Terrain roughness and atmospheric stability at a typical coastal site

Directional dependence of horizontal wind direction fluctuations (Σ_θ) is studied at the coastal site of Madras Atomic Power Project, Kalpakkam with significant inhomogeneity in roughness element distribution around the location of measurement. Σ_θ is measured by a potentiometric wind vane mounted on a 30 m meteorological tower. Values of Σ_θ showed as high as threefold variation for the same atmospheric stability depending on the effective roughness length of the upwind sector. Average Σ_θ values separated for sea- and land-breeze conditions, when correlated with Pasquill stability categories showed a monotonic decrease with increasing stability for land breeze but was found to increase for change from D to F category during sea breezes presumably due to the influence of an internal boundary-layer development.