Atmospheric rivers: California’s record-breaking storm: What is the ‘Pineapple Express’ phenomenon underlying it

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Source: The post is based on the article “California’s record-breaking storm: What is the ‘Pineapple Express’ phenomenon underlying it” published in the Indian Express on 12th January 2023.

What is the News?

Forecasters in the US have said that the rain arriving in California is caused by a “true Pineapple Express” -a specific example of a common atmospheric phenomenon resembling a conveyor belt for moisture.

Note: The global conveyor belt is a “constantly moving system” in the ocean driven by changes in temperature and salinity. 

What are atmospheric rivers?

Atmospheric rivers are long, narrow regions in the atmosphere that transport most of the water vapor outside the tropics.

Occurance: These rivers in the sky often occur on the US’s West Coast but can happen in other locations, including the eastern United States.

Moisture content: These rivers often channel moisture from the Caribbean. They carry a lot of moisture which is enough to equal or sometimes exceed the average flow of the Mississippi River at the point where it flows into the Gulf of Mexico.

How do atmospheric rivers aid rainfall or storms?

When atmospheric river moisture begins to interact with land, it can fall as rain or snow. These rivers provide a continuous flow of moisture so, the precipitation will usually be abundant.

According to the NOAA, between 30% and 50% of the annual precipitation on the US’s West Coast occurs from just a few atmospheric river events.

Over the past two weeks, California and other parts of the West Coast have been hit with a series of atmospheric rivers.

What are atmospheric river families, and what are their impacts?

When the atmospheric rivers come back-to-back then they are called “atmospheric river families”. The effects can be serious, like extensive flooding.

What is a true Pineapple Express?

Atmospheric rivers come in different shapes and sizes. A Pineapple Express is a strong atmospheric river that builds up in the tropical pacific, according to the NOAA.

Some necessary conditions for pineapple express are, a) The moisture is pulled from the tail end. This tail end must start near Hawaii, b) The river must stretch continuously through the atmosphere to the U.S. West Coast.


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