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

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. This
study presents data from the mobile Atmospheric Monitoring System (ATMONSYS) Differential Absorption Lidar
(DIAL), operated with a novel titanium sapphire (Ti:Sa) laser concept, for the first time. The ATMONSYS DIAL aims to
resolve turbulence throughout the PBL with 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 good
agreement with Kolmogorov’s law, demonstrating the system’s capability to resolve turbulence. However, deviations
from Kolmogorov behavior are observed at certain frequency ranges. By combining the ATMONSYS DIAL with an adja-
cent high-quality Doppler wind lidar, some of these deviations are mitigated in the co-spectra due to independent noise
... mehrfrom both instruments. However, intermediate deviations from Kolmogorov behavior persist, likely due to surrounding
surface heterogeneities. The agreement of the co-spectra with Kolmogorov’s law at the highest frequencies demonstrates
that the ATMONSYS DIAL is capable of resolving turbulent latent energy fluxes down to the measurement’s Nyquist fre-
quency of 5 × 10−2 Hz. A system cross-intercomparison of the ATMONSYS DIAL with two adjacent water vapor Ra-
man lidars and radiosondes shows overall good agreement between the sensors, despite minor DIAL deficiencies un-
der certain conditions with broken clouds passing over the lidar. The observed profile-to-profile DIAL fluctuations and
sensor-to-sensor deviations, in combination with low statistical uncertainty, highlight the advantage of humidity lidars,
such as the ATMONSYS DIAL, in capturing both short-term and small-scale dynamics of the lowermost atmosphere.