Group seminar on 14. May, 14:15
Aeolus assimilation effects on equatorial waves and the QBO in the ECMWF system
Dr. Robin Pilch Kedzierski
The Aeolus satellite provided the first spaceborne Doppler Wind Lidar (DWL) observations, whose assimilation in forecasting systems led to improvements especially in the tropical upper troposphere and lower stratosphere (UTLS). We use 2-year observing system experiments (OSEs) analyzed from July 2019 to June 2021. The control experiment is without Aeolus but with all other operationally assimilated observations in the ECMWF system. The other experiment assimilates Aeolus on top of all other observations. We analyze differences between the OSEs in terms of equatorial wave properties and the zonal-mean flow. Systematic changes to equatorial waves by Aeolus assimilation include amplification of Kelvin and n=1 Rossby waves in the upper-troposphere and reduction of Inertia-gravity wave amplitudes throughout the equatorial troposphere and stratosphere. Aeolus assimilation sharpens shear zones of zonal-mean zonal winds during normal QBO downward progression and especially during the 2019/20 QBO disruption in the lower stratosphere.