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Prof. Nikolaos Hatzianastassiou
Laboratory of Meteorology, Department of Physics, University of Ioannina, 45110 Ioannina, Greece

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0 Aerosol-cloud interactions
0 Aerosol physical properties
0 Aerosol-radiation interactions
0 Radiation and climate
0 Shortwave and longwave radiation transfer and budgets

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Journal article
Published: 23 July 2021 in Remote Sensing
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A satellite algorithm able to identify Dust Aerosols (DA) is applied for a climatological investigation of Dust Aerosol Episodes (DAEs) over the greater Mediterranean Basin (MB), one of the most climatologically sensitive regions of the globe. The algorithm first distinguishes DA among other aerosol types (such as Sea Salt and Biomass Burning) by applying threshold values on key aerosol optical properties describing their loading, size and absorptivity, namely Aerosol Optical Depth (AOD), Aerosol Index (AI) and Ångström Exponent (α). The algorithm operates on a daily and 1° × 1° geographical cell basis over the 15-year period 2005–2019. Daily gridded spectral AOD data are taken from Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua Collection 6.1, and are used to calculate the α data, which are then introduced into the algorithm, while AI data are obtained by the Ozone Monitoring Instrument (OMI) -Aura- Near-UV aerosol product OMAERUV dataset. The algorithm determines the occurrence of Dust Aerosol Episode Days (DAEDs), whenever high loads of DA (higher than their climatological mean value plus two/four standard deviations for strong/extreme DAEDs) exist over extended areas (more than 30 pixels or 300,000 km2). The identified DAEDs are finally grouped into Dust Aerosol Episode Cases (DAECs), consisting of at least one DAED. According to the algorithm results, 166 (116 strong and 50 extreme) DAEDs occurred over the MB during the study period. DAEDs are observed mostly in spring (47%) and summer (38%), with strong DAEDs occurring primarily in spring and summer and extreme ones in spring. Decreasing, but not statistically significant, trends of the frequency, spatial extent and intensity of DAECs are revealed. Moreover, a total number of 98 DAECs was found, primarily in spring (46 DAECs) and secondarily in summer (36 DAECs). The seasonal distribution of the frequency of DAECs varies geographically, being highest in early spring over the eastern Mediterranean, in late spring over the central Mediterranean and in summer over the western MB.

ACS Style

Maria Gavrouzou; Nikolaos Hatzianastassiou; Antonis Gkikas; Christos Lolis; Nikolaos Mihalopoulos. A Climatological Assessment of Intense Desert Dust Episodes over the Broader Mediterranean Basin Based on Satellite Data. Remote Sensing 2021, 13, 2895 .

AMA Style

Maria Gavrouzou, Nikolaos Hatzianastassiou, Antonis Gkikas, Christos Lolis, Nikolaos Mihalopoulos. A Climatological Assessment of Intense Desert Dust Episodes over the Broader Mediterranean Basin Based on Satellite Data. Remote Sensing. 2021; 13 (15):2895.

Chicago/Turabian Style

Maria Gavrouzou; Nikolaos Hatzianastassiou; Antonis Gkikas; Christos Lolis; Nikolaos Mihalopoulos. 2021. "A Climatological Assessment of Intense Desert Dust Episodes over the Broader Mediterranean Basin Based on Satellite Data." Remote Sensing 13, no. 15: 2895.

Preprint content
Published: 04 March 2021
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After the outbreak of SARS-CoV-2 in December 2019 and its spread worldwide in the following months and seasons, the governments around the world were forced, one by one, to impose lockdown measures in their countries during the ‘Covid Year’ of 2020, trying to slowdown or even stop the spread of the virus. These nationwide lockdowns, included measures that led to the reduction of human movement, such as transportation, in urban areas, while they also diminished the industrial activity. Since transportation and industrial activity are among the major sources of emission of anthropogenic aerosols, it is possible that a change, namely a decrease, of the atmospheric aerosol loading is observed during the year 2020. 

In this study, we examine and quantify the possible effect of worldwide Covid19-related lockdowns on air quality, and more specifically on the aerosol optical depth, which is a good measure of aerosol loading. The analysis is done at global scale using Collection 6.1 Level-3 daily 1°x1° latitude-longitude gridded spectral Aerosol Optical Depth (AOD) data from Moderate Resolution Imaging Spectroradiometer (MODIS) on AQUA satellite during the period 2003-2020. We assess the possible anomaly in AOD values during 2020 by comparing their annual, seasonal and monthly mean values with the corresponding climatological ones for the period 2003-2019. A trend analysis is also performed using time series of deseasonalized AOD anomalies during the period 2003-2020. Special emphasis is given to specific great urban areas, as well as to areas where stricter measures were taken for limiting the virus’ spread. For these areas of interest, a further analysis using higher resolution (10km x 10km) MODIS Level-2  AOD data was made in order to capture local changes in AOD that could be hindered by the coarser resolution Level-3 data. Finally, for these regions, the AOD changes estimated using MODIS Level-2 data are intercompared with the corresponding ones using data from local AERONET (AErosol RObotic NETwork) stations. Preliminary results show a clear reduction in AOD values, mainly starting from April 2020 and becoming more clear in late spring and early summer (May and June) of 2020.

ACS Style

Vasilis Margaritis; Nikolaos Hatzianastassiou; Marios Bruno Korras Carraca; Maria Gavrouzou. The effect of SARS-CoV-2 on atmospheric particulate matter (AOD) as observed by satellites. 2021, 1 .

AMA Style

Vasilis Margaritis, Nikolaos Hatzianastassiou, Marios Bruno Korras Carraca, Maria Gavrouzou. The effect of SARS-CoV-2 on atmospheric particulate matter (AOD) as observed by satellites. . 2021; ():1.

Chicago/Turabian Style

Vasilis Margaritis; Nikolaos Hatzianastassiou; Marios Bruno Korras Carraca; Maria Gavrouzou. 2021. "The effect of SARS-CoV-2 on atmospheric particulate matter (AOD) as observed by satellites." , no. : 1.

Preprint content
Published: 04 March 2021
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The incoming solar radiation at the top of the atmosphere (TOA), and especially at the Earth’s surface, determines the energy balance of our planet and regulates its climate. During the last decades, variations in the incoming surface solar radiation (SSR) have been observed, which depend on the atmosphere’s transparency. This phenomenon, known as global dimming and brightening (GDB), plays an important role in climate change and global warming. The present study examines the variability and changes of both SSR and the outgoing solar radiation at the TOA (OSR) based on long-term satellite data and ground truth measurements, but also reanalysis data, also with an aim to inter-compare and validate the changes of SSR (ΔSSR or GDB) and OSR (ΔOSR) in order to ensure the highest accuracy of the findings. For this analysis, mean monthly SSR and OSR fluxes are used at the global scale and over the last several decades. More specifically, SSR and OSR solar fluxes are used from the Modern-Era Retrospective Analysis for Research and Applications v.2 (MERRA-2) reanalysis data for the 40-year period 01/1980 - 12/2020 and from the satellite Clouds and the Earth's Radiant Energy System Energy Balanced and Filled (CERES-EBAF) database for the 20-year period 03/2000 - 07/2020. The spatial resolution of CERES-EBAF dataset is 1°×1° latitude and longitude. MERRA-2 data, originally provided on a 0.5°×0.625° horizontal grid, are regridded on the CERES-EBAF spatial resolution (1°×1°). The SSR and ΔSSR fluxes from MERRA-2 and CERES are compared to each other, and they are both assessed through comparisons against ground measurements from the two major reference station networks, namely the Global Energy Balance Archive (GEBA), and the Baseline Surface Radiation Network (BSRN). The OSR and ΔOSR fluxes from MERRA-2 are assessed through comparison against corresponding fluxes from the CERES satellite measurements. The data analysis examines the spatio-temporal distribution and the trends of SSR (ΔSSR or GDB) and OSR, using both radiation fluxes and their deseasonalized anomalies. Special emphasis is given to the accurate estimation of GDB and the associated uncertainty, while attempting to reduce this uncertainty using the results of the analysis at the top of the atmosphere.

