Analysis of the long-term precipitation series at Athens,Greece

In this paper, the characteristics of the long-term precipitation series at Athens (1858–1985) have been statistically analyzed. This study covers both the history and the analysis of the data. The ten-year mean amounts, the monthly and annual amounts averaged over the intervals 1858–1890, 1891–1985, 1951–1980, 1858–1985, the mean number of hours of precipitation and the precipitation intensity are given. The analysis of long-term time series of climatic data (in particular precipitation) is a useful tool for the study of past climate. Different statistical techniques are used in order to depict monthly, seasonal and annual variations, as well as trends, periodicities and recurrence intervals of the amount, intensity and number of precipitation days. The analysis reveals many interesting characteristics. These characteristics of the precipitation regime are extended to a time scale from seasonal variation to a semi-secular trend. The study of such long-term series may be helpful not only in practical applications of rainfall, but also for explaining the possible physical or anthropogenic mechanisms of climatic fluctuations and tendencies. The series of precipitation at Athens is one of the longest in south-eastern Europe.     

Mean monthly air temperatures in Athens, Greece

Summary  In this paper some statistical parameters of the mean monthly air temperatures in Athens are examined, namely trends, periodicities and cross-correlations between months. It is found that there is not any significant trend for most of the months and the periodicities don’t allow the extraction of any general conclusion. On the other hand, cross-correlation analysis shows that some correlation between the temperature in certain months exists. Received March 10, 2000     

Temporal variations of atmospheric tides over Athens,Greece

Summary The mean daily march of pressure (hourly values) for each month of the 96 year period 1894–1989 in Athens, Greece is studied using Fourier analysis. The annual variation of the harmonic parameters (amplitude, time of maximum,x andy-components) is examined. The globally excited 2nd and 3rd harmonics show in general the same behaviour as in other places of the Earth. Similar features show the corresponding parameters of the daily solar radiation march. The first harmonic displays some local characteristics. The long period fluctuations study revealed statistically significant trends in most parameters of the 2nd harmonic, most strikingly the 0.5 h shift in the time of its maximum during the 20th century. Power spectrum analysis showed the existence of a biennial oscillation inB ₁, thex-component of the first harmonic, but this oscillation is mainly confined to the second half of the entire period. A periodicity of about 6 years which could be associated to the Southern Oscillation was also found inB ₁ while inA ₁, they-component, a periodicity close to the 11-year solar cycle and another one close to the nutation of the Earth's axis are present. The lunar tides are too small to be detected by the same methods. However the semilunar tide was revealed to be 10–20 times smaller than the semisolar.With 8 Figures     

南极中山站太阳紫外辐射测值比较

比较分析了2017年南极中山站3种仪器测量地面太阳紫外B（UVB）波段和紫外A（UVA）波段的辐照度。以Brewer光谱仪测值为参考,国产宽波段FSUVB日射表在UVB（波段280~315 nm）的辐照度相对误差为（55±75）%,误差随大气臭氧总量的增加呈上升趋势,但在南极“臭氧洞”期间偏低。Yankee UVB宽波段日射表在UVB（波段280~320 nm）的辐照度相对误差为（-31±22）%;国产宽波段FSUVA日射表在UVA（波段315~400 nm）的辐照度相对误差为（23±5.9）%。太阳天顶角低于80°的晴天以Tropospheric Ultraviolet Visible（TUV）辐射模式计算结果为参考时,FSUVB,Yankee UVB和FSUVA辐照度的平均相对误差分别为（30±37）%,（-22±19）%和（27±6.4）%,而Brewer相对误差未超过3.5%。国产宽波段UV日射表测值偏高,反映出波长较长的杂散光对太阳辐照度测值影响明显。     

Some meteorological aspects of air pollution in Athens,Greece

Summary The purpose of this paper is to examine some meteorological aspects of air pollution in the Athens area, Greece. Over recent years much attention has been directed to the importance of spells of weather in providing conditions that give rise to inversion of temperature at or near ground level, and hence to risks of severe incidents of air pollution. So, emphasis is given to the importance of anticyclonic conditions, associated with pronounced stability during ground level radiation inversions, when the same sampling sites show high concentration of both SO₂ and smoke. Fifteen years of surface and radiosonde data obtained from Hellinikon Airport Athens are used for a climatological base. The meteorology of high concentration episodes has also been examined and the synoptic characteristics for the onset and end of such episodes have been identified. Finally, trends of pollution episodes and calculation of an air stagnation index for Athens have been obtained, which give a predicting indication about the occurrence of high pollution concentration.With 11 Figures     

Theoretical Simulation of Solar Ultraviolet Fluxes Measured on the 8 July 1974 Stratoprobe I flights

Solar ultraviolet fluxes in the wavelength region 1900 to 2300Å were measured during the first balloon flight of Project stratoprobe on July 8, 1974, over a range of solar zenith angles at a float altitude of 28.6 km. High‐resolution computer simulations of the measured spectra were made for a range of solar zenith angles of 40° to 80° over the wavelength region 2050 to 2150A, and comparisons made with the observed spectra at 40° and 47 °. Qualitative agreements were obtained but there were significant discrepancies between the simulated and experimentally obtained fluxes. Sources of the discrepancies are discussed.     

