Resumen
In this paper, we use historical wind direction observations taken aboard sailing ships to build a new index for the frequency of the easterly winds in the strait of Gibraltar, in southern Spain. The new series starts in the late 19th century, adding almost 100 years to comparable previous series. We have found large interannual and decadal fluctuations in the frequency of the easterly winds in Gibraltar along the 20th century, although no long-term trends have been revealed. We show that the changes in the frequency of the easterly winds in Gibraltar appear significantly related to the North Atlantic Oscillation and to anomalies in the sea level pressure across the North Atlantic and large areas of Europe.