The macrometeorological spectrum—a preliminary study

The whole of the modern treatment of wind engineering depends on the 1957 work by Van der Hoven in which he identified the macrometeorological spectrum, the micrometeorological spectrum and the spectral gap between them centred, roughly, on a frequency of 1 cycle/h. Since then, very little work seems to have been done on the macrometeorological spectrum. This paper reports the analysis of a long (up to 30 years) record of hourly mean wind speeds recorded at 17 m above ground on an open site at Boscombe Down, Wilts, UK. The broadband macrometeorological spectrum was very similar to that reported by Van der Hoven. Additionally, periodic deterministic components were identified corresponding to an annual cycle, a diurnal cycle and harmonics up to the sixth of the diurnal cycle. A model for the diurnal cycle is suggested which would produce these harmonic effects. This model implies that the diurnal cycle is intermittent and may be associated with the anti-cyclonic portion of the wind climate. The implications of the results on the derivation of design wind speeds are briefly discussed.