London: A new study has shown that trade winds in the tropical Atlantic have weakened and the pattern of ocean surface temperature has changed.
And as a result, the equatorial Amazon and the Guinea Coast are seeing more rainfall and the Sahel less.
The raw observations of winds over the ocean suggest that the winds have grown stronger during the last 60 years.
The trend is, however, largely due to a change in the placement of the anemometers, the instruments measuring wind speed.
Hiroki Tokinaga and Shang-Ping Xie at the International Pacific Research Center, University of Hawaii at Manoa, corrected this wind bias using wind-wave heights.
Applying their new correction technique to observations along these routes from 1950 to 2009 together with other observations, they found the trade winds in the tropical Atlantic had weakened significantly during this period.
Although ocean surface temperature in the tropical Atlantic has risen, the pattern has changed and with it the climate. The cold tongue of water that stretches out from the eastern tropical Atlantic coast has warmed more than the western part of the basin.
At the same time, the weakened trade winds have resulted in less upwelling of cold water and nutrients in the eastern tropical Atlantic. These latter changes could impact marine life.
Accompanying these changes in wind and ocean temperature is a very significant increase in rainfall, not only over the ocean but also over adjacent land areas such as the equatorial coastal regions of the Amazon and the Guinea Coast.
The study has also suggested that the year-to-year variations of ocean temperature and rainfall have weakened during recent decades, implying fewer extreme events.
The findings have been published Nature Geoscience.