How La Nina affects weather
The El Nino–Southern Oscillation (ENSO) is the Earth’s most influential driver of climate variability. La Nina, the cold phase of the ENSO cycle, is partly causing Somalia’s drought. A prolonged La Nina cycle which began in late 2020 and is expected to last until the end of the year has caused dry air to come down around Africa.
Neutral CONDITIONS
The Walker Circulation is an east-west vertical atmospheric circulation above the Equatorial Pacific
Moist air rises over normally warm seas, causing abundant rainfall over Asia and Australia
Atmospheric winds
Walker
Circulation
Somalia
Cool
Warm
Pacific Ocean
Easterly trade winds push warm surface waters westward
Upwelling of cold water cools the air, giving South America a cooler and dryer climate
LA NINA CONDITIONS
Marked by cooler-than-average sea surface temperatures across the east-central Equatorial Pacific
Strengthening trade winds push warm waters and rain clouds towards Asia
Dry air comes down in South America and Africa
Somalia
Cooler than normal
Warmer
than normal
Pacific Ocean
Surface waters in the central and eastern Pacific Ocean become significantly cooler, increasing the upwelling of cold water
Transition zone
between warm surface
water and cold deep water
OCEANIC NINO INDEX
Measures sea surface temperature anomalies in the tropical Pacific Ocean to track El Nino and La Nina cycles
La Nina
(cold phase)
Neutral
El Nino
(warm phase)
°C
1990
’95
2000
’05
’10
’15
’20
Sources: Australia Bureau of Meteorology; NOAA National Weather Service
W. Foo | Reuters, June 16, 2022
How La Nina affects weather
The El Nino–Southern Oscillation (ENSO) is the Earth’s most influential driver of climate variability. La Nina, the cold phase of the ENSO cycle, is partly causing Somalia’s drought. A prolonged La Nina cycle which began in late 2020 and is expected to last until the end of the year has caused dry air to come down around Africa.
Neutral CONDITIONS
The Walker Circulation is an east-west vertical atmospheric circulation above the Equatorial Pacific
LA NINA CONDITIONS
Marked by cooler-than-average sea surface temperatures across the east-central Equatorial Pacific
Moist air rises over normally warm seas, causing abundant rainfall over Asia and Australia
Strengthening trade winds push warm waters and rain clouds towards Asia
Dry air comes down in South America and Africa
Atmospheric winds
Walker
Circulation
Somalia
Somalia
Cooler than normal
Cool
Warmer
than normal
Warm
Pacific Ocean
Pacific Ocean
Surface waters in the central and eastern Pacific Ocean become significantly cooler, increasing the upwelling of cold water
Easterly trade winds push warm surface waters westward
Upwelling of cold water cools the air, giving South America a cooler and dryer climate
Transition zone
between warm surface
water and cold deep water
OCEANIC NINO INDEX
Measures sea surface temperature anomalies in the tropical Pacific Ocean to track El Nino and La Nina cycles
La Nina (cold phase)
Neutral
El Nino (warm phase)
°C
1990
’95
2000
’05
’10
’15
’20
Sources: Australia Bureau of Meteorology; NOAA National Weather Service
W. Foo | Reuters, June 16, 2022