Long term trends in ocean wind speed and wave height

Abstract

Satellite altimeters have now been operational since 1985, providing global data of oceanic wind speed and wave height. In the present study a combined database covering 23 years of altimeter data from 7 separate satellites has been developed. This data has been consistently calibrated and carefully cross-validated to ensure that it represents a stable database over this extended period. In this study all the procedures carried out to form the altimeter database are described. In addition, an analysis of this database to investigate long term trends which have occurred (if there are any) in the global wind speed and wave climates over this period of time is conducted. This analysis shows that there has been a general global trend of increasing values of wind speed and, to a lesser degree, wave height, over the 23 year period. The rate of increase is greater for extreme events, as represented by monthly 90th and 99th percentile values, compared to the mean condition. These results are statistically significant and clearly demonstrate that extreme events have intensified over this period. Previous attempts to investigate global trends in oceanic wind speed and wave height relied on visual observations, point measurements or numerical modelling. Due to limitations of the data sets, these studies have either been inconclusive or indicate regionally increasing trends, consistent with the present analysis of the global oceanic wind and wave climate. Additional validation against trends from various different data sources such as oceanic buoys (point measurements) and numerical modelling is in good agreement with findings presented here. Should such trends continue in the future, it will have significant consequences for engineering design, air-sea interaction, upper-ocean mixing and potentially boost capacities of renewable energy