ACS Style

Michael Stamatis; Nikolaos Hatzianastassiou; Marios Bruno Korras Carraca; Christos Matsoukas; Martin Wild; Ilias Vardavas. Comparative analysis of the incoming surface and outgoing top of atmosphere solar radiation based on MERRA-2 & CERES data. 2021, 1 .

AMA Style

Michael Stamatis, Nikolaos Hatzianastassiou, Marios Bruno Korras Carraca, Christos Matsoukas, Martin Wild, Ilias Vardavas. Comparative analysis of the incoming surface and outgoing top of atmosphere solar radiation based on MERRA-2 & CERES data. . 2021; ():1.

Chicago/Turabian Style

Michael Stamatis; Nikolaos Hatzianastassiou; Marios Bruno Korras Carraca; Christos Matsoukas; Martin Wild; Ilias Vardavas. 2021. "Comparative analysis of the incoming surface and outgoing top of atmosphere solar radiation based on MERRA-2 & CERES data." , no. : 1.

Preprint content
Published: 04 March 2021
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Mediterranean Basin (MB), due to its position near to the greatest world deserts (the Sahara Desert in North Africa and the deserts of Middle East), is frequently affected by dust transport. This results in dust episodes, associated with high Dust Aerosol (DA) loads reaching the northern parts of MB, taking place every year with different intensity, but with specific seasonal and spatial characteristics. The seasonal and spatial characteristics of Dust Aerosol Episodes (DAEs) in the region are connected to specific atmospheric conditions that favor the injection of DA into the region’s atmosphere, as well as to specific atmospheric circulation characteristics favoring the transport to the MB.

DA not only are affected by, but they also can affect the atmospheric conditions and thus the regional weather and climate regime. Specifically, due to their ability to absorb the shortwave, but also the longwave, radiation, DA can modify the temperature structure of the atmosphere as well as the radiative budget. In addition, DA are effective Ice Nuclei (IN), and also, under mature stages, Cloud Condensation Nuclei (CCN), thus affecting cloud properties. These effects of DA become more important, but also complicated, when high dust loads are associated with other aerosol types, e.g. sea-salt (SS) and biomass burning (BB) over a region with high solar radiation, diverse topography and cloud regimes such as the MB.

In the present study, the atmospheric circulation (geopotential height and mean sea level pressure), as well as the meteorological conditions (cloud fraction, cloud optical thickness, cloud phase, temperature and humidity profiles and vertical velocity) before, during and after an extreme Dust Aerosol Episode Case (DAEC) that took place over the western MB on June 16, 2016 are examined. The studied DAEC is identified using a satellite algorithm, which uses MODIS C6.1 and OMI OMAERUV derived aerosol optical properties.  Emphasis is given to the understanding of the 3-D structure of the episode and its possible effects on the atmospheric temperature and humidity regime, as well as on cloud properties. For this reason, different reanalyses and satellite data, namely from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis Project), MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, Version 2) and MODIS databases, are analyzed. In addition, the vertical aerosol profile is obtained from MERRA-2 data.

ACS Style

Maria Gavrouzou; Nikos Hatzianastassiou; Antonis Gkikas; Marios-Bruno Korras-Carraca; Christos Lolis; Nikos Mihalopoulos. Atmospheric circulation and meteorological conditions during dust aerosol episodes over the broader Mediterranean Basin. The case of 16 June 2016. 2021, 1 .

AMA Style

Maria Gavrouzou, Nikos Hatzianastassiou, Antonis Gkikas, Marios-Bruno Korras-Carraca, Christos Lolis, Nikos Mihalopoulos. Atmospheric circulation and meteorological conditions during dust aerosol episodes over the broader Mediterranean Basin. The case of 16 June 2016. . 2021; ():1.

Chicago/Turabian Style

Maria Gavrouzou; Nikos Hatzianastassiou; Antonis Gkikas; Marios-Bruno Korras-Carraca; Christos Lolis; Nikos Mihalopoulos. 2021. "Atmospheric circulation and meteorological conditions during dust aerosol episodes over the broader Mediterranean Basin. The case of 16 June 2016." , no. : 1.

Article
Published: 13 February 2021 in Water, Air, & Soil Pollution
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In this paper, the factors that determine the particulate matter concentrations with diameter less than 10μm (PM10) are investigated for the provincial city of Ioannina, NW Greece. The analysis reveals that even in a generally medium-sized city as Ioannina (120,000 habitants), PM10 levels exceed the European Union’s standards (mean daily PM10<50 μg/m3) quite often during the cold period of the year. The diurnal and intra-annual patterns of PM10 indicate that road traffic and residential heating are the main contributors of PM10 in the city, while residential heating is the main contributor during the cold period of the year, leading to very high concentrations (80 μg/m3) around 10 p.m. The inter-annual variation over the study period 2010–2012 and 2014–2017, constrained by the availability of quality surface PM10 measurements, shows that apart from meteorological parameters (e.g., wind speed, rain, and daily minimum temperature), which are significantly correlated with PM10, social-economic factors also determine the levels of atmospheric particulate matter. Indeed, during the years of deep austerity, in the middle of the study period, the number of days with poor and very poor conditions, defined according to the European Air Quality Index, has increased. This resulted from a decrease of consumption of conventional fuels for residential heating (e.g., oil) and the strengthened use of alternative and cheaper solutions such as wood or pellet burning, which emit more particulate matter.

ACS Style

O. Α. Sindosi; N. Hatzianastassiou; G. Markozannes; E. C. Rizos; E. Ntzani; A. Bartzokas. PM10 Concentrations in a Provincial City of Inland Greece in the Times of Austerity and Their Relationship with Meteorological and Socioeconomic Conditions. Water, Air, & Soil Pollution 2021, 232, 1 -19.

AMA Style

O. Α. Sindosi, N. Hatzianastassiou, G. Markozannes, E. C. Rizos, E. Ntzani, A. Bartzokas. PM10 Concentrations in a Provincial City of Inland Greece in the Times of Austerity and Their Relationship with Meteorological and Socioeconomic Conditions. Water, Air, & Soil Pollution. 2021; 232 (2):1-19.

Chicago/Turabian Style

O. Α. Sindosi; N. Hatzianastassiou; G. Markozannes; E. C. Rizos; E. Ntzani; A. Bartzokas. 2021. "PM10 Concentrations in a Provincial City of Inland Greece in the Times of Austerity and Their Relationship with Meteorological and Socioeconomic Conditions." Water, Air, & Soil Pollution 232, no. 2: 1-19.

