Harry Kambezidis | National Observatory of Athens (original) (raw)

Papers by Harry Kambezidis

Research paper thumbnail of A Look At The Solar Radiation Climate In Athens During The Brightening Period

Research paper thumbnail of A Look At The Solar Radiation Climate In Athens During The Brightening Period

Research paper thumbnail of Solar Energy Received on Flat-Plate Collectors Fixed on 2-Axis Trackers: Effect of Ground Albedo and Clouds

Energies, 2024

This study investigates the performance of isotropic and anisotropic diffuse models to estimate ... more This study investigates the performance of isotropic and anisotropic diffuse models to
estimate the total solar energy received on flat-plate collectors fixed on dual-axis trackers. These
estimations are applied at twelve sites selected in both hemispheres with different terrain and envi
ronmental conditions. The diffuse (or transposition) models used in this study are the isotropic Liu
Jordan (L&J), Koronakis (KOR), Badescu (BAD), and Tian (TIA), and the anisotropic Hay (HAY),
Reindl (REI), Klucher (KLU), Skartveit and Olseth (S&O), and Steven and Unsworth (S&U). These
models were chosen because of their simplicity in the calculations and minimum number of input
values. The results show that a single transposition model is not efficient for all sites; therefore, the
most appropriate models are selected for each site under all, clear, intermediate, and overcast con
ditions in skies. On the other hand, an increase in the ground albedo in the vicinity of the solar
installation can increase the annual inclined solar availability on a two-axis tracker by at least 9%
on average. Further, a linear dependence of the annual inclined solar energy on the variation of the
ground albedo was found. Also, a linear relationship exists between the annual diffuse-fraction and
cloud-modification factor values at the 12 sites.

Research paper thumbnail of Atmospheric Processes over the Broader Mediterranean Region: Effect of the El Niño–Southern Oscillation?

Research paper thumbnail of Atmospheric Processes over the Broader Mediterranean Region: Effect of the El Niño-Southern Oscillation

Atmosphere, 2024

The Mediterranean area is considered a hot spot on our planet because it represents the crossroad... more The Mediterranean area is considered a hot spot on our planet because it represents the crossroads of various aerosols. Several studies have shown that the weather in the region is affected by the North-Atlantic Oscillation, which, in turn, is well connected with the El Niño–Southern
Oscillation (ENSO) phenomenon. Nevertheless, no study has investigated the ENSO effect on the solar radiation and atmospheric aerosols in this region. The present study considers a greater area around the Mediterranean Sea over the period 1980–2022. The results show that there exists a loose but significant dependence, in some cases, of the optical properties of aerosols (aerosol optical depth, Ångström exponent, cloud optical depth) and solar radiation (net short-wave and net long-wave radiation, direct aerosol radiative forcing) on ENSO events. The results of this study provide motivation for further investigations, since such results can increase the accuracy of general circulation models that deal with climate change. Besides the ENSO effect, the enrichment of the Mediterranean atmosphere in suspended particles from great volcanic eruptions is shown. The inter-annual variation of the examined parameters is presented. A classification of the existing aerosols over the area is also provided.

Research paper thumbnail of Analysis of the total, annual, and inter-annual hourly mean direct solar normal irradiation

Arabian Journal of Geosciences, 2022

The elaboration of a time series demands long periods of measurements. In this paper, a methodolo... more The elaboration of a time series demands long periods of measurements. In this paper, a methodology is described and used to systematically organize time/space series of climatic data. The methodology allows a statistical and climatic analysis more interesting. The methodology allows to categorize the series in different time partitions and in subdivisions. The methodology is described using a database of Hb\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${H}_{b}$$\end{document} and fractions transmitted on the terrestrial surface (Ktb\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${Kt}_{b}$$\end{document}) obtained from Botuc...

Research paper thumbnail of Atmospheric Turbulence Derived from Laser Doppler Anemometry Technique

SUMMARY This paper presents results about atmospheric turbulence in the form of power spectral de... more SUMMARY This paper presents results about atmospheric turbulence in the form of power spectral density of the w-wind component. Such results are rarely presented in the international literature because of the difficulty that these systems have in order to derive atmospheric turbulence parameters, as explained in the text. The data for the analysis was gathered during CLEOPATRA experimental campaign around Munich area in the period May-July 1992. The power spectral densities derived seem to follow the-5i3 law. KEY WORDS: Atmospheric turbulence, laser doppler anemometry, w-wind component power spectral density.

