La Nina is in "full swing," as NASA put it, and that means cool, wet conditions in the Northwest, icy cold in the Plains and drought in the Southeast (not to mention rain in Australia and other international effects).
La Nina references cooler than usual temperatures in the Pacific Ocean. It alternates with El Nino, which describes warmer conditions.
January is typically the strongest time for the effects of La Nina, so this season's is nearing its peak.
Here's how NASA described this La Nina:
The cooler water temperatures associated with La Niña are caused by an increase in easterly sea surface winds. Under normal conditions these winds force cooler water from below up to the surface of the ocean. When the winds increase in speed, more cold water from below is forced up, cooling the ocean surface.
With this La Niña, the sea-surface temperatures are about two degrees colder than normal in the eastern Pacific and thats a pretty significant difference, says David Adamec of NASAs Goddard Space Flight Center, Greenbelt, Md. I know it doesnt sound like much, but remember this is water that probably covers an area the size of the United States. Its like you put this big air conditioner out there - and the atmosphere is going to feel it.
While this air conditioner may be located in the equatorial Pacific Ocean, it has a great influence on the weather here in the United States and across the globe.
The cool water temperatures of a La Niña slow down cloud growth overhead, causing changes to the rainfall patterns from South American to Indonesia. These changes in rainfall affect the strength and location of the jet stream -- the strong winds that guide weather patterns over the United States. Since the jet stream regulates weather patterns, any changes to it will have a great impact on the United States. ...
The cooler waters of a La Niña event also increase the growth of living organisms in this part of the ocean. La Niñas amplify the normal conditions in the Pacific. These typically cool and abundant waters experience an increase in phytoplankton growth when the water temperature drops even further.
The increased circulation that brings up cold water from below also brings up with it nutrients from the deeper waters. These nutrients feed the organisms at the bottom of the food chain, starting a reaction that increases life in the ocean. NASAs SeaWiFS satellite documented this increase in phytoplankton during the last La Niña period in 1998.
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