Impact of the Aeolus Level‐2B horizontal line‐of‐sight winds in the Environment and Climate Change Canada global forecast system

Abstract

The European Space Agency Aeolus mission was launched in August 2018. This satellite carries the first Doppler lidar able to provide global measurements of wind profiles. Aeolus Level‐2B products have been generated and monitored by the European Centre for Medium‐Range Weather Forecasts (ECMWF) in near real‐time since a few weeks after the launch. These products include the horizontal line‐of‐sight (HLOS) winds that are suitable for data assimilation in numerical weather prediction systems. This article presents a series of observing system experiments conducted over summer 2019 to assess the value of the Level‐2B HLOS winds and their impact on the Environment and Climate Change Canada global forecasts. The impact of atmospheric motion vectors (AMVs) on forecasts is also examined and compared with the impact of HLOS winds. Two datasets are used: the HLOS winds produced in near real‐time at ECMWF and those reprocessed later in fall 2020. It is found that the near real‐time data are significantly biased and should be corrected. A look‐up table bias correction based on observation minus background departures is applied to this dataset as initially proposed by ECMWF. The reprocessed data are of better quality and bias corrected using the telescope's primary mirror temperature variations as predictor. The impacts of the near real‐time and reprocessed HLOS winds on forecasts are generally positive for both temperature and wind. The impacts are largest in the troposphere over the Tropics and polar regions. The positive impacts on forecasts are larger with the reprocessed data, particularly in the stratosphere, where a significant degradation over the Southern Hemisphere is found from assimilating the near real‐time data. The normalized forecast error reductions at days 1 and 2 for the wind are ∼1.25% over the Tropics and Southern Hemisphere. The positive impact of the HLOS winds on forecasts is enhanced by ∼40% when the AMVs are not assimilated in the control experiment. The forecast error reduction from assimilating AMVs is, however, two times larger than from assimilating HLOS winds in the extratropics. Conversely, the impact of HLOS winds on forecasts is generally larger in the Tropics.

Investigation of links between dynamical scenarios and particularly high impact of Aeolus on numerical weather prediction (NWP) forecasts

“…The study introduced the experimental setup and the data quality and consistency and provided an overview of the systematic changes in the analysis and impact on forecast error. The results overall confirm the promising statistical improvements demonstrated in the global impact studies of Garrett et al (2022), Laroche and St-James (2022), Pourret et al (2022), andRennie et al (2021).…”

“…Their assimilation into global NWP models led to a significant impact on the analysis and forecasts over Europe and around the development of tropical cyclones, as well as their interaction with the midlatitude waveguide (Pu et al, 2010;Weissmann and Cardinali, 2007;Weissmann et al, 2012). Since the launch of the Aeolus satellite in August 2018, several observing system experiment (OSE) studies have been conducted to investigate the impact of the Rayleigh and Mie HLOS wind observations in various NWP models (Garrett et al, 2022;Laroche and St-James, 2022;Pourret et al, 2022;Rennie et al, 2021). Most of these studies concentrated on global forecast error statistics showing large overall improvements.…”

The impacts of assimilating Aeolus horizontal line-of-sight winds on numerical predictions of Hurricane Ida (2021) and a mesoscale convective system over the Atlantic Ocean

“…1. Mie-clear and Rayleigh-cloudy products are not used in this study due to their poor quality (Rennie et al, 2021a;Pourret et al, 2022;Laroche and St-James, 2022).…”

“…The forward model H(𝒙𝒙) of the Mie-cloudy and Rayleigh-clear HLOS winds (Pourret et al, 2022;Laroche and St-James, 2022;Rennie et al, 2021a) is defined as:…”

Investigation of dynamical scenarios leading to particularly high impact of Aeolus on NWP forecasts

“…Their assimilation into global NWP models led to a significant impact on the analysis and forecasts over Europe and around the development of tropical cyclones, as well as their interaction with the midlatitude waveguide (Pu et al, 2010;Weissmann and Cardinali, 2007;Weissmann et al, 2012). Since the launch of the Aeolus satellite in August 2018, several observing system experiment (OSE) studies have been conducted to investigate the impact of the Rayleigh and Mie HLOS wind observations in various NWP models (Garrett et al, 2022;Laroche and St-James, 2022;Pourret et al, 2022;Rennie et al, 2021). Most of these studies concentrated on global forecast error statistics showing overall large improvements.…”