Sensitivity of Aeolus HLOS winds to temperature and pressure specification in the L2B processor

Matic Šavli,Vivien Pourret,Jean-François Mahfouf,Christophe Payan

doi:10.5194/amt-14-4721-2021

Abstract

Abstract. The retrieval of wind from the first Doppler wind lidar of European Space Agency (ESA) launched in space in August 2018 is based on a series of corrections necessary to provide observations of a quality useful for numerical weather prediction (NWP). In this paper we examine the properties of the Rayleigh–Brillouin correction necessary for the retrieval of horizontal line-of-sight wind (HLOS) from a Fabry–Pérot interferometer. This correction is taking into account the atmospheric stratification, namely temperature and pressure information that are provided by a NWP model as suggested prior to launch. The main goal of the study is to evaluate the impact of errors in simulated atmospheric temperature and pressure information on the HLOS sensitivity by comparing the Integrated Forecast System (IFS) and Action de Recherche Petite Echelle Grande Echelle (ARPEGE) global model temperature and pressure short-term forecasts collocated with the Aeolus orbit. These errors are currently not taken into account in the computation of the HLOS error estimate since its contribution is believed to be small. This study largely confirms this statement to be a valid assumption, although it also shows that model errors could locally (i.e. jet-stream regions, below 700 hPa over both earth poles and in stratosphere) be significant. For future Aeolus follow-on missions this study suggests considering realistic estimations of errors in the HLOS retrieval algorithms, since this will lead to an improved estimation of the Rayleigh–Brillouin sensitivity uncertainty contributing to the HLOS error estimate and better exploitation of space lidar winds in NWP systems.

Highlights

The European Space Agency (ESA)’s Aeolus wind satellite was launched on 22 August 2018
Despite the relatively large observation errors of the Aeolus wind observations compared to radiosondes or airborne lidar wind observations (e.g. Witschas et al, 2020; Martin et al, 2021), a list of OSEs provided by various global and regional models showed a significant impact on the numerical weather prediction (NWP; Aeolus CAL/VAL workshop: https://nikal.eventsair.com/QuickEventWebsitePortal/ 2nd-aeolus-post-launch-calval-and-science-workshop/ aeolus, last access: 17 May 2021) such as was suggested by several pre-launch studies
The variability shown by the two percentiles is mostly induced by the fact that inside each bin horizontal line-of-sight wind (HLOS) wind velocity varies by 10 m s−1 and is less effected by the fact that atmospheric conditions, i.e. temperature and pressure, vary significantly over the same range bin

Summary

Introduction

Aeolus is one of the Earth Explorer missions proposed by ESA as a demonstration paving the way towards measuring wind from space globally (Stoffelen et al, 2005). In this view the continuous effort to better understand and to improve the wind retrieval has been undertaken by ESA, Aeolus Data Innovation and Science Cluster (DISC), and Aeolus CAL/VAL teams since launch. An increasing effort is undertaken to better understand the various sources of observation errors. Such is a systematic error arising due to a so-called dark current signal anomalies of single accumulation charge-coupled device (ACCD) pixels Despite the relatively large observation errors of the Aeolus wind observations compared to radiosondes or airborne lidar wind observations (e.g. Witschas et al, 2020; Martin et al, 2021), a list of OSEs (observation system experiments) provided by various global and regional models showed a significant impact on the numerical weather prediction (NWP; Aeolus CAL/VAL workshop: https://nikal.eventsair.com/QuickEventWebsitePortal/ 2nd-aeolus-post-launch-calval-and-science-workshop/ aeolus, last access: 17 May 2021) such as was suggested by several pre-launch studies

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Conclusion