Atmospheric River Brings Heavy Rain to California

What’s in today’s article?

• Why in the News?
• What is an Atmospheric River?
• How Long do Atmospheric Rivers Last?
• How Does El Niño Affect Atmospheric Rivers?
• How Does Climate Change Affect These Storms?
• How will the Atmospheric River Help the Region?

Why in the News?

• Southern California has been inundated with massive rainfall, with the risk of landslides rising on the soaked ground.

What is an Atmospheric River?

• An atmospheric river is a plume of moisture, or water vapor, that moves from the tropics and is dumped over a region as heavy rain or snow.
• Atmospheric rivers are narrow bands that tend to occur on the eastern side of strong mid-latitude storms.
• On average, the Earth has four to five active atmospheric rivers at any time. Each moves the equivalent of the liquid water that flows through the mouth of the Amazon River.
• When this atmospheric river reaches land, it releases moisture, producing heavy snow and rain.
• The rain that hit California is part of a weather system called the Pineapple Express, which is an atmospheric river that originates in the subtropical waters around Hawaii.

How Long do Atmospheric Rivers Last?

• Studies have found that atmospheric rivers generally last 20 hours over an area along the coastline.
• A single atmospheric river can move around in the ocean for up to five days.
• And that an atmospheric river can cause a single location along the coast to be inundated with heavy rainfall from 12 to 72 hours.

How Does El Niño Affect Atmospheric Rivers?

• El Niño is a naturally occurring climate pattern characterized by abnormally warm ocean waters in the tropical Pacific that drives heavy rains and storms.
• An average of seven to 10 strong atmospheric rivers make landfall in California each year.
• El Niño years tend to bring a higher level of moisture and make atmospheric rivers along the West Coast of the U.S. more frequent.
• However, it is not clear whether El Niño is the sole driver behind more precipitation and higher storm intensity.

How Does Climate Change Affect These Storms?

There are three main ways that climate change could affect atmospheric rivers in the future:

• More rain: Experts say a warmer atmosphere in the future will hold more moisture, which could lead to more precipitation and an intensification of storms.
• More frequent and more intense: Atmospheric rivers already account for nearly 90 percent of California’s flood damage. Research suggests that as temperatures warm, atmospheric rivers could occur in closer succession and drop more rainfall in a season.
• Less snow: As temperatures warm, some research suggests that instead of snow, the rivers could bring rain to certain regions.

How will the Atmospheric River Help the Region?

• Before two consecutive wet years including the present one, California had experienced drought conditions for decades.
• California’s water year is measured from October to September. The rainfall, thus, is welcome.

Q1. What do you mean by Horse Latitude?

The horse latitudes are regions located at about 30 degrees north and south of the equator. These latitudes are characterized by calm winds and little precipitation.

Q2. What is the Tropical Easterly Jet Stream?

The Tropical Easterly Jet (jet stream) is the meteorological term referring to an upper level easterly wind that starts in late June and continues until early September. 

Source: The river in the sky: What is an atmospheric river and how do they impact California weather? | NOAA