Unexpected vertical wind speed profiles in the boundary layer over the southern North Sea

Abstract

Shallow atmospheric internal boundary layers over the southern part of the North Sea are common. Analysis of one year of meteorological data from the FINO1 research platform in the German Bight reveals that vertical wind speed profiles frequently do not conform to the expected modified logarithmic profile of Monin–Obukhov similarity theory. The wind profiles are mostly characterized by local maxima or kinks within the first 100m over the sea surface. The data reveals the most frequent occurrence of a single maximum, but multiple maxima are often present, and there are sometimes even reversed profiles with the wind speed decreasing with height. The expected modified logarithmic profile occurs for a minority of cases. The evidence suggests the frequent presence of internal boundary layers that propagate from coastal land masses that surround the North Sea. A census of vertical wind speed profiles is presented that shows how different inflection states are linked with wind speed and atmospheric stability. The kinks are most prevalent in the upper part of the measurement range near the 100m hub height of modern offshore the wind turbines, so that internal boundary layers represent a possible concern for the offshore wind energy industry in the North Sea region.