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In January and February 2020, the joint EUREC4A/ATOMIC field campaign took place in the Tropical Atlantic near Barbados, with the goal to advance our understanding of the interplay between clouds, convection and circulation including their role in climate change. Within the scope of this campaign, several unique satellite-based datasets have been collected, including very high-spatial resolution multispectral images with 10x10m² pixel size acquired by polar-orbiting Copernicus Sentinel-2 satellites. In this presentation, the first analysis of these high-resolution observations focused on tropical trade cumuli is given. This cloud type is characterized by small-scale spatiotemporal variability that is unresolved at the spatial resolution of current meteorological satellite imagers.Using the high-resolution Sentinel-2 observations, we will show the clouds can be considered as individual objects with associated properties, such as shape and size parameters, but also their mean radiative properties. A novel technique will be presented for deriving cloud height from Sentinel-2 observations, which exploits the geometric relationship between cloud objects and their shadows. Furthermore, the cloud fraction and cloud size distribution are calculated for various trade cumulus scenes. The uncertainties arising from choices in our cloud detection scheme will be discussed.We show that a substantial fraction of clouds has equivalent diameters below the pixel size of commonly used meteorological satellite instruments. Consequently, and consistent with previous studies, the cloud size distribution and domain-average cloud fraction from coarse-resolution satellite imagers are shown to be biased and highly sensitive to pixel resolution. In addition, a large fraction of pixels identified as cloudy contains significant clear-sky contributions, and it is no longer possible to characterize clouds as objects. We will discuss how this affects the accuracy of cloud property determination and biases estimates of cloud radiative forcing.

In the framework of the Joint Aeolus Tropical Atlantic Campaign (JATAC), a temporary ground-based ACTRIS aerosol remote sensing station has been setup by TROPOS at the Ocean Science Center Mindelo (OSCM) in June 2021. The instrumental capabilities for aerosol profiling at the OSCM comprise a multiwavelength-Raman-polarization lidar Polly XT and an AERONET sun photometer. Furthermore, a scanning HALO photonics Doppler lidar is utilized to study the dynamics near the observational site. Continuous 24/7 observations have been performed since June 2021, thus covering the four intensive observational periods of JATAC (July 2021, September 2021, June 2022, September 2022).In this presentation, we want to discuss the capabilities of Aeolus to observe the aerosol conditions including the Saharan dust layer (SAL) above the Cabo Verdean islands. The time series of the ground-based PollyXT lidar from June 2021 until today has shown, that dust is omnipresent above the local boundary layer in the summer months. The maximum dust layer top height has been observed in July with 7 km. The SAL top height has then decreased to 3 km in November. Some rainy periods were observed in September/October, especially in the year 2022 for the fourth intensive JATAC campaign.We will utilize the direct Aeolus overpasses over Mindelo each Friday during these four periods (and for other seasons) to make a long(er)-term assessment of the Aeolus aerosol capabilities (L2A) involving also products from the most recent algorithm versions (Baselines). Due to the capabilities of the ground-based PollyXT lidar, we can directly compare the 2 main products of Aeolus: The extinction coefficient and the co-polar backscatter coefficient. Doing so, we can also quantify the influence of the missing polarization component in the Aeolus aerosol products which is important for the planning of the potential Aeolus follow-on mission, for which the polarization capabilities are still under discussion.Finally, the lessons learnt from the current Aeolus Cal/Val on Cabo Verde can be also used for the upcoming EarthCARE mission as TROPOS has started to setup a permanent ACTRIS aerosol and cloud remote sensing supersite at Mindelo.

The Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) is the combination of multiple active and passive instruments on a single platform. The Atmospheric Lidar (ATLID) provides vertical information of clouds and aerosol particles along the satellite track. In addition, the Multi-Spectral Imager (MSI) collects the multispectral information from the visible till the infrared wavelengths over a swath width of 150 km across the track. The ATLID–MSI Column Products processor (AM-COL) described in this paper combines the high vertical resolution of the lidar along track and the horizontal resolution of the imager across track to better characterize the 3-dimensional scene. ATLID Level 2a (L2a) data from the ATLID Layer Products processor (A-LAY) and MSI L2a data from the MSI Cloud Products processor (M-CLD) and the MSI Aerosol Optical Thickness processor (M-AOT) as well as MSI Level 1c (L1c) data are used as input to produce the synergistic columnar products: the ATLID–MSI Cloud Top Height (AM-CTH) and the ATLID–MSI Aerosol Column Descriptor (AM-ACD). The coupling of ATLID (measuring at 355 nm) and MSI (at ≥ 670 nm) provides multispectral observations of the aerosol properties. Especially, the Ångström exponent from the spectral aerosol optical thickness (AOT 355 nm/670 nm) adds valuable information for aerosol typing. The AOT across track, the Ångström exponent and the dominant aerosol type are stored in the AM-ACD product. The accurate detection of the Cloud Top Height (CTH) with lidar is limited to the ATLID track. The difference of the CTH detected by ATLID and MSI is calculated along track. The similarity of MSI pixels across track with those along track is used to transfer the calculated CTH difference to the entire MSI swath. In this way, the accuracy of the CTH is increased to achieve the EarthCARE mission goal aiming to derive the radiative flux at the top of the atmosphere with an accuracy of 10 Wm−2 for a 100 km2 snapshot view of the atmosphere. The synergistic CTH difference is stored in the AM-CTH product. The quality status depending on day/night conditions or the presence of multiple cloud or aerosol layers is provided with the products. The algorithm was successfully tested using the common EarthCARE test scenes. Two definitions of the CTH from the model-truth cloud extinction fields are compared: An extinction-based threshold of 20 Mm−1 provides the geometric CTH and a cloud-optical-thickness threshold of 0.25 describes the radiative CTH. The first one is detected with ATLID, the second one with MSI.

ESA’s Cloud, Aerosol and Radiation Explorer EarthCARE is the first mission which will provide measurements from active profiling, passive imaging and a broad-band radiometer from a single satellite platform. The passive multi-spectral imager (MSI) features four solar and three thermal infrared channels, and has a swath of 150 km and a spatial pixel resolution of 500 m. The MSI observations will provide across-track information on clouds and aerosol to extend the active profiling information into the swath. In this paper, we present the algorithm used for retrieving the cloud optical and physical products (M-COP), specifically cloud optical thickness, effective radius and top height. The algorithm is based on the solar and terrestrial MSI channels within an optimal estimation framework. The advantage of optimal estimation is that it enables full error propagation given by the uncertainties in measurements and a-priori information. The MSI cloud algorithm has been successfully exercised on different imagers and on synthetically generated MSI observations.

The EarthCARE satellite mission will provide new insights into aerosol-cloud and radiation interactions by means of synergistic observations of the Earth's atmosphere from a collection of active and passive remote sensing instruments, flying on a single satellite platform. The Multi-Spectral Imager (MSI) will provide visible and infrared images in the cross-track direction with a 150 km swath and a pixel sampling at 500 m. The suite of MSI cloud algorithms will deliver cloud macro- and micro-physical properties complementary to the vertical profiles measured from the ATmospheric LIDar (ATLID) and the Cloud Profiling Radar (CPR) instruments. The MSI cloud mask algorithm (M-CM) provides a cloud flag, cloud phase and cloud type product which are essential parameters for the cloud optical and physical properties (M-COP) as well as for the aerosol optical properties (M-AOT). Synthetic test scenes from the EarthCARE end-to-end simulator provide a first overview of the expected performance of the M-CM products before launch. Validation of the MSI cloud mask algorithm against satellite products from MSG SEVIRI and MODIS demonstrates a good performance of the algorithm. The MSI cloud detection performance is not completely aligned with that from MODIS, which is however not surprising when considering the rather limited number of spectral channels of MSI in comparison to MODIS. The direct comparison to MODIS shows that some threshold tuning should be done especially over desert or sun glint regions once real observations are available. However the MSI bands are less affected by sun glint because of the asymmetric view of the imager.

