Wind Speed Gradients and Wakes Mapped Using SAR for a Study Area in South-East China.

The rapid increase of offshore wind installations in the south-China sea near the coast triggers a new demand for studying the effects of horizontal wind speed gradients and the wind power variation within the coastal zone. The advent of Synthetic Aperture Radar (SAR) data offers an opportunity to map wind speed gradients and wind farm wakes with high spatial resolution. We have retrieved wind maps at 10 m above mean sea level (m.s.l.) from Sentinel-1 SAR and Envisat Advanced SAR observations. Generally, the speed of the prevailing south-easterly winds and wind power declined about 8% and 22%, respectively. Although the southern offshore wind farms (OWFs) were not in operation before December 2019, the wind velocity deficit at the upstream side of northern OWFs were between 8-12 %. After the southern OWFs became online, the region between OWFs is subjected to wind wakes and coastal upwelling effects. The coastal upwelling phenomena speeds up the wind at the downstream sides of OWFs that reduce the wind wakes up to 8-10%. The wind wakes extended 20 km beyond the southern OWFs.