The Atmospheric Raman Temperature and Humidity Sounder: Highlights of Four Years of Automated Measurements of the Atmospheric Boundary Layer and Free Troposphere

Abstract

Since there are only a very few suitable remote sensing measurements, the thermodynamic field of the atmospheric boundary layer and lower free troposphere is largely still Terra Incognita. To close this gap, we developed an automated thermodynamic profiler based on the Raman lidar technique, the Atmospheric Raman Temperature and Humidity Sounder (ARTHUS) (Lange et al. 2019).It uses only the ice-safe 355-nm radiation of an injection-seeded Nd:YAG laser as transmitter. The laser power is about 20 W at 200 Hz. The diameter of the receiving telescope is 40 cm. Four receiving channels (elastic, water vapor, two rotational Raman signals) allow for four independently measured parameters: temperature (T), water vapor mixing ratio (WVMR), particle extinction coefficient, and particle backscatter coefficient.With these data, ARTHUS resolves, e.g., the strength of the inversion layer at the atmospheric boundary layer (ABL) top, elevated lids in the free troposphere, and turbulent fluctuations. Furthermore, in combination with Doppler lidars, sensible and latent heat flux profiles in the convective ABL and thus flux-gradient relationships can be studied (Behrendt et al. 2020). Consequently, ARTHUS can be applied for process studies of land-atmosphere feedback, weather and climate monitoring, model verification, and data assimilation.Resolutions of the measurements are a few seconds and meters in the lower troposphere. With the data, also the statistical uncertainties of the measured parameters are derived. Continuous operations over long periods were achieved not only at the Land Atmosphere Feedback Observatory (LAFO) at University of Hohenheim but also during several field campaigns elsewhere covering a large variety of atmospheric conditions.During the EUREC4A field campaign (Stevens et al, 2020), ARTHUS was deployed onboard the research vessel Maria S Merian between 18 January and 18 February 2020 to study ocean-atmosphere interaction. Here, ARTHUS was collocated with two Doppler lidars: one in vertically pointing mode and one in a 6-beam scanning mode.Between 15 July and 20 September 2021, ARTHUS was deployed at the Lindenberg Observatory of the German Weather Service (DWD). The objective of the campaign was to investigate the long-term stability of ARTHUS by comparisons with four local radiosondes. Indeed, the very high accuracy during day and night were verified.ARTHUS participated in WaLiNeAs (Water Vapor Lidar Network Assimilation) between 15 September and 10 December 2022. For this campaign, ARTHUS was deployed at the west coast of Corsica. The objective was to implement an integrated prediction tool to enhance the forecast of heavy precipitation events in southern France, primarily demonstrating the benefit of assimilating vertically resolved WVMR lidar data in the new version of the French operational AROME numerical weather prediction system.At the conference, highlights of ARTHUS’ measurements during WaLiNeAs will be shown.