Search Results (27)

Dust plays a significant role in the atmospheric radiative balance by altering both shortwave and longwave radiation fluxes. While deserts are the primary sources of dust emissions, atmospheric circulation can transport dust over long distances, impacting air quality and climate in remote regions. These transport episodes, commonly known as dust events, vary in intensity and effects. Despite extensive research, uncertainties persist regarding their precise radiative impacts. This study examines the direct radiative effects of dust events in 2024 (a year marked by heightened dust activity) over Limassol, Cyprus. A comprehensive approach is employed, integrating radiative transfer modelling, ground-based solar radiation measurements, and dust optical property analysis. The LibRadtran radiative transfer package is used to simulate atmospheric radiative transfer under dust-laden conditions, incorporating key dust optical properties such as Aerosol Optical Depth, Single Scattering Albedo, and the Asymmetry Parameter retrieved from the Limassol’s AERONET station. Observations from solar radiation station at the ERATOSTHENES Centre of Excellence serve as validation for the model. This study quantifies the radiative impact of dust by evaluating changes in surface irradiance, providing valuable insights into the role of dust in atmospheric energy balance. Full article

We present an example of how a doctoral network can bring together multidisciplinary expertise and novel scientific advances in atmospheric dust. This network (Dust-DN) has started operations and is a strategic alliance of high-profile partners, able to leverage unique facilities for atmospheric research and innovative space missions. The network aims to improve our understandings of dust processes and microphysics, identify the signature of source regions, address the socio-economic impacts of dust transport and improve the quantification of the role of dust in the climate system. The first results have already been achieved and are shown here, and many more are expected to follow. 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

In this study, we present comprehensive climatologies of effective ultraviolet (UV) quantities and photosynthetically active radiation (PAR) over Cyprus for the period 2004 to 2023, leveraging the synergy of earth observation (EO) data and radiative transfer model simulations. The EO dataset, encompassing satellite and reanalysis data for aerosols, total ozone column, and water vapor, alongside cloud modification factors, captures the nuanced dynamics of Cyprus’s atmospheric conditions. With a temporal resolution of 15 min and a spatial of 0.05° × 0.05°, these climatologies undergo rigorous validation against established satellite datasets and are further evaluated through comparisons with ground-based global horizontal irradiance measurements provided by the Meteorological Office of Cyprus. This dual-method validation approach not only underscores the models’ accuracy but also highlights its proficiency in capturing intra-daily cloud coverage variations. Our analysis extends to investigating the long-term trends of these solar radiation quantities, examining their interplay with changes in cloud attenuation, aerosol optical depth (AOD), and total ozone column (TOC). Significant decreasing trends in the noon ultraviolet index (UVI), ranging from −2 to −4% per decade, have been found in autumn, especially marked in the island’s northeastern part, mainly originating from the (significant) positive trends in TOC. The significant decreasing trends in TOC, of −2 to −3% per decade, which were found in spring, do not result in correspondingly significant positive trends in the noon UVI since variations in cloudiness and aerosols also have a strong impact on the UVI in this season. The seasonal trends in the day light integral (DLI) were generally not significant. These insights provide a valuable foundation for further studies aimed at developing public health strategies and enhancing agricultural productivity, highlighting the critical importance of accurate and high-resolution climatological data. 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

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

While solar power applications are growing rapidly worldwide, information about solar energy availability, its characteristics and the factors that affect it are essential. Among other parameters, a reference spectrum (ASTMG-173-03) is adopted, relying on Standard Test Conditions (STC), under which Photovoltaic (PV) devices are evaluated. However, these rigorously defined conditions can vary considerably from realistic environmental conditions. The objective of the present work is to assess the impact of the variability of atmospheric composition on the spectral distribution of the incident solar spectral irradiance (SSI) and, therefore, its implication on various PV materials performance. Ground-based measurements of global horizontal SSI have been conducted using a Precision Spectroradiometer (PSR) in the framework of the ASPIRE (Atmospheric parameters affecting SPectral solar IRradiance and solar Energy) project in Athens, Greece. The gathered data in combination with spectrally resolved radiative transfer under clear-sky conditions contributed to the investigation of the atmospheric variables that attenuate irradiance (e.g., aerosols). In addition, since PV modules’ spectral absorptivity differs according to the semiconductor material used, the impact of the above-mentioned spectral features on PV performance has been investigated in order to estimate the spectral impact between the theoretical and outdoor conditions on the yield of different PV technologies. Overall, the results denote that smoke has a more significant effect than dust, while the effect on various technologies varies. The highest deviation compared to the STC was observed in the case of a-Si, reaching an absolute difference of 45% in the case of smoke particles in the atmosphere, while the maximum deviation between the different technologies reached approximately 7%. 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

In this study, we examine the direct effect of atmospheric aerosols on two components of downwelling surface solar irradiance, Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI), under clear-sky conditions and their implications for solar energy, focusing on the broader Mediterranean Basin, over an 18-year time period between 2003 and 2020. In addition to the aerosol optical depth (AOD) from satellite retrievals and model data that have been used in previous studies, the present study utilizes ground-based direct measurements of AOD and aerosol optical properties from the AErosol RObotic NETwork (AERONET) to assess the direct effect of aerosols on GHI and DNI. Full article

