Low Level Jets over the Southern North Sea

Abstract

An extensive analysis of Low Level Jets (LLJs) over the Southern North Sea is presented. The study is based on observational data from a wind LiDAR and a passive microwave radiometer, operated from May 2015 to October 2016 on the FINO1 platform, as well as on mesoscale simulations by WRF-ARW. Besides evaluations on LLJ occurrence, intensity, direction, height, wind shears and boundary layer stability based on 250 days of measurements, two case studies were investigated in detail. It indicates that LLJs are a very frequent phenomenon above the Southern North Sea as they occurred on the majority of the days during the measuring period. Our study suggests that highest probabilities for LLJs to occur are during winds within the sector East to South. Most detections were found for the period between the evening until morning while the lowest amount of detections was found at 1400 UTC. Considerable amounts of LLJs occurred at heights that are in the ranges of modern offshore wind turbine heights and rotor sizes. Moreover, the case studies showed strong wind shears and veering below the jet cores. Further findings suggest, that baroclinic effects in the coastal zone due to differential surface heating of land and sea as well as inertial oscillations may form and modify these jets.