The impact of offshore wind farms on the latent heat flux

Unique airborne meteorological in-situ measurements have been used to study the impact of offshore wind farms on the latent heat flux in the marine boundary layer. 22 out of the total 42 flights collected during the WIPAFF project in the years 2016 and 2017 allowed for such an evaluation during various atmospheric conditions. The measurements revealed a significant increase of the vertical latent heat flux, mainly in the upward direction above the offshore wind farm cluster Amrumbank West, Nordsee Ost, Meerwind Sud/Ost or Godewind located in the German Bight. For thermally stable conditions, eight out of nine flights showed an enhanced turbulent latent heat flux downstream of the wind farms at hub height, with an increase of up to +70 W m-2 compared to the undisturbed flow. For flights during neutral thermal conditions, 10 out of 13 cases showed an increase, with the largest difference with respect to undisturbed flow of +600 W m-2 above the wind farm. Our observations suggest that the impact of offshore wind farms on the latent heat flux in the marine boundary layer is more frequent during stable conditions, but more prominent during neutral conditions and may trigger cloud development in the vicinity of the farm.