A note on smoke concentration prediction in Athens,Greece

Summary In this paper an attempt for predicting smoke concentration levels in Athens for spring and autumn is presented. The regression models are based on equations relating wind speed and smoke values. It is found that both of them become more effective if corrections related to wind speed categories are applied to the equations. In this way good prediction is achieved for the next 24 hours.With 4 Figures     

Study of small ions concentration in the air above Athens, Greece

Measurements of positive and negative small atmospheric ion concentrations have been made regularly since 1968 at the National Observatory of Athens (NOA). In this paper the 17-year period 1968–1984 is summarized. The diurnal and annual variations are examined, and Fourier analysis is also used for the study of the diurnal variation. The concentrations of small ions follow a double diurnal course. The maxima occur near 3–5 h and 13–16 h local time (LT = GMT + 2 h). The minima are observed at 6–8 h and 21–23 h. The annual course of small ions presents maximum concentration values around the summer season. The mean of the small ion concentration (SIC) for the 17-year period (1968–1984) is n₊ = 188.8 ions/cm³ for positive ions and n₋ = 151.1 ions/cm³ for negative ions. Their ratio is equal to 1.25. The year-to-year variation of SIC for the examined period shows a negative trend. The results from multiple regression analysis show that wind speed and SIC are positively correlated, while relative humidity, smoke and sulphur dioxide are negatively correlated.     

Variability of the Linke and Unsworth-Monteith turbidity parameters in Athens, Greece

Summary  This work studies the variability of the Linke (T _L ) and Unsworth-Monteith (T _U ) turbidity parameters in the urban atmosphere of Athens. Beam irradiance observations performed at the Actinometric Station of the National Observatory of Athens are used in the period 1975–1995. This study examines (i) the inter-annual variation of T _L and T _U , (ii) their mean seasonal variability, (iii) their monthly average variation, and (iv) their mean daily variation. Also, for various air-mass origins, the mean seasonal variations of T _L and T _U are given. The frequency of occurrence of the parameters in various ranges is also shown. An innovative interpretation of the impact of the Saharan dust on the radiative properties in the atmosphere of Athens is attempted. Received May 19, 2000 Revised October 17, 2000     

Aspects of the occurrence of persistent surface inversions over Athens basin,Greece

Summary In this study the climatology and the effects of persistent nocturnal surface temperature inversions and their relationship to the meteorological processes are discussed. Emphasis is given to the importance of the relevant synoptic situations, the sea-breeze, the stability and the temperature characteristics. The application of some inversions characteristics to local pollution potential is also examined. The results show that many aspects of Athens air quality reflect the pronounced effect of persistent inversions, e.g. the frequency of pollution episodes, the accumulation of pollutants etc.

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Zusammenfassung Vorliegende Studie beschäftigt sich mit der Klimatologie und den Auswirkungen von andauernden nächtlichen Temperaturinversionen in Bodennähe sowie deren Zusammenhang mit meteorologischen Prozessen. Besonderes Augenmerk ist dabei den relevanten synoptischen Bedingungen — der Seebrise, der Stabilität und den Temperaturcharakteristika — gewidmet. Auch die Auswirkungen von manchen Inversionseigenschaften auf das Potential zu örtlicher Luftverschmutzung werden untersucht. Die Ergebnisse zeigen, daß in wesentlichen Aspekten die Luftqualität über Athen die Auswirkungen persistenter Inversionen widerspiegelt, so zum Beispiel in Häufigkeit und Intensität von Luftverschmutzungen.

