Part I - Introduction



General Strategy

The campaign will combine in situ measurements made with towers, balloons and airplanes with the remote sensing capability. The measurements will be intensified during the late afternoon transition.

Two sites (hereafter "super-site 1 and 2") will concentrate the ground-based instruments and intensive flying over operations. They are associated with two different observational strategies: (1) vertical structure and (2) spatial heterogeneity, respectively.

(1) In super-site 1, a sodar, UHF and VHF wind profilers, a microwave radiometer, a ceilometer, a backscatter lidar and radiosoundings will give a complete view of the mean vertical structure of the troposphere. In addition, a vertically-pointing Doppler lidar will give the structure of the vertical wind, with a resolution in time and space high enough for turbulence statistics studies and entrainment zone exploration. In situ measurement of turbulence will be made on the 60-m high tower and with a tethered-balloon-borne probe. The radiation divergence in the surface layer will be estimated on another 10-m high tower.

(2) In super-site 2, several sonic anemometers will be deployed over three adjacent surfaces (a moorland, a maize field and a forest), in order to measure the differences in the structure and evolution of the transition among different vegetated surfaces. The surface layer above the moorland and the maize field will be extensively probed by two tethered balloons, while UASs will fly low over the three surfaces.

A network of two UHF radars and one sodar wind profilers (located on super sites 1 and 2, and on a third position that makes a triangle, see Fig. 3) will give continuous profiles of the mean wind for the study of the 3D atmospheric circulation.

Airplanes and unmanned aerial vehicles (UASs) will probe the atmosphere over both super-sites, focusing on either vertical structure or spatial variability. The two airplanes (Piper Aztec and Sky Arrow) will probe an area of a few tens of kilometres across centred around the super-sites (Fig. ), with horizontal legs at different levels within and just above the CBL. UASs will also fly over both super-sites, at low levels when combined with the manned airplanes, and up to 2 km height otherwise.

Figure 3: Satellite picture (source: Google Earth - 2006 image) of the site.

Over the 3.5 planned weeks, we expect 10 days during which the aircraft, the UASs and the balloons (tethered and radiosoundings) will be deployed intensively, while other instruments will work continuously during the whole period. Those richly documented days will constitute real cases on which the numerical simulation will be based.

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