Validation of Aeolus winds using radiosonde observations and numerical weather prediction model equivalents

Abstract

Abstract. In August 2018, the first Doppler wind lidar, developed by the European Space Agency (ESA), was launched on board the Aeolus satellite into space. Providing atmospheric wind profiles on a global basis, the Earth Explorer mission is expected to demonstrate improvements in the quality of numerical weather prediction (NWP). For the use of Aeolus observations in NWP data assimilation, a detailed characterization of the quality and the minimization of systematic errors is crucial. This study performs a statistical validation of Aeolus observations, using collocated radiosonde measurements and NWP forecast equivalents from two different global models, the ICOsahedral Nonhydrostatic model (ICON) of Deutscher Wetterdienst (DWD) and the European Centre for Medium-Range Weather Forecast (ECMWF) Integrated Forecast System (IFS) model, as reference data. For the time period from the satellite's launch to the end of December 2019, comparisons for the Northern Hemisphere (23.5–65∘ N) show strong variations of the Aeolus wind bias and differences between the ascending and descending orbit phase. The mean absolute bias for the selected validation area is found to be in the range of 1.8–2.3 m s−1 (Rayleigh) and 1.3–1.9 m s−1 (Mie), showing good agreement between the three independent reference data sets. Due to the greater representativeness errors associated with the comparisons using radiosonde observations, the random differences are larger for the validation with radiosondes compared to the model equivalent statistics. To achieve an estimate for the Aeolus instrumental error, the representativeness errors for the comparisons are determined, as well as the estimation of the model and radiosonde observational error. The resulting Aeolus error estimates are in the range of 4.1–4.4 m s−1 (Rayleigh) and 1.9–3.0 m s−1 (Mie). Investigations of the Rayleigh wind bias on a global scale show that in addition to the satellite flight direction and seasonal differences, the systematic differences vary with latitude. A latitude-based bias correction approach is able to reduce the bias, but a residual bias of 0.4–0.6 m s−1 with a temporal trend remains. Taking additional longitudinal differences into account, the bias can be reduced further by almost 50 %. Longitudinal variations are suggested to be linked to land–sea distribution and tropical convection that influences the thermal emission of the earth. Since 20 April 2020 a telescope temperature-based bias correction scheme has been applied operationally in the L2B processor, developed by the Aeolus Data Innovation and Science Cluster (DISC).

Airborne lidar observations of wind, water vapor, and aerosol profiles during the NASA Aeolus calibration and validation (Cal/Val) test flight campaign

“…As the DC-8 proceeded westward toward the start of the Aeolus line, the midtroposphere moist layer strengthened and deepened, and a weak overturning circulation associated with convective detrainment could be observed in the WV distributions, evidenced by the moist layer at and above ∼ 8 km altitude extending northward from the deep tropics. HALO's ability to measure and infer dynamical processes via high vertical resolution WV and aerosol measurements is critical for an improved understanding of the radiative transfer that drives large-scale circulation, which can, in turn, effect low tropospheric stability, cloud formation, and convective aggregation (Stevens et al, 2017;Holloway et al, 2017;Mapes et al, 2017;Lebsock et al, 2017).…”

Californian Wildfire Smoke Over Europe: A First Example of the Aerosol Observing Capabilities of Aeolus Compared to Ground‐Based Lidar

“…On‐board of this satellite is the Atmospheric Laser Doppler Instrument (ALADIN), which is a high spectral resolution (HSR, Lux et al., 2020; Wandinger, 1998) Doppler lidar (LIght Detection And Ranging). ALADIN is the first lidar instrument on a European satellite and the first instrument in space that actively can measure profiles of an horizontal wind component (Baars, Herzog, et al., 2020; Martin et al., 2021; Reitebuch, 2012; Witschas et al., 2020). It follows the very successful CALIPSO mission (Winker et al., 2009) with its elastic polarization lidar CALIOP on‐board, which is delivering aerosol and cloud profiles since 2006 (e.g., Young et al., 2018).…”

A new lidar design for operational atmospheric wind and cloud/aerosol survey from space

“…Our first airborne backscatter lidar was developed in the 1990s in the frame of the French CNES-CNRS (National Center for Scientific Research) project LE-ANDRE (Lidar pour l'Etude des Aérosols des Nuages et Du RayonnEment) for atmospheric studies. Since it was operating at similar wavelengths, it was involved in the validation of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)-CALIPSO observations of cirrus clouds (Mioche et al, 2010). It was then upgraded to add a high spectral resolution (HSR) channel and renamed as LEANDRE-New Generation (LNG).…”