This current drives the surface water away from the equator, and draws water up from below. Winds also cause warm surface water to accumulate on the western side of the Pacific. As a result, nutrient-rich water rises from deeper levels to replace the surface water that has drifted away. These nutrients are responsible for supporting the large fish population commonly found in these areas. During an El Ni o year, the warm water expands downward, limiting the amount of nutrient-rich deep water tapped by upwelling processes.
Fish then die off or move elsewhere, such as southward off Chile or north toward California.
El Ni o Tutorial . Jet streams play a key role in the weather, in steering storms and helping determine where storms form. During a La Ni a year, winter temperatures are generally warmer than normal in the southeastern United States, and cooler than normal in the Northwest. The National Weather Service's online dictionary. Career Center Automotive Real Estate Legal Center Travel Getaways See our privacy policy , terms of use , ad rates and legal notices .