Search Results (37)

Vertically retrieved optical properties by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) were investigated in the case of three selected events over Athens and Thessaloniki with documented high pollen concentrations. Hirst-type volumetric samplers were used to detect and characterize the pollen during the CALIPSO overpasses. Only cases with a total pollen concentration greater than 400 grains m⁻³ for at least two hours per day were considered severe pollen events, while model simulations were used to exclude the presence of other depolarizing aerosol types. This study provides mean values of lidar-derived optical properties inside the detected pollen layers; i.e., optical values represent the atmosphere with the presence of pollen, in urban cities of Greece. Specifically, three observed aerosol layers, one over Athens and two over Thessaloniki with particulate color ratios of 0.652 ± 0.194, 0.638 ± 0.362, and 0.456 ± 0.284, and depolarization ratios of 8.70 ± 6.26%, 28.30 ± 14.16%, and 8.96 ± 6.87%, respectively, were misclassified by CALIPSO as marine-dusty marine, dust, and polluted dust. In cases of intense pollen presence, CALIPSO vertical profiles and aerobiological monitoring methods may be used synergistically to better characterize the atmospheric pollen layers. Full article

The Mediterranean, and particularly its Eastern basin, is a crossroad of air masses advected from Europe, Asia and Africa. Anthropogenic emissions from its megacities meet over the Eastern Mediterranean, with natural emissions from the Saharan and Middle East deserts, smoke from frequent forest fires, background marine and pollen particles emitted from ocean and vegetation, respectively. This mixture of natural aerosols and gaseous precursors (Short-Lived Climate Forcers—SLCFs in IPCC has short atmospheric residence times but strongly affects radiation and cloud formation, contributing the largest uncertainty to estimates and interpretations of the changing cloud and precipitation patterns across the basin. The SLCFs’ global forcing is comparable in magnitude to that of the long-lived greenhouse gases; however, the local forcing by SLCFs can far exceed those of the long-lived gases, according to the Intergovernmental Panel on Climate Change (IPCC). Monitoring the spatiotemporal distribution of SLCFs using remote sensing techniques is important for understanding their properties along with aging processes and impacts on radiation, clouds, weather and climate. This article reviews the current state of scientific know-how on the properties and trends of SLCFs in the Eastern Mediterranean along with their regional interactions and impacts, depicted by ground- and space-based remote sensing techniques. Full article

North Africa, the Middle East, and Europe (NAMEE domain) host a variety of suspended particles characterized by different optical and microphysical properties. In the current study, we investigate the importance of the lidar ratio (LR) on Cloud-Aerosol Lidar with Orthogonal Polarization–Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIOP-CALIPSO) aerosol retrievals towards assessing aerosols’ impact on the Earth-atmosphere radiation budget. A holistic approach has been adopted involving collocated Aerosol Robotic Network (AERONET) observations, Radiative Transfer Model (RTM) simulations, as well as reference radiation measurements acquired using spaceborne (Clouds and the Earth’s Radiant Energy System-CERES) and ground-based (Baseline Surface Radiation Network-BSRN) instruments. We are assessing the clear-sky shortwave (SW) direct radiative effects (DREs) on 550 atmospheric scenes, identified within the 2007–2020 period, in which the primary tropospheric aerosol species (dust, marine, polluted continental/smoke, elevated smoke, and clean continental) are probed using CALIPSO. RTM runs have been performed relying on CALIOP retrievals in which the default and the DeLiAn (Depolarization ratio, Lidar ratio, and Ångström exponent)-based aerosol-speciated LRs are considered. The simulated fields from both configurations are compared against those produced when AERONET AODs are applied. Overall, the DeLiAn LRs leads to better results mainly when mineral particles are either solely recorded or coexist with other aerosol species (e.g., sea-salt). In quantitative terms, the errors in DREs are reduced by ~26–27% at the surface (from 5.3 to 3.9 W/m²) and within the atmosphere (from −3.3 to −2.4 W/m²). The improvements become more significant (reaching up to ~35%) for moderate-to-high aerosol loads (AOD ≥ 0.2). Full article

