Historical trends in windspeed over the Northern Hemisphere in observations and reanalyses 

We analyse trends in annual mean wind speed from 1980 to 2010. Observational data (HadISD3) indicate a decline in wind speed across North America, Europe, and central and eastern Asia, a phenomenon referred to as global wind speed stilling. However, a suite of reanalyses fails to accurately reproduce this trend, often showing inconsistencies in the direction of the trend. Additionally, the reanalyses significantly underestimate wind speed variability. We further investigate the sources of discrepancies between the observations and reanalyses. Our findings suggest that the erroneous trends in the reanalyses primarily stem from inaccuracies in simulating high-frequency wind speed variability. In contrast, lower-frequency variability remains consistent between observations and reanalyses. These errors in simulating wind speed trends have significant implications for understanding and predicting wind power variability.