Title: Measurement of ABL Turbulent Fluxes with the Duke HOP in Support of CHATS
ARO Grant 52861EVII; PI: R Avissar; Period: 04/20/07-01/19/08
The main objective of the Canopy Horizontal Array Turbulence Studies (CHATS) was to provide the relevant data needed to improve the parameterization of sub-filter-scale (SFS) processes in the roughness sub-layer that is affected by canopy-atmosphere interactions. For that purpose, NCAR deployed in March-June 2007 an array of sonic anemometers at different heights and lateral separations (see picture at right) in a homogeneous walnut orchard in the Central Valley of California so as to capture the influence of the wake-scale motions in the lee of vegetation. Together with this array, other instruments (including a high tower and a new eye-safe lidar) were operating during the field campaign. While this equipment provided an excellent dataset at the tree-to-orchard scale, this experiment needed a general characterization of the entire ABL so that a full picture of the dynamics involved in the land-atmosphere interactions taking place above the orchard could be assessed. This missing link was occasionally provided by the Duke HOP, which flew about 25 hours in 6 days distributed over the period April-June 2007. For each day, two, 2-hour flights were performed (morning and early afternoon). During these flights, the Duke HOP measured 3D turbulence, temperature, moisture, and CO2 in six transects at several heights from tree top to the top of the atmospheric boundary layer (see pictures below). Holder et al (2008) explain how these flights were also used to evaluate the performance of the Duke HOP as compared to tower observations (the tall tower erected at the experimental site is seen in the IR picture below).
The following perspective maps show the CHATS experimental site, located south-west of Davis, CA (highlighted in yellow), and the horizontal and vertical flight tracks above the site. Note Davis Airport, which was conveniently located about 5 miles north of the site for refueling. The lower two pictures show the infrared signature of the HOP in flight above the orchard.
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