Horizontal Anisotropy of Turbulent Fluctuations in Surface and Air Temperatures Over a Flat, Homogeneous Surface

Abstract Longitudinal and lateral integral length scales describe the characteristic horizontal structure of energy‐containing turbulent structures in a flow. The ratio describes the anisotropy of the structures where indicates structures elongated along the mean wind direction. This ratio is thought to vary with height above the surface and be controlled by surface roughness, shear, and stability, but almost all investigations in the literature consider only neutral atmospheric stability. The present work investigates spatial length scales of temperature fluctuations and uses a horizontally arrayed distributed fiber‐optic temperature sensor to construct 2D spatial correlation fields from which and are calculated in a desert surface layer with low roughness over a range of atmospheric stabilities. Time‐sequential thermography is used to calculate length scales of temperature fluctuations at the surface interface. is generally found to increase with increasing boundary layer height, with increasing wind speed, and with decreasing instability, while is more constant, both for the surface temperature and air temperature field. We find more isotropic turbulence at low wind speeds and more unstable atmospheric regimes and more anisotropic turbulence in (near‐)neutral atmospheric stabilities at higher wind speeds. The length scales at the surface are found to be larger than the near‐surface atmosphere and generally higher than values reported in the literature.