The ATMONSYS water vapor DIAL: Advanced measurements of short-term variability in the planetary boundary layer

Abstract. High-resolution measurements of water vapor concentrations and their transport throughout the turbulent planetary boundary layer (PBL) and beyond are key for an enhanced understanding of atmospheric processes. Therefore, data from the mobile atmospheric monitoring system (ATMONSYS) differential absorption lidar (DIAL) is presented for the first time. The ATMONSYS DIAL has been developed with the goal of resolving turbulence throughout the PBL at a sampling frequency of 10 s and vertical resolutions of less than 200 m. General measuring capabilities during high-noon, clear-sky, summer conditions with a maximum vertical measurement range of >3 km and statistical uncertainties of <5 % are demonstrated. The analysis of turbulence spectra shows an overall good agreement with Kolmogorov's law, demonstrating its general capability of resolving turbulence, although deviations to the Kolmogorov behaviour can be observed at certain frequency ranges. By the combination of the ATMONSYS DIAL with an adjacent high-quality Doppler wind lidar, some of those deviations are evaded in the co-spectra due to independent noise of both instruments. However, the intermediate deviations from the expected Kolmogorov behavior in the co-spectra persist. Under consideration of the surrounding landscape, an impact of present surface heterogeneities on those intermediate frequency deviations seems plausible. Agreement of the co-spectra with Kolmogorov's law at the highest frequencies reveals that the ATMONSYS DIAL is capable to resolve turbulent latent energy fluxes down to the measurement's Nyquist frequency of 5 · 10^-2 Hz. A system cross-intercomparison of the ATMONSYS DIAL with two adjacent water vapor Raman lidars and radiosondes shows good agreement between all sensors, despite minor DIAL deficiencies under certain conditions with shreded clouds surpassing the lidar. Observed profile-to-profile DIAL fluctuations and sensor-to-sensor deviations, in combination with low statistical uncertainty, show the advantage of humidity lidars, such as the ATMONSYS DIAL, to capture both short-term and small-scale dynamics of the lowermost atmosphere.