41 research outputs found
Secondary ozone peaks in the troposphere over the Himalayas
No full textAbstract. Layers with strongly enhanced ozone concentrations in the middle–upper troposphere, referred to as secondary ozone peaks (SOPs), have been observed in different regions of the world. Here we use the global ECHAM5/MESSy atmospheric chemistry model (EMAC) to (i) investigate the processes causing SOPs, (ii) explore both their frequency of occurrence and seasonality, and (iii) assess their effects on the tropospheric ozone budget over the Himalayas. The vertical profiles of potential vorticity (PV) and a stratospheric ozone tracer (O3s) in EMAC simulations, in conjunction with the structure of SOPs, suggest that SOPs over the Himalayas are formed by stratosphere-to-troposphere transport (STT) of ozone. The spatial distribution of O3s further shows that such effects are in general most pronounced in the northern part of India. Model simulated ozone distributions and backward air trajectories show that ozone rich air masses, associated with STT, originate as far as northern Africa and the North Atlantic Ocean, the Middle East, as well as in nearby regions in Afghanistan and Pakistan, and are rapidly (within 2–3 days) transported to the Himalayas. Analysis of a 15-year (2000–2014) EMAC simulation shows that the frequency of SOPs is highest during the pre-monsoon season (e.g. 11 % of the time in May), while no intense SOP events are found during the July–October period. The SOPs are estimated to enhance the tropospheric column ozone (TCO) over the central Himalayas by up to 21 %.
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Future Projections in Agricultural Drought Characteristics for Greece Under Different Climate Change Scenarios
No full textChanges in agricultural drought frequency (DF), duration (DD) and severity (DS) in Greece are investigated based on 11 high-resolution EURO-CORDEX regional climate model simulations covering the period 1971–2100 under three different Representative Concentration Pathways (RCP2.6, RCP4.5 and RCP8.5) with the use of the SPI and SPEI. Increases in DF, DD and DS are more prominent in the 2071–2100 period under RCP8.5. Central and southern Greece, the Aegean islands and Crete experience the largest increases under RCP4.5 and RCP8.5. Under RCP2.6, changes in DD and DS are less pronounced, especially over northern Greece
Spatiotemporal Evolution of Seasonal Crop-Specific Climatic Indices under Climate Change in Greece Based on EURO-CORDEX RCM Simulations
No full textThis study presents an updated assessment of the projected climate change over Greece in the near future (2021–2050) and at the end of the 21st century (2071–2100) (EOC), relative to the reference period 1971–2000, and focusing on seasonal crop-specific climatic indices. The indices include days (d) with: a maximum daily near-surface temperature (TASMAX) > 30 °C in Spring, a TASMAX > 35 °C in Summer (hot days), a minimum daily near-surface temperature (TASMIN) < 0 °C (frost days) in Spring, a TASMIN > 20 °C (tropical nights) in Spring–Summer and the daily precipitation (PR) > 1 mm (wet days) in Spring and Summer covering the critical periods in which wheat, tomatoes, cotton, potato, grapes, rice and olive are more sensitive to water and/or temperature stress. The analysis is based on an ensemble of 11 EURO-CORDEX regional climate model simulations under the influence of a strong, a moderate, and a no mitigation Representative Concentration Pathway (RCP2.6, RCP4.5 and RCP8.5, respectively). The indices related to TASMAX are expected to increase by up to 11 days in Spring and 40 days in Summer, tropical nights to rise by up to 50 days, frost days to decrease by up to 20 days, and wet days to decline by up to 9 days in Spring and Summer, at the EOC with an RCP8.5. The increased heat stress and water deficit are expected to have negative crop impacts, in contrast to the positive effects anticipated by the decrease in frost days. This study constitutes a further step towards identifying the commodities and/or regions in Greece which, under climate change, are or will be significantly impacted