The mineralogical composition of airborne dust particles is an important but often neglected parameter for several physiochemical processes, such as atmospheric radiative transfer and ocean biochemistry. We present the development of the METAL-WRF module for the simulation of the composition of desert dust minerals in atmospheric aerosols. The new development is based on the GOCART-AFWA dust module of WRF-Chem. A new wet deposition scheme has been implemented in the dust module alongside the existing dry deposition scheme. The new model includes separate prognostic fields for nine (9) minerals: illite, kaolinite, smectite, calcite, quartz, feldspar, hematite, gypsum, and phosphorus, derived from the GMINER30 database and also iron derived from the FERRUM30 database. Two regional model sensitivity studies are presented for dust events that occurred in August and December 2017, which include a comparison of the model versus elemental dust composition measurements performed in the North Atlantic (at Izaña Observatory, Tenerife Island) and in the eastern Mediterranean (at Agia Marina Xyliatos station, Cyprus Island). The results indicate the important role of dust minerals, as dominant aerosols, for the greater region of North Africa, South Europe, the North Atlantic, and the Middle East, including the dry and wet depositions away from desert sources. Overall, METAL-WRF was found to be capable of reproducing the relative abundances of the different dust minerals in the atmosphere. In particular, the concentration of iron (Fe), which is an important element for ocean biochemistry and solar absorption, was modeled in good agreement with the corresponding measurements at Izaña Observatory (22% overestimation) and at Agia Marina Xyliatos site (4% overestimation). Further model developments, including the implementation of newer surface mineralogical datasets, e.g., from the NASA-EMIT satellite mission, can be implemented in the model to improve its accuracy. Full article

The Etesian winds characterize the summertime circulation in the Eastern Mediterranean. Etesians are modulated by the Indian summer monsoon (ISM), but their response to other external forcings is not understood. Here, we investigate the response of Etesians to the Novarupta/Katmai 1912 volcanic eruption with the aid of 20th Century reanalysis and station-based wind observations. We demonstrate a robust reduction in the total number of days with Etesian winds in July and August 1913. We also detect a strong cooling and weakened surface pressure gradients in the Eastern Mediterranean, which explains the decline in Etesian winds in the post-eruption summer. Full article

In this work, we utilize space-based radar products from CloudSat mission and provide statistics on the properties of the clouds observed above the PANGEA (PANhellenic GEophysical observatory of Antikythera) observatory, located in the Eastern Mediterranean. We found that the variable atmospheric conditions that prevailed above the region in 2007–2017 resulted in complex cloud structures. From the clouds observed, 39.8% were low-level clouds formed at the top of the marine boundary layer (≤2 km), 34.2% were mid-level clouds (between 2–7 km), and 25.9% were high-level or deep convective clouds (between 7–15 km). Thin clouds (<1 km depth) are observed in 33% of the cases, while thick clouds (>6 km) in 15% of the cases. The results of this study can be used from regional and climate models to evaluate their cloud predictions and investigate the performance of different cloud microphysics schemes. Full article

In the framework of the ESA-NASA Joint Aeolus Tropical Atlantic Campaign (JATAC), the ASKOS experiment was implemented during the summer and autumn of 2021 and 2022. ASKOS comprised roughly 9 weeks of measurements in the Saharan dust outflow towards the North Atlantic, with operations conducted from the Cabo Verde Islands. Through its unprecedented dataset of synergistic measurements in the region, ASKOS will allow for the calibration and validation of the aerosol/cloud product from Aeolus and the preparation of the terrain for EarthCARE cal/val activities. Moreover, ASKOS marks a turning point in our ability to study Saharan dust properties and the processes affecting its atmospheric transport, as well as the link to other components of the Earth’s system, such as the effect of dust particles on cloud formation over the Eastern Atlantic and the effect of large and giant particles on radiation. This is possible through the synergy of diverse observations acquired during the experiment, which include intense 24/7 ground-based aerosol, cloud, wind, and radiation remote sensing measurements, and UAV-based aerosol in situ measurements within the Saharan air layer, up to 5.3 km altitude, offering particle size-distributions up to 40 μm as well as sample collection for mineralogical analysis. We provide an outline of the novel measurements along with the main scientific objectives of ASKOS. The campaign data will be publicly available by September of 2023 through the EVDC portal (ESA Validation Data Center). Full article

The European Space Agency’s AEOLUS mission provides vertical profiles of the horizontal line-of-sight (HLOS) wind component in the troposphere and lower stratosphere, as well as secondary products with retrievals of extinction and backscatter coefficients. Under the scope of the ESA L2A+ project, we present an assimilation system of both wind and aerosol information from AEOLUS in a regional numerical weather prediction model (WRF). This study aims to highlight the impact of such a dataset on desert dust transport through assimilation experiments over the broader North Atlantic Ocean region, which features high dust transport events through the Saharan Air Layer. The results will be validated through comparisons with observations from the ESA-ASKOS/JATAC experiments. Full article

An increase in the frequency of wildfire occurrence is predicted in all climate model estimates, implying significant health impacts, due to the emission of combustion products. Application of pollutant dispersion models at strategic and operational levels is imperative for safety reasons and for compliance with European Civil Protection Mechanism policies. Here, we describe the dispersion of smoke from the forest fire of Penteli-Attica (Greece) on 19 July 2022, which burnt a total area of 2781.7 hectares. High-resolution dispersion simulations, air-quality measurements, and remote sensing observations are used to describe the transport of smoke and facilitate effective smoke control in areas where air quality impacts are likely to be significant. Full article

