Science.-La Niña returns for the second winter in a row

Madrid, 13 (European Press)

For the second year in a row, La Niña has been activated in the eastern Pacific and is expected to continue until at least the spring of 2022 in the northern hemisphere.

As part of the El Niño-Southern Oscillation cycle, La Niña occurs when active eastern trade winds intensify the flow of cooler waters from the depths of the eastern equatorial Pacific, causing widespread cooling of the Pacific surface. near the equator.

These stronger-than-usual trade winds also push warm tropical surface waters westward toward Asia and Australia. This dramatic cooling of the ocean’s surface layers affects the atmosphere by modulating the moisture content throughout the Pacific Ocean. La Niña coupling between the atmosphere and the oceans alters the global atmospheric circulation and can cause changes in the path of mid-latitudes jet streams in ways that intensify precipitation in some areas and cause droughts in others.

In the western Pacific, precipitation can increase significantly in Indonesia and Australia during La Niña. Clouds and rain become scattered over the central and eastern Pacific, which could lead to drier conditions in Brazil, Argentina, and other parts of South America and wetter conditions in Central America. In North America, conditions are often cooler and windy throughout the Pacific Northwest, while the weather generally becomes warmer and drier in the southern United States and northern Mexico.

The image above shows conditions in the central and eastern Pacific Ocean observed from November 26 to December 5, 2021 by the Sentinel-6 Michael Freilich satellite and analyzed by scientists at NASA’s Jet Propulsion Laboratory (JPL).

The balloon shows an anomaly in sea level height. Shades of blue signify lower than average sea level; Natural sea level conditions are shown in white; Red indicates areas where the ocean is higher than normal. The expansion and contraction of the ocean surface is a good indicator of temperatures because warmer water expands to fill a larger volume, while cooler water contracts.

“A moderate La Niña can be seen in the Sentinel-6 data as an area below normal sea level along and below the equator in the central and eastern Pacific,” Josh said in a statement. Climate scientist and oceanographer at JPL. He noted that the deep depression over Ecuador is not the water body of La Niña; It is a change in the north tropical countercurrent, which tends to strengthen during La Niña events.

More droughts in the southwestern United States

“This La Niña is likely to be bad news for the southwestern United States, which should get less rain than usual this winter,” Willis said. “This La Niña may not come as a huge surprise, but it is still an undesirable sign for an area already mired in severe drought.”

The La Niña event that began in late 2020 fits into a broader weather pattern that has persisted for nearly two decades: a cold (negative) phase of the Pacific Decadal Oscillation (PDO). For most of the 1980s and 1990s, the Pacific Ocean was trapped in a warm phase of PDO, which coincided with several strong El Niño events. But since 1999, the cold phase has prevailed. The long-term drought in the southwestern United States matches this trend, Willis said.

In a report released on December 9, 2021, the National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center noted that November sea surface temperatures in the eastern tropical Pacific ranged from 0.7 to 1.2 degrees Celsius below the long-term average. Forecasters predict La Niña conditions will continue through winter in the northern hemisphere, with a 60 percent chance of the ocean returning to neutral conditions during April through June.