Wednesday, April 21, 2021

NASA spots El Niño changes that change weather


The El Niño building in the Pacific Ocean was partially to blame for the largest two-day snowfall in Baltimore history last month. Using computer modeling and visualization, scientists at NASA say El Niño’s patterns of ocean temps have led to precipitation patterns this winter that have been wetter than in the past for parts of California and across the East Coast.

“During an El Niño, the precipitation averaged out over the entire globe doesn’t change that much, but there can be big changes to where it happens,” said George Huffman, a research meteorologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

“You end up with this interesting observation where you get both floods and droughts just by taking the usual precipitation pattern and doing a shift,” he said.

A new NASA visualization shows the 2015 El Niño unfolding in the Pacific Ocean. Sea surface temperatures are creating this year different patterns than seen in the bigger El Niño of 1997-1998. Computer models are just one tool that NASA scientists are using to study this large El Niño event, and compare it to other events in the past.

“The start of an El Niño is important,” said Robin Kovach, a research scientist with the Global Modeling and Assimilation Office at Goddard. “The ’97 El Niño was much stronger in the Eastern Pacific, with much warmer water up to the coast of South America,” she said. In 2015, the warmest waters are instead in the Central Pacific and extend west of the International Date Line.

Goddard’s computer models, with input from ocean buoys, atmospheric models, satellite data and other sources, can also simulate what ocean water temperatures could do in the coming months. The GMAO seasonal forecast, which takes 18 hours to complete, and creates more than 9 Terabytes of data, shows that this 2015 El Niño could be different until the end.

What it causes: a shift in US precipitation patterns

El Niño is a natural phenomenon that occurs every two to seven years. It is created through a shift in wind and ocean circulation.

In normal, non-El Niño conditions, Pacific trade winds near the equator blow from east to west, moving warm surface water with them. During an El Niño, trade winds move from west to east—from Southeast Asia to South America—moving warm water to the eastern tropical Pacific Ocean. The warm ocean water evaporates, adds moisture to the air, and falls as precipitation over nearby regions.

In the visualization above, rain accumulation over the United States from December 1, 2015, to February 15, 2016, is shown. Blue and green areas indicate light precipitation, and red patches indicating areas with high-accumulated rainfall.

At the beginning of December, the Pacific Northwest and Southeastern United States accumulated a lot of rainfall while the Midwest experienced a significant amount in the middle of the month. Over Christmas and New Year’s Day, heavy precipitation fell over the Southeast, particularly in Georgia, Tennessee, Virginia, North Carolina, and Alabama, which experienced flash flooding.

In January, patches of California and areas near the Gulf of Mexico, especially towards the end of the month, experienced high levels of rainfall. (This is the moisture that contributed to the heavy snowfall during the Baltimore blizzard of January 22-23.)

In early and mid-February, large, heavy patches of rain quickly developed over the Southeast region. This visualization also shows that some areas of the country, like southern California, did not receive rain consistently through the winter months.

“It’s not necessarily correct that it’s going to be wet in California the whole time. The precipitation shifts depend on what time and where you happen to be,” Mr Huffman said.

As El Niño wanes, a La Niña event may follow, just like after the strong 1997-1998 El Niño.

La Niña is a similarly periodical natural occurring event related to ocean temperatures in the Pacific Ocean. Instead of warm water collecting off the coast of South America like in El Niño, La Niña is characterized by colder surface water near South America. La Niña can also spur abnormal weather patterns across the world.

Press Release
This information was provided in a press release.

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