Aeolus

We will provide an independent and credible measurement of radial wind speed, wind profile, 3D wind vector, aerosol-backscattering ratio (Rb), aerosol extinction coefficient, extinction-to-backscatter (Sa) ratio (limited in the atmospheric boundary layer and troposphere), sea surface wind vectors using the Mobile Doppler wind lidar / HSRL (High Spectral Resolution Lidar) with an iodine filter during ADM-ADM-Aeolus and EarthCARE overpass the lidar site. Aerosol-backscattering ratio (Rb), aerosol extinction coefficient, extinction-to-backscatter (Sa) ratio and cloud base height is also available using Multi-wavelength Raman-Polarization lidar. The ground-based lidars located in Qingdao and Beijing can probe the typical coastal and continental atmospheric environment respectively. The wind profile and sea surface wind vector can be provided by a coherent Doppler lidar in China Sea occasionally if the voyage is available. In addition to the lidar observations, wind profiles and other relevant meteorological data from radiosonde could also be provided. These results can be compared with the data products of ADM-Aeolus and EarthCARE, and we will analyze the comparison results and present assessment reports to ESA.

The ESA’s ADM-Aeolus mission is designed to fly, for the first time in space, a High Spectral Resolution Doppler Lidar operating at Ultra Violet laser wavelength 355 nm. The high spectral resolution means that two interferometers are used in order to separate the backscattered signals by air molecules from the one by particles.  Provided the system is carefully calibrated, both the co-polar backscatter coefficient and the extinction coefficient can be retrieved without any a priori assumption on the aerosol type. Usual elastic backscatter lidar retrievals that rely on a climatological value of the BER (backscatter-to-extinction ratio) suffer from large uncertainties due to the dependence of the BER on many parameters such as the composition of particle mixture, particle size, shape, orientation and refractive index. On the contrary, the Aeolus mission will provide unambiguous solutions of aerosol properties. With a launch scheduled in 2017, ADM-Aeolus has also the potential to fill in the gap between the CALIPSO and EarthCare missions.

The L2A processor has been developed to provide the scientific communities with aerosol profiles derived from the backscattered signals: backscatter coefficient, extinction coefficient, scattering ratio, backscatter-to-extinction ratio and local optical depth. The L2A is made of three main modules . The first one, called SCA, retrieves the aerosol properties using the pure particulate and molecular signals derived from the signals received in both interferometers : the Fabry-Perot (Rayleigh channel) for molecules and the Fizeau (Mie channel) for particles. The second one, called the MCA, uses a climatological value of the BER to retrieve the aerosol properties in case the Mie channel could not be used. Finally, the feature finder, aims at improving the horizontal resolution of the L2A by retrieving the aerosol properties at a smaller horizontal scale by identifying similar aerosol or cloud features between different lidar measurements. The feature finder is still under development and is very challenging due to the small laser energy (80 mJ).

In this presentation, the different components of the L2A processor will be presented as well as the algorithms and the different aerosol products. Typical example of aerosol retrievals in the case of simple simulated atmospheric scenarios and more complex scenes observed during the NASA’s LITE (Lidar In-space Technology Experiment) experiment will be shown. From these retrievals, the potential and limitation of ADM-Aeolus will be discussed.

The Atmospheric Dynamics Mission (ADM-Aeolus) is an ESA Earth Explorer Core Mission. The mission shall demonstrate the potential of high spectral resolution Doppler Wind lidars for operational measurements of wind profiles and their use in Numerical Weather Prediction (NWP). The Aeolus wind profile measurements are horizontally projected line-of-sight winds (close to the u wind component during most of the orbit) from the surface to 30 km, with a vertical resolution from 500 m (planetary boundary layer) to 2 km (stratosphere). The horizontal along-track observation size is 87 km. The measurements are provided in clear air (molecular channel), through optically thin aerosol and cloud layers and at the top of optically thick clouds (particle channel). Spin-off products are profiles of co-polar backscatter and extinction coefficients.

