Borne, M.

Cress, A.

Fink, Andreas H.

Knippertz, P.

Rennie, M.

Weissmann, M.

English

KITopen

EGU21-9449https://doi.org/10.5194/egusphere-egu21-9449EGU General Assembly 2021© Author(s) 2022. This work is distributed underthe Creative Commons Attribution 4.0 License.The Impact of Aeolus wind observations on the West AfricanMonsoonMaurus Borne1, Peter Knippertz1, Martin Weissmann2, Michael Rennie3, and Alexander Cress41Institute of Meteorology and Climate Research - Department Troposphere Research (IMK-TRO), Karlsruher Institut fürTechnologie (KIT), Karlsruhe, Germany2Faculty of Earth Sciences, Geography and Astronomy, University of Vienna, Vienna, Austria3European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, United Kingdom4Deutscher Wetterdienst (DWD), Offenbach am Main, GermanyTropical Africa is characterized by the world-wide largest degree of mesoscale convectiveorganisation. During boreal summer, the wet phase of the West African Monsoon (WAM), themidlevel African easterly jet (AEJ) over the Sahel allows for the formation of synoptic-scale Africaneasterly waves (AEWs) with a maximum intensity close to the West African coast. AEWs interactwith convection and its mesoscale organization through modifications in humidity, temperatureand vertical wind shear, and often serve as initial disturbances for tropical cyclogenesis. Inaddition, rainfall can be modulated by other types of tropical waves such as Kelvin or mixedRossby gravity waves. Upper-tropospheric conditions are dominated by the Tropical Easterly Jet(TEJ), whose variability appears to be connected to convective activity. Overall, our quantitativeunderstanding of the WAM system is still limited. The observational network over the region issparse and rainfall forecasts with current Numerical Weather Prediction models are hardly betterthan climatology.The Aeolus satellite launched in 2018 offers a great opportunity to further investigate the WAMwith an unprecedented density of free-tropospheric wind data. Assimilating Aeolus windobservations in denial experiments using the current operational system of the European Centrefor Medium-Range Weather Forecasts (ECMWF) shows that the main circulation features of theWAM are greatly impacted: the AEJ and the TEJ are systematically weaker and stronger respectivelyby~1m/s in the analysis fields including Aeolus data. As a consequence AEWs also show aweakening in the propagation amplitude. We are currently investigating the contributions of theHLOS (horizontal line-of-sight) Rayleigh and Mie wind observations to these observed differences.Mie observations (i.e., those related to backscatter from hydrometeors and aerosol particles)seems to contribute strongly to the difference in the AEJ, which lies within a convectively activeregion with a high aerosol load. On the other hand, the difference seen in the TEJ appears tooriginate mostly in the Rayleigh (i.e., clear air) observations. Surprisingly, the ascending anddescending HLOS observations contribute differently to the data impact, possibly revealing aremaining bias or model problems with the diurnal cycle. Future work will include systematiccomparisons between the operational systems of DWD and ECMWF to understand the influence ofdifferent data assimilation approaches as well as the impact on forecasts.Powered by TCPDF (www.tcpdf.org)

The Impact of Aeolus wind observations on the West African Monsoon

https://publikationen.bibliothek.kit.edu/1000142007/141031463

The Impact of Aeolus wind observations on the West African Monsoon

Abstract

Similar works

Full text

Available Versions

KITopen