Synchronized kite-balloons measurements revealed the development of a nocturnal stable layer in an urban green park. The vertical structure of the park cool island is discussed. A stable layer developed in the park. In the surrounding urban area, neutral stratification was maintained all night. In spite of different weather conditions on the two nights measured, the park stable layer developed up to similar height (50 m). Three temperature profiles measured at a flat area in the park showed similar vertical gradients from surface to tree height (ca. 10 m). This means that the horizontal distribution of air temperature measured at the surface level represents the lowest 10 m of the atmospheric boundary layer.
Calm, clear sky conditions triggered the development of a colder layer in the park than the surrounding area. The maximum height of the colder layer was found to be 71 m. The cooling energy for cold air formation over park was estimated to be 5 Wm-2.