Journal article
Published: 21 January 2021 in Remote Sensing
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A satellite-based algorithm is developed and used to determine the presence of dust aerosols on a global scale. The algorithm uses as input aerosol optical properties from the MOderate Resolution Imaging Spectroradiometer (MODIS)-Aqua Collection 6.1 and Ozone Monitoring Instrument (OMI)-Aura version v003 (OMAER-UV) datasets and identifies the existence of dust aerosols in the atmosphere by applying specific thresholds, which ensure the coarse size and the absorptivity of dust aerosols, on the input optical properties. The utilized aerosol optical properties are the multiwavelength aerosol optical depth (AOD), the Aerosol Absorption Index (AI) and the Ångström Exponent (a). The algorithm operates on a daily basis and at 1° × 1° latitude-longitude spatial resolution for the period 2005–2019 and computes the absolute and relative frequency of the occurrence of dust. The monthly and annual mean frequencies are calculated on a pixel level for each year of the study period, enabling the study of the seasonal as well as the inter-annual variation of dust aerosols’ occurrence all over the globe. Temporal averaging is also applied to the annual values in order to estimate the 15-year climatological mean values. Apart from temporal, a spatial averaging is also applied for the entire globe as well as for specific regions of interest, namely great global deserts and areas of desert dust export. According to the algorithm results, the highest frequencies of dust occurrence (up to 160 days/year) are primarily observed over the western part of North Africa (Sahara), and over the broader area of Bodélé, and secondarily over the Asian Taklamakan desert (140 days/year). For most of the study regions, the maximum frequencies appear in boreal spring and/or summer and the minimum ones in winter or autumn. A clear seasonality of global dust is revealed, with the lowest frequencies in November–December and the highest ones in June. Finally, an increasing trend of global dust frequency of occurrence from 2005 to 2019, equal to 56.2%, is also found. Such an increasing trend is observed over all study regions except for North Middle East, where a slight decreasing trend (−2.4%) is found.

ACS Style

Maria Gavrouzou; Nikolaos Hatzianastassiou; Antonis Gkikas; Marios-Bruno Korras-Carraca; Nikolaos Mihalopoulos. A Global Climatology of Dust Aerosols Based on Satellite Data: Spatial, Seasonal and Inter-Annual Patterns over the Period 2005–2019. Remote Sensing 2021, 13, 359 .

AMA Style

Maria Gavrouzou, Nikolaos Hatzianastassiou, Antonis Gkikas, Marios-Bruno Korras-Carraca, Nikolaos Mihalopoulos. A Global Climatology of Dust Aerosols Based on Satellite Data: Spatial, Seasonal and Inter-Annual Patterns over the Period 2005–2019. Remote Sensing. 2021; 13 (3):359.

Chicago/Turabian Style

Maria Gavrouzou; Nikolaos Hatzianastassiou; Antonis Gkikas; Marios-Bruno Korras-Carraca; Nikolaos Mihalopoulos. 2021. "A Global Climatology of Dust Aerosols Based on Satellite Data: Spatial, Seasonal and Inter-Annual Patterns over the Period 2005–2019." Remote Sensing 13, no. 3: 359.

Proceedings
Published: 13 November 2020 in Environmental Sciences Proceedings
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The present study was a first attempt to quantitatively evaluate an existing satellite-based rain estimation algorithm using measurements from a network of ground-based meteorological stations. The study domain was the Epirus region (the rainiest region in Greece) where the Laboratory of Meteorology and Climatology of Ioannina University operates eight meteorological stations distributed across the study domain. The utilized version of the rain estimation algorithm used the Meteosat-11 brightness temperature in the 10.8 μm channel (BT10.8μm) to estimate the rain intensity on a 4 km pixel basis, after discriminating the rain/non-rain pixels with a simple thresholding method. The rain recordings of the meteorological stations’ network were spatiotemporally correlated with the Meteosat-11 data. These correlations led to a dataset with 1323 pairs of rain recordings and their relative rain estimations from the satellite-based algorithm. A statistical analysis of these pairs of values was conducted revealing a mean error (ME) of 0.22 mm/hour (14% error with respect to the mean value of the recordings). The computed probability of false detection (POFD), probability of detection (POD), and the bias score were equal to 0.22, 0.69, and 0.88, respectively. The evaluation statistics are promising for operationally using this algorithm for rain estimation on a real-time basis.

ACS Style

Stavros Kolios; Nikos Hatzianastassiou; Christos J. Lolis. Evaluation of a Satellite-Based Rain Estimation Algorithm Using a Network of Meteorological Stations. Preliminary Results in a Region with Complex Terrain. Environmental Sciences Proceedings 2020, 4, 32 .

AMA Style

Stavros Kolios, Nikos Hatzianastassiou, Christos J. Lolis. Evaluation of a Satellite-Based Rain Estimation Algorithm Using a Network of Meteorological Stations. Preliminary Results in a Region with Complex Terrain. Environmental Sciences Proceedings. 2020; 4 (1):32.

Chicago/Turabian Style

Stavros Kolios; Nikos Hatzianastassiou; Christos J. Lolis. 2020. "Evaluation of a Satellite-Based Rain Estimation Algorithm Using a Network of Meteorological Stations. Preliminary Results in a Region with Complex Terrain." Environmental Sciences Proceedings 4, no. 1: 32.

Conference paper
Published: 13 November 2020 in Environmental Sciences Proceedings
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The overarching goal of the current study is to quantify the aerosol-induced clear-sky direct radiative effects (DREs) within the Earth-atmosphere system at the global scale and for the 40-year period 1980–2019. To this aim, the MERRA-2 aerosol radiative properties, along with meteorological fields and surface albedo, are used as inputs to the Foundation for Research and Technology-Hellas (FORTH) radiative transfer model (RTM). Our preliminary results, representative for the year 2015, reveal strong surface radiative cooling (down to −45 Wm−2) over areas where high aerosol loadings and absorbing particles (i.e., dust and biomass burning) dominate. This reduction of the incoming solar radiation in the aforementioned regions is largely attributed to its absorption by the overlying suspended particles resulting in atmospheric warming reaching up to 40 Wm−2. At the top of the atmosphere (TOA), negative DREs (planetary cooling) are computed worldwide (down to −20 Wm−2) with few exceptions over bright surfaces (warming up to 5 Wm−2). Finally, the strong variations between the obtained DREs of different aerosol species (dust, sea salt, sulfate, and organic/black carbon) as well as between hemispheres and surface types (i.e., land vs. ocean) are also discussed.

ACS Style

Marios-Bruno Korras-Carraca; Antonis Gkikas; Arlindo M. Da Silva; Christos Matsoukas; Nikolaos Hatzianastassiou; Ilias Vardavas. Optical Properties and Direct Radiative Effects of Aerosol Species at the Global Scale Based on the Synergistic Use of MERRA-2 Optical Properties and the FORTH Radiative Transfer Model. Environmental Sciences Proceedings 2020, 4, 4 .

