Contributions from the DISC to accomplish the Aeolus mission objectives

The Aeolus Data Innovation and Science Cluster (DISC) supports the Aeolus mission with a wide range of activities from instrument and product quality monitoring over retrieval algorithm improvements to numerical weather prediction (NWP) impact assessments for wind and aerosols. The Aeolus DISC provides support to ESA, Cal/Val teams, numerical weather prediction (NWP) centers, and scientific users for instrument special operations and calibration, for the re-processing of Aeolus products from the past and through the provision of bi-annual updates of the L1A, L1B, L2A and L2B operational processors. The Aeolus DISC is coordinated by DLR with partners from ECMWF, KNMI, Météo-France, TROPOS, DoRIT, ABB, s&t, serco, OLA, Physics Solutions, IB Reissig and Les Myriades involving more than 40 scientists and engineers. The presentation will highlight the Aeolus DISC activities with a focus for the year 2021 and early 2022 since the last Aeolus workshop in November 2020. This covers the evolution of the instrument performance including investigations of the cause of the on-going signal loss and the achieved improvement via dedicated laser tests in 2021. In addition, refinements of algorithms and correction of the wind bias will be discussed - including a known remaining seasonal bias in October and March as encountered during the re-processing campaigns. Finally, the strategy for the on-going and future re-processing campaigns will be addressed to inform the scientific community about the availability and quality of the re-processed data products. The Aeolus mission has fully achieved its mission objectives including the unprecedented demonstration of direct-detection Doppler wind lidar technology and high-power laser operation in space in the ultraviolet spectral region over its planned full mission lifetime of 3 years and 3 months. Aeolus wind products have clearly demonstrated positive impact on forecasts using several NWP models. Since early 2020, and thus only 1.5 years after launch, the Aeolus wind products are used in operation at various NWP centers worldwide. This was achieved even despite the larger than expected wind random errors due to lower initial atmospheric signal levels and the observed signal losses during the operation of the first and second laser. In addition to this incredible success, first scientific studies demonstrated the use of Aeolus for atmospheric dynamics research in the stratosphere and for the analysis of aerosol transport. These achievements of the Aeolus mission and its success were only possible with the essential and critical contributions from the Aeolus DISC. This demonstrates the need and potential for setting up such scientific consortia covering a wide range of expertise from instrument, processors, and scientific use of products for Earth Explorer type missions. The invaluable experience gained by the Aeolus DISC during the more then 3 years of Aeolus mission in orbit (preceded by a period of 20 years before launch by a similar study team) is a pre-requisite for a successful preparation of an operational follow-on Aeolus-2 mission

Polar Stratospheric Clouds in Aeolus optical products as gravity wave tracers in the early polar winters

The first Doppler Wind Lidar in space is the European Space Agency’s Earth Explorer Aeolus, launched in 2018: it has been measuring for more than 3 years wind profiles on a global scale, exceeding its expected lifetime. The mission successfully demonstrated that wind profiles obtained by a spaceborne DWL are of great benefit for Numerical Weather Prediction models improvement. Aeolus retrieves wind by measuring the Doppler shift in the laser beam reflected by a molecule or aerosol particle. The satellite is equipped with a single payload able to deliver near-realtime collocated profiles of wind and optical products. This thesis aims to highlight the unique opportunity that Aeolus products entail in the study of the dynamical aspects of cloud formation. Especially suited for this kind of study are Polar Stratospheric Clouds (PSCs), which have been observed from space as soon as the satellite era begun due to their important role in the ozone hole chemistry. Many studies show that Gravity Waves are an important trigger for PSC formation, especially in the early winter. In fact, in order to form, PSCs require very low temperatures, as low as −80◦ C, to condense the little water vapor present in the polar stratosphere. These temperatures occur every year over the South Pole, yet when these temperatures are just approach, GW-induced temperature perturbations become relevant as they may trigger PSC formation whereas synoptic scale temperatures would not allow it. Gravity waves are crucial in the climate system as they redistribute energy in the form of momentum, driving winds and weather patterns. Gravity waves are a small-scale perturbation due to vertical forcing of the main air flow. As such, they can arise from a variety of phenomena such as orographic lifting, tropospheric deep convection but also breaking of a planetary wave. There is a joint effort in building a Gravity Wave climatology, which would improve our ability to predict weather and climate patterns. This has mostly focused on well know hostspot of gravity wave activity. The objective of this thesis is to test weather PSCs can be characterized with a GW from a spaceborne simultaneous measure of cloud and wind profile. The focus of the present work is twofold: first to create a PSC climatology and validate it with previous studies, second to test whether the sensed PSCs can be characterized as GW- or non-GW-induced, by looking at the wind field perturbations. To achieve such goal I created a PSC Mask product, by handling the backscatter products with a filtering routine. The filtering is based on a backscatter threshold, geographical selection and altitude selection. This filtering tool produced a good agreement with an existing PSC Mask product developed for the CALIPSO satellite lidar. This validation was quite relevant since CALIPSO lidar is meant to be measuring clouds. A quantitative analysis of Aeolus PSC detection ability is carried out, based on a seasonal occurrence frequency

