# Wind Lidar and Radiosonde Measurements of Low-Level Jets in Coastal Areas of the German Bight
## 6 Conclusions  
LLJs occur frequently at the coast of the North Sea, with a maximum occurrence in spring and summer and during the night. As stable stratifications decouple friction force from the air above and lead to an acceleration of wind speed in the form of an LLJ, the frequent observations of LLJ events are in agreement with the observations that stable stratifications above the North Sea are present frequently, around one-third of the year. As both spatial and temporal variability of the LLJ are significant, wind profile measurements in the direct vicinity of the wind park are necessary to improve the representation of the effect. At Heligoland, an LLJ occurred on 42.5% of all days for an entire year during all seasons, with most events in spring and summer. This is in agreement with the observations that stable stratifications above the North Sea are present around one-third of the year [34]. With the extent exceeding 100 km in longitudinal and latitudinal directions, several wind parks can be affected by LLJs. WRF simulations were capable of reproducing the LLJ in the wind profile at the time and location of the airborne observations, and therefore constitute a suitable tool for investigating this particular wind phenomenon. Further, they were used to estimate the extent of the LLJ in the German Bight. [PERSON] and [PERSON] wrote the manuscript; [PERSON], [PERSON], [PERSON], T.R. and B.C. analysed the lidar data; [PERSON] and [PERSON] operated the lidar systems; [PERSON] performed the numerical simulations. All authors commented and contributed to the text. All authors have read and agreed to the published version of the manuscript. The airborne and lidar observations have been funded by the project WIPAFF of the German Federal Ministry for Economic Affairs and Climate Action under grant number 0325783B. The Heligoland lidar observations have been partly funded by the project AVATAR, German Federal Ministry for Economic Affairs and Climate Action, grant number 20Y1501F. Ongoing lidar measurements and their analysis is funded by the project X-Wakes, German Federal Ministry for Economic Affairs and Climate Action, grant number 03 EE3008B. We acknowledge support by the Open Access Publication Funds of Technische Universitat Braunschweig. Figure 13: WRF simulation of 2 June 2017 showing the cross section in almost north–south direction, from land to the wind park. (**a**) shows 08:00 UTC, (**b**) shows 09:00 UTC. The area above land is indicated in red, up to a distance of 35 km. The lower figure shows the horizontal distribution of wind speed in the German Bight at 100 m altitude. Data Availability Statement: Lidar data of the Heligoland site are publicly available at PANGAEA [68]. Lidar data of the Norderney site will be published at PANGAEA in the same way at the end of the X-Wakes project. The radiosonde data sets are available at [[http://opendata.dwd.de/climate_environment/CDC/observations_germany/](http://opendata.dwd.de/climate_environment/CDC/observations_germany/)]([http://opendata.dwd.de/climate_environment/CDC/observations_germany/](http://opendata.dwd.de/climate_environment/CDC/observations_germany/)), accessed on 1 April 2022. The airborne data are available at PANGAEA [52]. Acknowledgments: The wind lidar data have been analysed during many student projects. In particular, the authors would like to thank [PERSON], [PERSON], [PERSON], and [PERSON] for their analyses during their diploma, bachelor, and master theses. The authors would like to thank the aircraft crew [PERSON], [PERSON], [PERSON], and [PERSON] for the successful airborne measurements. The installation and remote supervision of the Heligoland wind lidar have been performed by [PERSON] of UL International. The authors would like to thank [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] for the opportunity to install the wind lidar at Heliigoland at the facilities of the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, and the German Weather Service for providing access to the study site at Norderney.