Seit bereits mehr als drei Jahren liefert der einzigartige Windsatellit Aeolus vertikale Profile der zonalen Windgeschwindigkeit auf globaler Skala. Der im August 2018 gestartete ESA-Satellit trägt das weltweit erste Doppler Windlidar (ALADIN) im All und misst damit Windgeschwindigkeiten von 30 km Höhe bis zum Wolkenoberrand, in wolkenfreier Atmosphäre sogar bis zum Boden. Verschiedene Referenzmessungen vom Boden, Flugzeug, Schiff oder Ballon sowie Vergleiche mit Modelldaten deuten auf eine hohe Qualität der Windprofile hin. Die Windmessungen werden in Rayleigh (in wolkenfreier Atmosphäre) und Mie (an Wolken und Aerosolen) unterteilt. Seit Anfang 2019 werden die Windmessungen von Aeolus an verschiedenen Wettervorhersagezentren assimiliert und konnten dabei positive Einflüsse auf die Qualität der Wettervorhersage bewirken. Windfelder am Wolkenoberrand werden vorwiegend von geostationären Satelliten abgeleitet und liefern einen wichtigen Beitrag zum globalen Beobachtungssystem. Diese Windfelder beruhen auf passiver Satellitenfernerkundung und weisen erhebliche Unsicherheit in ihrer Höhenbestimmung auf. Aktive Windmessungen von Aeolus können dazu beitragen, diese Unsicherheiten zu quantifizieren. Auch wenn Aeolus‘ Alleinstellungsmerkmal die Messung von Windprofilen in wolkenfreier Troposphäre darstellt, liefert er wertvolle Informationen vom Wolkenoberrand.Der vorliegende Beitrag vergleicht Windmessungen von Aeolus am Wolkenoberrand mit kollokierten Windfeldern von Meteosat SEVIRI. Unterschiede bei der abgeleiteten Höheninformation der Windvektoren am Wolkenoberrand werden in Hinblick auf die verschiedenen Messmethoden diskutiert. Ein besonderes Augenmerk der Studie liegt auf einer zweiwöchigen Periode im November 2019, in welcher die Vertikalauflösung der gemessenen Profile von Aeolus speziell für Vergleiche mit Wolkenwindfeldern angepasst wurde, um deren Höhenzuordnung zu validieren. Zusätzlich zur Wind- und Höheninformation von Wolken werden auch deren optische und mikrophysikalische Eigenschaften analysiert. Abschließend werden die Limitierungen beider Methoden diskutiert.

Der ESA-Satellit Aeolus wurde im August 2018 mit dem Ziel gestartet, durch globale Messungen von Windprofilen die Wettervorhersage zu verbessern. Dazu hat Aeolus das High-Spectral-Resolution (HSR) Doppler-Lidar ALADIN (Atmospheric Laser Doppler Instrument) an Bord, welches es ermöglicht, vertikale Profile einer Windkomponente (West-Ost) aktiv zu messen. Diese Messungen werden inzwischen von mehreren Wetterdiensten assimiliert und es konnte ein positiver Einfluss auf die Vorhersagen gezeigt werden. Zusätzlich zu den Windprofilen können mit diesem Lidar auch Aerosol- und Wolkenprofile als Nebenprodukte gemessen werden. Es ist das erste Mal, dass so eine komplexe Technik vom Weltall aus zum Einsatz kommt und bedarf daher einer ausgiebigen Validierung.Ein wichtiger Beitrag zur Validierung der Wind- und Aerosolprodukte von Aeolus wurde dabei in dem Kooperationsprojekt EVAA (Experimentelle Validierung und Assimilation von Aeolus-Beobachtungen) zwischen der Ludwig-Maximilians-Universität München, dem deutschen Zentrum für Luft- und Raumfahrt (DLR), dem Deutschen Wetterdienst (DWD) sowie dem Leibniz-Institut für Troposphärenforschung (TROPOS) geleistet. Anhand von bodengebundenen Wind- und Aerosol-Referenzmessungen als auch durch Radiosonden, konnten wichtige Erkenntnisse über den zeitlichen Verlauf sowie die Charakteristik des systematischen und zufälligen Fehlers der Aeolus-Beobachtungen gewonnen werden. Durch die Assimilation der Aeolus-Messungen im Wettermodell ICON des DWD, konnte ihr Einfluss auf die Wettervorhersage quantifiziert werden.In diesem Beitrag wollen wir die Ergebnisse von unseren Langzeit-Vergleichsmessungen mit Radiosonden in Leipzig, Punta Arenas (Chile) und Radar-Windprofilern über Deutschland präsentieren und das Potential und die Grenzen von Aeolus diskutieren. Um die Verbesserung der Wettervorhersage durch die neuartigen Windbeobachtungen zu quantifizieren, wird ihr Einfluss im Wettermodell ICON demonstriert.Zusätzlich werden wir einen Einblick in die Möglichkeiten der Aerosolprofilmessungen von Aeolus gegeben. Dazu wird als Beispiel der Transport von Rauchaerosol von den Bränden in Kalifornien im Jahre 2020 bis nach Mitteleuropa diskutiert. Damals waren große Mengen Rauch über Leipzig gemessen wurden, die für eine sichtliche Abschwächung des Sonnenlichts sorgten. Diese Rauchschwaden konnten sowohl von Aeolus als auch mit einem bodengebundenen Forschungslidar, genannt PollyXT, beobachtet werden und sind daher ein hervorragendes Beispiel, um die Potentiale von Aeolus bzgl. Aerosol- und Wolkenmessungen zu diskutieren.