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With 11 Figures     

Estimating the ecological footprint of the heat island effect over Athens, Greece

Heat island is a very well documented climatic phenomenon that has an important energy and environmental impact in the urban environment. The main energy problems are related to the important increase of the energy consumption for cooling purposes as well as to the important increase of the peak electricity load. Heat island in Athens, Greece, is measured during the last decade and its energy impact is calculated in details. The aim of the present paper is to estimate the direct and indirect environmental impact of the heat island effect in Athens. This is achieved through the estimation of the additional ecological footprint caused by the urban heat island phenomenon over the city. The ecological footprint estimation is performed at a first step by calculating the increase of the cooling demand caused by the heat island over the whole city and then by translating the energy to environmental cost. Two years annual experimental data from many urban stations have been used. The results show that the ecological footprint because of the heat island ranges 1.5–2 times the city’s political area that have to be reserved every year to compensate the additional CO₂ emissions caused by the presence of the heat island effect while the maximum potential ecological footprint, provided that all buildings are air conditioned, is almost 110,000 hectares.     

Synoptic and mesoscale weather conditions during air pollution episodes in Athens,Greece

Based on regular climatological and air quality data from the Greater Athens Area (GAA), the air pollution episodes observed in Athens during the period 1983–1990 were analysed and classified. The main characteristics of atmospheric conditions during days with high air pollution concentrations are summarized too. Model simulations show that the worst air pollution episodes in Athens occur during days with a critical balance between synoptic and mesoscale circulations and/or during days with warm advection in the lower troposphere.     

The behaviour of aerosol optical depth during clear summer days in Athens,Greece

Summary The integral aerosol optical depths (k ) at the hour of 08:20 Local Standard Time (LST), are compared with those calculated previously at 11:20 and 14:20 LST, for clear days during summer in Athens over the period 1962–1988. The mean values at 08:20 LST were consistently lower than the values at 11:20 and 14:20 LST. The influence of the vertical wind profile on the values ofk was also investigated. A comparison was made of the wind profiles at 02:00 and 14:00 LST, for days in which the 11:20 and 14:20 LST values ofk were 0.200 andk 0.350, respectively. The corresponding bulk wind shear s was also found for the period 1980–1988. The most significant results occurred with the first category of days. The resultant wind velocities from the surface to the 900 hPa level, in each hour were higher by 2–4 m·s^–1 with respect to the corresponding values for the second category. At 02:00 LST the bulk wind shear showed a considerable difference (1.8) between the two categories of days in the surface to 700 hPa layer at 02:00 LST. Finally, the associated weather conditions that appear to initiate a period of low values ofk (k 0.200) at 11:20 and 14:20 LST were examined for the period 1980–1988. Fifteen such cases were identified and it was found that they all occurred after the passage of weak cold fronts.With 6 Figures     

Mesoscale and macroscale aspects of the morning Urban Heat Island around Athens,Greece

Summary This paper examines the characteristics of the morning Urban Heat Island (UHI) in Athens basin, Greece. The study is performed by using and analyzing mesoscale and synoptic data covering the period 1990–2001. The UHI was estimated using the 0600 Local Time (LT) minimum temperature differences between rural and urban areas of the city. The analysis results in 7 UHI classes. A strong UHI was found for the 1/3 of days. The specific meteorological characteristics (surface and upper air, cooling rate) of each UHI class were revealed and examined. The spatial and temporal characteristics of the UHI were also identified. The UHI is largest on nights with clear skies and low relative humidity. In all seasons the UHI switches on rapidly in afternoon. During spring and summer, sea breeze commonly reduces and delays the UHI. Cases documenting the sensitivity and rapidity of changes of the UHI to changes in classes (cloud cover, wind) are also presented. The cooling rate is higher in the urban area under negative and lower under positive UHI conditions. Mesoscale and macroscale phenomena were examined during the different UHI classes through a weather type scheme. It was emerged that high UHI classes are associated with anticyclonic conditions or advection in the lower troposphere, while low UHI classes are associated with strong northeasterly winds. Anticyclonic conditions which frequently occur in spring and early summer, reduce or reverse the UHI to Urban Cooling Island.     

Evidence of katabatic flows deduced from a 84 m meteorological tower in Athens,Greece

The identification of katabatic flows and their characteristics observed on a simple slope (the western side of Hymettos mountain) for a six-month period (January to June, 1990) are presented. This is the first application of data obtained from an 84 m high meteorological research tower recently erected at the National Center for Scientific Research Demokritos in Athens, Greece. The tower is described with respect to construction and instrumentation. The topography of the region and the observational site are also described. Criteria for the identification of katabatic flows are presented, while the frequency of occurrence of such flows is estimated. Finally, two case studies are analysed in order to reveal the special characteristics of the katabatic flows.     

