Winds from Aeolus lidar SEA surface reFLECTance (SEA-FLECT) is an ESA funded project with the aim to explore the potential of the Aeolus observations to monitor sea surface winds.
(https://aeolus-surface-wind.aer.com/index.html)

This project aims to explore Aeolus observations beyond the main mission objectives. Where the main mission objective is to explore doppler shift of the lidar return signal, here the relation between the intensity of the lidar return signal and surface wind speed is being explored.

The physical basis of the SEA-FLECT project, is the high reflectance of the ocean white caps in the UV part of the EM spectrum. The fraction of white caps covered surface is strongly dependent on surface wind speed. The larger the wind speed, the larger the white cap fraction.

It can be expected that regions with larger surface wind speeds, are more reflective than the regions with reduced wind speed.

To explore the potential of the Aeolus surface return to monitor the surface wind speed over the open ocean, requires A) a well radiometrically calibrated Aeolus return from the range bin which contains the ocean surface, B) a well characterisation of the atmospheric contribution and C) well characterisation of the sub-surface contribution of this return.

To investigate the potential, first suitable Fields of View needs to be identified. This is done through a decision tree which classifies Aeolus observations according to presence of clouds, aerosols and signal to noise.

Aeolus surface returns over regions at various places over the global oceans, which are characterised by low chlorophyll concentrations (so-called oligotrophic) are being analysed.

In addition, the return signal over different land surfaces is being analysed to foster the understanding of the information content of the signal. This towards an basic understanding of the absolute calibration of the observations.

During the proposed oral presentation, the SEA-FLECT project is briefly introduced, together with the latest results of the analysis.

Dust modelling faces a series of challenges that should be addressed adequately towards improving the performance of numerical simulations in terms of reproducing dust life cycle components. Among several factors, well-documented in literature but yet not well-resolved, winds consist a critical aspect since they act as the determinant force on dust emission and transport. In the framework of the NEWTON (ImproviNg dust monitoring and forEcasting through Aeolus Wind daTa assimilatiON) ESA project, emphasis is given on the potential improvements on regional dust simulations attributed to the assimilation of Aeolus wind profiles. More specifically, we are performing short-term dust forecasts for two regions of interest (ROI) including the broader Mediterranean basin (ROI1) and the W. Sahara-Tropical Atlantic Ocean (ROI2). The WRF initial and boundary conditions are derived by the ECMWF IFS outputs produced with (hel4) and without (hel1) the consideration of Aeolus HLOS winds assimilation. By contrasting hel4 and hel1 experiments, we are assessing the impact of Aeolus assimilation on key meteorological parameters affecting dust emission over sources and dust transport over downwind areas. Dust numerical outputs, from both model configurations, are evaluated against ground-based (AERONET, PollyXT and EMEP) and spaceborne (LIVAS, MIDAS) observations in order to objectively assess the positive impact of Aeolus winds assimilation on dust forecasts and monitoring. For ROI1, in October 2020, there is strong evidence of a better representation of the Mediterranean desert dust outbreaks’ spatiotemporal patterns based on the hel4 experiment. Such improvements are driven by “corrections” of wind fields throughout the atmosphere. An identical analysis for ROI2 is under preparation taking advantage of the wealth of data acquired in the framework of the Joint Aeolus Tropical Atlantic Campaign (JATAC), that took place in Cape Verde (September 2021). Finally, NEWTON progress, activities and achievements are disseminated via the official website (https://newton.space.noa.gr) and the EO4Society portal (https://eo4society.esa.int/).