The Data Innovation and Science Cluster (DISC) is a core element of ESA's data quality strategy for the Aeolus mission, which was launched in August 2018. Aeolus provides for the first-time global observations of vertical profiles of horizontal wind information by using the first Doppler wind lidar in space. The Aeolus DISC is responsible for monitoring and improving the quality of the Aeolus aerosol and wind products, for the upgrade of the operational processors as well as for impact studies and support of data usage. It has been responsible for multiple significant processor upgrades which reduced the systematic error of the Aeolus observations drastically. Only due to the efforts of the Aeolus DISC team members prior to and after launch, the systematic error of the Aeolus wind products could be reduced to a global average below 1 m/s which was an important pre-requisite for making the data available to the public in May 2020 and for its use in operational weather prediction. In 2020, the reprocessing of earlier acquired Aeolus data, another important task of the Aeolus DISC, also started. In this way, also observations from June to December 2019 with significantly better quality could be made available to the public, and more data will follow this and next year. Without the thorough preparations and close collaboration between ESA and the Aeolus DISC over the past decade, many of these achievements would not have been possible.

The European Space Agency's (ESA) wind mission, Aeolus, hosts the first space-based Doppler Wind Lidar (DWL) world-wide. Its scientific objectives are to improve weather forecasts and to advance the understanding of atmospheric dynamics and its interaction with the atmospheric energy and water cycle. The primary data product is profiles of horizontally projected line-of-sight winds from the surface up to about 30 km, and spin-off products are profiles of cloud and aerosol optical properties. Aeolus was launched on 22 August 2018, and the Atmospheric LAser Doppler INstrument (ALADIN) switch-on was completed with first high energy output in wind mode on 4 September 2018. The on-ground data processing facility worked excellent, allowing L2 product output in near-real-time (within 3 hours of sensing) from the start of the mission. During the first 20 months in orbit, ESA, the Aeolus Data Innovation and Science Cluster (DISC), Aeolus calibration and validation (CAL/VAL) teams and industry worked on the instrument commissioning, calibration, validation and product improvements, leading to the public release of the Level 2B (L2B) wind product in May 2020. The Aeolus L2B wind data were then of such good quality that four weather centers started to use the product in their daily forecasts during 2020, and more have plans to follow in 2021. As of May 2020, the biases of the near-real-time data were on average close to the mission requirements, although the random errors were higher than expected due to lower than expected atmospheric return signal on orbit. Other issues encountered in-flight were for example drifts in the instrument alignment and nonoptimal telescope focus and temperature control, leading to drifts in the laser emitted output energy and/or internal and atmospheric path signal strength and long term evolutions on the wind product bias. A further issue encountered was a gradually increasing number of “hot pixels”, i.e. pixels with elevated background signals, appearing on the ALADIN ACCDs over time. Mitigation strategies for these issues arebeing implemented, or are considered for a potential follow-on mission. The Aeolus optical properties spin-off product (L2A) has been further improved after launch, including methods for improved aerosol and cloud backscatter discrimination. The product has been used to study smoke emissions, e.g. from the early 2020 Australian fires, and has been successfully experimentally assimilated in Copernicus Atmosphere Monitoring Service (CAMS) model C-IFS. After two and a half years in orbit, and despite of some performance issues related to the ALADIN instrument, Aeolus has already achieved most of its scientific objectives. Finally, the mission was recently extended until end 2022.

ESA supported airborne and ground-based campaigns constitute an essential element in the development and operation of satellite missions, providing the opportunity to test novel observation technologies, acquire representative data for the development of the mission concepts, processors and use cases, as well as in their calibration and validation phases once in orbit.For the Aeolus Doppler Wind Lidar satellite mission, ESA has implemented a campaign programme that started in 2007 and has continued beyond the launch of the mission on 22. August 2018. Building on the successful WindVal-I and –II campaigns with DLR’s A2D and 2µm Doppler Wind Lidar systems on-board the DLR Falcon aircraft, a number of validation campaigns have been successfully implemented: WindVal-III in November 2018, AVATAR-E in May 2019, and AVATAR-I in September 2019. In addition, ESA supported the CNES pre-Stratéole-2/TAPAPA campaign with eight stratospheric balloons having been launched from the Seychelles in November/December 2019 providing unique upper level wind data in the Tropics. The validation by stratospheric balloons has been extended in the frame of a collaboration with Loon LLC for a test case covering the months August and September 2019.As the largest impact of the Aeolus observations is expected in the Tropics, and in particular over the Tropical oceans, ESA, in close collaboration with NASA and European partners, is currently implementing a Tropical campaign in July 2021. With its base in Cape Verde the activity comprises both airborne and ground-based activities addressing the tropical winds and aerosol validation, as well as a wide range of science objectives. The location is unique as it allows the study of the Saharan Aerosol layer, African Easterly Waves and Jets, the Tropical Easterly Jet, as well as deep convection in ITCZ and tropical cyclogenesis, with a focus on the impact of Saharan dust on micro-physics in tropical cloud systems. The campaign builds on remote and in-situ observations from aircraft (DLR Falcon-20, the Safire Falcon-20, the NASA DC-8 and an Aerovizija/UNG light aircraft) and drone systems, as well as an extensive aerosol and cloud measurement programme with a range of lidar, radar and radiometer systems coordinated by NOA.This paper will provide a summary of the Aeolus campaign activities, focussing on the completed and planned post launch campaigns.

