What is an “atmospheric lake”, a new type of storm that scientists have spotted over the Indian Ocean?

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Representative image. | Photo credit: iStock Images

Highlights

  • They were discovered in an equatorial location known for its almost negligible wind speeds
  • A new research team is being assembled to conduct a comprehensive study of this unique phenomenon.
  • If year-long water vapor in an atmospheric lake were liquefied, it would create a puddle a few centimeters deep but about 1,000 km wide

A new type of weather phenomenon, forming mostly in the western Indian Ocean, has been observed, with characteristics that prompted Brian Mapes, an atmospheric scientist at the University of Miami who discovered it. , to call it an “atmospheric lake”.

The compact, slow-moving storm hovering over the Indian Ocean is unlike conventional vortex-formed storms, and instead contains large concentrations of water vapor dense enough to produce plenty of precipitation.

These atmospheric lakes have been likened to atmospheric rivers of which we are well aware. Atmospheric rivers are long, narrow plumes of dense moisture. But unlike atmospheric rivers, slow-moving atmospheric lakes separate from the weather system that comes to produce them.

“We call these detached, floating bodies of water ‘atmospheric lakes’, in contrast to ‘atmospheric rivers’ of rain-laden steam, which are continuous from source to shore in an instant,” read the study’s abstract. presented to the American Geophysical Union. Fall meeting in 2021.

To put it bluntly, these atmospheric lakes do not seem to be in a great hurry. They were discovered in an equatorial location known for its almost negligible wind speeds. And according to a five-year review of weather data, the region’s longest storm lasted a total of 27 days. The researchers identified 17 such atmospheric lakes within 10 degrees of the equator that lasted more than six days over the five-year period. In other places where they have occurred, they periodically turn into tropical cyclones.

A new research team is being assembled to conduct a comprehensive study of this unique phenomenon. Among the various questions scientists will probe will be why exactly these atmospheric lakes disconnect from the river-lake patterns from which they emerge, and whether this may have anything to do with global patterns of atmospheric winds, or, perhaps, due to the internal winds which allow them to propel themselves.

“The winds that carry them ashore are so tempting, delicately close to zero [wind speed’, that everything could affect them,” says Mapes. “That’s when you need to know, do they self-propel, or are they driven by some very much larger-scale wind patterns that may change with climate change.” 

And therein lies the rub. If indeed, rising temperatures borne out of a changing climate do affect the formation and trajectory of these atmospheric lakes, it could have significant implications for the east coast of Africa – a typically dry region in dire need of rainfall. 

As Mapes notes, if a year’s worth of water vapour in an atmospheric lake was liquified, it would create a puddle just a few centimetres deep but roughly 1,000 km wide. That level of precipitation would be hugely welcome in the dry lowlands of eastern African nations where millions live.

“It’s a place that’s dry on average, so when these [atmospheric lakes] happen, they are surely very important,” Mapes said. “I look forward to learning more local knowledge about them in this region with a venerable and fascinating nautical history where observant sailors coined the word monsoon for wind patterns, and surely notice those occasional thunderstorms as well,” said he added.

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