AMA Style

Marios-Bruno Korras-Carraca, Antonis Gkikas, Arlindo M. Da Silva, Christos Matsoukas, Nikolaos Hatzianastassiou, Ilias Vardavas. Optical Properties and Direct Radiative Effects of Aerosol Species at the Global Scale Based on the Synergistic Use of MERRA-2 Optical Properties and the FORTH Radiative Transfer Model. Environmental Sciences Proceedings. 2020; 4 (1):4.

Chicago/Turabian Style

Marios-Bruno Korras-Carraca; Antonis Gkikas; Arlindo M. Da Silva; Christos Matsoukas; Nikolaos Hatzianastassiou; Ilias Vardavas. 2020. "Optical Properties and Direct Radiative Effects of Aerosol Species at the Global Scale Based on the Synergistic Use of MERRA-2 Optical Properties and the FORTH Radiative Transfer Model." Environmental Sciences Proceedings 4, no. 1: 4.

Conference paper
Published: 13 November 2020 in Environmental Sciences Proceedings
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In the present study, dust aerosol episodes (DAEs) in the broader Mediterranean Basin (MB) are investigated over a 15-year (2005–2019) period using contemporary MODIS Collection 6.1 and OMI OMAERUV satellite data and a satellite algorithm applying a thresholding technique on selected aerosol optical properties. The algorithm operates on a daily and 1° × 1° pixel level basis, first identifying the presence of dust, and consequently requiring the presence of unusually high dust loads, i.e., dust episodes. Apart from the presence of pixel-level DAEs, an extended spatial coverage of dust is also required. Thus, a specific day is characterized as a Dust Aerosol Episode Day (DAED), when at least 30 episodic pixels exist over Mediterranean Basin (MB). According to the algorithm results, 166 DAEDs (116 strong and 50 extreme) took place in the MB from 2005 to 2019. Most DAEDs occurred in spring (47%) and summer (38%), while a different seasonality is observed for strong and extreme episodes. The interannual variability of DAEDs reveal a decreasing trend, which is however not statistically significant.

ACS Style

Maria Gavrouzou; Nikos Hatzianastassiou; Antonis Gkikas; Nikos Mihalopoulos. A 15-Year Climatology of Desert Dust Episodes in the Broader Mediterranean Basin. Environmental Sciences Proceedings 2020, 4, 1 .

AMA Style

Maria Gavrouzou, Nikos Hatzianastassiou, Antonis Gkikas, Nikos Mihalopoulos. A 15-Year Climatology of Desert Dust Episodes in the Broader Mediterranean Basin. Environmental Sciences Proceedings. 2020; 4 (1):1.

Chicago/Turabian Style

Maria Gavrouzou; Nikos Hatzianastassiou; Antonis Gkikas; Nikos Mihalopoulos. 2020. "A 15-Year Climatology of Desert Dust Episodes in the Broader Mediterranean Basin." Environmental Sciences Proceedings 4, no. 1: 1.

Journal article
Published: 29 August 2020 in Atmosphere
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Recent advances in particle sensor technologies have led to an increased development and utilization of low-cost, compact, particulate matter (PM) monitors. These devices can be deployed in dense monitoring networks, enabling an improved characterization of the spatiotemporal variability in ambient levels and exposure. However, the reliability of their measurements is an important prerequisite, necessitating rigorous performance evaluation and calibration in comparison to reference-grade instrumentation. In this study, field evaluation of Purple Air PA-II devices (low-cost PM sensors) is performed in two urban environments and across three seasons in Greece, in comparison to different types of reference instruments. Measurements were conducted in Athens (the largest city in Greece with nearly four-million inhabitants) for five months spanning over the summer of 2019 and winter/spring of 2020 and in Ioannina, a medium-sized city in northwestern Greece (100,000 inhabitants) during winter/spring 2019–2020. The PM2.5 sensor output correlates strongly with reference measurements (R2 = 0.87 against a beta attenuation monitor and R2 = 0.98 against an optical reference-grade monitor). Deviations in the sensor-reference agreement are identified as mainly related to elevated coarse particle concentrations and high ambient relative humidity. Simple and multiple regression models are tested to compensate for these biases, drastically improving the sensor’s response. Large decreases in sensor error are observed after implementation of models, leading to mean absolute percentage errors of 0.18 and 0.12 for the Athens and Ioannina datasets, respectively. Overall, a quality-controlled and robustly evaluated low-cost network can be an integral component for air quality monitoring in a smart city. Case studies are presented along this line, where a network of PA-II devices is used to monitor the air quality deterioration during a peri-urban forest fire event affecting the area of Athens and during extreme wintertime smog events in Ioannina, related to wood burning for residential heating.

ACS Style

Iasonas Stavroulas; Georgios Grivas; Panagiotis Michalopoulos; Eleni Liakakou; Aikaterini Bougiatioti; Panayiotis Kalkavouras; Kyriaki Fameli; Nikolaos Hatzianastassiou; Nikolaos Mihalopoulos; Evangelos Gerasopoulos. Field Evaluation of Low-Cost PM Sensors (Purple Air PA-II) Under Variable Urban Air Quality Conditions, in Greece. Atmosphere 2020, 11, 926 .

AMA Style

Iasonas Stavroulas, Georgios Grivas, Panagiotis Michalopoulos, Eleni Liakakou, Aikaterini Bougiatioti, Panayiotis Kalkavouras, Kyriaki Fameli, Nikolaos Hatzianastassiou, Nikolaos Mihalopoulos, Evangelos Gerasopoulos. Field Evaluation of Low-Cost PM Sensors (Purple Air PA-II) Under Variable Urban Air Quality Conditions, in Greece. Atmosphere. 2020; 11 (9):926.

Chicago/Turabian Style

Iasonas Stavroulas; Georgios Grivas; Panagiotis Michalopoulos; Eleni Liakakou; Aikaterini Bougiatioti; Panayiotis Kalkavouras; Kyriaki Fameli; Nikolaos Hatzianastassiou; Nikolaos Mihalopoulos; Evangelos Gerasopoulos. 2020. "Field Evaluation of Low-Cost PM Sensors (Purple Air PA-II) Under Variable Urban Air Quality Conditions, in Greece." Atmosphere 11, no. 9: 926.

Preprint content
Published: 23 March 2020
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Aerosols, due to their interaction primary with the shortwave, but also with the longwave radiation, constitute a significant climate component, and at the same time an important, but still uncertain, factor of the contemporary climatic change. Apart from radiation, aerosols also interact with clouds, acting as Cloud Condensation Nuclei (CCN) and/or Ice Nuclei (IN), modifying the cloud optical and physical properties like cloud albedo, extent, lifetime or precipitation producing ability. Hence, it is also expected that high loads of specific aerosol types, such as desert dust, can induce even stronger effects on the above mentioned cloud properties.

More specifically, dust aerosols, which are inserted in the atmosphere mainly from the great world deserts, represent the major global aerosol component. These aerosols can remain suspended in the air and travel for several days, reaching areas far away from their sources. The Mediterranean Basin (MB), which is one of the most responsive regions to climate change, due to its location (nearby the Sahara desert in North Africa and the deserts of Middle East), is frequently affected from massive and extended dust transport. Because of the potentially significant role of these dust episodes, and their seasonal and inter-annual variability, they are worth to be studied and monitored through time.

