Full-scale wind speed spectra of 5 Year time series in urban boundary layer observed on a 325 m meteorological tower

In the Urban Boundary Layer (UBL), the vertical structure is generally divided into four layers, namely urban canopy (UC), roughness sublayer (RS), inertial sublayer (IS) and mixing layer (ML), respectively. Full-scale wind speed spectra of a five-year time series in different layers are used to investigate the spectral characteristic in UBL. Due to the similar spectral characteristics in IS and ML, these two layers are combined into a single layer, namely, IS & ML. The results show peaks at a frequency of about 1 year-1 and 1 day-1, and a gap in the mesoscale in the horizontal wind speed spectrum at 47 m. It matches well with the spectra in other classical studies. In three layers, the spectra show different characteristic and distribution of spectral energy. For horizontal spectrum, the mesoscale spectral energy of the layer with higher altitude is obviously larger. With the increase of the height, the gap becomes flat and finally be filled in IS & ML. For vertical spectrum, the characteristics of spectra in the UC and RS are similar, and a diurnal peak can be found. In IS & ML, the proportion of spectral energy in the macroscale obviously increases, and the diurnal peak disappears.

Automated summary

This study investigated the spectral characteristics in the Urban Boundary Layer (UBL) using full-scale wind speed spectra of a five-year time series. The results showed different spectral characteristics and distribution of spectral energy in different layers in UBL.