La Nina, which in Spanish translates to “little girl,” essentially means a cold occurrence. Wintertime temperatures in a La Nina year are above average in the south and below average in the north. High winds carry warm water to Asia during La Nina episodes, and air masses increase along the west coast of the Americas.
This implies that cold, nutrient-rich water rises to the top of the Pacific, forcing the jet stream northward. Because of this, the US’s southern states frequently endure drought, but the Pacific Northwest and Canada frequently experience severe rainfall and flash flooding.
What is ENSO?
The ENSO cycle, a fluctuating warming and cooling pattern, directly impacts how much rain falls in the tropics and can significantly impact weather in the United States and other countries.
La Nina can develop when temperatures are below average. It cannot form when temps are at or close to average, a condition known as ENSO-neutral. The air pressure component is a little trickier. It pertains to the differential in air pressure between the equatorial Pacific’s western and eastern regions.
Measurements from Tahiti, located more than 5,000 miles to the east, as well as Darwin, on Australia‘s north-central coast, are used by scientists. Conditions favor establishing El Nino when pressure is greater than usual in Darwin and less than average in Tahiti. When the contrary happens, La Nina could form.
How El Nino Relates to La Nina
It is unclear to scientists exactly what initiates the process. However, sporadic air pressure changes over the equatorial Pacific, impacting the trade winds, typically sweeping from east to west. The water’s surface, which has been warmed by the sun, is moved along by the winds.
Additional warm water is transported westward during a La Nina when the trade winds pick up. Deep water then rises up in the frigid eastern Pacific to take its place. Less water goes westward during El Nino, which weakens the trade winds, warming the central and eastern Pacific more often than usual.
By convection, warm, humid air emerging from the sea surface and generating thunderstorms, a vast body of warm ocean water radiates a great deal of heat up into the atmosphere. The heat also impacts east-west and north-south air circulation.
The differences between the two are affected by where all that convection is located. Convection develops in the eastern Pacific during El Nino since the warm water remains there. While there is a La Nina, the eastern Pacific continues to be cooler, and convection takes place much further to the west.
How Often Does La Nina Occur?
In general, El Nino and La Nina happen every two to seven years, with El Nino happening slightly more frequently than La Nina. They occasionally persist longer but often last for the greater part of a year. La Ninas can “double dip,” where one develops, stops when sea surface temperatures reach ENSO-neutral levels, and then develops again when temperatures drop.
Does Climate Change Affect La Nina?
As long as greenhouse gas emissions cause the planet to warm, experts are uncertain how El Nino and La Nina will evolve. According to some studies, really powerful incidents will occur more frequently than now. Yet, how or if that would impact rainy or dry trends in the United States and abroad is unclear. Scientists say the 2022 cycle was the warmest on record and 2023 will be warmer.
The photo featured at the top of this post is © Mike Hardiman/Shutterstock.com
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