Atmospheric rivers and their impact on climate

These moisture-generating substances provide nutrients to local water supplies and increase the risk of flooding.

Color-enhanced satellite imagery showing an atmospheric river in January 2020 (white, blue, and green areas at top of image).

Atmospheric rivers are similar to normal rivers in that they are responsible for transporting water for thousands of miles. There’s a difference, though: the moisture they carry is water vapor, not liquid water. They also carry a lot.

According to NOAA, a typical atmospheric river carries as much liquid water as the average discharge of the Mississippi River into the ocean. If an atmospheric river event is particularly intense, it can transport as many as seven to 15 Mississippi River water.

The intense water vapor associated with these systems has been a boon to many parts of the world, including the western United States, where it has suppressed drought. But for all their benefits, atmospheric rivers can also be bad news, as their rich moisture can easily flood certain areas, triggering torrential rains, mudslides and flooding. By increasing atmospheric humidity (higher temperatures increase the air’s ability to hold water vapor), climate change will undoubtedly increase the strength of these rivers, and the precipitation they bring, according to a recent study in the journal Nature.

Atmospheric River Science

Atmospheric rivers originate in the tropical Pacific Ocean. They’re linked to a climate pattern called the Madden-Julian Oscillation (MJO) — an easterly disturbance of clouds, heavy rainfall and winds that move across the tropics every 30 to 60 days. When these disturbances bring heavy rainfall, they “wet” the environment ahead of them in their path, creating columns of water vapor 250 to 375 miles wide that we call atmospheric rivers.

If the MJO is in a convective (stormy and wet) phase, over the far western Pacific Ocean, and certain weather features, such as a blocking high in the Gulf of Alaska, are also present, this water vapor The column would then be steered northeast by the jet stream, aiming for the west coast of the United States.

Once an atmospheric river flows inland and sweeps over mountains, its water vapor rises, cools, condenses, and produces heavy precipitation.

How to study atmospheric rivers?

The California Water 2015 study offers scientists one of the greatest opportunities to study atmospheric rivers to date. During the multi-year research program, several ships equipped with weather instruments, including the USS Ronald H. Brown of the National Oceanic and Atmospheric Administration, intercepted several landfalling atmospheric river events off the coast of California, And watch them directly as they pass overhead. Observations were also made from the air; several aircraft flew directly into the river in the air, releasing airdrop sondes.

On land, weather forecasters detect and study the presence and strength of atmospheric rivers by monitoring what is called composite water vapor, or the concentration of water vapor in a column of air. Atmospheric rivers are mainly composed of water vapour, wind and aerosols. Integrated water vapor transport, or how water vapor is transported over horizontal distances, is equally important.

Meteorological satellite images in the infrared, visible and microwave bands are also used to detect atmospheric rivers, numerical weather models and map relative humidity (700 mbar) and wind speed (300 mbar ) as well as the high-altitude map. They are often thought of as conveyor belts of clouds and moisture that stretch across the Pacific Ocean to the west coast of the United States.

Where does the atmospheric river occur?/strong>

Atmospheric rivers frequently affect the west coasts of the world’s land masses, most notably western North America, but they also occur in Europe, East Asia, and South Africa. (Atmospheric rivers also occur in western Greenland and Antarctica, but these events are less studied).

They are responsible for as much as 50 percent of precipitation events along the coastlines of California and neighboring Canada and Alaska, according to NOAA.

One ​​of the most famous atmospheric river formations is the Pineapple Express—a continuous flow of water vapor originating in the waters off the Hawaiian Islands. In Mount Rainier National Park in Washington state in November 2006, a powerful “Pineapple Express” event brought nearly 18 inches of rain in 36 hours, triggering flooding that closed the park for six months and years later In December 2010, a string of Pineapple Express events brought 11 to 25 inches of rain from western Washington to Southern California and covered the Sierras with 75 percent of the year’s snowpack.

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