Long-term variation in the North Pacific using satellite-derived wind data set/J-OFURO over the last decade and other data sets over a longer record

Time series of gridded data sets of surface winds (from Qscat (J-OFURO)) constructed by satellite microwave sensors covering almost a decade (1999-2009) are used to examine long-term change in surface wind fields over the world's oceans. Evidence has been provided by most previous studies that wind speeds have a tendency to increase over time in many area, and we verify whether or not this tendency persists. Results reveal that zonal winds tended to be weaker over the study period in the region of the North Pacific where westerly winds prevail. Time series of different types of data sets based on numerical model products and voluntary ship measurements present similar features of weakening westerly winds, even allowing for discrepancies among the data sets. These time series also exhibit a tendency of enhanced westerly winds in periods prior to the start of the twenty-first century, which means that the long-term trend in wind speed has changed from positive in the 1980s/1990s to negative in the 2000s. Examinations of time series for each season reveal that the above feature is found in winter, suggesting that it is related to the strength of the Aleutian Low.