrated the wrath of the ‘wet season´ - and all cannot be blamed on Julia - because there is another culprit.

It sneakily snakes her soggy way around the globe, bringing storms, floods, mudslides, misery and also, life-giving rains and reprieve to many areas around the tropical and sub-tropical world. This is the Intertropical Convergence Zone (ITCZ).

What is the ITCZ?

The ITCZ is known by other names, such as ‘Monsoon Trough’ or ‘The Doldrums’. It is a band of clouds, rain, and storms that encircles the globe and forms over the hottest parts of the world, roughly in line with where the sun is directly overhead (but lagging in the distance by 1-2 months due to the lagging heating of the ocean).

Where the land and ocean are the hottest, the air heats up and thus continually rises, forming rain and storm clouds. The rising air is replaced by winds that rush in to fill the void – these winds are known as ‘Trade Winds’. The Trade Winds rush into the ITCZ from, roughly the north and the south, replacing the rising air and causing more air movement in the upward direction.

Why is the ITCZ known as the Doldrums when there are winds rushing into it?

When the northerly and southerly Trade Winds meet, they push against each other and are forced to rise up into the ITCZ. As the wind rises, the area immediately below them remains calm and windless. Therefore, another name for the ITCZ, a much older name, is The Doldrums. Sailships stuck in The Doldrums need to wait for the ITCZ to move past them so they can start to take advantage of the surrounding Trade Winds once again.

How the ITCZ moves throughout the year

The Intertropical Convergence Zone forms over the hottest parts of the land and sea, and these hot areas move with the seasons. For this reason, in July, the ITCZ sits over Mexico, Central America (including Costa Rica), Colombia and Venezuela. For January, it shifts south, sitting over southern Colombia and northern Brazil. Because land heats faster than water, so if the Zone is situated over land, it tends to be pulled more north in July and more south in January.

In Conclusion Hopefully, you now have a better understanding of the global weather pattern that impacts our life here (as I write this in early November, and the ITCZ stretches across the entire territory of Costa Rica).

So the next time someone complains about the rainy weather, be it at a party or a line in the checkout, you can feel confident to interject and endow them with a long and winding conversation about the ITCZ!

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