In September 2020, extremely strong wildfires in the western United States of America (i.e., mainly in California) produced large amounts of smoke, which was lifted into the free troposphere. These biomass‐burning‐aerosol (BBA) layers were transported from the US west coast toward central Europe within 3–4 days turning the sky milky and receiving high media attention. The present study characterizes this pronounced smoke plume above Leipzig, Germany, using a ground‐based multiwavelength‐Raman‐polarization lidar and the aerosol/cloud product of ESA’s wind lidar mission Aeolus. An exceptional high smoke‐AOT >0.4 was measured, yielding to a mean mass concentration of 8 μg m−3. The 355 nm lidar ratio was moderate at around 40–50 sr. The Aeolus‐derived backscatter, extinction and lidar ratio profiles agree well with the observations of the ground‐based lidar PollyXT considering the fact that Aeolus’ aerosol and cloud products are still preliminary and subject to ongoing algorithm improvements., Plain Language Summary: In September 2020, extremely strong wildfires in the western USA (i.e., mainly in California) produced large amounts of smoke. These biomass burning aerosol (BBA) layers were transported from the US west coast towards central Europe within 3‐4 days. This smoke plume was observed above Leipzig, Germany, for several days turning the sky milky and receiving high media attention ‐ it was the highest perturbation of the troposphere in terms of AOT ever observed over Leipzig. The first smoke plume arrived on 11 September 2020, just in time for a regular overpass of the Aeolus satellite of the European Space Agency (ESA). Aeolus accommodates the first instrument in space that actively measures profiles of a horizontal wind component in the troposphere and lower stratosphere. Aeolus has been launched to improve weather forecasts while assimilating the Aeolus wind profile data in near–real time. But Aeolus also delivers profiles of aerosol and cloud optical properties as spin‐off products. We performed a first assessment of the aerosol profiling capabilities of Aeolus while precisely analyzing the smoke plume above Leipzig with a ground‐based multiwavelength‐Raman‐polarization lidar. But we also show the dramatic impact of fires in the western USA on atmospheric conditions over central Europe., Key Points: Smoke from the extraordinary 2020 Californian wild fires traveled within 3–4 days toward Europe Highest Aerosol Optical Thickness ever measured in the free troposphere over Leipzig, Germany, Central Europe, with ground‐based lidar Unique opportunity for a first assessment of the aerosol optical profiles of the spaceborne wind lidar mission Aeolus, German Federal Ministry for Economic Affairs and Energy (BMWi), German Federal Ministry for Education and Research (BMBF), European Union’s Horizon 2020 Research and Innovation Program

The European Space Agency (ESA)’s wind mission, Aeolus, was launched on 22 August 2018. It is a member of the ESA Earth Explorer family and its main objective is to demonstrate the potential of Doppler wind Lidars in space for improving weather forecast and to understand the role of atmospheric dynamics in climate variability. Aeolus carries a single instrument called ALADIN: a high sophisticated spectral resolution Doppler wind Lidar which operates at 355 which is the first of its kind to be flown in space.Aeolus provides profiles of single horizontal line-of-sight winds (primary product) in near-real-time (NRT), and profiles of atmospheric backscatter and extinction. The instrument samples the atmosphere from about 30 km down to the Earth’s surface, or down to optically thick clouds. The required precision of the wind observations is 1-2.5 m/s in the troposphere and 3-5 m/s in the stratosphere while the systematic error requirement be less than 0.7 m/s. The mission spin-off product includes information about aerosol and cloud layers. The satellite flies in a polar dusk/dawn orbit (6 am/pm local time), providing ~16 orbits per 24 hours with an orbit repeat cycle of 7 days. Global scientific payload data acquisition is guaranteed with the combined usage of Svalbard and Troll X-band receiving stations.After almost three years in orbit and despite performance issues related to its instrument ALADIN, Aeolus has achieved most of its objectives. Positive impact on the weather forecast has been demonstrated by multiple NWP centres world-wide with four European meteorological centres now are assimilating Aeolus winds operationally. Other world-wide meteo centers wull start to assimilate data in 2021. The status of the Aeolus mission will be presented, including overall performance, planned operations and exploitation. Scope of the paper is also to inform about the programmatic highlights and future challenges.

