Characteristics of the low-level jets observed over Dunkerque (North Sea French coast) using 4 years of wind lidar data

Abstract

This study investigates the occurrence and characteristics of low-level jets (LLJs) up to 200 m above sea level in the North Sea area, specifically in the southernmost part of the basin, at the entrance of the English Channel. Using a short-range Doppler lidar installed in Dunkerque Port, on the northern coast of France, wind profiles were recorded for 4 years and analyzed statistically. LLJs were detected on more than 11,000 of the 10-min average wind profiles (5% of time), with similar jet core height and core speed distributions as in other sites in the southern North Sea area, and a similar annual cycle. However, there were differences in the core directions and the daily cycle, with afternoon northeastly jets being the most frequent in Dunkerque, whereas southwesterly nocturnal jets were dominant in the other North Sea sites. This suggests that wind channeling in the Dover Strait is likely a major factor for LLJ formation in Dunkerque region. The study also examined the conditions of LLJ occurrence using European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis v5 and ultrasonic anemometer data, but the different types of LLJs sharing the same core direction and occurrence conditions made it difficult to quantify specific jet formation mechanisms. This is the first experimental study on the North Sea shore, and at the entrance of the English Channel, providing valuable insights into the LLJ behavior in the region.