Aeolus carries the novel Doppler Wind lidar instrument ALADIN. Recently the two ALADIN laser transmitters were qualified and delivered for further instrument integration. The instrument delivery and satellite qualification will follow in 2016, and launch readiness is scheduled for first quarter 2017.

The expected impact of Aeolus observations on NWP has been investigated in a number of studies, all demonstrating significant forecast impact especially in the tropics, over the oceans and in the upper troposphere. These areas are currently poorly sampled by direct wind observation systems, and are therefore less well constrained in state-of-the-art models. Furthermore, the interaction between atmospheric circulation and low level cloud formation is a growing area of research both in NWP and climate modelling. Aeolus Near-Real-Time (NRT) delivery of backscatter and extinction profiles is also of great interest to the air quality community.

An Announcement of Opportunity (AO) call for calibration and validation (CAL/VAL) and the first Aeolus CAL/VAL workshop have been held in preparation of launch. The large range of international CAL/VAL activities have been mapped and linked in the so-called CAL/VAL Implementation Plan, which is the hand-book for mission and product quality assessment after launch. Furthermore, airborne pre-launch campaigns have been performed, exercising amongst others formation flying, satellite under-flights, calibration procedures, and data processing aspects.

The Aeolus mission, its status and launch preparation activities will be presented together with the Aeolus products and their impact and use in NWP and troposphere and lower stratosphere research. A brief overview of the pre-launch campaigns and planned CAL/VAL activities will also be presented.

The mesoscale models for numerical weather prediction (NWP) in Europe have reached the horizontal resolution close to 1 km. A large resolution increase in the last decade has not been followed by the increase in number of observations to initialize the models. In particular, there is a large need for direct wind observations as well as for the humidity data in order to improve mesoscale analyses.

In this presentation we discuss the initial value problem on mesoscale and the potential impact of the space-borne Doppler wind lidar (DWL) observations expected from the ESA ADM-Aeolus mission. The ADM-Aeolus DWL measurements will provide wind profiles along the horizontal line of sight (HLOS). Their successful application needs to  involve the data assimilation to reconstruct the wind vectors. Several studies addressed the potential impact of ADM-Aeolus winds but they exclusively focused on the global NWP and they applied the variational assimilation framework.

The present study applies the limited-area Weather Research and Forecasting model and the ensemble adjustment Kalman filter (DART/WRF) over a Euro-Atlantic domain. We focus on the potential of DWL HLOS winds to improve the state estimate in the early stage of baroclinic development over the northern Atlantic. In particular, we evaluate the impact of the flow-dependent background-error covariances on the uncertainty of analyzed winds and the added value of  the HLOS profiles.

With the ADM-Aeolus launch planned for 2017, the applied framework is that of the observing system assimilation experiment (OSSE) with nature run simulated by the high-resolution ECMWF simulation. The assimilated HLOS wind profiles are prepared by the chain of processors used to retrieve the ADM-Aeolus winds. This is then used for the ensemble data assimilation with the DART/WRF system. We show that HLOS winds with expected error characteristics provide anaysis increments similar to that of the wind vector profiles.

ESA met many challenges in developing the space hardware to obtain, for the first time, wind profile information from space and is now ready for a launch in 2017. The mission cal/val and processing and monitoring in the ground segment will be discussed. The presentation will further discuss processing near clouds and optimal spatial sampling and processing of the Aeolus data for the benefit of meteorological analyses. Global, but also regional NWP users will be able to use the data, due to the development of a fast processing track. NWP centres will assimilate these wind data into numerical prediction models and the key output will be improved weather forecasts and a better understanding of atmospheric dynamics to the benefit of climate research. Moreover, vertically-resolved clouds and aerosol Level 2 data products will be generated, providing continuity to a series of space-borne lidar missions (CALIPSO, CATS, EarthCare). Based on recent studies, expectations from the Aeolus atmospheric dynamics mission, instrument measurements and applications will be presented at the symposium.

Acknowledgements

This presentation is supported by the ESA Aeolus mission team, the Aeolus Mission Advisory Group and Aeolus project collegues to whom the author is very grateful.