Changes in ocean surface wind with a focus on trends in regional and monthly mean values

Data collected from ships and satellites has frequently been used to estimate trends in surface wind speed. Although these data sets consistently show an increase in global average wind speed over recent decades, the magnitude of this increase varies depending on the data source used. Observations of the ocean surface by satellites, namely altimeter and SSM/I, provide reasonably long datasets with global coverage. These well calibrated and validated datasets are analysed for linear trends of regional mean monthly time series and mean time series for each calendar month over the period from 1991 to 2008. Differences between the resulting trends are investigated and discussed. The data indicate that the observed global trend is not uniformly distributed and can be linked to a significant positive trend in regional average time series across equatorial regions and the Southern Ocean. When trends for each calendar month are considered, the Southern Ocean showed a consistent increase for at least three continuous months. Although altimeter trends are consistently stronger than trends from SSM/I, the two datasets share similarities. For example, for some regions the trends are up to 2.0 times the global average trend. The data also show that the month of May exhibits one of largest positive trends and this was found across the North Indian Ocean which may indicate a shift in the onset time of the monsoon season.