In the present study, a modified version of a satellite algorithm, which is fully described by Gavrouzou et al. in another study of this conference, is used for the determination of strong and extreme dust episodes in the Mediterranean Basin over the period 2005-2018. The algorithm, using MODIS C6.1 spectral Aerosol Optical Depth (AOD) and OMI OMAERUV Aerosol Index (AI) as input data, ran on a daily and an 1°x1° pixel level basis and determined the occurrence and intensity of dust episodes whenever the AI is greater than 1 and the Angstrom Exponent (AE), which is calculated from spectral AOD data, is lower than 0.4. Any day is characterized as an episodic one when the dust optical depth (DOD) exceeds a computed threshold value (mean value plus two or four standard deviations for strong and extreme episodes, respectively) on at least 30 pixels of the study area. According to the algorithm results, 148 dust episode days (104 strong and 44 extreme) are found during the 2005-2018 period in the Mediterranean Basin. Most of the episodes occur in July (27 strong- and 3 extreme-episode days) and April (25 strong- and 6 extreme-episode days) while dust episodes are not detected at all in November and December. It is also found that in April, March and May take place the highest number of extreme MB episodes (23 out of the total 44 ones).

ACS Style

Nikos Hatzianastassiou; Maria Gavrouzou; Antonis Gkikas; Nikos Mihalopoulos. A climatology of dust episodes in the broader Mediterranean Basin using satellite MODIS C6.1 and OMI OMAERUV data. 2020, 1 .

AMA Style

Nikos Hatzianastassiou, Maria Gavrouzou, Antonis Gkikas, Nikos Mihalopoulos. A climatology of dust episodes in the broader Mediterranean Basin using satellite MODIS C6.1 and OMI OMAERUV data. . 2020; ():1.

Chicago/Turabian Style

Nikos Hatzianastassiou; Maria Gavrouzou; Antonis Gkikas; Nikos Mihalopoulos. 2020. "A climatology of dust episodes in the broader Mediterranean Basin using satellite MODIS C6.1 and OMI OMAERUV data." , no. : 1.

Preprint content
Published: 23 March 2020
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Aerosol measurements are carried out worldwide in order to reduce the uncertainties about the impact of aerosols on climate. Over the past two decades, different methods (ground- or satellite-based) for measuring aerosol properties have been developed, covering a variety of approaches with different temporal and spatial scales, which can be considered complementary. Aerosol optical properties are essential for assessing the effects of aerosols on radiation and climate. Aerosol single scattering albedo (SSA), along with optical depth and asymmetry parameter, is one of the three key optical properties that are necessary for radiation transfer and climate models. At the same time, SSA strongly depends on different aerosol types, thus enabling the identification of these different aerosol particles. However, despite the strong need for aerosol SSA products with global and climatological coverage, and the significant progress in retrieving SSA from satellite measurements, the satellite SSA retrievals are still subjected to uncertainties.

In this study, we perform an evaluation of the OMAERUVd (PGE Version V1.8.9.1) daily L3 (1° x 1° latitude-longitude) aerosol SSA data, which are based on the enhanced two-channel OMAERUV algorithm that essentially uses the ultraviolet radiance data from Aura/Ozone Monitoring Instrument (OMI), through comparisons against daily SSA products from 541 globally distributed Aerosol Robotic Network (AERONET) stations for a 15-year period (2005-2019). The comparison is performed between the available OMAERUVd SSA data at 354 nm, 388 nm, and 500 nm, and the AERONET SSA data at 440 nm (or 443 nm). The comparison is made on an annual and seasonal basis in order to reveal possible seasonally dependent patterns, as well as on a climatological and a year-to-year basis. The statistical metrics, such as Coefficient of Correlation (R) and Bias, are computed for individual AERONET stations as well as for all stations. The effect of availability of common OMI and AERONET data pairs on the comparison is assessed by making comparisons when at least 10, 50 and 100 common pairs are available.

The results show that about 50% (75%) of OMI-AERONET matchups agree within the absolute difference of ±0.03 (±0.05) for the 500 nm OMI SSA and the 440 nm (or 443 nm) AERONET SSA. The corresponding percentage for the 388 nm OMI SSA and the 440 nm (or 443 nm) AERONET SSA increases to 58% (81%), while the corresponding numbers for the 354 nm SSA OMI and the 440 nm (or 443 nm) AERONET are 43% (67%). It is found that in overall, OMI tends mainly to overestimate (underestimate) SSA for the 500 nm (354 nm) products in comparison to AERONET 440 nm (or 443 nm) with a total bias of 0.025 (-0.024), or 2.7% (2.6%) in relative percentage terms with respect to AERONET (mean AERONET value equal to 0.908), and an overall R value of 0.399 (0.386). At 388 nm, OMI tends to retrieve higher SSA over regions where biomass burning occurs, against lower SSA values elsewhere, with overall bias and R values equal to -0.002 (0.22%) and 0.395, respectively.

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Periklis Drakousis; Marios-Bruno Korras-Carraca; Hiren Jethva; Omar Torres; Nikos Hatzianastassiou. Global OMI Aerosol Single Scattering Albedo evaluation using ground-based AERONET. 2020, 1 .

AMA Style

Periklis Drakousis, Marios-Bruno Korras-Carraca, Hiren Jethva, Omar Torres, Nikos Hatzianastassiou. Global OMI Aerosol Single Scattering Albedo evaluation using ground-based AERONET. . 2020; ():1.

Chicago/Turabian Style

Periklis Drakousis; Marios-Bruno Korras-Carraca; Hiren Jethva; Omar Torres; Nikos Hatzianastassiou. 2020. "Global OMI Aerosol Single Scattering Albedo evaluation using ground-based AERONET." , no. : 1.

Journal article
Published: 21 March 2020 in Atmosphere
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Downward surface solar radiation (SSR) trends for the first decade of the 2000s were computed using a radiative transfer model and satellite and reanalysis input data and were validated against measurements from the reference global station networks Global Energy Balance Archive (GEBA) and Baseline Surface Radiation Network (BSRN). Under all-sky conditions, in spite of a somewhat patchy structure of global dimming and brightening (GDB), an overall dimming was found that is weaker in the Northern than in the Southern Hemisphere (−2.2 and −3.1 W m−2, respectively, over the 2001–2009 period). Dimming is observed over both land and ocean in the two hemispheres, but it is more remarkable over land areas of the Southern Hemisphere. The post-2000 dimming is found to have been primarily caused by clouds, and secondarily by aerosols, with total cloud cover contributing −1.4 W m−2 and aerosol optical thickness −0.7 W m−2 to the global average dimming of −2.65 W m−2. The evaluation of the model-computed GDB against BSRN and GEBA measurements indicates a good agreement, with the same trends for 65% and 64% of the examined stations, respectively. The obtained model results are in line with other studies for specific world regions and confirm the occurrence of an overall solar dimming over the globe during the first decade of 21st century. This post-2000 dimming has succeeded the global brightening observed in the 1990s and points to possible impacts on the ongoing global warming and climate change.

