On Trends in Historical Marine Wind Data

Abstract Compilations of surface winds from ship reports since 1854 show a number of long period variations, including a trend toward strengthening winds over the past three decades. Some investigators indicate that these variations are real changes in the climate system, while others suggest that they are artifacts of the evolution of measurement techniques. In an attempt to resolve this issue, we have examined individual ship reports from three regions with high data densities: South China Sea, North Pacific, and North Atlantic shipping lanes. We find that the apparent surface wind strengthening from the 1950s to the present is a consequence of the increasing use of anemometers in place of sea-state estimates. The specific causes are the operational use of an incorrect conversion from Beaufort force to wind speed, and the widespread assumption that the height of shipborne anemometers is 10 m, whereas the actual mean height is 19.3 m. Correcting the conversion scale and setting the height to be 20 m larg...