Global aerosol monitoring infrastructure is regularly complemented by new instrumentation to deepen our understanding of aerosols, which are key agents of the global radiative budget. Here, we introduce LARISSA (Lidar Aerosol Retrieval based on Information from Surface Signal of Aeolus) as a complementary and independent retrieval of AOD (Aerosol Optical Depth) for the Aeolus mission. LARISSA relies on the combination of lidar surface returns (LSR) from Aeolus and collocated near surface wind speeds over oceans to retrieve AOD. The proposed AOD retrieval is based on the parametrization of sea surface reflectance for non-nadir incidences (~37.5o for Aeolus) and is applied for the intensive observation period (IOP) of Aeolus in autumn 2019. First, we identified abundant LSR signals over oceans, where 19-34% (depending on the orbit) markedly exceeded the noise estimates during the IOP. Notably, this one week of the observations revealed distinct LSR gradients not only between land (strong signal) and ocean (weak signal), but also the palpable gradients between very bright (sea ice, fresh snow), bright (arid ecosystems, bare land) and dark land surfaces (productive ecosystems). Second, we discerned the reasonable agreement between the AODLARISSA estimates and the reference AOD from AEL-PRO (optimal estimation-based retrieval from extinction profiles of Aeolus) at the 14-30 m/s wind speed range for the entire IOP. This finding indicates that the sensitivity of LSR to near-wind speed estimates is somewhat palpable only at such mid-to-high wind speed range. Overall, the findings about reasonable agreement between AODLARISSA and AODAELPRO are promising because the final LARISSA algorithm will be valuable for aerosol studies as it does not require the assumptions about aerosol type or microphysics. Moreover, we identified the notable ability of Aeolus to distinguish the surface type, depending on the strength of LSR signal even for a very short period of observations. The latter finding potentially opens the window toward the auxiliary use of lidar data for the land cover classification research.

Besides the primary objective of Aeolus to measure horizontal wind profiles on a global scale, Aeolus can also provide profiles of aerosol and cloud properties as spin-off products. With its high-spectral resolution lidar ALADIN onboard, it is the first space mission able to directly measure vertical profiles of the particle extinction and backscatter coefficient independently with the so-called HSRL (high spectral resolution lidar) technique. The power of this technique is, that in contrast to elastic backscatter lidars like the one on Calipso, no aerosol/particle type has to be assumed a priori the retrieval of the particle optical property profiles. It is therefore the first time, that the so-called lidar ratio (extinction-to-backscatter ratio) can be directly retrieved from space and thus allowing particle typing.

However, Aeolus has the drawback that circular polarized light is emitted but only the co-polar component is detected. This leads to the loss of signal in case of polarizing particles like mineral dust, volcanic ash, or ice crystals. Due to this loss in signal, the backscatter coefficient is underestimated while the particle-specific lidar ratio is overestimated. This effect makes particle typing challenging.

In this presentation, we will discuss the potential and the limitations of the current Aeolus set up for the determination of particles types on the basis of 3 example measurements for which sophisticated ground-based multiwavelength-Raman-polarization lidar (i.e. PollyXT) observations are available as ground truth.
These three cases comprise urban haze observation made over Leipzig, Germany, smoke from the Australian wildfires in January 2020 measured over Punta Arenas, Chile, and Saharan Dust observation at Leipzig or on Cabo Verde.
We will present the comparison of the intensive particle properties measured from ground and from space and show to what extend Aeolus can be used for particle typing. In this context, we will discuss also the perspective for a potential Aeolus follow-on, which might have enhanced polarization capabilities.