Future Projections of Precipitation Extremes for Greece Based on an Ensemble of High-Resolution Regional Climate Model Simulations
No full textAn assessment of the projected changes in precipitation extremes for the 21st century is presented here for Greece and its individual administrative regions. The analysis relies on an ensemble of high-resolution Regional Climate Model (RCM) simulations following various Representative Concentration Pathways (RCP2.6, RCP4.5, and RCP8.5). The simulated changes in future annual total precipitation (PRTOT) under the examined scenarios are generally negative but statistically non-robust, except towards the end of the century (2071–2100) over high-altitude mountainous regions in Western Greece, Peloponnese, and Crete under RCP8.5. The pattern of change in the number of very heavy precipitation days (R20) is linked to the respective pattern of the PRTOT change with a statistically robust decrease of up to −5 days per year only over parts of the high-altitude mountainous regions in Western Greece, Peloponnese, and Crete for 2071–2100 under RCP8.5. Contrasting the future tendency for decrease in total precipitation and R20, the changes in the intensity of precipitation extremes show a tendency for intensification. However, these change patterns are non-robust for all periods and scenarios. Statistical significance is indicated for the highest 1-day precipitation amount in a year (Rx1day) for the administrative regions of Thessaly, Central Greece, Ionian Islands, and North Aegean under RCP8.5 in 2071–2100. The changes in the contribution of the wettest day per year to the annual total precipitation (RxTratio) are mainly positive but non-robust for most of Greece and all scenarios in the period 2021–2050, becoming more positive and robust in 2071–2100 for RCP8.5. This work highlights the necessity of taking into consideration high-resolution multi-model RCM estimates in future precipitation extremes with various scenarios, for assessing their potential impact on flood episodes and the strategic planning of structure resilience at national and regional level under the anticipated human-induced future climate change
Future Projections of Photovoltaic Power Generation Potential Change in Greece Based on High-Resolution EURO-CORDEX RCM Simulations
No full textHere, we assess the projected changes in photovoltaic power generation potential (PVpot) in Greece for the 21st century. Our analysis is based on an ensemble of high-resolution Regional Climate Model (RCM) simulations from the EURO-CORDEX initiative following three different Representative Concentration Pathways (RCPs), namely, RCP2.6 (strong mitigation), RCP4.5 (moderate mitigation), and RCP8.5 (no further mitigation). The spatial patterns of the PVpot changes in the near future (2021–2050) and at the end of the century (2071–2100) relative to the 1971–2000 baseline period are presented along with the corresponding statistical robustness. In addition, we analyze time series of the projected PVpot changes. Finally, we isolate the effects of specific climatic variables on the projected PVpot changes and discuss the importance of PV energy production in Greece
Gabriele d'Annunzio - Η αλήθεια πίσω από τις λέξεις όπως αυτή προκύπτει μέσα από τη συγκριτική υφολογική και υφομετρική ανάλυση των έργων Notturno και Contemplazione della Morte
No full textΟ Gabriele d’Annunzio, αποτέλεσε ένα από τα πιο αμφιλεγόμενα πρόσωπα της σύγχρονης Ιταλικής λογοτεχνίας που ακόμα και σήμερα, 81 έτη μετά το θάνατό του, διαθέτει φανατικούς αναγνώστες και μελετητές του πολύμορφου έργου του. Ο Vate, που σημαίνει βάρδος αλλά και προφήτης όπως μεγαλοπρεπώς συνήθιζαν οι θαυμαστές του να τον αποκαλούν προσδίδοντας και μία δόση μυστικισμού γύρω από την προσωπικότητά του, επέμενε να επιδεικνύει μία τάση εμμονής γύρω από την ιδέα του Θανάτου. Άλλωστε, ο Θάνατος και η Τέχνη είναι αιώνια αδέρφια, όπως γλαφυρά αναφέρει στο ποίημά του Il Gombo από την ποιητική του συλλογή Alcyone (1903). Η επιλογή των έργων, στην παρούσα εργασία, δεν είναι τυχαία αφού αποτελούν δύο από τα πιο χαρακτηριστικά δείγματα γραφής του, όπου ο Θάνατος είναι o μεγάλος πρωταγωνιστής, αντικείμενο προβληματισμού και μελέτης του D’Annunzio. Τα δύο