Land-Sea Contrast of Nearshore Wind Conditions: Case Study in Mutsu-Ogawara

Abstract

To develop offshore wind energy, we investigated nearshore wind conditions, notably the land-sea contrast, using the coastal area of Mutsu-Ogawara, Aomori Prefecture as a case study. We found that wind conditions were substantially different between onshore (MT-A1) and offshore (MT-B) sites, even when the latter were only 1.5 km apart. The mean wind speed at 55 m above sea level at MT-B was higher than that at the onshore site by up to 20% monthly and 12% annually. For winds from the landward side, the Iref value (turbulence intensity at a mean wind speed of 15 m/s) at MT-B was 37% lower than that at MT-A1. Because such high wind speeds and low turbulence conditions are preferable for the operation of wind turbines, an offshore wind farm would have advantageous wind conditions, even if placed close to the coastline. Moreover, we found that the land-sea contrast is caused not only by mechanical factors, such as roughness length, but also by thermodynamic factors such as seasonal variations of atmospheric stability over land and sea.