TY - JOUR
T1 - Impact of Aeolus wind lidar observations on the representation of the West African monsoon circulation in the ECMWF and DWD forecasting systems
AU - Borne, Maurus
AU - Knippertz, Peter
AU - Weissmann, Martin
AU - Martin, Anne
AU - Rennie, Michael
AU - Cress, Alexander
N1 - Publisher Copyright:
© 2023 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
PY - 2023/4/1
Y1 - 2023/4/1
N2 - Aeolus is the first satellite mission to acquire vertical profiles of horizontal line-of-sight winds globally and thus fills an important gap in the Global Observing System, most notably in the Tropics. This study explores the impact of this dataset on analyses and forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) and Deutscher Wetterdienst (DWD), focusing specifically on the West African Monsoon (WAM) circulation during the boreal summers of 2019 and 2020. The WAM is notoriously challenging to forecast and is characterized by prominent and robust large-scale circulation features such as the African Easterly Jet North (AEJ-North) and Tropical Easterly Jet (TEJ). Assimilating Aeolus generally improves the prediction of zonal winds in both forecasting systems, especially for lead times above 24 h. These improvements are related to systematic differences in the representation of the two jets, with the AEJ-North weakened at its southern flank in the western Sahel in the ECMWF analysis, while no obvious systematic differences are seen in the DWD analysis. In addition, the TEJ core is weakened in the ECMWF analysis and strengthened on its southern edge in the DWD analysis. The regions where the influence of Aeolus on the analysis is greatest correspond to the Intertropical Convergence Zone (ITCZ) region for ECMWF and generally the upper troposphere for DWD. In addition, we show the presence of an altitude- and orbit-dependent bias in the Rayleigh-clear channel, which causes the zonal winds to speed up and slow down diurnally. Applying a temperature-dependent bias correction to this channel contributes to a more accurate representation of the diurnal cycle and improved prediction of the WAM winds. These improvements are encouraging for future investigations of the influence of Aeolus data on African Easterly Waves and associated Mesoscale Convective Systems.
AB - Aeolus is the first satellite mission to acquire vertical profiles of horizontal line-of-sight winds globally and thus fills an important gap in the Global Observing System, most notably in the Tropics. This study explores the impact of this dataset on analyses and forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) and Deutscher Wetterdienst (DWD), focusing specifically on the West African Monsoon (WAM) circulation during the boreal summers of 2019 and 2020. The WAM is notoriously challenging to forecast and is characterized by prominent and robust large-scale circulation features such as the African Easterly Jet North (AEJ-North) and Tropical Easterly Jet (TEJ). Assimilating Aeolus generally improves the prediction of zonal winds in both forecasting systems, especially for lead times above 24 h. These improvements are related to systematic differences in the representation of the two jets, with the AEJ-North weakened at its southern flank in the western Sahel in the ECMWF analysis, while no obvious systematic differences are seen in the DWD analysis. In addition, the TEJ core is weakened in the ECMWF analysis and strengthened on its southern edge in the DWD analysis. The regions where the influence of Aeolus on the analysis is greatest correspond to the Intertropical Convergence Zone (ITCZ) region for ECMWF and generally the upper troposphere for DWD. In addition, we show the presence of an altitude- and orbit-dependent bias in the Rayleigh-clear channel, which causes the zonal winds to speed up and slow down diurnally. Applying a temperature-dependent bias correction to this channel contributes to a more accurate representation of the diurnal cycle and improved prediction of the WAM winds. These improvements are encouraging for future investigations of the influence of Aeolus data on African Easterly Waves and associated Mesoscale Convective Systems.
KW - aeolus satellite
KW - African easterly jet
KW - data assimilation
KW - doppler wind lidar
KW - numerical weather prediction impact
KW - observing system experiments
KW - tropical easterly jet
UR - http://www.scopus.com/inward/record.url?scp=85150738628&partnerID=8YFLogxK
U2 - 10.1002/qj.4442
DO - 10.1002/qj.4442
M3 - Article
SN - 0035-9009
VL - 149
SP - 933
EP - 958
JO - Quarterly Journal of the Royal Meteorological Society
JF - Quarterly Journal of the Royal Meteorological Society
IS - 752
ER -