In June and July, surface water temperatures in the tropical Atlantic were 0.5 to 1°C colder than the usual average for this season. This annual phenomenon, however, did not result in an “Atlantic Nina” event.
The Atlantic also has its Nino and its Nina. The National Oceanic and Atmospheric Administration (NOAA, forecasting and research center, American equivalent of Météo France) has just reminded us of this by issuing a warning in mid-August about the current phenomenon.
While surface waters from the entire North Atlantic to the Arctic have never been so warm, the equatorial zone located approximately equidistant from South America and Africa has experienced a marked temperature difference of nearly 1°C. This cooling occurred at a time when the trade winds, these regular equatorial winds, are particularly weak this year.
Difference in tropical Atlantic Ocean temperatures from the 40-year average. Credit: NOAA
In these regions, winds and water temperature are in fact closely linked to form a seasonal cycle. The waters are warmer in spring and drop to around 25°C during the months of June, July and August. This cooling is linked to the winds that are strengthened by solar radiation. They push the warm surface waters up towards the north and thus facilitate their replacement by colder waters coming from the deeper layers of the ocean.
For an Atlantic Nino (warming) or Nina (cooling) to be declared, the thresholds of 0.5°C in one direction or the other must be crossed for three months and for at least two years in a row. If NOAA sounded the alarm in mid-August, it is because such differences had never been recorded since 1982 and the first measurements of the surface temperature in the Atlantic.
In spring 2024, the waters were 1°C warmer in this area compared to the average of the last four decades, then reaching a cold anomaly in June. A Nina could therefore be forming, which would have been an event. There has been no Nino since 2000 and during this period, the[…]
- sciencesetavenir.fr
