After several months of flirting, the tropical Pacific ocean and atmosphere appear to have coupled just in time for Valentine’s Day and now meet the criteria for El Niño conditions. Is it true love? Time will tell, but forecasters expect weak El Niño conditions to persist through the spring.
For a few months now, the tropical Pacific has met the first two criteria of our “Is It El Niño Conditions?
That is, the sea surface temperature in the Niño3.4 region of the tropical Pacific Ocean has been more than 0.5°C above the long-term average, and models were predicting it would stay that way for the next several seasons.
What’s new over the past month is that we’re seeing signs of El Niño-related changes in the atmosphere, with increased clouds and rain in the central Pacific indicating a weaker Walker circulation. One measurement of the strength of the Walker circulation, the Equatorial Southern Oscillation Index, was -0.6 during January, indicating more rising air than average over the eastern Pacific, and less than average over the western Pacific. These changes are enough evidence that the atmosphere is responding to the warmer ocean, leading us to conclude we have El Niño conditions!
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Image via NOAA.