Air streams known as Trade winds converge at the Intertropical Convergence Zone (ITCZ), it is a belt of low pressure that circles the Earth roughly at the equator and is thought to form a meteorological barrier between the two hemispheres.
"The trade winds act as the steering flow for tropical storms that form over the Atlantic, Pacific, and Indian Oceans that make landfall in North America, Southeast Asia, and India, respectively."
In cloudless skies in the Western Pacific, researchers have found an atmospheric chemical line about 30 miles wide, an additional barrier high up above the Western Pacific that prevents the pollution from forest fires in countries such as Thailand and Sumatra contaminating the pristine skies above the Southern Ocean. Levels of carbon monoxide – a by-product of burning – were four times higher on the northern side. To the south, cyclones above Australia bring in clean maritime air. "The two systems do not mix, creating an invisible chemical barrier." Powerful storms may be lifting highly polluted air from the surface to high in the atmosphere where pollutants will remain longer with potential global affects.
At the time, the ITCZ lay much further south, over Central Australia. So the researchers concluded that they must have come across another "hidden" barrier. The shallow waters of the Western Pacific may help form the barrier.
