Obtaining turbulence statistics of thermally driven anabatic flow by sonic-hot-film combo anemometer

Achieving a better understanding of atmospheric boundary layer flows, and of slope flows in particular, is of paramount importance for the research of climate processes and production of accurate weather forecasts. We addressed the need for high resolution statistics that describe the turbulence of thermally driven anabatic (upslope) flows by the implementation of a novel sonic-hot-film anemometer, the combo probe. A field experiment was staged to obtain continuous 8-day measurements of a thermally driven anabatic flow diurnal cycle on a moderate slope by a single combo probe mounted atop a 2 m high mast. Variations of the mean and fluctuating upslope velocity field components and temperature exhibit a strong correlation of the developing flow with the diurnal solar heating cycle. The provided detailed analysis of turbulence statistics includes characteristic length scales and spectra of velocity fluctuations almost up to the Kolmogorov scale. Identification of spectral shape similarity led to the introduction of a suitable normalization and comparison of the results to a theoretical model. Additionally, empirical fits of several parameters are produced and discussed with respect to variations of thermal forcing that were derived in terms of bulk temperature differences and buoyancy fluxes up the slope. The main outcomes are spectra resolved down to small scales and turbulence statistics made available for numerical simulations and future studies with slow instruments.