Scientists track giant ocean vortex from space

Credit: Seung Joon Yang @ Wikipedia

This natural phenomenon is over 100,000 square miles in area, typically persists for about 200 days per year and is strongly linked to monsoons, but is not well understood.

Researchers have found a new way to use satellites to monitor the Great Whirl, a massive whirlpool the size of Colorado that forms each year off the coast of East Africa, they report in a new study.

Using 23 years of satellite data, the new findings show the Great Whirl is larger and longer-lived than scientists previously thought, reports Phys.org.

At its peak, the giant whirlpool is, on average, 275,000 square kilometers (106,000 square miles) in area and persists for about 200 days out of the year. Watch an animation of the Great Whirl’s evolution here.

More than being just a curiosity, the Great Whirl is closely connected to the monsoon that drives the rainy season in India. Monsoon rains fuel India’s $2 trillion agricultural economy, but how much rain falls each year is notoriously difficult to forecast.

If researchers can use their new method to discern a pattern in the Great Whirl’s formation, they might be able to better predict when India will have a very dry or very wet season compared to the average.

“If we’re about to connect these two, we might have an advantage in predicting the strength of the monsoon, which has huge socioeconomic impacts,” said Bryce Melzer, a satellite oceanographer at Stennis Space Center in Mississippi and lead author of the new study in AGU’s journal Geophysical Research Letters.

A swirling sea

The Great Whirl is a huge whirlpool that forms every spring off the coast of Somalia, when winds blowing across the Indian Ocean change direction from west to east. English geographer Alexander Findlay first described the Great Whirl in his navigational directory for the Indian Ocean in 1866.

According to Findlay, Lieutenant Taylor of the British Royal Navy described a “great whirl of current” circulating clockwise at about the same latitude at Xaafuun, Somalia. “A very heavy confused sea is created by this whirl,” Findlay wrote. The phenomenon became known as the Great Whirl, and sailors have long been wary of its strong waves and intense currents.

The Great Whirl starts to form in April but its currents are deepest and strongest from June to September, during the official Indian monsoon season. A 2013 study using satellite data found that at its peak, the Whirl can grow to more than 500 kilometers (300 miles) wide, making it wider than the Grand Canyon is long.

The Great Whirl’s circular currents extend hundreds of meters downward and can go farther than 1 kilometer (0.6 miles) deep in some areas. The inertia it generates keeps the Whirl going well past the end of monsoon season in September, until typically disappearing late in the fall.

Full article here – includes short video.