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Atmospheric rivers are rivers of low water vapor in the Earth’s atmosphere.
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They can drop heavy rain or snow on parts of the United States, causing flooding.
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Milder versions can alleviate droughts, but stronger ones can be dangerous.
Two atmospheric rivers crashed into the West Coast in late January and early February. Massive amounts of rain fell on Southern California, causing floods and mudslides and killing at least nine people, the Los Angeles Times reported.
“An atmospheric river is literally a river of water vapor in the sky,” atmospheric scientist Jason Cordeira of the Scripps Institution of Oceanography’s Center for Western Air and Water Extremes told Business Insider.
Like rivers on land, they come in different sizes and densities. National Oceanic and Atmospheric Administration. They can stretch up to 1,245 miles long and 620 miles wide and carry more water than a dozen Mississippi Rivers.
Below we answer some FAQs about atmospheric rivers.
1. What causes rivers in the atmosphere?
Atmospheric rivers form when moisture moves from the tropics through narrow channels in the atmosphere.
When they make landfall and encounter large mountain ranges like California’s Sierra Nevada, they can bring heavy rain, snow and flooding, Cordeira said.
“Atmospheric rivers do not form spontaneously,” Cordeira said. They often develop alongside extratropical storms.
The cold fronts of these hurricanes help accumulate water vapor that atmospheric rivers can carry thousands of miles, Cordeira said, adding that “the east side of ocean basins or the west side of continents are really good places for these storms.”
This includes California, Oregon and Washington in the US, as well as parts of Europe, Chile, New Zealand and Australia. But they could also affect the northeastern United States, he added.
Atmospheric rivers are so common that eight to 10 of them exist at a time in the oceans of the northern and southern hemispheres, Cordeira said.
2. Do El Niño and La Niña have an impact?
Cordeira said different weather conditions, such as El Niño and La Niña, could make the West Coast more or less likely to see atmospheric rivers, but that’s not necessarily a guarantee.
For example, 2023 was a La Niña year when atmospheric rivers are less likely to form. But a relatively high number (46) reached the US West Coast, according to the Scripps Institution of Oceanography.
“But there are also relatively dry years where very few atmospheric rivers reach land,” Cordeira said.
3. How long does an atmospheric river last?
The average life cycle of an atmospheric river is three to seven days, Cordeira said. Usually what stops it is rain.
“Things that remove water vapor from the sky will cause an atmospheric river to die,” Cordeira said.
When rivers flow into land masses with large mountains, the mountains cool the air, “and as it cools, it condenses and produces precipitation and takes a lot of that precipitation out,” Cordeira said.
Once the river reaches land, it usually rains in about a day, he added.
4. Is an atmospheric river similar to a hurricane?
Cordeira said atmospheric rivers and hurricanes have a few things in common, but “the processes that lead to hurricanes in the atmosphere are different from the processes that lead to atmospheric rivers.”
Both draw tropical moisture from lower latitudes and bring it to higher latitudes, Cordeira said. Both can have heavy rains and strong winds, but they are not directly related, he said. “They are distant cousins, although they share some of the same ingredients.”
5. Are rivers in the atmosphere a new thing?
People growing up in the ’90s probably didn’t hear much about atmospheric rivers when they were young.
This phenomenon existed, but the media often enthusiasm They call it the “pineapple express” – a powerful atmospheric river that carries moisture from the tropics near Hawaii to the West Coast of the USA.
In 1994, MIT researchers Yong Zhu and Reginald E. Newell published a paper. paper about “atmospheric rivers and bombs”.
The term came into widespread use in academic research since that time.
Later, in 2019, University of California, San Diego Researchers went one step further and announced A new scale for measuring the strength of atmospheric rivers, similar to categories used for hurricanes.
An atmospheric river receives a rating from AR-1 to AR-5, depending on the amount of moisture and the duration of the event; The AR-1 is the weakest and least threatening.
6. Are there any benefits to rivers in the atmosphere?
Some states depend on atmospheric rivers to prevent drought.
“Most droughts in California and the West Coast of the United States actually occur due to the lack of atmospheric rivers reaching land,” Cordeira said. said. Rain or snow can fill reservoirs or add snowpack to mountains.
7. Is there an atmospheric river due to climate change?
It is difficult to attribute the severity of a single weather event to the climate crisis. But atmospheric rivers will likely contain more moisture as the atmosphere and oceans warm, Cordeira said.
“It’s likely going to be more intense and more of a broader storm” because of the increased humidity, he said. Moisture can fall as rain instead of snow, meaning not as much water will drip from the mountains during the summer months.
Warmer temperatures could also mean frequent “families” of atmospheric rivers where two or three events occur in tandem, Cordeira said. This happened in early 2024, when two heavy rains drenched Southern California.
When that happens, the risk of flooding increases, Cordeira said. Soils that are already saturated with water cannot absorb any more moisture, and overflowing rivers may overflow.
“If two or three of them happened in a row, you can imagine how severe the effects would be,” he said.
Read the original article on Business Insider