Studying Land-Atmosphere Feedback Processes With a Synergy of Six Scanning Lidars

We will present the strategy and results of a combination of six scanning lidars to investigate the interplay between daytime surface fluxes, surface layer gradients, convective boundary layer dynamics and development, as well as the characteristics of the interfacial layer and the lower free troposphere. Our observations were made above the agricultural fields of University of Hohenheim [1], Stuttgart, Germany in spring and summer 2025 in the frame of the research unit Land Atmosphere Feedback Initiative (LAFI, https://lafi-dfg.de/) of the German Research Foundation (DFG). For this, the automated Raman lidar ARTHUS (Atmospheric Temperature and Humidity Sounder) built in our institute in recent years, was extended with a scanner for atmospheric measurements in the surface layer just above the canopy. ARTHUS [2] is an eye-safe rotational Raman lidar with five receiver channels detecting the elastic backscatter signal at 355 nm, two rotational Raman signals with opposite temperature dependence, as well as the two vibrational Raman signals of water vapor and carbon dioxide. These scanning measurements were performed during intensive observation periods for 50 minutes of each hour while during the remaining 10 minutes of each hour as well as during non-IOP days vertical pointing measurements were made. These surface layer observations of ARTHUS were combined with data measured with two Doppler lidars making simultaneously cross-cutting low-level scans for horizontal wind profiling near the surface. Two more Doppler lidars were measuring vertical wind fluctuations and horizontal wind speed and direction. One of these two Doppler lidars was operated in constant vertical pointing mode while the other was operated in a six-beam scanning mode with an elevation angle of 45°. Our water vapor differential absorption lidar (WVDIAL) made vertical-pointing observations of turbulent moisture fluctuations up to the free troposphere. The WVDIAL uses a Titanium-Saphire laser pumped with the second-harmonic radiation of a Nd:YAG laser as transmitter emitting online and offline laser pulses near 820 nm with 200 Hz into the atmosphere. The atmospheric backscatter signals are collected with a 80-cm telescope. While also the WVDIAL can scan in any direction, it was operated in constant vertical-pointing mode during LAFI.

 

[1]        Späth, F., et al.: The land–atmosphere feedback observatory: a new observational approach for characterizing land–atmosphere feedback. Geoscientific Instrumentation, Methods and Data Systems (2023). DOI: 10.5194/gi-12-25-2023

[2]        Lange, D. et al.: Compact Operational Tropospheric Water Vapor and Temperature Raman Lidar with Turbulence Resolution. Geophys. Res. Lett. (2019). DOI: 10.1029/2019GL085774