Turbulence measurements over a suburban landscape using scintillometry and eddy covariance

Understanding boundary layer processes in urban areas is necessary for improving predictive capabilities in response to land use development and climate change. Over regions of mixed land cover spatially-integrated observations are particularly valuable, as they supply representative measurements at scales comparable to model grids or satellite products. Scintillometry, a ground-based remote sensing technique, can provide turbulent heat fluxes at the kilometre-scale. Fluxes are calculated from structure parameters of temperature and humidity via similarity theory; these structure parameters are calculated from refractive index fluctuations sensed by the instrument. Conventional single-wavelength scintillometry yields the sensible heat flux, whilst a system of two scintillometers of different wavelengths enables determination of both sensible and latent heat fluxes. Results from two scintillometer paths (2.8 km and 5.5 km in length) in the town of Swindon, UK, are presented and discussed alongside eddy covariance data. The behaviour of the structure parameters is analysed with regard to temporal (daily and seasonal) and spatial variations, as well as differences between measurement techniques. In transforming structure parameters to fluxes, the applicability of similarity theory is considered through (a) the scaling of temperature and humidity with stability and (b) the temperature-humidity correlation coefficient derived from both eddy covariance and scintillometry. Finally, the turbulent fluxes are investigated with particular attention given to seasonal variability in environmental controls, namely the changing availability of surface moisture and energy. The influence of land cover is also explored; the findings demonstrate the value of scintillometry for integrating surface heterogeneity. The results presented offer improved understanding of turbulent transport processes and surface-atmosphere exchanges over suburban landscapes.