Rivers in the sky, sometimes known as the Maya or Pineapple Express, account for most of the horizontal moisture transported outside of the tropics – the Tropic of Cancer and Tropic of Capricorn – and even up into the Arctic.
Horizontal moisture transport is water moving from east to west or north to south, as opposed to moisture moving vertically from the ocean to the atmosphere.
“These narrow rivers move a significant amount of water through the air, even though they take up a relatively small area,” said Carolyn Reynolds, Ph.D., head of the Probabilistic Prediction Research Office at NRL. “Large atmospheric rivers can transport as much moisture as the Amazon.”
On average, just a few atmospheric river events are responsible for 30 to 50 percent of the annual rainfall on the West Coast, according to the National Oceanographic and Atmospheric Administration.
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