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Abstract
A fraction of the earth radiated IR energy is directly used to warm up the air just above the ground. This radiative process is even more efficient during clear air days and can be responsible of the formation of thermals. Thermals play an important role in the thermodynamic processes within the boundary layer. Consequently, there is a need for their observations. There are different ways to monitor the vertical motion of the air from remote-sensing instruments. The Doppler lidar (μm-wavelength) observes the vertical wind by measuring the velocity of aerosols (nm-μm). The Doppler radar, of which the wavelength (cm) is much larger, cannot detect such small particles. Another scattering mechanism, variation of the refractivity index, is measured in the case of the radar.
This paper presents and discusses measurements of the vertical wind carried out by the radar TARA during clear air conditions within EUCAARI IMPACT campaign, that took place in May 2008 in the Netherlands. The campaign covered intensive ground-based and airborne measurements in the vicinity of the CESAR observatory in Cabauw. TARA (Transportable Atmospheric Radar) is a 9.1 cm wavelength Doppler radar, which performs measurements with high temporal (3-18 s) and spatial resolution (3-30 m).
The principle of the radar measurement, the data processing, and the selection of spatial and time resolutions needed to estimate the vertical wind are introduced. Specific days are selected to discuss the results. Finally, comparisons with other sensors present during the campaign are performed to evaluate the performances of the vertical wind radar measurements in clear air conditions.