Research paper thumbnail of The solar radiation climate of Athens: Variations and tendencies in the period 1992–2017, the brightening era

Solar Energy, 2018

Solar radiation at the surface of the Earth undergoes short-and long-term variations mostly influ... more Solar radiation at the surface of the Earth undergoes short-and long-term variations mostly influenced by changes in atmospheric composition and cloud cover. These two factors characterise the solar radiation climate at a place. This study deals with the solar radiation climate over Athens focusing on the variations and trends of the global and diffuse horizontal irradiances recorded at the Actinometric Station of the National Observatory of Athens. The analysis shows that the global radiation over Athens in the period 1992-2017 presents a maximum in July and in May, June around noon under all and clear skies. For the diffuse component, this occurs in spring and in May (noontime) under all-and clear-sky conditions. The global radiation trends are positive (+0.41%/ decade and +2.36%/decade for all and clear skies, respectively), while its diffuse counterpart shows negative trends (−6.93%/decade and −9.27%/decade for similar sky conditions, respectively) in the period 1992-2017. These findings confirm the recovery in the solar radiation levels over Athens in the recent 25 years.

Research paper thumbnail of Improving the estimation of the true mean monthly and true mean annual air temperatures in Greece

Atmospheric Science Letters, 2015

The true mean monthly/annual air‐temperature estimations are usually based on the monthly average... more The true mean monthly/annual air‐temperature estimations are usually based on the monthly averages of meteorological observations performed at standard hours. The performance of this combination varies as it depends on local climate of the particular meteorological station; it consequently allows for small/large deviations from its exact value. This study examines the possible deviations in Greece and suggests ways of improving the derived estimates. Two cases are considered. (1) An area has one thermograph and a number of thermometric stations. (2) An area has several thermographs and many thermometric stations. Solutions for minimizing the estimation error in both cases are provided.

Research paper thumbnail of Laser-Doppler Wind Measurements in the Planetary Boundary Layer

The aim of this work is to investigate the representativity of LDA mean wind velocity measurement... more The aim of this work is to investigate the representativity of LDA mean wind velocity measurements and variations of wind velocity profiles in the planetary boundary layer undei different atmospheric stabilities and earth surface roughnesses in presenci of mesoscale variations of the wind. The comparison of the theoretically calculated relative error of LDA estimates with the experimental results shows good agreement, Based on these investigations, the optimum measurement procedure can be defined for different stability conditions of the atmospheric boundary layer. Zusammenfassung windmessungen in der planelaren Grenzschicht mit dem Lcser.Doppler Anemometer Mit der vorliegenden Arbeit soll untersucht werden, wie reprasentativ LDA-Messungen zur Bestimmung der mittleren Windgeschwindigkeit und der Variation von Windprofilen-in der planetaren Grundschicht sind. Dies geschieht bei verschiedenen atmospharischen Stabilit[ten und Rauhigkeitsparametern in Anwesenheit von mesoskaligen Variationen des Windes. Der Ver-gleich der theoretisch berechneten relativen MeBfehler mit den experimentellen Ergebnissen zeigt gute Ubereinstimmung. Aufgrund dieser Untersuchungen kann'die optimale MeBlrozedur fiir verschiedene Stabilitetsbedingungen in der atmosph6rischen Grenzschicht definiert werden.

Research paper thumbnail of Surface winds and horizontal mesoscale wind spectra in Athens, Greece

