The El Nino-Southern Oscillation is a cycle of wind and ocean temperatures in the tropics. Ordinarily, the trade winds blow westward across the Pacific, building up large mass of very warm water to the east of the Philippines. This large-scale wind circulation is called the Walker circulation (named in honor of the mathematician Gilbert Walker), and results from cooler, higher-pressure air in the east moving toward warmer, lower-pressure air in the west. The east-to-west trade winds drive a surface current which brings water toward the western edge of the basin. But this pressure differential, and the associated winds, is not constant.
The Pacific Walker circulation has three modes: warm (El Nino), neutral, and cool (La Nina). In warm mode, the east-west pressure differential shrinks, the trade winds weaken, and the warm water of the western Pacific flows eastward and impacts the western coasts of Central and South America. In neutral mode, the trade winds are at average strength, and the eastward flow of warm water is limited. In cool mode, the pressure differential is greater, the trade winds are stronger, and warm water is pushed farther west than average.
El Nino received its name because the effects are typically felt beginning around Christmas, and last until April. They include heavy rain along the west coast of Central and South America, and wet weather in California and along the gulf coast and southeastern US. The warm water shuts down the normal upwelling of cold water along the west coast of South America, harming fisheries. During La Nina events, storm tracks are more northerly, so the pacific Northwest is wetter, as well as the upper northwest and Great Lakes of the US, while from California to the southeast it tends to be dry and warm. Upwelling along the west coast of South America is strong and fisheries there tend to flourish.
The Southern Oscillation is a related atmospheric cycle, monitored across the Pacific. In El Nino years, pressure to the west (measured at Darwin, Australia), on the boundary between the Pacific and Indian Oceans, is greater (negative index), and pressure in the central Pacific (at Tahiti) is lower. La Nina episodes feature higher pressure in Tahiti and lower pressure in Australia (positive index).
Tomorrow: structure of the ocean.
This post was previously published on Dailykos.com.
You Might Also Like These From The Good Men Project
|Compliments Men Want to Hear More Often||Relationships Aren’t Easy, But They’re Worth It||The One Thing Men Want More Than Sex||..A Man’s Kiss Tells You Everything|
Join The Good Men Project as a Premium Member today.
All Premium Members get to view The Good Men Project with NO ADS.
A $50 annual membership gives you an all access pass. You can be a part of every call, group, class and community.
A $25 annual membership gives you access to one class, one Social Interest group and our online communities.
A $12 annual membership gives you access to our Friday calls with the publisher, our online community.
Register New Account
Need more info? A complete list of benefits is here.
Photo credit: Shutterstock