ESA’s Aeolus satellite observations are expected to have the biggest impact for the improvement of numerical weather prediction in the Tropics. An especially important case relating to the evolution, dynamics, and predictability of tropical weather systems is the outflow of Saharan dust, its interaction with cloud microphysics and impact on the development of tropical storms over the Atlantic Ocean. The Atlantic Ocean off the coast of West Africa and the eastern Caribbean uniquely allows the study of the Saharan Aerosol layer, African Easterly Waves and Jet, Tropical Easterly Jet, as well as the deep convection in the Intertropical Convergence Zone and their relation to the formation of convective systems, and the long-range transport of dust and its impact on air quality.
The Joint Aeolus Tropical Atlantic Campaign (JATAC) deployed on Cabo Verde and the US Virgin Islands is addressing the validation and preparation of the ESA missions Aeolus, EarthCARE and WIVERN, as well as supporting the related science objectives raised above.
The JATAC campaign started in July 2021 with the deployment of ground-based instruments at the Ocean Science Center Mindelo (OSCM, Cabo Verde), including the EVE lidar, the PollyXT lidar, a W-band Doppler cloud radar and a sunphotometer. By mid-August, the CPEX-AW campaign started their operations from the US Virgin Islands with NASA’s DC-8 flying laboratory in the Western Tropical Atlantic and Caribbean with the Doppler Aerosol Wind Lidar (DAWN), Airborne Precipitation and Cloud Radar (APR-3), the Water Vapor DIAL and HSRL (HALO), a microwave sounder (HAMSR) and dropsondes. In September, a European aircraft fleet was deployed to Sal (Cabo Verde) with the DLR Falcon-20 carrying the ALADIN Airborne Demonstrator (A2D) and the 2-µm Doppler wind lidar, and the Safire Falcon-20 carrying the high-spectral-resolution Doppler lidar (LNG), the RASTA Doppler cloud radar, in-situ cloud and aerosol instruments among others. The Aerovizija Advantic WT-10 light aircraft with filter-photometers and nephelometers for in-situ aerosol characterisation was operating in close coordination with the ground-based observations from Mindelo.
More than 35 flights of the four aircraft were performed. 17 Aeolus orbits were underflown, four of which completed by simultaneous observations of three aircraft, with a perfect collocation of Aeolus and the ground-based observation for two cases. Several flights by the NASA DC-8 and the Safire Falcon-20 have been dedicated to cloud microphysics and dust events. The EVE lidar has been operating on a regular basis, while the PollyXT and several other ground-based instruments were continuously operating during the campaign period. For further characterisation of the atmosphere, radiosondes were launched up to twice daily from Sal airport. Additionally, there were radiosonde launches from western Puerto Rico and northern St Croix, US Virgin Islands. The JATAC was supported by dedicated numerical weather and dust simulations supporting the forecasting efforts needed for successful planning of the flights and addressing open science questions. While the airborne activities were completed end September, the ground-based observations are continuing into 2022.

The paper will present a JATAC overview.

The NASA CPEX-AW is part of the Joint Aeolus Tropical Atlantic Campaign (JATAC) in 2021. Specific science objectives of CPEX-AW include: 1) better understanding interactions of convective cloud systems and tropospheric winds as part of the joint NASA-ESA Aeolus Cal/Val effort over the tropical Atlantic, 2) observing the vertical structure and variability of the marine boundary layer in relation to initiation and lifecycle of the convective cloud systems, convective processes (e.g., cold pools), and environmental conditions within and across the ITCZ, 3) Investigating how the African easterly waves and dry air and dust associated with Sahara Air Layer control the convectively suppressed and active periods of the ITCZ, and 4) Investigating interactions of wind, aerosol, clouds, and precipitation and effects on long range dust transport and air quality over the western Atlantic.

The CPEX-AW science team and the NASA DC-8 aircraft were deployed to St. Croix, the US Virgin Islands, from 18 August – 10 September 2021, to address the science objectives. DC-8 is equipped with the Doppler Aerosol Wind Lidar (DAWN), Airborne Precipitation and Cloud Radar 3rd Generation (APR-3), High Altitude Lidar Observatory (HALO) Water Vapor DIAL and HSRL, High Altitude Microwave Sounding Radiometer (HAMSR), and GPS dropsondes. During the field campaign, CPEX-AW team launched soundings from the North Coast of St. Croix and the west coast of Puerto Rico. It also took colocated measurements over the saildrones that measure ocean surface and ocean current data in collaboration with the NOAA field campaign. In this overview, we will present highlights from CPEX-AW:
• More than 120 researchers including graduate students and postdocs participated in CPEX-AW in St. Croix, Puerto Rico, and remotely.
• We have flown seven research missions that collected unprecedented data from DAWN, HALO, APR-3, HAMSR, and dropsondes, in a wide arrange of conditions from strong dust outbreak events to tropical storms.
• Underflown six Aeolus overpasses for a total of 5,836 km, which provide valuable data sets for Aeolus Cal/Val and studies of impact on weather forecasting.
• Complex wind and convection in pre-Tropical Storm (TS) Ida and Ida over the Gulf of Mexico before the major Hurricane Ida made landfall, long lasting TS Kate and its interaction with dust and dry air over the central Atlantic, and dry air intrusion in Hurricane Larry.

We will also present updates on post-field campaign data analysis and modeling studies on Aeolus Cal/Val, new insights on interactions of wind, convective clouds, dry air and dust over the tropical Atlantic, and impacts of Aeolus and airborne data on numerical modeling and prediction of high-impact weather such as tropical cyclones.