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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.
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 StyleMaria 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 StyleMaria 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.
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.
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 StyleStavros 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 StyleStavros 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.
The use of weather types for the definition of seasons is examined. Specifically, an objective definition of seasons is attempted for the southern Balkans based on the intra-annual variations of the frequencies of the objectively defined weather types. The methodology includes a combined application of Principal Component Analysis and k-means Cluster Analysis on daily grid point meteorological data obtained from the ERA5 database, for the 40-year period 1979–2018. The methodology is used at first for the classification of weather types and then for the definition of seasons based on the intra-annual variations of the weather types’ frequency. The application of the methodology results in nine weather types and four seasons. The characteristics of the defined weather types are connected to the prevalence of specific atmospheric circulation patterns, the windward or leeward character of the various sub-regions, and the thermal characteristics of the earth’s surface. The four seasons generally correspond to the conventional ones, but they present differences regarding their onset and cessation dates and their duration.
C. J. Lolis; G. Kotsias. The use of weather types in the definition of seasons: the case of southern Balkans. Theoretical and Applied Climatology 2020, 142, 1199 -1219.
AMA StyleC. J. Lolis, G. Kotsias. The use of weather types in the definition of seasons: the case of southern Balkans. Theoretical and Applied Climatology. 2020; 142 (3-4):1199-1219.
Chicago/Turabian StyleC. J. Lolis; G. Kotsias. 2020. "The use of weather types in the definition of seasons: the case of southern Balkans." Theoretical and Applied Climatology 142, no. 3-4: 1199-1219.
An objective definition of climatologically homogeneous areas in the southern Balkans is attempted with the use of daily 0.25° × 0.25° ERA5 meteorological data of air temperature, dew point, zonal and meridional wind components, Convective Available Potential Energy, Convective Inhibition, and total cloud cover. The classification of the various grid points into climatologically homogeneous areas is carried out by applying Principal Component Analysis and K-means Cluster Analysis on the mean spatial anomaly patterns of the above parameters for the 10-year period of 2008 to 2017. According to the results, 12 climatologically homogenous areas are found. From these areas, eight are mainly over the sea and four are mainly over the land. The mean intra-annual variations of the spatial anomalies of the above parameters reveal the main climatic characteristics of these areas for the above period. These characteristics refer, for example, to how much warmer or cloudy the climate of a specific area is in a specific season relatively to the rest of the geographical domain. The continentality, the latitude, the altitude, the orientation, and the seasonal variability of the thermal and dynamic factors affecting the Mediterranean region are responsible for the climate characteristics of the 12 areas and the differences among them.
Christos J. Lolis; Georgios Kotsias; Aristides Bartzokas. Objective Definition of Climatologically Homogeneous Areas in the Southern Balkans Based on the ERA5 Data Set. Climate 2018, 6, 96 .
AMA StyleChristos J. Lolis, Georgios Kotsias, Aristides Bartzokas. Objective Definition of Climatologically Homogeneous Areas in the Southern Balkans Based on the ERA5 Data Set. Climate. 2018; 6 (4):96.
Chicago/Turabian StyleChristos J. Lolis; Georgios Kotsias; Aristides Bartzokas. 2018. "Objective Definition of Climatologically Homogeneous Areas in the Southern Balkans Based on the ERA5 Data Set." Climate 6, no. 4: 96.
In this paper we present an experimental validated system for measuring rainfall due to radio frequency (RF) signal attenuation at 2 GHz. Measurements took place in Ioannina, NW Greece, starting in April 2015 and lasting for twelve months. The primary acquired extensive results have shown reliable and accurate measurements for rainfall amounts smaller than 1 mm for 5 min periods. The very important innovation is that this paper presents significant earth-to-earth measurements due to rainfall attenuation (at 2 GHz) in order to act as a map for future investigation and as a prior knowledge for the behavior of other systems operating at frequencies around S-band.
Vasilis Christofilakis; Giorgos Tatsis; Constantinos T. Votis; Spyridon K. Chronopoulos; Panos Kostarakis; Christos J. Lolis; Aristides Bartzokas. Rainfall Measurements Due to Radio Frequency Signal Attenuation at 2 GHz. Journal of Signal and Information Processing 2018, 09, 192 -201.
AMA StyleVasilis Christofilakis, Giorgos Tatsis, Constantinos T. Votis, Spyridon K. Chronopoulos, Panos Kostarakis, Christos J. Lolis, Aristides Bartzokas. Rainfall Measurements Due to Radio Frequency Signal Attenuation at 2 GHz. Journal of Signal and Information Processing. 2018; 09 (03):192-201.
Chicago/Turabian StyleVasilis Christofilakis; Giorgos Tatsis; Constantinos T. Votis; Spyridon K. Chronopoulos; Panos Kostarakis; Christos J. Lolis; Aristides Bartzokas. 2018. "Rainfall Measurements Due to Radio Frequency Signal Attenuation at 2 GHz." Journal of Signal and Information Processing 09, no. 03: 192-201.
C. J. Lolis. A climatology of convective available potential energy in the Mediterranean region. Climate Research 2017, 74, 15 -30.
