Study Explains why North Receives more Tropical Rainfall than the South

The Northern Hemisphere receives more rain than the southern hemisphere, but nobody knows why. Now, a new study has found that oceanic currents from the poles are responsible for tropical rains in the North.

The study was conducted by researchers at University of Washington and colleagues.

"It rains more in the Northern Hemisphere because it's warmer," said Dargan Frierson, a UW associate professor of atmospheric sciences and one of the study authors. "The question is: What makes the Northern Hemisphere warmer? And we've found that it's the ocean circulation."

The study was based on data from NASA's Clouds and Earth's Radiant Energy System, or CERES. Researchers found that the Southern hemisphere gets more sunlight, which ideally should have made the hemisphere the wetter one.

But, this doesn't happen due to the thermohaline circulation (THC), which is mostly driven by surface temperatures and salinity.

According to the researchers, the ocean conveyor belt that originates from Greenland, travels up to Antarctica, and then begins to flow northward. The absence of this current would lead to more rains in the south. Note that it takes about 1,000 years for the conveyor belt to complete one cycle.

The Day after Tomorrow                                                                                                                 

The oceanic current that researchers studied is similar to the one shown in the movie 'The Day After Tomorrow.' Experts believe that the current will shift southward in the future (about 100 years from now), but the shift wouldn't be as dramatic.

Shifts in rainfall pattern have occurred in the past and are likely to occur in the future. However, a growing body of research suggests that human activities are tweaking climatic conditions across the earth. A recent study by Frierson and colleagues had found that air pollution from Northern Hemisphere had shifted rain-belts south, causing drought in the Sahel region, Africa.

Another study has gown that the Northern Hemisphere is getting warmer than the Southern, which could eventually shift tropical rainfall pattern.

"A lot of the changes in the recent past have been due to air pollution," Frierson said in a news release. "The future will depend on air pollution and global warming, as well as ocean circulation changes. That makes tropical rainfall particularly hard to predict."

The study is published in the journal Nature Geoscience.