Long-term validations of annual wind speeds by the local forecast model and the microwave scatterometer around Japan

This study investigated the interannual variability (IAV) of sea surface wind speeds in the Northwest Pacific Ocean with the local forecast mode (LFM) and the satellite-borne microwave scatterometer. The IAV of wind speed is an essential parameter for evaluating the reliability of annual mean wind speeds (MWSs) during wind resource assessment. In previous study, the distribution of standard deviations (SDs) of annual MWSs at 10 m height above the sea level from the Meteorological Operational Satellite Program of Europe (MetOp) -A, -B and -C/Advanced SCATterometer (ASCAT) from 2009 to 2020 showed some areas with high SDs above 5% around Japan (120 – 160 °E, 14 - 49°N). It is indicated that there are two factors for high SDs, 1) the characteristics of the microwave scatterometer, and 2) the effect of sea surface temperature (SST). High SST leads to unstable atmospheric stability conditions, and the vertical wind shear decreases and vice versa. Accordingly, the IAV of offshore wind speeds increases in areas with current meander or transition zones between warm and cold currents. In this study, the SD with the LFM wind speed provided by the Japan Meteorological Agency with about 2 km spatial resolutions is shown in addition to the wind speed from the scatterometer to clarify clearly separate these two factors. Furthermore, an effect of tropical cyclones to the IAV of wind speed from the scatterometer is shown. The observation period of the scatterometer is extended from the previous study, and the analysis is conducted using a total of 15 years of data until 2023.