Il Nuovo Cimento C, 1986

SummaryThis paper reports briefly on the spatial variability of the wind regime in the Athens reg... more SummaryThis paper reports briefly on the spatial variability of the wind regime in the Athens region by examining mean wind speeds (at 5 sites) and frequency distributions of speed and direction for 3 sites. At 3 locations, some wind roses have been prepared for the representation of the flow in the area. These wind roses should only be used as a guide to the initial identification of important localized effects and not as the sole representation of the flow. Besides, spectral analysis of hourly wind velocities obtained, also, at a site in Athens, illustrated a shift of the major sources of kinetic energy from the locally induced diurnal oscilation in Summer to synoptic variations in Winter. The physical significance of the summer oscillation is also known to be location dependent. The method illustrates locally induced variations within the flow and seasonal transfer of energy from synoptic sources in Winter to diurnal sea-breeze and Etesian wind systems in Summer.RiassuntoNel presente lavoro è succintamente descritta la mutabilità spaziale del vento nel circondario di Atene, esaminando i valori medi della velocità del vento (in 5 località) e la loro frequenza di distribuzione (in 3 località). Per le 3 località sono stati tracciati alcuni diagrammi di vento, rappresentativi del flusso di vento alla località. Questi diagrammi dovranno essere considerati una specie di guida per la determinazione delle determinanti caratteristiche locali della topografia, anche perchè non riportano la rappresentazione completa del flusso. Per di piú l'analisi spettrale fornisce la scala dei sistemi sinottici per stagione dell'anno. L'analisi spettroscopica di dati di velocità del vento, registrati ogni ora, ad Atene, indica la differenziazione delle sorgenti di energia cinetica delle oscillazioni diurne localmente indotte e variazioni sinottiche durante l'inverno. È anche indicata la dipendenza dell'oscillazione estiva dalla località. In particolare il metodo illustra variazioni indotte localmente nel flusso ed anche il trasferimento stagionale di energia da sorgenti sinottiche durante l'inverno a diurni sistemi di vento mare-brezza e venti estivi (meltems) durante l'estate.РезюмеВ этой статье предлагается анализ пространственной изменчивости ветров в Афинах, на основе исследовании средних скоростей ветра (в 5 точках) и частотных распределений скорости и направления в 3 точках. В 3 точках исследуются розы бетров. Эти розы используются для начальной идентификации важных локаляных эффектов. Спектральный анализ скоростей ветров, полыченный в Афинах, показывает сдвнт большинства источников кинетигеской энергии от локльно индуцированных суточных осцилляций летом до синоптических изменений зимой. Отмечается, что физическая значимость летних осцилляций зависит от местоположения. Предложенный метод иллюстрирует локльно индуцированные изменения внутри потока и сезонный перенос энергии от синоптических истчников зимой до суточных бризов и северо-западных пассатных ветров летом.

Research paper thumbnail of Estimation of sunrise and sunset hours for locations on flat and complex terrain: review and advancement

Renewable Energy, 1997

This work concerns the calculation of sunrise and sunset hours at a location on complex terrain. ... more This work concerns the calculation of sunrise and sunset hours at a location on complex terrain. This is particularly important to all solar irradiance and illuminance codes that estimate solar irradiance or illuminance on horizontal or inclined surfaces on a specific day at a location on non-fiat terrain. Specific formulas are given.

Research paper thumbnail of Mapping Atmospheric Corrosion on Materials of Archaeological Importance in Athens

Water, Air, & Soil Pollution, 2011

Atmospheric pollution is known to induce corrosion effects on various materials. For Greece, ston... more Atmospheric pollution is known to induce corrosion effects on various materials. For Greece, stone deterioration could emerge severe costs in the case of damaging cultural monuments. This work aims to investigate the corrosion process on materials of archaeological importance (marble, limestone, and sandstone) in the Greater Athens Area (GAA) by using sophisticated geoanalytical methods together with dose–response functions for selected materials, in order to derive corrosion maps for GAA in the period 2000–2009. Also, a corrosion trend analysis is performed, which can be a very helpful tool for the prediction of potential risks to monuments of cultural heritage due to atmospheric pollution. The corrosion effects on the selected materials are generally weak. Nevertheless, increasing corrosion trends are found in the eastern regions of GAA for all sheltered materials and in the northern parts of GAA for unsheltered marble. The technique is finally applied to 12 locations in GAA, which include some of the most important archaeological monuments of Athens, and provides comprehensive results for the estimation of the impact of atmospheric corrosion on the structural materials of these archaeological sites.

Research paper thumbnail of Mapping Atmospheric Corrosion on Modern Materials in the Greater Athens Area

Water, Air, & Soil Pollution, 2013

In this study, we investigate the corrosion effects on modern materials at various sheltered and ... more In this study, we investigate the corrosion effects on modern materials at various sheltered and unsheltered locations in the Greater Athens Area (GAA) due to atmospheric pollution, since materials deterioration could emerge severe economic costs in the near future. The preselected materials are weathering steel, copper, bronze, zinc, and aluminum, which are mainly used in modern constructions in the GAA. The method applied in this study leads in the production of corrosion maps for GAA in the period 2000–2009 by using sophisticated geoanalytical methods together with dose–response functions for the selected materials. The corrosion effects are significant for weathering steel, moderate for copper and bronze and weak for zinc and aluminum. Also, a corrosion trend analysis is performed, which can be a very helpful tool for future protection of such materials from atmospheric pollution. The results show increasing corrosion trends for weathering steel and copper in the eastern regions of GAA, probably caused by the recent operation of the Athens International Airport at Spata, while no corrosion trends were observed to the other materials. The method applied in this work provides comprehensive results for the estimation of the impact of atmospheric corrosion on various construction materials.

