How does La Niña differ from El Niño?
La Niña is the ENSO phase with cooler-than-normal central and eastern tropical Pacific waters and often stronger trade winds and east-west temperature contrast.
Formation process and geographic mechanism
Stronger trades pile warm surface water westward and enhance cold upwelling near South America. Tropical rainfall shifts west and the Walker circulation may strengthen. Atmospheric wave changes produce roughly opposite seasonal effects to El Niño in some regions. The pattern is not a perfect mirror and local outcomes vary by event.
Spatial outcomes, measurement and management
La Niña may persist across one or more years and influence consecutive winters. It can temporarily lower global mean temperature somewhat but does not remove the long-term human-driven warming trend. Agriculture, water management and preparedness use ENSO as probability information. Regional seasonal forecasts and current observations are still required for local decisions.