ACS Style

Nikolaos Hatzianastassiou; Eleftherios Ioannidis; Marios-Bruno Korras-Carraca; Maria Gavrouzou; Christos D. Papadimas; Christos Matsoukas; Nikolaos Benas; Angeliki Fotiadi; Martin Wild; Ilias Vardavas. Global Dimming and Brightening Features during the First Decade of the 21st Century. Atmosphere 2020, 11, 308 .

AMA Style

Nikolaos Hatzianastassiou, Eleftherios Ioannidis, Marios-Bruno Korras-Carraca, Maria Gavrouzou, Christos D. Papadimas, Christos Matsoukas, Nikolaos Benas, Angeliki Fotiadi, Martin Wild, Ilias Vardavas. Global Dimming and Brightening Features during the First Decade of the 21st Century. Atmosphere. 2020; 11 (3):308.

Chicago/Turabian Style

Nikolaos Hatzianastassiou; Eleftherios Ioannidis; Marios-Bruno Korras-Carraca; Maria Gavrouzou; Christos D. Papadimas; Christos Matsoukas; Nikolaos Benas; Angeliki Fotiadi; Martin Wild; Ilias Vardavas. 2020. "Global Dimming and Brightening Features during the First Decade of the 21st Century." Atmosphere 11, no. 3: 308.

Journal article
Published: 04 February 2020 in Atmosphere
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This study examines the carbonaceous-aerosol characteristics at three contrasting urban environments in Greece (Ioannina, Athens, and Heraklion), on the basis of 12 h sampling during winter (January to February 2013), aiming to explore the inter-site differences in atmospheric composition and carbonaceous-aerosol characteristics and sources. The winter-average organic carbon (OC) and elemental carbon (EC) concentrations in Ioannina were found to be 28.50 and 4.33 µg m−3, respectively, much higher than those in Heraklion (3.86 µg m−3 for OC and 2.29 µg m−3 for EC) and Athens (7.63 µg m−3 for OC and 2.44 µg m−3 for EC). The winter OC/EC ratio in Ioannina (6.53) was found to be almost three times that in Heraklion (2.03), indicating a larger impact of wood combustion, especially during the night, whereas in Heraklion, emissions from biomass burning were found to be less intense. Estimations of primary and secondary organic carbon (POC and SOC) using the EC-tracer method, and specifically its minimum R-squared (MRS) variant, revealed large differences between the sites, with a prevalence of POC (67–80%) in Ioannina and Athens and with a larger SOC fraction (53%) in Heraklion. SOC estimates were also obtained using the 5% and 25% percentiles of the OC/EC data to determine the (OC/EC)pri, leading to results contrasting to the MRS approach in Ioannina (70–74% for SOC). Although the MRS method provides generally more robust results, it may significantly underestimate SOC levels in environments highly burdened by biomass burning, as the fast-oxidized semi-volatile OC associated with combustion sources is classified in POC. Further analysis in Athens revealed that the difference in SOC estimates between the 5% percentile and MRS methods coincided with the semi-volatile oxygenated organic aerosol as quantified by aerosol mass spectrometry. Finally, the OC/Kbb+ ratio was used as tracer for decomposition of the POC into fossil-fuel and biomass-burning components, indicating the prevalence of biomass-burning POC, especially in Ioannina (77%).

ACS Style

Dimitris G. Kaskaoutis; Georgios Grivas; Christina Theodosi; Maria Tsagkaraki; Despina Paraskevopoulou; Iasonas Stavroulas; Eleni Liakakou; Antonis Gkikas; Nikolaos Hatzianastassiou; Cheng Wu; Evangelos Gerasopoulos; Nikolaos Mihalopoulos. Carbonaceous Aerosols in Contrasting Atmospheric Environments in Greek Cities: Evaluation of the EC-tracer Methods for Secondary Organic Carbon Estimation. Atmosphere 2020, 11, 161 .

AMA Style

Dimitris G. Kaskaoutis, Georgios Grivas, Christina Theodosi, Maria Tsagkaraki, Despina Paraskevopoulou, Iasonas Stavroulas, Eleni Liakakou, Antonis Gkikas, Nikolaos Hatzianastassiou, Cheng Wu, Evangelos Gerasopoulos, Nikolaos Mihalopoulos. Carbonaceous Aerosols in Contrasting Atmospheric Environments in Greek Cities: Evaluation of the EC-tracer Methods for Secondary Organic Carbon Estimation. Atmosphere. 2020; 11 (2):161.

Chicago/Turabian Style

Dimitris G. Kaskaoutis; Georgios Grivas; Christina Theodosi; Maria Tsagkaraki; Despina Paraskevopoulou; Iasonas Stavroulas; Eleni Liakakou; Antonis Gkikas; Nikolaos Hatzianastassiou; Cheng Wu; Evangelos Gerasopoulos; Nikolaos Mihalopoulos. 2020. "Carbonaceous Aerosols in Contrasting Atmospheric Environments in Greek Cities: Evaluation of the EC-tracer Methods for Secondary Organic Carbon Estimation." Atmosphere 11, no. 2: 161.

Journal article
Published: 01 November 2019 in Atmosphere
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A global climatology of absorbing carbonaceous aerosols (ACA) for the period 2005–2015 is obtained by using satellite MODIS (Moderate Resolution Imaging Spectroradiometer)-Aqua and OMI (Ozone Monitoring Instrument)-Aura aerosol optical properties and by applying an algorithm. The algorithm determines the frequency of presence of ACA (black and brown carbon) over the globe at 1° × 1° pixel level and on a daily basis. The results of the algorithm indicate high frequencies of ACA (up to 19 days/month) over world regions with extended biomass burning, such as the tropical forests of southern and central Africa, South America and equatorial Asia, over savannas, cropland areas or boreal forests, as well as over urban and rural areas with intense anthropogenic activities, such as the eastern coast of China or the Indo-Gangetic plain. A clear seasonality of the frequency of occurrence of ACA is evident, with increased values during June–October over southern Africa, during July–November over South America, August–November over Indonesia, November–March over central Africa and November–April over southeastern Asia. The estimated seasonality of ACA is in line with the known annual patterns of worldwide biomass-burning emissions, while other features such as the export of carbonaceous aerosols from southern Africa to the southeastern Atlantic Ocean are also successfully reproduced by the algorithm. The results indicate a noticeable interannual variability and tendencies of ACA over specific world regions during 2005–2015, such as statistically significant increasing frequency of occurrence over southern Africa and eastern Asia.

ACS Style

Nikolaos Hatzianastassiou; Nikoleta Kalaitzi; Maria Gavrouzou; Antonis Gkikas; Marios-Bruno Korras-Carraca; Nikolaos Mihalopoulos. A Climatological Satellite Assessment of Absorbing Carbonaceous Aerosols on a Global Scale. Atmosphere 2019, 10, 671 .

AMA Style

Nikolaos Hatzianastassiou, Nikoleta Kalaitzi, Maria Gavrouzou, Antonis Gkikas, Marios-Bruno Korras-Carraca, Nikolaos Mihalopoulos. A Climatological Satellite Assessment of Absorbing Carbonaceous Aerosols on a Global Scale. Atmosphere. 2019; 10 (11):671.