Research paper thumbnail of Diffuse solar irradiation model evaluation in the North Mediterranean Belt area

Solar Energy, 2001

The performance of daily and hourly diffuse horizontal solar irradiation models and correlations ... more The performance of daily and hourly diffuse horizontal solar irradiation models and correlations is examined using an assembled data set of multivariate meteorological time series from countries in the North Mediterranean Belt area. The correlations reviewed use only daily global, hourly global or daily diffuse irradiation as input, for the daily or hourly time scale. The best overall performance was presented by the Frutos correlation for the estimation of the daily diffuse radiation by an adapted version of the Liu and Jordan correlation for the mean daily diffuse radiation profile, and by the Hollands and Crha model for estimation of hourly diffuse values from the corresponding global values. The results show that the best correlation for each site varies. Two empirical piecewise correlations were also developed by the authors with the help of the data bank available, yielding models that showed even better fits to the data. The results show some seasonal and location dependence.

Research paper thumbnail of Solar position and right ascension

Solar Energy, 1993

Abstract A new correction of right ascension, proposed by the authors, permits smooth SUNAE algor... more Abstract A new correction of right ascension, proposed by the authors, permits smooth SUNAE algorithm runs, minute by minute, for a period of a year.

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

Meteorology and Atmospheric Physics, 2000

This work studies the variability of the Linke (T L) and Unsworth-Monteith (T U) turbidity parame... more 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.

Research paper thumbnail of Air Temperature Model Evaluation in the North Mediterranean Belt Area

Journal of Applied Meteorology, 2002

A comparative assessment of air temperature models, using hourly and daily air temperature measur... more A comparative assessment of air temperature models, using hourly and daily air temperature measurements in 34 different stations in the north Mediterranean belt, is presented. Four air temperature models were used to estimate hourly and daily mean air temperature from daily maximum, daily minimum, and monthly mean air temperature. Root-mean-square error (rmse), scatter graphs, and cumulative frequency curves were used to determine the performance of each model. The best overall performance for estimating hourly air temperature from monthly mean values was presented by Erbs's model; the ''standard'' model gave the best performance for estimating daily mean air temperature from daily minimum and maximum air temperature values. The results show that the Erbs and standard models are the best for all stations used. A new Climatic Synthetic Time Series for the Mediterranean Belt Temperature Model (CLIMEDTEM) for estimating daily air temperature was developed by the authors with the help of available data banks, yielding a stochastic model that showed fits to the data with rmse values of 14%.

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

Climatic Change, 1989

In this paper, the characteristics of the long-term precipitation series at Athens (1858-1985) ha... more 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 chmatxc fluctuations and tendencies. The series of precipitation at Athens is one of the longest in southeastern Europe.

Research paper thumbnail of Comments on an analytical-empirical method for determining the roughness length and zero-plane displacement by A. K. Lo

Boundary-Layer Meteorology, 1995

Research paper thumbnail of A Look At The Solar Radiation Climate In Athens During The Brightening Period

Research paper thumbnail of A Look At The Solar Radiation Climate In Athens During The Brightening Period

Research paper thumbnail of Solar Energy Received on Flat-Plate Collectors Fixed on 2-Axis Trackers: Effect of Ground Albedo and Clouds

Energies, 2024

This study investigates the performance of isotropic and anisotropic diffuse models to estimate ... more This study investigates the performance of isotropic and anisotropic diffuse models to
estimate the total solar energy received on flat-plate collectors fixed on dual-axis trackers. These
estimations are applied at twelve sites selected in both hemispheres with different terrain and envi
ronmental conditions. The diffuse (or transposition) models used in this study are the isotropic Liu
Jordan (L&J), Koronakis (KOR), Badescu (BAD), and Tian (TIA), and the anisotropic Hay (HAY),
Reindl (REI), Klucher (KLU), Skartveit and Olseth (S&O), and Steven and Unsworth (S&U). These
models were chosen because of their simplicity in the calculations and minimum number of input
values. The results show that a single transposition model is not efficient for all sites; therefore, the
most appropriate models are selected for each site under all, clear, intermediate, and overcast con
ditions in skies. On the other hand, an increase in the ground albedo in the vicinity of the solar
installation can increase the annual inclined solar availability on a two-axis tracker by at least 9%
on average. Further, a linear dependence of the annual inclined solar energy on the variation of the
ground albedo was found. Also, a linear relationship exists between the annual diffuse-fraction and
cloud-modification factor values at the 12 sites.

