Mesoscale Flows and Turbulence Measurements on Forested Slope during Peridgão 2017

Numerous field campaigns have found the importance of surface conditions on boundary layer evolution. Specifically, soil properties were found to control surface fluxes of heat, moisture, and momentum that significantly modulated the atmospheric boundary layer (ABL) over flat and sparsely vegetated surfaces. There have been increasing numbers of studies related to canopy impacts on the boundary layer, such as CHATS, however few canopy studies over complex terrain have been performed with limited instrumentation. The recent Perdigão campaign greatly augmented the previous datasets available by instrumenting a unique, parallel ridge mountain in Perdigão, Portugal in unprecedented spatial and temporal resolution using traditional mast mounted sensors, instrumented aerial platforms, and remote sensing instrumentation.

To aid the canopy studies, the Army Research Laboratory deployed sonic anemometers within the canopy transecting the ridges perpendicularly and placed five additional heavily instrumented meteorological masts on the northeast facing slope to investigate detailed slope flows. At each of these towers, there was an average of six levels of temperature, relative humidity, and wind sensors located above & below the canopy height which allowed a detailed study of the sub-canopy layer. In addition to the towers, two scanning Doppler LiDARs were oriented such that they performed synchronized dual Doppler virtual tower scans, extending from the canopy interface to several hundred meters above.

Five-minute averaged data from the intensive observing period (IOP) (1 May – June 15, 2017) are analyzed to determine the impact of flow regime and stability on turbulence above and below the canopy and flow within the canopy. The mean characteristics of flow on the slope will be presented as well as flow regimes that cause large deviations from the mean. Important parameters that represent these regimes will also be presented.