Chicago/Turabian Style

Nikolaos Hatzianastassiou; Nikoleta Kalaitzi; Maria Gavrouzou; Antonis Gkikas; Marios-Bruno Korras-Carraca; Nikolaos Mihalopoulos. 2019. "A Climatological Satellite Assessment of Absorbing Carbonaceous Aerosols on a Global Scale." Atmosphere 10, no. 11: 671.

Journal article
Published: 30 April 2019 in Remote Sensing
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This study presents the development of an artificial neural network (ANN) model to quantitatively estimate the atmospheric aerosol load (in terms of aerosol optical depth, AOD), with an emphasis on dust, over the Mediterranean basin using images from Meteosat satellites as initial information. More specifically, a back-propagation ANN model scheme was developed to estimate visible (at 550 nm) aerosol optical depth (AOD550 nm) values at equal temporal (15 min) and spatial (4 km) resolutions with Meteosat imagery. Accuracy of the ANN model was thoroughly tested by comparing model estimations with ground-based AOD550 nm measurements from 14 AERONET (Aerosol Robotic NETwork) stations over the Mediterranean for 34 selected days in which significant dust loads were recorded over the Mediterranean basin. Using a testbed of 3076 pairs of modeled and measured AOD550 nm values, a Pearson correlation coefficient (rP) equal to 0.91 and a mean absolute error (MAE) of 0.031 were found, proving the satisfactory accuracy of the developed model for estimating AOD550 nm values.

ACS Style

Stavros Kolios; Nikos Hatzianastassiou. Quantitative Aerosol Optical Depth Detection during Dust Outbreaks from Meteosat Imagery Using an Artificial Neural Network Model. Remote Sensing 2019, 11, 1022 .

AMA Style

Stavros Kolios, Nikos Hatzianastassiou. Quantitative Aerosol Optical Depth Detection during Dust Outbreaks from Meteosat Imagery Using an Artificial Neural Network Model. Remote Sensing. 2019; 11 (9):1022.

Chicago/Turabian Style

Stavros Kolios; Nikos Hatzianastassiou. 2019. "Quantitative Aerosol Optical Depth Detection during Dust Outbreaks from Meteosat Imagery Using an Artificial Neural Network Model." Remote Sensing 11, no. 9: 1022.

Journal article
Published: 21 January 2019 in Remote Sensing
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Clouds are of high importance for the climate system but they still remain one of its principal uncertainties. Remote sensing techniques applied to satellite observations have assisted tremendously in the creation of long-term and homogeneous data records; however, satellite data sets need to be validated and compared with other data records, especially ground measurements. In the present study, the spatiotemporal distribution and variability of Total Cloud Cover (TCC) from the Satellite Application Facility on Climate Monitoring (CM SAF) Cloud, Albedo And Surface Radiation dataset from AVHRR data—edition 2 (CLARA-A2) and the International Satellite Cloud Climatology Project H-series (ISCCP-H) is analyzed over Europe. The CLARA-A2 data record has been created using measurements of the Advanced Very High Resolution Radiometer (AVHRR) instrument onboard the polar orbiting NOAA and the EUMETSAT MetOp satellites, whereas the ISCCP-H data were produced by a combination of measurements from geostationary meteorological satellites and the AVHRR instrument on the polar orbiting satellites. An intercomparison of the two data records is performed over their common period, 1984 to 2012. In addition, a comparison of the two satellite data records is made against TCC observations at 22 meteorological stations in Europe, from the European Climate Assessment & Dataset (ECA&D). The results indicate generally larger ISCCP-H TCC with respect to the corresponding CLARA-A2 data, in particular in the Mediterranean. Compared to ECA&D data, both satellite datasets reveal a reasonable performance, with overall mean TCC biases of 2.1 and 5.2% for CLARA-A2 and ISCCP-H, respectively. This, along with the higher correlation coefficients between CLARA-A2 and ECA&D TCC, indicates the better performance of CLARA-A2 TCC data.

ACS Style

Vasileios Tzallas; Nikolaos Hatzianastassiou; Nikos Benas; Jan Fokke Meirink; Christos Matsoukas; Jr. Paul Stackhouse; Ilias Vardavas. Evaluation of CLARA-A2 and ISCCP-H Cloud Cover Climate Data Records over Europe with ECA&D Ground-Based Measurements. Remote Sensing 2019, 11, 212 .

AMA Style

Vasileios Tzallas, Nikolaos Hatzianastassiou, Nikos Benas, Jan Fokke Meirink, Christos Matsoukas, Jr. Paul Stackhouse, Ilias Vardavas. Evaluation of CLARA-A2 and ISCCP-H Cloud Cover Climate Data Records over Europe with ECA&D Ground-Based Measurements. Remote Sensing. 2019; 11 (2):212.

Chicago/Turabian Style

Vasileios Tzallas; Nikolaos Hatzianastassiou; Nikos Benas; Jan Fokke Meirink; Christos Matsoukas; Jr. Paul Stackhouse; Ilias Vardavas. 2019. "Evaluation of CLARA-A2 and ISCCP-H Cloud Cover Climate Data Records over Europe with ECA&D Ground-Based Measurements." Remote Sensing 11, no. 2: 212.

Journal article
Published: 21 June 2018 in Atmospheric Chemistry and Physics
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The direct radiative effect (DRE) during 20 intense and widespread dust outbreaks, which affected the broader Mediterranean basin over the period March 2000–February 2013, has been calculated with the NMMB-MONARCH model at regional (Sahara and European continent) and short-term temporal (84 h) scales. According to model simulations, the maximum dust aerosol optical depths (AODs) range from ∼ 2.5 to ∼ 5.5 among the identified cases. At midday, dust outbreaks locally induce a NET (shortwave plus longwave) strong atmospheric warming (DREATM values up to 285 W m−2; Niger–Chad; dust AODs up to ∼ 5.5) and a strong surface cooling (DRENETSURF values down to −337 W m−2), whereas they strongly reduce the downward radiation at the ground level (DRESURF values down to −589 W m−2 over the Eastern Mediterranean, for extremely high dust AODs, 4.5–5). During night-time, reverse effects of smaller magnitude are found. At the top of the atmosphere (TOA), positive (planetary warming) DREs up to 85 W m−2 are found over highly reflective surfaces (Niger–Chad; dust AODs up to ∼ 5.5) while negative (planetary cooling) DREs down to −184 W m−2 (Eastern Mediterranean; dust AODs 4.5–5) are computed over dark surfaces at noon. Dust outbreaks significantly affect the mean regional radiation budget, with NET DREs ranging from −8.5 to 0.5 W m−2, from −31.6 to 2.1 W m−2, from −22.2 to 2.2 W m−2 and from −1.7 to 20.4 W m−2 for TOA, SURF, NETSURF and ATM, respectively. Although the shortwave DREs are larger than the longwave ones, the latter are comparable or even larger at TOA, particularly over the Sahara at midday. As a response to the strong surface day-time cooling, dust outbreaks cause a reduction in the regional sensible and latent heat fluxes by up to 45 and 4 W m−2, respectively, averaged over land areas of the simulation domain. Dust outbreaks reduce the temperature at 2 m by up to 4 K during day-time, whereas a reverse tendency of similar magnitude is found during night-time. Depending on the vertical distribution of dust loads and time, mineral particles heat (cool) the atmosphere by up to 0.9 K (0.8 K) during day-time (night-time) within atmospheric dust layers. Beneath and above the dust clouds, mineral particles cool (warm) the atmosphere by up to 1.3 K (1.2 K) at noon (night-time). On a regional mean basis, negative feedbacks on the total emitted dust (reduced by 19.5 %) and dust AOD (reduced by 6.9 %) are found when dust interacts with the radiation. Through the consideration of dust radiative effects in numerical simulations, the model positive and negative biases for the downward surface SW or LW radiation, respectively, with respect to Baseline Surface Radiation Network (BSRN) measurements, are reduced. In addition, they also reduce the model near-surface (at 2 m) nocturnal cold biases by up to 0.5 K (regional averages), as well as the model warm biases at 950 and 700 hPa, where the dust concentration is maximized, by up to 0.4 K. However, improvements are relatively small and do not happen in all episodes because other model first-order errors may dominate over the expected improvements, and the misrepresentation of the dust plumes' spatiotemporal features and optical properties may even produce a double penalty effect. The enhancement of dust forecasts via data assimilation techniques may significantly improve the results.