Contributions from the DISC to the Aeolus Mission in 2022 and 2023

The Aeolus Data Innovation and Science Cluster (DISC) supports the Aeolus mission with a wide range of activities from instrument and product quality monitoring over retrieval algorithm improvements to numerical weather prediction (NWP) impact assessments for wind and aerosol forecasts. The Aeolus DISC provides support to ESA, Cal/Val teams, numerical weather prediction (NWP) centers, and scientific users for instrument special operations and calibration, for the re-processing of Aeolus products and through the provision of bi-annual updates of the L1A, L1B, L2A and L2B operational processors. The Aeolus DISC is coordinated by DLR with partners from ECMWF, KNMI, Météo-France, TROPOS, DoRIT, ABB, s&t, serco, OLA, Physics Solutions, IB Reissig and Les Myriades involving more than 40 scientists and engineers. The presentation will highlight the Aeolus DISC activities with a focus for the year 2022 and early 2023 since the last Aeolus workshop in Taormina, Italy during April 2022. This covers the evolution of the instrument performance including the significantly enhanced performance wrt. signal levels and random errors since the switch back to the flight model FM-A laser in October-November 2022. In addition, refinements of algorithms and processor updates will be outlined, which were introduced for the baseline B15 (13 September 2022) and B16 (expected to be released in spring 2023). A summary of the quality for the 3rd re-processing campaign for initial FM-A data (September 2018 - June 2019) will be give and an outlook to the 4th re-processing campaign covering the complete Aeolus mission. An outlook will also introduce some of the planned instrument activities in summer 2023 at the end of the expected mission lifetime of Aeolus. The Aeolus mission has fully achieved its mission objectives including the unprecedented demonstration of direct-detection Doppler wind lidar technology and high-power laser operation in space in the ultraviolet spectral region for more than 4 ½ years up to now - exceeding the planned mission lifetime of 3 years and 3 months. Aeolus wind products have clearly demonstrated positive impact on forecasts using several NWP models. Since early 2020, and thus only 1.5 years after launch, the Aeolus wind products were used in operation at ECMWF and at various NWP centers worldwide. This incredible success of Aeolus paved the way for the decision taken by the member states of ESA in November 2022 on the way forward of an operational follow-on wind lidar mission. These achievements of the Aeolus mission and its success were only possible with the essential and critical contributions from the Aeolus DISC. This demonstrates the need and potential for setting up such scientific consortia covering a wide range of expertise from instrument, processors, and scientific use of products for Earth Explorer type missions. The invaluable experience gained by the Aeolus DISC during the more than 4 years of Aeolus mission in orbit (preceded by a period of 20 years before launch by a similar study team) is a pre-requisite for the successful preparation of an operational follow-on wind lidar mission planned within the EUMETSAT Polar System (EPS) program