Forecasting volcanic ash transport is crucial for aviation, but its accuracy is subject to both the prevailing wind fields and the knowledge of the source term of the eruption, i.e., variation of emission rate and column height with time. In this study, we use data from the high spectral resolution lidar (HSRL) in space, Aeolus, to examine their impact on the estimation of the emission rates of volcanic particles through inversion techniques. For the inverse modelling, we couple the output of the FLEXPART Lagrangian particle dispersion model with lidar observations towards estimating the emission rates of volcanic particles released from an Etna eruption. The case study used here is the Etna eruption on the 12 March 2021, well captured by the ground-based lidar station of the PANGEA observatory located at the remote island of Antikythera in Greece, downwind of the Etna volcano. It is concluded that the inversion algorithm with Aeolus wind fields assimilation optimizes both the vertical emission distribution and the Etna emission rates. Full article

Remote sensing of particulate matter (PM) absolute concentration levels can address the need for continuous wide-area monitoring in urban environments, which arises from the adverse effects of air pollution on human health. Raymetrics PMeye is a unique aerosol monitoring system designed around a state-of-the-art polarization scanning UV lidar that offers large-area PM concentration monitoring and high spatial resolution source localization. The PMeye lidar employs a novel inversion scheme for converting raw lidar signals to PM concentrations. This study demonstrates the effectiveness and accuracy of remote monitoring PM concentration measurement results in the region of Attica, Greece. Potential synergistic use with inversion modeling techniques and dispersion models to support an advanced warning system for the population and local authorities of the Athens metropolitan area is also discussed. Full article

The most extreme manifestation of a fire–weather interaction is the formation of pyrocumulonimbus (pyroCb) thunderstorms, triggered by super-heated updrafts, which can eject smoke at altitudes exceeding 20 Km. In this study, we investigated climate-related impacts from the most intensive pyroCb-triggered injection of smoke in the stratosphere: the Australian New Year wildfires in 2019/2020. We first provide a general overview of the vision and objectives of the StratoFIRE project. With the aid of the global chemistry-climate model EMAC, we then simulate radiative and chemical perturbations in the stratosphere in relation to 0.9 Tg smoke in the stratosphere assuming different injection heights, from 13 to 16 Km. The simulation of stratospheric optical depth perturbations were found to be sensitive to the assumed injection height, with a maximum height at 16 Km showing the best agreement with the GLOSSAC and SAGE-ISS aerosol extinction observations. Full article

The eVe lidar is a scanning system that can perform combined linear/circular polarization and Raman measurements at 355 nm and consists of the European Space Agency’s (ESA) reference aerosol lidar system. eVe was deployed in the ASKOS campaign, which was held in Cabo Verde during the summer/autumn of 2021 and 2022, for the validation of the aerosol products of the ESA’s Aeolus mission. During the campaign, eVe performed routine linear/circular depolarization measurements during Aeolus overpasses as well as dual-field-of-view measurements for the investigation of multiple scattering effects on dust layers. Herein, we present an overview of the acquired measurements and findings. Full article

Windblown dust plays a crucial role in the Earth system, impacting climate, ecosystems, human activities, and health. The spatiotemporal evolution of dust plumes during transport is determined by wind, the primary driver of dust emission. In this study, we utilize outputs from the ECMWF-IFS, assimilating quality-assured Aeolus wind profiles, to initialize dust simulations with the WRF-Chem model. The aim is to assess the impact of Aeolus wind observations on modeling the desert dust cycle. Focusing on the ASKOS/JATAC campaign in September 2021 near Cabo Verde, we qualitatively and quantitatively evaluate the simulated dust-related outputs, revealing that even small differences in wind significantly affect the simulated dust emission rates and dust optical depth. Full article

The overarching objective of the present study is to assess the quality of the CALIOP–CALIPSO aerosol retrievals towards understanding their advantages and deficiencies. Such analysis is a prerequisite prior to their utilization in a radiation transfer model (RMT) for estimating the clear-sky shortwave (SW) aerosol-induced direct radiative effects (DREs) within the Earth–Atmosphere system. The study region encompasses North Africa, the Middle East, and Europe (NAMEE domain), and the period of interest ranges from 2007 to 2020. A holistic approach has been adopted involving spaceborne retrievals (CALIOP–CALIPSO and MODIS-Aqua) and ground-based measurements (AERONET). Overall, CALIOP underestimates columnar aerosol optical depth (AOD), particularly in dust-rich areas, attributed to various factors (e.g., lidar ratio). In order to demonstrate the significance of an appropriate definition of the lidar ratio, focusing on DREs, three example dust cases are investigated. The CALIPSO dust extinction coefficient profiles are used as inputs to the libRadtran Radiative Transfer Model (RTM) along with other crucial parameters. For each study case, two RTM runs are performed using the default (CALIPSO) and an updated (DeliAn) dust lidar ratio. Our results indicate remarkable differences (up to ~22%) on the surface and atmospheric DREs while varying from 17% to 27% at TOA. Full article