Research paper thumbnail of Atmospheric Processes over the Broader Mediterranean Region: Effect of the El Niño–Southern Oscillation?

Research paper thumbnail of Atmospheric Processes over the Broader Mediterranean Region: Effect of the El Niño-Southern Oscillation

Atmosphere, 2024

The Mediterranean area is considered a hot spot on our planet because it represents the crossroad... more The Mediterranean area is considered a hot spot on our planet because it represents the crossroads of various aerosols. Several studies have shown that the weather in the region is affected by the North-Atlantic Oscillation, which, in turn, is well connected with the El Niño–Southern
Oscillation (ENSO) phenomenon. Nevertheless, no study has investigated the ENSO effect on the solar radiation and atmospheric aerosols in this region. The present study considers a greater area around the Mediterranean Sea over the period 1980–2022. The results show that there exists a loose but significant dependence, in some cases, of the optical properties of aerosols (aerosol optical depth, Ångström exponent, cloud optical depth) and solar radiation (net short-wave and net long-wave radiation, direct aerosol radiative forcing) on ENSO events. The results of this study provide motivation for further investigations, since such results can increase the accuracy of general circulation models that deal with climate change. Besides the ENSO effect, the enrichment of the Mediterranean atmosphere in suspended particles from great volcanic eruptions is shown. The inter-annual variation of the examined parameters is presented. A classification of the existing aerosols over the area is also provided.

Research paper thumbnail of Analysis of the total, annual, and inter-annual hourly mean direct solar normal irradiation

Arabian Journal of Geosciences, 2022

The elaboration of a time series demands long periods of measurements. In this paper, a methodolo... more The elaboration of a time series demands long periods of measurements. In this paper, a methodology is described and used to systematically organize time/space series of climatic data. The methodology allows a statistical and climatic analysis more interesting. The methodology allows to categorize the series in different time partitions and in subdivisions. The methodology is described using a database of Hb\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${H}_{b}$$\end{document} and fractions transmitted on the terrestrial surface (Ktb\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${Kt}_{b}$$\end{document}) obtained from Botuc...

Research paper thumbnail of Atmospheric Turbulence Derived from Laser Doppler Anemometry Technique

SUMMARY This paper presents results about atmospheric turbulence in the form of power spectral de... more SUMMARY This paper presents results about atmospheric turbulence in the form of power spectral density of the w-wind component. Such results are rarely presented in the international literature because of the difficulty that these systems have in order to derive atmospheric turbulence parameters, as explained in the text. The data for the analysis was gathered during CLEOPATRA experimental campaign around Munich area in the period May-July 1992. The power spectral densities derived seem to follow the-5i3 law. KEY WORDS: Atmospheric turbulence, laser doppler anemometry, w-wind component power spectral density.

Research paper thumbnail of The solar radiation climate of Athens: Variations and tendencies in the period 1992–2017, the brightening era

Solar Energy, 2018

Solar radiation at the surface of the Earth undergoes short-and long-term variations mostly influ... more Solar radiation at the surface of the Earth undergoes short-and long-term variations mostly influenced by changes in atmospheric composition and cloud cover. These two factors characterise the solar radiation climate at a place. This study deals with the solar radiation climate over Athens focusing on the variations and trends of the global and diffuse horizontal irradiances recorded at the Actinometric Station of the National Observatory of Athens. The analysis shows that the global radiation over Athens in the period 1992-2017 presents a maximum in July and in May, June around noon under all and clear skies. For the diffuse component, this occurs in spring and in May (noontime) under all-and clear-sky conditions. The global radiation trends are positive (+0.41%/ decade and +2.36%/decade for all and clear skies, respectively), while its diffuse counterpart shows negative trends (−6.93%/decade and −9.27%/decade for similar sky conditions, respectively) in the period 1992-2017. These findings confirm the recovery in the solar radiation levels over Athens in the recent 25 years.

Research paper thumbnail of Improving the estimation of the true mean monthly and true mean annual air temperatures in Greece

Atmospheric Science Letters, 2015

The true mean monthly/annual air‐temperature estimations are usually based on the monthly average... more The true mean monthly/annual air‐temperature estimations are usually based on the monthly averages of meteorological observations performed at standard hours. The performance of this combination varies as it depends on local climate of the particular meteorological station; it consequently allows for small/large deviations from its exact value. This study examines the possible deviations in Greece and suggests ways of improving the derived estimates. Two cases are considered. (1) An area has one thermograph and a number of thermometric stations. (2) An area has several thermographs and many thermometric stations. Solutions for minimizing the estimation error in both cases are provided.