The modification of an existing cloud property retrieval scheme for the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument on board the geostationary Meteosat satellites is described to utilize its high-resolution visible (HRV) channel for increasing the spatial resolution of its physical outputs. This results in products with a nadir spatial resolution of 1×1 km2 compared to the standard 3×3 km2 resolution offered by the narrowband channels. This improvement thus greatly reduces the resolution gap between current geostationary and polar-orbiting meteorological satellite imagers. In the first processing step, cloudiness is determined from the HRV observations by a threshold-based cloud masking algorithm. Subsequently, a linear model that links the 0.6 µm, 0.8 µm, and HRV reflectances provides a physical constraint to incorporate the spatial high-frequency component of the HRV observations into the retrieval of cloud optical depth. The implementation of the method is described, including the ancillary datasets used. It is demonstrated that the omission of high-frequency variations in the cloud-absorbing 1.6 µm channel results in comparatively large uncertainties in the retrieved cloud effective radius, likely due to the mismatch in channel resolutions. A newly developed downscaling scheme for the 1.6 µm reflectance is therefore applied to mitigate the effects of this scale mismatch. Benefits of the increased spatial resolution of the resulting SEVIRI products are demonstrated for three example applications: (i) for a convective cloud field, it is shown that significantly better agreement between the distributions of cloud optical depth retrieved from SEVIRI and from collocated MODIS observations is achieved. (ii) The temporal evolution of cloud properties for a growing convective storm at standard and HRV spatial resolutions are compared, illustrating an improved contrast in growth signatures resulting from the use of the HRV channel. (iii) An example of surface solar irradiance, determined from the retrieved cloud properties, is shown, for which the HRV channel helps to better capture the large spatiotemporal variability induced by convective clouds. These results suggest that incorporating the HRV channel into the retrieval has potential for improving Meteosat-based cloud products for several application domains.

Since 2007, a series of ESA supported airborne campaigns have been essential to the development of the Aeolus Doppler Wind Lidar satellite mission, which was successfully launched on 22 September 2018 and is providing a novel wind and aerosol profile data.A core element of the Aeolus Cal/Val activities is DLR’s A2D wind lidar on-board the DLR Falcon aircraft, an airborne demonstrator for the Aeolus ALADIN satellite instrument flown in combination with the 2-µm Doppler Wind Lidar reference system. Following the pre-launch WindVal-I and –II campaigns in 2015 and 2016, a number of calibration and validation campaigns have been successfully implemented: WindVal-III providing early Cal/Val results in November 2018 only three months after the Aeolus launch, AVATAR-E in May 2019 focussing on the Cal/Val over Central Europe, and AVATAR-I in September 2019 providing Cal/Val information in the North Atlantic and Arctic flying from Iceland.The airborne validation is also being supported through balloon flights in the tropical UTLS and lower stratosphere in the frame of the CNES Stratéole-2 stratospheric balloon activities. In the frame of the ESA supported pre-Stratéole-2 campaign, eight stratospheric balloons have been launched from the Seychelles in November/December 2019 providing unique upper level wind data for the Aeolus validation.The largest impact of the Aeolus observations is expected in the Tropics, and in particular over the Tropical oceans, where only a limited number of wind profile information is provided by ground based observations. Aeolus provides key direct measurements which are of importance to correctly constrain the wind fields in models. In addition, Aeolus observations have the potential to further enhance our current knowledge on aerosols and clouds by globally providing optical properties products that include atmospheric backscatter and extinction coefficient profiles, lidar ratio profiles and scene classification. In the tropics, a particularly interesting case is the outflow of Saharan dust and its impact on micro-physics in tropical cloud systems. The region off the coast of West Africa allows the study of the Saharan Aerosol layer, African Easterly Waves and Jets, Tropical Easterly Jet, as well as the deep convection in ITCZ. Together with international partners, ESA is currently implementing a Tropical campaign in July 2020 with its base in Cape Verde that comprises both airborne and ground-based activities addressing the tropical winds and aerosol validation, as well as science objectives. The airborne component includes the DLR Falcon-20 carrying the A2D and 2-µm Doppler Wind lidars, the NASA P-3 Orion with the DAWN and HALO lidar systems, the APR Ku-, Ka- and W-band Doppler radar and drop sondes, and a Slovenian small aircraft providing in-situ information from aethalometers, nephelometers and optical particle counters. The ground-based component led by the National Observatory of Athens is a collaboration of European teams providing aerosol and cloud measurements with a range of lidar, radar and radiometer systems, as well as a drone providing in-situ aerosol observations. In addition, the participation airborne capabilities by NOAA and LATMOS/Meteo France are currently being investigated.This paper will provide a summary of the Aeolus campaign focussing on the planned tropical