AMA StyleC. J. Lolis. A climatology of convective available potential energy in the Mediterranean region. Climate Research. 2017; 74 (1):15-30.
Chicago/Turabian StyleC. J. Lolis. 2017. "A climatology of convective available potential energy in the Mediterranean region." Climate Research 74, no. 1: 15-30.
Cj Lolis; M Türkeş. Atmospheric circulation characteristics favouring extreme precipitation in Turkey. Climate Research 2016, 71, 139 -153.
AMA StyleCj Lolis, M Türkeş. Atmospheric circulation characteristics favouring extreme precipitation in Turkey. Climate Research. 2016; 71 (2):139-153.
Chicago/Turabian StyleCj Lolis; M Türkeş. 2016. "Atmospheric circulation characteristics favouring extreme precipitation in Turkey." Climate Research 71, no. 2: 139-153.
Monthly mean satellite data from the Global Precipitation Climatology Project (GPCPv2) are used to examine the year-by-year variability of precipitation over the Mediterranean Basin and its changes over the period 1979–2010. The results show that the mean annual precipitation averaged over the study area has slightly increased from 1979 to 2010 by 1.28 mm or by 0.2% (trend not statistically significant at the 95% confidence level). Nevertheless, examining the trends at a local scale, spatial and temporal patterns are revealed, with opposite trends in adjacent areas and increasing precipitation in summer and autumn against almost unchanged or decreasing precipitation in winter and spring, respectively. Inter-decadal changes of precipitation are detected, with precipitation decreasing in the 1980s, then increasing through the late 1990s and finally declining in the 2000s before levelling off since 2007. These changes are significantly anti-correlated (R = −0.57, up to −0.66 in winter) with the North Atlantic Oscillation (NAO) index, thus confirming the critical role of this large-scale teleconnection for the regional precipitation over the basin.
Nikolaos Hatzianastassiou; Christos D. Papadimas; Christos J. Lolis; Aristides Bartzokas; Vincenzo Levizzani; John D. Pnevmatikos; Basil D. Katsoulis. Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data. Part-II: inter-annual variability and trends. International Journal of Climatology 2016, 36, 4755 -4766.
AMA StyleNikolaos Hatzianastassiou, Christos D. Papadimas, Christos J. Lolis, Aristides Bartzokas, Vincenzo Levizzani, John D. Pnevmatikos, Basil D. Katsoulis. Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data. Part-II: inter-annual variability and trends. International Journal of Climatology. 2016; 36 (15):4755-4766.
Chicago/Turabian StyleNikolaos Hatzianastassiou; Christos D. Papadimas; Christos J. Lolis; Aristides Bartzokas; Vincenzo Levizzani; John D. Pnevmatikos; Basil D. Katsoulis. 2016. "Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data. Part-II: inter-annual variability and trends." International Journal of Climatology 36, no. 15: 4755-4766.
The precipitation regime over the Mediterranean basin is investigated for the period 1979–2010 using monthly mean satellite data from the Global Precipitation Climatology Project (GPCPv2). The results show that a clear contrast exists between the more rainy northern part of the study region (Southern Europe) and the drier southern area (North Africa, Iberian Peninsula) and between the western sides (rainsides) of the Iberian, Italian and Balkan peninsulas and their eastern sides (rainshadows). The mean annual precipitation averaged over the study area is P = 593 ± 203 mm year−1, but it has a strong spatial variability ranging from 20 mm year−1 (North Africa) to 1500 mm year−1 (Alps). A significant seasonal variability exists, with the early winter and late autumn months (November and December) being the wettest with precipitation amounts larger than 60 mm month−1. The GPCPv2 satellite precipitation data are satisfactorily correlated with rain gauge measurements from 433 stations within the study area (correlation coefficient R = 0.78 for all stations on a yearly basis, with values ranging between 0.72 and 0.82, depending on the season) with a slight overestimation. They also compare well with the higher spatial and temporal resolution Tropical Rainfall Measuring Mission (TRMM) data, which supports the validity of the present study.
Nikolaos Hatzianastassiou; Christos D. Papadimas; Christos J. Lolis; Aristides Bartzokas; Vincenzo Levizzani; John D. Pnevmatikos; Basil D. Katsoulis. Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data, part I: evaluation and climatological patterns. International Journal of Climatology 2016, 36, 4741 -4754.
AMA StyleNikolaos Hatzianastassiou, Christos D. Papadimas, Christos J. Lolis, Aristides Bartzokas, Vincenzo Levizzani, John D. Pnevmatikos, Basil D. Katsoulis. Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data, part I: evaluation and climatological patterns. International Journal of Climatology. 2016; 36 (15):4741-4754.
Chicago/Turabian StyleNikolaos Hatzianastassiou; Christos D. Papadimas; Christos J. Lolis; Aristides Bartzokas; Vincenzo Levizzani; John D. Pnevmatikos; Basil D. Katsoulis. 2016. "Spatial and temporal variability of precipitation over the Mediterranean Basin based on 32-year satellite Global Precipitation Climatology Project data, part I: evaluation and climatological patterns." International Journal of Climatology 36, no. 15: 4741-4754.