During the HOPE campaign the ‘University of BASILicata UV-Raman lidar system’ (BASIL) was installed close to the HALO photonics Streamline Doppler Wind Lidar of the Juelich ObservatorY for Cloud Evolution (JOYCE). We used this opportunity to calculate profiles of the turbulent humidity flux including an estimate of the uncertainty. Profiles indicate a loss of humidity to the free troposphere for the investigated case with a rather large uncertainty of 50%.

Volume scans of the HATPRO microwave radiometer were used to determine the horizontal gradient of humidty which, together with the horizontal wind, allow an estimate of the advection.

All quantities together are then used to investigate the water vapor budget of the boundary layer. It shows up that especially uncertainites of the vertical flux divergence are very large and a closure is not really feasible. The reason for the large uncertainties are the large integral length scales for <q'w'> which even for a 2 hour averaging period allow not to sample enough plumes. We thus must conclude that it is in general difficult to derive turbulent fluxes with sufficient accuracy from remote sensing instruments fixed on the ground.