ACS Style

Antonis Gkikas; Vincenzo Obiso; Carlos Pérez García-Pando; Oriol Jorba; Nikos Hatzianastassiou; Lluis Vendrell; Sara Basart; Stavros Solomos; Santiago Gassó; José Maria Baldasano. Direct radiative effects during intense Mediterranean desert dust outbreaks. Atmospheric Chemistry and Physics 2018, 18, 8757 -8787.

AMA Style

Antonis Gkikas, Vincenzo Obiso, Carlos Pérez García-Pando, Oriol Jorba, Nikos Hatzianastassiou, Lluis Vendrell, Sara Basart, Stavros Solomos, Santiago Gassó, José Maria Baldasano. Direct radiative effects during intense Mediterranean desert dust outbreaks. Atmospheric Chemistry and Physics. 2018; 18 (12):8757-8787.

Chicago/Turabian Style

Antonis Gkikas; Vincenzo Obiso; Carlos Pérez García-Pando; Oriol Jorba; Nikos Hatzianastassiou; Lluis Vendrell; Sara Basart; Stavros Solomos; Santiago Gassó; José Maria Baldasano. 2018. "Direct radiative effects during intense Mediterranean desert dust outbreaks." Atmospheric Chemistry and Physics 18, no. 12: 8757-8787.

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Published: 10 November 2017
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The direct radiative effect (DRE) of 20 intense and widespread dust outbreaks that affected the broader Mediterranean basin during the period March 2000 – February 2013, has been calculated with the regional NMMB-MONARCH model. The DREs have been calculated based on short-term simulations (84 hours) for a domain covering the Sahara and most part of the European continent. At midday, desert dust outbreaks induce locally a NET (shortwave plus longwave) strong atmospheric warming (DREATM values up to 285 Wm−2), a strong surface cooling (DRENETSURF values down to −337 Wm−2) whereas they strongly reduce the downward radiation at the ground (DRESURF values down to −589 Wm−2). During nighttime, reverse effects of smaller magnitude are found. At the top of the atmosphere (TOA), positive (planetary warming) DREs up to 85 Wm−2 are found over highly reflective surfaces while negative (planetary cooling) DREs down to −184 Wm−2 are computed over dark surfaces at noon. Desert dust outbreaks significantly affect the regional radiation budget, with regional clear-sky NET DRE values ranging from −13.9 to 2.6 Wm−2, from −43.6 to 4 Wm−2, from −26.3 to 3.9 Wm−2 and from −3.7 to 28 Wm−2 for TOA, SURF, NETSURF and ATM, respectively. Although the shortwave (SW) DREs are larger than the longwave (LW) ones, the latter are comparable or even larger at TOA, particularly over the Sahara at midday. As a response to the strong surface cooling during daytime, dust outbreaks cause a reduction of the regional sensible and latent heat fluxes by up to 45 Wm−2 and 4 Wm−2, respectively, averaged over land areas of the simulation domain. Dust outbreaks reduce the temperature at 2 meters by up to 4 K during day, whereas a reverse tendency of similar magnitude is found during night. Depending on the vertical distribution of dust loads and time, mineral particles heat (cool) the atmosphere by up to 0.9 K (0.8 K) during daytime (nighttime) within atmospheric dust layers. Beneath and above the dust clouds, mineral particles cool (warm) the atmosphere by up to 1.3 K (1.2 K) at noon (night). When dust radiative effects are taken into account in numerical simulations, the total emitted dust and dust AOD, computed on a regional mean basis, are decreased (negative feedback) by 19.5 % and 6.9 %. The consideration of dust radiative effects in numerical simulations improves the model predictive skills. More specifically, it reduces the model positive and negative biases for the downward surface SW and LW radiation, respectively, with respect to Baseline Surface Radiation Network (BSRN) measurements. In addition, they also reduce the model near-surface (at 2 meters) nocturnal cold biases by up to 0.5 K (regional averages), as well as the model warm biases at 950 and 700 hPa, where the dust concentration is maximized, by up to 0.4 K.

ACS Style

Antonis Gkikas; Vincenzo Obiso; Carlos Pérez García-Pando; Oriol Jorba; Nikos Hatzianastassiou; Lluis Vendrell; Sara Basart; Santiago Gassó; José Maria Baldasano. Direct radiative effects of intense Mediterranean desert dust outbreaks. 2017, 2017, 1 -67.

AMA Style

Antonis Gkikas, Vincenzo Obiso, Carlos Pérez García-Pando, Oriol Jorba, Nikos Hatzianastassiou, Lluis Vendrell, Sara Basart, Santiago Gassó, José Maria Baldasano. Direct radiative effects of intense Mediterranean desert dust outbreaks. . 2017; 2017 ():1-67.

Chicago/Turabian Style

Antonis Gkikas; Vincenzo Obiso; Carlos Pérez García-Pando; Oriol Jorba; Nikos Hatzianastassiou; Lluis Vendrell; Sara Basart; Santiago Gassó; José Maria Baldasano. 2017. "Direct radiative effects of intense Mediterranean desert dust outbreaks." 2017, no. : 1-67.

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Published: 10 November 2017
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Antonis Gkikas; Vincenzo Obiso; Carlos Pérez García-Pando; Oriol Jorba; Nikos Hatzianastassiou; Lluis Vendrell; Sara Basart; Santiago Gassó; José Maria Baldasano. Supplementary material to "Direct radiative effects of intense Mediterranean desert dust outbreaks". 2017, 1 .

AMA Style

Antonis Gkikas, Vincenzo Obiso, Carlos Pérez García-Pando, Oriol Jorba, Nikos Hatzianastassiou, Lluis Vendrell, Sara Basart, Santiago Gassó, José Maria Baldasano. Supplementary material to "Direct radiative effects of intense Mediterranean desert dust outbreaks". . 2017; ():1.

Chicago/Turabian Style

Antonis Gkikas; Vincenzo Obiso; Carlos Pérez García-Pando; Oriol Jorba; Nikos Hatzianastassiou; Lluis Vendrell; Sara Basart; Santiago Gassó; José Maria Baldasano. 2017. "Supplementary material to "Direct radiative effects of intense Mediterranean desert dust outbreaks"." , no. : 1.