Trade Winds in Tropical Atlantic Have Weakened

Wind-wave heights logged by ship crews were used to correct 60 years of biased ocean wind data.

With 70% of our planet covered with water, understanding the effect it has on our lives and the world around us is important, but sadly, the necessity for understanding it is also a hindrance in doing so; with so much water, it is difficult to acquire accurate and reliable measurements.

Scientists have long attempted to pin down just how the recent trend towards global warming has affected regional climates, rather than just the overall trend. People care about what is happening to them, more than they do what is happening to everyone.

Unsurprisingly, with so much water on our planet, understanding the regional climates needs reliable water data.

Fixing the Biased Data

Hiroki Tokinaga and Shang-Ping Xie at the University of Hawai’i, Mānoa’s, International Pacific Research Center, have developed a new method to remove the bias that has cropped up in observations of the winds over the oceans.

The raw observations are taken by ships that traverse our oceans, using anemometer’s which, over the past 60 years, have been placed higher on ships which themselves have been increasing in height.

Tokinaga and Xie have corrected the bias by applying wind-wave heights to the data previously gathered, and found that along the three major ship routes which provide meteorological data between 1950 and 2009, the trade winds in the tropical Atlantic have weakened significantly.

Their findings were published in the online edition of the journal Nature Geoscience.

Alongside the findings that the trade winds have weakened and the ocean temperatures have increased, is an increase in rainfall along the equatorial coastal regions of the Amazon and the Guinea Coast.

An example is found at Ibadan, in their August rainfall totals, which had increased by 79 mm/month from 1950 to 1998, a huge 93% increase over the long-term average for 1900–1949.

Tokinaga and Xie reason that the pattern of ocean warming and trade-wind changes are caused by the asymmetric reduction in surface solar radiation due to man-produced aerosols, the reduction affecting the Northern more than the Southern Hemisphere.

Reversing Difficulties

However, simply reversing the factors that have caused these conditions is not necessarily immediately beneficial.

Over the past 60 years, there have been fewer extreme weather events in the region, on top of the increased rainfall and heat. If aerosol emissions decreased over the coming decades, the tropical Atlantic climate may revert to its original state, allowing extreme weather events to return and stress an already stressed series of populations.

“If the year-to-year variability, for example, is to recover in the future, the resulting increase in climate extremes would add burdens to an ecosystem and to a society already stressed by global warming,” said Tokinaga.

Source: University of Hawai’i, Mānoa
Image Source: andreweland

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