The European Space Agency (ESA)’s wind mission, Aeolus, was launched on 22 August 2018. Aeolus is a member of the ESA Earth Explorer family and its main objective is to demonstrate the potential of Doppler wind Lidars in space for improving weather forecast and to understand the role of atmospheric dynamics in climate variability. Aeolus carries a single instrument called ALADIN: a high sophisticated spectral resolution Doppler wind Lidar which operates at 355 which is the first of its kind to be flown in space. It provides profiles of single horizontal line-of-sight winds (primary product) in near-real-time (NRT), and profiles of atmospheric backscatter and extinction. The instrument samples the atmosphere from about 30 km down to the Earth’s surface, or down to optically thick clouds. The required precision of the wind observations is 1-2.5 m/s in the troposphere and 3-5 m/s in the stratosphere while the systematic error requirement be less than 0.7 m/s. The mission spin-off product includes information about aerosol and cloud layers. The satellite flies in a polar dusk/dawn orbit (6 am/pm local time), providing ~16 orbits per 24 hours with an orbit repeat cycle of 7 days. Global scientific payload data acquisition is guaranteed with the combined usage of Svalbard and Troll X-band receiving stations.The status of the Aeolus mission will be provided, including its performance assessment, planned operations and exploitation in the near future. This comprises the outcome of the instrument in its early operation phase, calibration and validation activities and a general review of the main scientific findings. Scope of the paper is also to inform about the programmatic highlights and future challenges.

The representation of warm convective clouds in atmospheric models and satellite observations can considerably deviate from each other partly due to different spatial resolutions. This study aims to establish appropriate metrics to evaluate high-resolution simulations of convective clouds by the ICON Large-Eddy Model (ICON-LEM) with observations from Meteosat SEVIRI over Germany. The time series and frequency distributions of convective cloud fraction and liquid water path (LWP) are analyzed. Furthermore, the study focuses on size distributions and decorrelation scales of warm convective cloud fields. The investigated metrics possess a pronounced sensitivity to the apparent spatial resolution. At the fine spatial scale, the simulations show higher occurrence frequencies of large LWP values and a factor of two to four smaller convective cloud fractions. Coarse-graining of simulated fields to the optical resolution of Meteosat essentially removes the differences between the observed and simulated metrics. The distribution of simulated cloud sizes compares well with the observations and can be represented by a power law, with a moderate resolution sensitivity. A lower limit of cloud sizes is identified, which is 8–10 times the native grid resolution of the model. This likely marks the effective model resolution beyond which the scaling behaviour of considered metrics is not reliable, implying that a further increase in spatial resolution would be desirable to better resolve cloud processes below 1 km. It is finally shown that ICON-LEM is consistent with spatio-temporal decorrelation scales observed with Meteosat having values of 30 min and 7 km, if transferred to the true optical satellite resolution. However, the simulated Lagrangian decorrelation times drop to 10 min at 1 km resolution, a scale covered by the upcoming generation of geostationary satellites.

The spatiotemporal evolution of warm convective cloud fields over central Europe is investigated on the basis of 30 cases using observations from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board the geostationary Meteosat platforms. Cloud fields are tracked in successive satellite images using cloud motion vectors. The time-lagged autocorrelation is calculated for spectral reflectance and cloud property fields using boxes of 16 × 16 pixels and adopting both Lagrangian and Eulerian perspectives. The 0.6-μm reflectance, cloud optical depth, and water path show a similar characteristic Lagrangian decorrelation time of about 30 min. In contrast, significantly lower decorrelation times are observed for the cloud effective radius and droplet density. It is shown that the Eulerian decorrelation time can be decomposed into an advective component and a convective component using the spatial autocorrelation function. In an Eulerian frame cloud fields generally decorrelate faster than in a Lagrangian one. The Eulerian decorrelation time contains contributions from the spatial decorrelation of the cloud field advected by the horizontal wind. A typical spatial decorrelation length of 7 km is observed, which suggests that sampling of SEVIRI observations is better in the temporal domain than in the spatial domain when investigating small-scale convective clouds. An along-track time series of box-averaged cloud liquid water path is derived and compared with the time series that would be measured at a fixed location. Supported by previous results, it is argued that this makes it possible to discriminate between local changes such as condensation and evaporation on the one hand and advective changes on the other hand.