έργα, Contemplazione della Morte (1912) και Notturno (1916), θα γραφτούν σε δύο πολύ σημαντικές περιόδους της ζωής του, όπου η συναισθηματική του φόρτιση είναι μεγάλη. Το πρώτο έργο το γράφει κατά την περίοδο της φυγής του στη Γαλλία βρισκόμενος εν διωγμό από τους πιστωτές του στην Ιταλία, ενώ το δεύτερο το γράφει κατά την περίοδο της ενεργής του ανάμιξης με τις αλυτρωτικές εκφάνσεις της Ιταλίας στις αρχές του 20ου αιώνα. Και στα δύο έργα, ο Θάνατος κατέχει κεντρικό ρόλο αφού ο συγγραφέας μπαίνει σε μία άτυπη αναμέτρηση μαζί του, μέσα από τις περιγραφές της τραγικής απώλειας κοντινών του ανθρώπων. Με την παρούσα εργασία, η οποία έχει διττό χαρακτήρα, επιχειρούμε αφενός να αναδείξουμε αυτό που προκύπτει μέσω της συγκριτικής υφολογίας των δύο έργων και αφετέρου να επαληθεύσουμε με μετρήσιμα στοιχεία, που προκύπτουν από την υφομετρική ανάλυση, αυτό που η συγκριτική υφολογία αναδεικνύει ως βασικό φιλολογικό συμπέρασμα σχετικά με την άποψη του συγγραφέα για το Θάνατο και τον τρόπο με τον οποίον τελικά τον αντιμετωπίζει.Gabriele d'Annunzio was one of the most controversial figures in modern Italian literature who, even today, 81 years after his death, has fervent readers and scholars of his varied work. Vate, which means both a bard and a prophet, as his admirers used to majestically call him adding a dose of mysticism to his personality, insisted on displaying a tendency to persist around the idea of Death. After all, Death and Art are eternal brothers, as he gleefully mentions in his poem Il Gombo from his poetic collection Alcyone (1903). The selection of works in the present work is not accidental since they are two of the most characteristic examples of his writing, where Death is the great protagonist, the subject of D'Annunzio's concern and study. The two works, Contemplazione della Morte (1912) and Notturno (1916), were written in two very important periods of his life, when his emotional burden is high. The first work was written during his escape to France being persecuted by his creditors in Italy, while the second was written during his active involvement with the irredentist manifestations of Italy in the early 20th century. In both works, Death plays a central role as the writer engages in an informal confrontation with Him through the descriptions of the tragic loss of people who were close to him. In the present work, which has a dual nature, we attempt to show, on the one hand, what emerges through the contrastive stylistics of the two works, and, on the other hand, to verify with measurable evidence derived from the stylometric analysis, what contrastive stylistics highlights as a key literary conclusion concerning the author's view of Death and the way he ultimately deals with it
A Global Climatology of Tropopause Folds in CAMS and MERRA‐2 Reanalyses
No full textTropopause folds are the main mechanism underlying stratosphere-to-troposphere transport and influence tropospheric composition and weather systems by triggering convection. Here, we present the global climatology of tropopause folds in Copernicus Atmosphere Monitoring Service (CAMS) and Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalysis of atmospheric composition products for the time period from 2003 to 2018. We applied a 3-D labeling algorithm in CAMS and MERRA-2 reanalysis data to detect tropopause folding events. In constructing their climatologies, we show that the bulk of the folds are vertically shallow and are mainly found at the subtropical zones in the vicinity of the jet streams, while deeper folds also occur over the storm tracks, consistent with previous studies. The spatiotemporal characteristics of fold climatology are captured in a similar manner in CAMS and MERRA-2, with MERRA-2 capturing slightly higher frequencies during all seasons. In quantitative terms, there is a good agreement between CAMS and MERRA-2 fold frequencies with spatiotemporal R2 values of ∼0.9 for DJF, MAM, and JJA, and 0.75 for SON. The two reanalysis products are in close agreement regarding the intra- and interannual variability in fold frequency, with temporal correlation scores higher than 0.7 over the subtropical bands where the majority of folds are found. The agreement between the two reanalyses is lower in the Southern Hemisphere compared to the Northern Hemisphere. Thus, the global climatology of tropopause folds in both CAMS and MERRA-2 reanalyses are similar to those of previous studies
A deep stratosphere-to-troposphere ozone transport event over Europe simulated in CAMS global and regional forecast systems: Analysis and evaluation
No full textAbstract. Stratosphere-to-troposphere transport (STT) is the dominant natural source of tropospheric ozone, which can occasionally influence ground-level ozone concentrations relevant for air quality. Here, we analyse and evaluate the Copernicus Atmosphere Monitoring Service (CAMS) global and regional forecast systems during a deep STT event over Europe for the time period from 04 to 09 January 2017. The predominant synoptic condition is described by a deep upper level trough over eastern and central Europe favouring the formation of tropopause folding events along the jet stream axis and therefore the intrusion of stratospheric ozone into the troposphere. Both global and regional CAMS forecast products reproduce the hook-shaped streamer of ozone-rich and dry air in the middle troposphere depicted from the observed satellite images of water vapor. The CAMS global model successfully reproduces the folding of the tropopause at various European sites, such as Trapani (Italy), where a deep folding down to 550 hPa is seen. The stratospheric ozone intrusions into the troposphere observed by WOUDC ozonesonde and IAGOS aircraft measurements are satisfactorily forecasted up to three days in advance by CAMS global model in terms of both temporal and vertical features of ozone. The fractional gross error (FGE) of CAMS ozone Day-1 forecast between 300 and 500 hPa is 0.13 over Prague, while over Frankfurt is 0.04 and 0.19, highlighting the contribution of data assimilation which in most cases improves the model performance. Finally, the meteorological/chemical forcing of CAMS global forecast system in the CAMS regional forecast systems is found to be beneficial for predicting the enhanced ozone concentrations in the middle troposphere during a deep STT event.
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Supplementary material to &quot;A deep stratosphere-to-troposphere ozone transport event over Europe simulated in CAMS global and regional forecast systems: Analysis and evaluation&quot;
No full textEvaluation of PM Chemical Composition in Thessaloniki, Greece Based on Air Quality Simulations
No full textThe average PM10 daily levels over the urban area of Thessaloniki, Greece, usually exceed the air quality limits and therefore the improved PM chemical composition and air quality modeling results that will facilitate the design of the most appropriate mitigation measures (e.g., limitations in wood combustion for heating purposes) are essential. The air quality modeling system WRF-CAMx was applied over a 2 × 2 km2 horizontal resolution grid covering the greater area of Thessaloniki for the year 2015, when Greece was still confronting the consequences of the financial crisis. The output hourly surface concentrations of twelve PM species at three sites of different environmental type characterization in the city of Thessaloniki were temporally and spatially analyzed. Carbonaceous aerosols (organic and elemental) are the major contributor to total PM10 levels during winter representing a 35–40% share. During summer, mineral aerosols (excluding dust) distribute by up to 48% to total PM10 levels, being the major contributor attributed to road traffic. PM species, during winter, increase in the morning and in the afternoon mainly due to road transport and residential heating, respectively, in addition with the unfavorable meteorological conditions. An underestimation of the primary organic carbon aerosol levels during winter is identified. The application of the modeling system using a different speciation profile for the fine particles emissions from residential heating based on observational data instead of the CAMS emissions profile revealed an improvement in the simulated OC/EC values for which a 50% increase was identified compared to the base run