The study presents results of the research project ASPIRE (atmospheric parameters affecting spectral solar irradiance and solar energy). A new dataset has been created for Athens, Greece, for one year (December 2020–November 2021), consisting of detailed measurements of spectral solar irradiance (SSI) from 300 to 1020 nm and its influencing parameters (clouds, aerosols, ozone, nitrogen dioxide, sulfur dioxide, water vapor). The new dataset is explored, and major results are presented. The datasets are available to scientists from interdisciplinary scientific communities for research and education purposes. Here, we present an overview of different studies within ASPIRE, dealing with effects of different aerosol types on solar measurements and PV-related outputs and also the evaluation of a nowcasting solar model under different atmospheric conditions. Full article

A brief overview of the newly established Solar Radiation and Energy Laboratory of the Eratosthenes’ Centre of Excellence is provided. The laboratory focuses on fundamental research and practical applications related to solar radiation levels, radiative transfer modeling, and atmospheric effects. The laboratory’s goal is to establish a scientific foundation that will support some of the most important sectors of the EU and Cyprus Smart Specialization Strategy, including energy, tourism, health, and agriculture, and become a reference point for the Eastern Mediterranean, Middle East, and North African region. Finally, some preliminary results concerning solar radiation climatology and a system for clear-sky ultraviolet index forecast over Cyprus are presented. Full article

In August 2021, extreme wildfires burned wide areas in Greece. The most severe events took place in the region of Attica and significantly affected the air quality over the city of Athens. In the same period, southern winds transferred dust from the Sahara Desert to the city. We chose a day with high dust and smoke loads to test a new method for the determination of the individual components of the aerosol mixture, based on actinometric and radiometric measurements and radiative transfer modelling. Then, we estimated the radiative effect of each of the aerosol mixture components. Assuming that dust particles are coarse while all other particles are fine, coarse to fine mode ratios were estimated and were compared with the corresponding ratios from a CIMEL sun photometer, resulting in quite good agreement. Full article

Desert dust atmospheric aerosols play an important role in the Earth-atmosphere system and constitute a key agent for the Earth’s climate through their radiative processes. However, dust radiative effects are still subjected to large uncertainties, due to the uncertain estimates of their optical properties. A radiative closure study, under cloudless sky, using measurements and model results of shortwave radiation at the Earth’s surface was performed. All measurements were gathered under Saharan dust conditions during the ASKOS campaign at Mindelo, Cabo Verde. Radiation measurements were compared with radiative transfer simulations, using as input concurrent retrievals of dust optical properties. Full article

Energy nowcasting is a valuable asset in managing energy loads and having real-time information on solar irradiation availability. In this study, we evaluate the spectrally integrated outputs of the SENSE system for solar irradiance nowcasting for the period of the ASPIRE (atmospheric parameters affecting spectral solar irradiance and solar energy) campaign (December 2020–December 2021) held in Athens, Greece. For the needs of the campaign, several ground-based instruments were operating, including two pyranometers, a pyrheliometer, a cloud camera, a CIMEL sunphotometer, and a precision spectral radiometer (PSR). Global horizontal irradiance (GHI) estimations were more accurate than direct normal irradiance (DNI). SENSE estimations are provided every 15 min, but when comparing bigger time intervals (hours-days), the statistics improved. A dedicated assessment of the SENSE’s inputs is performed in respect to ground-based retrievals, considering cloud conditions (from a sky imager), AOD, and precipitable water vapor from AERONET. The factor that established the larger errors was the visibility of the solar disc, which cannot be defined by the available sources of model inputs. Additionally, there were discrepancies between the satellite estimation of the clouds and the ground picture, which caused deviations in results. AOD differences affected more the DNI. Full article

Maximum efficiency of surfaces that exploit solar energy, including Photovoltaic Panels and Thermal collectors, is achieved by installing them in a certain inclination (tilt). Most common approach is to select an inclination angle equal to the location’s latitude. This is based on the astronomical calculations of the sun’s position throughout the year but ignores meteorological factors. Cloud coverage and aerosols tend to change the direct irradiance but also the radiance sky distribution, thus horizontal surfaces receive larger amounts than tilted ones in specific atmospheric conditions (e.g., cases of cloud presence). In the present study we used 15 years of data, from 25 cities in Europe and North Africa in order to estimate the optimal tilt angle and the related energy benefits based in real atmospheric conditions. Data were retrieved from Copernicus Atmospheric Monitoring Service (CAMS). Four diffuse irradiance, various models are compared, and their differences are evaluated. Equations, extracted from solar irradiance and cloud properties regressions, are suggested to estimate the optimal tilt angle in regions, where no climatological data are available. In addition, the impact of cloud coverage is parameterized using the Cloud Modification Factor (CMF) and an equation is proposed to estimate the optimal tilt angle. A realistic representation of the photovoltaic energy production and a subsequent financial analysis were additionally performed. The results are able to support the prognosis of energy outcome and should be part of energy planning and the decision making for optimum solar power exploitation into the international clean energy transitions. Finally, results are compared to a global study and differences on the optimal tilt angle at cities of Northern Europe is presented. Full article