The European Space Agency (ESA) wind mission, Aeolus, hosts the first space-based Doppler Wind Lidar (DWL) world-wide. The primary mission objective is to demonstrate the DWL technique for measuring wind profiles from space, intended for assimilation in Numerical Weather Prediction (NWP) models. The wind observations will also be used to advance atmospheric dynamics research and for evaluation of climate models. Mission spin-off products are profiles of cloud and aerosol optical properties. Aeolus was launched on 22 August 2018, and the Atmospheric LAser Doppler INstrument (Aladin) instrument switch-on was completed with first high energy output in wind mode on 4 September 2018 [1], [2]. The on-ground data processing facility worked excellent, allowing L2 product output in near-real-time from the start of the mission. First results from the wind profile product (L2B) assessment show that the winds are of very high quality, with random errors in the free Troposphere within (cloud/aerosol backscatter winds: 2.1 m/s) and larger (molecular backscatter winds: 4.3 m/s) than the requirements (2.5 m/s), but still allowing significant positive impact in first preliminary NWP impact experiments. The higher than expected random errors at the time of writing are amongst others due to a lower instrument out-and input photon budget than designed. The instrument calibration is working well, and some of the data processing steps are currently being refined to allow to fully correct instrument alignment related drifts and elevated detector dark currents causing biases in the first data product version. The optical properties spin-off product (L2A) is being compared e.g. to NWP model clouds, air quality model forecasts, and collocated ground-based observations. Features including optically thick and thin particle and hydrometeor layers are clearly identified and are being validated.

A threshold-based cloud mask for the high-resolution visible (HRV) channel (1 × 1 km2) of the Meteosat SEVIRI (Spinning Enhanced Visible and Infrared Imager) instrument is introduced and evaluated. It is based on operational EUMETSAT cloud mask for the low-resolution channels of SEVIRI (3 × 3 km2), which is used for the selection of suitable thresholds to ensure consistency with its results. The aim of using the HRV channel is to resolve small-scale cloud structures that cannot be detected by the low-resolution channels. We find that it is of advantage to apply thresholds relative to clear-sky reflectance composites, and to adapt the threshold regionally. Furthermore, the accuracy of the different spectral channels for thresholding and the suitability of the HRV channel are investigated for cloud detection. The case studies show different situations to demonstrate the behavior for various surface and cloud conditions. Overall, between 4 and 24% of cloudy low-resolution SEVIRI pixels are found to contain broken clouds in our test data set depending on considered region. Most of these broken pixels are classified as cloudy by EUMETSAT's cloud mask, which will likely result in an overestimate if the mask is used as an estimate of cloud fraction. The HRV cloud mask aims for small-scale convective sub-pixel clouds that are missed by the EUMETSAT cloud mask. The major limit of the HRV cloud mask is the minimum cloud optical thickness (COT) that can be detected. This threshold COT was found to be about 0.8 over ocean and 2 over land and is highly related to the albedo of the underlying surface.

A global vertically resolved aerosol data set covering more than 10 years of observations at more than 20 measurement sites distributed from 63° N to 52° S and 72° W to 124° E has been achieved within the Raman and polarization lidar network PollyNET. This network consists of portable, remote-controlled multiwavelength-polarization-Raman lidars (Polly) for automated and continuous 24/7 observations of clouds and aerosols. PollyNET is an independent, voluntary, and scientific network. All Polly lidars feature a standardized instrument design with different capabilities ranging from single wavelength to multiwavelength systems, and now apply unified calibration, quality control, and data analysis. The observations are processed in near-real time without manual intervention, and are presented online at http://polly.tropos.de/. The paper gives an overview of the observations on four continents and two research vessels obtained with eight Polly systems. The specific aerosol types at these locations (mineral dust, smoke, dust-smoke and other dusty mixtures, urban haze, and volcanic ash) are identified by their Ångström exponent, lidar ratio, and depolarization ratio. The vertical aerosol distribution at the PollyNET locations is discussed on the basis of more than 55 000 automatically retrieved 30 min particle backscatter coefficient profiles at 532 nm as this operating wavelength is available for all Polly lidar systems. A seasonal analysis of measurements at selected sites revealed typical and extraordinary aerosol conditions as well as seasonal differences. These studies show the potential of PollyNET to support the establishment of a global aerosol climatology that covers the entire troposphere.