Skip Navigation Links www.nws.noaa.gov 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

 
HOME > El Niño/La Niña > The ENSO Cycle > Mean Rainfall
 
 
December to February Normal Conditions

Ocean surface temperatures across the tropical Pacific contribute significantly to the observed patterns of tropical rainfall and tropical thunderstorm activity. The heaviest rainfall is typically observed across Indonesia and the western tropical Pacific, and least rainfall is normally found across the eastern equatorial Pacific.

The mean patterns of sea surface temperature and equatorial rainfall are accompanied by low level easterly winds (east- to- west flow) and upper level westerly winds across the tropical Pacific. Over the western tropical Pacific and Indonesia this wind pattern is associated with low air pressure and ascending motion, while over the eastern Pacific it is accompanied by high pressure and descending motion. Collectively, these conditions reflect the equatorial Walker Circulation, which is a primary large-scale circulation feature across the Pacific.

The subsurface ocean structure is characterized by a deep layer of warm water in the western tropical Pacific, and by a comparatively shallow layer of warm water in the eastern Pacific. This warm water is separated from the cold, deep ocean waters by the oceanic thermocline, which is normally deepest in the west and slopes upward toward the surface farther east. The resulting east-west variations in mean upper-ocean temperatures result in east-west variations in sea level height, which is higher in the west than in the east.

Go To Previous Page Go To Next Page
Back to Mean Sea Surface Temperatures Forward to Mean Wintertime Jet Streams over the North and South Pacific
Back to Table of Contents

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
5830 University Research Court
College Park, Maryland 20740
Page Author: Climate Prediction Center Internet Team
Page last modified: December 19, 2005
Disclaimer
Information Quality
Credits
Glossary
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities