C. C. Repapis

Assessment of the potential for photochemical air pollution in Athens - A comparison of emissions and air-pollutant levels in Athens with those in Los Angeles

Abstract The average areal density of pollutant emissions in Athens is estimated to be two to six times greater than in the Los Angeles basin. Concentration levels of the primary air pollutants, CO and SO2, are several times larger in Athens than in Los Angeles. Concentrations of the photochemical pollutants, NO2 and O3, however, are greater at Los Angeles stations inland 20 or more kilometers from the coast. The relatively lower levels of photochemical pollution in Athens are partially explained by differences in the summer atmospheric-circulation systems and the scale of the basins. Also, the concentration of NO in central Athens is so great as to inhibit the formation of O3.

Vertical ozone measurements in the troposphere over the Eastern Mediterranean and comparison with Central Europe

Vertical ozone profiles measured in the period 1996–2002 in the framework of the MOZAIC project (Measurement of Ozone and Water Vapor by Airbus in Service Aircraft) for flights connecting Central Europe to the Eastern Mediterranean basin (Heraklion, Rhodes, Antalya) were analysed in order to evaluate the high rural ozone levels recorded in the Mediterranean area during summertime. The 77 flights during summer (JJAS) showed substantially (10– 12 ppb, 20–40%) enhanced ozone mixing ratios in the lower troposphere over the Eastern Mediterranean frequently exceeding the 60 ppb, 8-h EU air quality standard, whereas ozone between 700 hPa and 400 hPa was only slightly (3– 5 ppb, 5–10%) higher than over Central Europe. Analysis of composite weather maps for the high and low ozone cases, as well as back-trajectories and vertical profiles of carbon monoxide, suggest that the main factor leading to high tropospheric ozone values in the area is anticyclonic influence, in combination with a persistent northerly flow in the lower troposphere during summertime over the Aegean. On the other hand the lowest ozone levels are associated with lowpressure systems, especially the extension of the Middle East low over the Eastern Mediterranean area.

Case study of UV-B modification during episodes of urban air pollution

Examination of the record of solar ultraviolet measurements made during the MEDCAPHOT study of air pollution in the Athens basin revealed a substantial reduction of UV-B on days with high levels of pollution. The magnitude of this relation is illustrated by a comparison of the UV on two days of a pollution episode with that on two days of low pollution.

The Southern Oscillation in the Stratosphere

Abstract The signal of the Southern Oscillation in the lower half of the Northern Hemisphere stratosphere in winter appears to be as follows: In the extreme of the Southern Oscillation when the trade winds are comparatively weak in the South Pacific Ocean, stratospheric geopotential heights and temperatures tend to be higher over the Arctic and lower in middle latitudes than in the opposite extreme. At the same time, the polar-night stratospheric jetstream tends to be weaker and the subtropical westerlies to be stronger. The conclusions are based on 11 extremes within a 15-year period and on data at standard pressure levels as high as 10 mb.

A note on the frequency of occurrence of severe winters as evidenced in monastery and historical records from Greece during the period 1200–1900 A.D.

SummaryMonastery and historical records for Greece during the period 1200–1900 A.D. have been used to obtain the number of “severe” winters which occurred during this time period. A winter was considered as being “severe” if long duration of snow cover and/or freezing of lakes in Greece were archived. Evidence is presented that the coldest periods in Greece during the period 1200–1900 A.D. occurred in the first half of the 15th century, in the second half of the 17th and in the 19th century. Geographical coherence is indicated with other areas in Europe, e.g., with The Netherlands, where historical records exist over the same period. The number of severe winters in 50-year intervals does show a positive correlation with the volcanic dust veil index.ZusammenfassungKloster- und andere historische Aufzeichnungen Griechenlands über den Zeitraum 1200 – 1900 wurden herangezogen, um die Anzahl der „strengen“ Winter zu ermitteln. Ein Winter wurde als „streng“ eingestuft, wenn lang anhaltende Schneedecke und/oder das Einfrieren von Seen in Griechenland verzeichnet wurden.Deutlich erweisen sich hierbei die erste Hälfte des 15. Jahrhunderts, die zweite Hälfte des 17. Jahrhunderts und das 19. Jahrhundert als kälteste Perioden in Griechenland während des genannten Zeitraums. Dies erwies sich als geographisch kohärent mit anderen Teilen Europas, z. B. mit den Niederlanden, für die historische Aufzeichnungen über den selben Zeitraum existieren. Die Anzahl der strengen Winter in 50-Jahr-Intervallen weist eine positive Korrelation mit dem Vulkanstaub-Index auf.

A 5‐year climatology of the solar erythemal ultraviolet in Athens, Greece

Observations of solar ultraviolet (UV) irradiance in Athens for the period 1993-1997 employing the Yankee Environmental Systems (YES) pyranometer (model UVB-1) are analysed to provide a climatological description of the erythemally active UV component in this urban Mediterranean environment. The role of cloud cover and the ozone column in the determination of the UV climate are estimated by a comparison of the record of UV irradiance with daily observations of total ozone at the University of Athens and of total solar radiation at the National Observatory of Athens. During the warmer months, June to September, there appears to be a substantial reduction of solar UV by atmospheric components other than ozone and clouds, a conclusion that is supported by comparing the observations with the predictions of radiative transfer models and with UV observations in a rural southern hemisphere environment reported by McKenzie et al. (1991).

Climatology of Upper Air Temperature in the Eastern Mediterranean Region

The goal of this study is to contribute to the climatology of upper air temperature in the Eastern Mediterranean region, during the period 1965–2007. For this purpose, both radiosonde station and NCEP/NCAR reanalysis gridded datasets of upper air temperature were used for seven barometric levels at 850, 700, 500, 300, 200, 150, and 100 hPa. The impact of atmospheric circulation, by means of correlation between upper air temperature at different barometric levels and specific climatic indices such as Mediterranean Oscillation Index (MOI), North Sea Caspian Pattern Index (NCPI) and North Atlantic Oscillation Index (NAOI), is also quantified.

The time-latitude distribution of solar flares accompanied by type IV radio bursts during the period 1956 to 1969

A list of nearly 350 flares accompanied by type IV radio bursts by Krüger et al. (1971), which covers a period of 14 yr (1956–1969), was expanded to include all PCA and solar cosmic ray events during this entire period. This list, which includes practically all of the most energetic events during the maxima of two consecutive solar cycles, was used to investigate the latitudinal distribution of the above-mentioned flares, as well as of all PCA events, solar cosmic ray events and plage regions associated with them.Histograms of these occurences show clearly the appearance of two peaks in both solar maxima, which confirm the observations of Gnevyshev (1967). Latitudinal analysis of these histograms shows that in cycle 20 the two peaks are independent and their relative strength varies strongly with latitude. In cycle 19, however, this effect is not clearly evident, possibly because of the extremely high level of activity during this cycle. In both cycles, the second maximum shows the highest concentration of the most energetic events.

A Neglected Long-Term Series of Ground-Level Ozone

Surface ozone concentration based on coloration of De James test-papers corresponding to daytime and nightime exposure was monitored daily at the Athens Observatory during the period 1901–1940. This neglected series was converted to ozone levels using hourly relative humidity (R.H.) data and the R.H.- ozone conversion chart of Linvill et al. (1980). The climatic fluctuations of the resulting long-term surface ozone series are presented in this report.

Possible evidence of the Southern Oscillation in total ozone at Arosa

SummaryStatistical tests of a possible association between total ozone at Arosa and indices of the Southern Oscillation give indefinite but not unpromising answers: linear correlation coefficients between 12-month running means are statistically significant for both halves of the period 1935–1980, whereas the squared coherences are statistically significant in the first but not in the second half of the period. The phases in both periods are consistent, however. Our investigation shows that a relationship between the total ozone amounts at Arosa and the Southern Oscillation, must be in the sense that when the sea level mean pressure is low over the central tropical South Pacific Ocean while it is high in the Indonesian region, the total ozone amounts at Arosa tend to be large, and conversely.ZusammenfassungStatistische Tests eines möglichen Zusammenhanges zwischen dem Gesamtozon über Arosa und Indizes der südlichen Oszillation geben zwar unbestimmte aber nicht aussichtslose Hinweise: Die linearen Korrelationskoeffizienten zwischen 12monatig übergreifenden Mittelwerten sind für beide Hälften der Periode 1935–1980 statistisch signifikant, während die Kohärenzen in der ersten, aber nicht in der zweiten Hälfte der Periode statistisch signifikant sind. Die Phasen sind jedoch in beiden Perioden übereinstimmend. Unsere Untersuchung zeigt, daß eine Beziehung zwischen dem Gesamtozongehalt über Arosa und der südlichen Oszillation in dem Sinne besteht, daß, wenn der mittlere Luftdruck am Boden im zentralen tropischen Südpazifischen Ozean niedrig ist, während er im Gebiet von Indonesien hoch ist, der Ozongehalt über Arosa eine Tendenz zu höheren Werten zeigt und umgekehrt.