Vertical velocity variance and its dependency on meteorological parameters in the convective boundary layer

Abstract

<p>The variability of vertical profiles of the normalized vertical velocity variance was examined to characterize turbulence and to investigate its dependence on meteorological parameters in the convective boundary layer. The vertical profiles of the vertical velocity variance were calculated using the Doppler lidar dataset from the FESSTVaL measurement campaign collected during two consecutive summer periods. The measurements took place around the Lindenberg meteorological observatory (MOL-RAO), near Berlin, Germany, representative of a flat-terrain covered with crops and patches of forest. The variability of a daily average of the normalized variance was analyzed during a period of a well-developed boundary layer. We classified the dataset into three main categories based on the presence of clouds and extracting only the periods without precipitation: clear-sky, cloud-topped, and rainy days. The mean profile of the normalized variance of the vertical velocity systematically increases from the rainy, cloud-topped to clear-sky days categories. The magnitude of the mean profile during the clear-sky and cloud-topped days is similar to the reference profile of Lenschow et al. (1980), although the variability among the days is large. The dependence of this variability of the normalized variance on the meteorological parameters was examined. We found that the relative humidity, Bowen ratio, surface latent heat flux, and cloud fraction relate to the variability of the normalized variance. A closer look at the cloud fraction during the cloud-topped days shows an increment of the normalized variance with a decrease of humidity in the boundary layer similar to the increment from rainy to cloudy and clear-sky days.</p>