Obtaining turbulence statistics of thermally driven anabatic flow by sonic-hot-film combo anemometer
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Obtaining turbulence statistics of thermally driven anabatic flow by sonic‑hot‑film combo anemometer Roni Hilel Goldshmid1 · Dan Liberzon1 Received: 26 December 2016 / Accepted: 12 November 2018 © Springer Nature B.V. 2018
Abstract 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. Keywords Anabatic flow · Combo probe · Thermal stratification · Turbulence spectra · Turbulence statistics
1 Introduction Investigation of atmospheric boundary layer (BL) flows constitute a major part of climate research since they govern heat and scalar transport. Transport of contaminants therein directly influence microclimates by affecting cloud formation which set the precipitation regimes [1–4]. Atmospheric BL flows developing in complex terrains are the most convoluted and therefore difficult to investigate. Flows on hill and mountain slopes are mainly set in motion by thermal forces originating from diurnal heating/cooling cycles and appear * Roni Hilel Goldshmid [email protected] 1
Civil and Environmental Engineering, The Technion, 3200003 Haifa, Israel
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Environmental Fluid Mechanics
in two configurations: anabatic (upslope) and katabatic (downslope) flows [5]. Many published studies cover various aspects of the more stable katabatic flows and significantly fewer published studies deal with turbulent anabatic flows, which evidences the relative difficulty to investigate upslope flows, especially experimentally. The major reason for difficulty of investigation is the lack of suitable instrumentation to cope with the inhomogeneity and non-stationary nature of the turbulent ana
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