The effect of air temperature and human thermal indices on mortality in Athens, Greece

This paper investigates whether there is any association between the daily mortality for the wider region of Athens, Greece and the thermal conditions, for the 10-year period 1992–2001. The daily mortality datasets were acquired from the Hellenic Statistical Service and the daily meteorological datasets, concerning daily maximum and minimum air temperature, from the Hellinikon/Athens meteorological station, established at the headquarters of the Greek Meteorological Service. Besides, the daily values of the thermal indices Physiologically Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) were evaluated in order to interpret the grade of physiological stress. The first step was the application of Pearson’s χ ² test to the compiled contingency tables, resulting in that the probability of independence is zero (p?=?0.000); namely, mortality is in close relation to the air temperature and PET/UTCI. Furthermore, the findings extracted by the generalized linear models showed that, statistically significant relationships (p?<?0.01) between air temperature, PET, UTCI and mortality exist on the same day. More concretely, on one hand during the cold period (October–March), a 10°C decrease in daily maximum air temperature, minimum air temperature, temperature range, PET and UTCI is related with an increase 13%, 15%, 2%, 7% and 6% of the probability having a death, respectively. On the other hand, during the warm period (April–September), a 10°C increase in daily maximum air temperature, minimum air temperature, temperature range, PET and UTCI is related with an increase 3%, 1%, 10%, 3% and 5% of the probability having a death, respectively. Taking into consideration the time lag effect of the examined parameters on mortality, it was found that significant effects of 3-day lag during the cold period appears against 1-day lag during the warm period. In spite of the general aspect that cold conditions seem to be favourable factors for daily mortality, the air temperature and PET/UTCI exceedances over specific thresholds depending on the distribution reveal that, very hot conditions are risk factors for the daily mortality.     

Solar ultraviolet absorption by sulphur dioxide in Thessaloniki,Greece

Abstract

This work presents the climatology of the sulphur dioxide column over Thessaloniki derived from three years of observation with the Brewer spectrophotometer. The SO₂ column averages 2.5 m atm‐cm and the shielding of UV‐B by SO₂ is investigated and compared with the changes in shielding resulting from an anticipated ozone reduction. Columnar and surface SO₂ concentrations over Thessaloniki appear to be typical of those in major industrial‐urban regions of the world. It is concluded that, for urban regions, predictions of changes in UV‐B as a result of man's activities must consider projections of changes in the SO₂ column as well as ozone.     

Solar dimming and brightening over Thessaloniki, Greece, and Beijing, China

This work presents evidence that ultraviolet (UV)-A solar irradiances show increasing trends at Thessaloniki, Greece, where air quality has been improving because of air pollution abatement strategies. In contrast, over Beijing, China, where air quality measures were taken later, solar brightening was delayed. It is shown that until the early 1990s, UV-A irradiances over Thessaloniki show a downward trend of –0.5% yr⁻¹, which reverses sign and becomes positive in the last decade (+0.8% yr⁻¹). This brightening is related to a decreasing trend in local aerosol amounts. Both the negative rate of change (dimming) and the positive rate of change (brightening) are amplified in the UV-A solar irradiances, compared with the total solar irradiance, by a factor of 2.6. Satellite derived short-wave radiation over Beijing showed negative changes of –0.4% (1984–1991) and –0.1% yr⁻¹ during 1994–2006. The negative trend in solar radiation continued even during 2000–2006. Satellite-derived aerosol optical depth (AOD) increased by +1.0% yr⁻¹ during 2000–2006, in agreement with in situ measurements of increasing AOD. Therefore, a statistically significant change from dimming to brightening in Beijing could not be seen in the last decade, but it is expected to occur in the near future.     

东疆黑戈壁太阳紫外辐射变化特征

本文利用东疆红柳河黑戈壁下垫面陆气相互作用观测站2017年太阳紫外辐射、总辐射和气象站天气现象观测数据，对东疆黑戈壁不同时间尺度和不同天气背景下的太阳紫外辐射A波段(UVA)和B波段（UVB）的变化特征进行了分析。结果表明：1）紫外辐射UVA和UVB日变化呈正态分布，UVA、UVB最大瞬时辐照度为67.97W·m-2、2.15W·m-2，日均最大曝辐量为2.09MJ·m-2和0.05MJ·m-2，年曝辐量为400.31 MJ·m-2和8.63 MJ·m-2；季节变化呈现夏季高，冬季低、春季高于秋季的特点；年变化呈现倒“U”型，年变化幅度呈夏季大，冬季小的趋势。2）紫外辐射占总辐射的比例呈夏高冬低的特点。不同天气下，其比例变化幅度也不相同，晴天大于雨天。3）太阳紫外辐射的月和年平均量以及紫外辐射年均值占总辐射年均值的比例，东疆黑戈壁地区都明显高于其他地区。