Research paper thumbnail of Laser-Doppler Wind Measurements in the Planetary Boundary Layer

The aim of this work is to investigate the representativity of LDA mean wind velocity measurement... more The aim of this work is to investigate the representativity of LDA mean wind velocity measurements and variations of wind velocity profiles in the planetary boundary layer undei different atmospheric stabilities and earth surface roughnesses in presenci of mesoscale variations of the wind. The comparison of the theoretically calculated relative error of LDA estimates with the experimental results shows good agreement, Based on these investigations, the optimum measurement procedure can be defined for different stability conditions of the atmospheric boundary layer. Zusammenfassung windmessungen in der planelaren Grenzschicht mit dem Lcser.Doppler Anemometer Mit der vorliegenden Arbeit soll untersucht werden, wie reprasentativ LDA-Messungen zur Bestimmung der mittleren Windgeschwindigkeit und der Variation von Windprofilen-in der planetaren Grundschicht sind. Dies geschieht bei verschiedenen atmospharischen Stabilit[ten und Rauhigkeitsparametern in Anwesenheit von mesoskaligen Variationen des Windes. Der Ver-gleich der theoretisch berechneten relativen MeBfehler mit den experimentellen Ergebnissen zeigt gute Ubereinstimmung. Aufgrund dieser Untersuchungen kann'die optimale MeBlrozedur fiir verschiedene Stabilitetsbedingungen in der atmosph6rischen Grenzschicht definiert werden.

Research paper thumbnail of Surface winds and horizontal mesoscale wind spectra in Athens, Greece

Il Nuovo Cimento C, 1986

SummaryThis paper reports briefly on the spatial variability of the wind regime in the Athens reg... more SummaryThis paper reports briefly on the spatial variability of the wind regime in the Athens region by examining mean wind speeds (at 5 sites) and frequency distributions of speed and direction for 3 sites. At 3 locations, some wind roses have been prepared for the representation of the flow in the area. These wind roses should only be used as a guide to the initial identification of important localized effects and not as the sole representation of the flow. Besides, spectral analysis of hourly wind velocities obtained, also, at a site in Athens, illustrated a shift of the major sources of kinetic energy from the locally induced diurnal oscilation in Summer to synoptic variations in Winter. The physical significance of the summer oscillation is also known to be location dependent. The method illustrates locally induced variations within the flow and seasonal transfer of energy from synoptic sources in Winter to diurnal sea-breeze and Etesian wind systems in Summer.RiassuntoNel presente lavoro è succintamente descritta la mutabilità spaziale del vento nel circondario di Atene, esaminando i valori medi della velocità del vento (in 5 località) e la loro frequenza di distribuzione (in 3 località). Per le 3 località sono stati tracciati alcuni diagrammi di vento, rappresentativi del flusso di vento alla località. Questi diagrammi dovranno essere considerati una specie di guida per la determinazione delle determinanti caratteristiche locali della topografia, anche perchè non riportano la rappresentazione completa del flusso. Per di piú l'analisi spettrale fornisce la scala dei sistemi sinottici per stagione dell'anno. L'analisi spettroscopica di dati di velocità del vento, registrati ogni ora, ad Atene, indica la differenziazione delle sorgenti di energia cinetica delle oscillazioni diurne localmente indotte e variazioni sinottiche durante l'inverno. È anche indicata la dipendenza dell'oscillazione estiva dalla località. In particolare il metodo illustra variazioni indotte localmente nel flusso ed anche il trasferimento stagionale di energia da sorgenti sinottiche durante l'inverno a diurni sistemi di vento mare-brezza e venti estivi (meltems) durante l'estate.РезюмеВ этой статье предлагается анализ пространственной изменчивости ветров в Афинах, на основе исследовании средних скоростей ветра (в 5 точках) и частотных распределений скорости и направления в 3 точках. В 3 точках исследуются розы бетров. Эти розы используются для начальной идентификации важных локаляных эффектов. Спектральный анализ скоростей ветров, полыченный в Афинах, показывает сдвнт большинства источников кинетигеской энергии от локльно индуцированных суточных осцилляций летом до синоптических изменений зимой. Отмечается, что физическая значимость летних осцилляций зависит от местоположения. Предложенный метод иллюстрирует локльно индуцированные изменения внутри потока и сезонный перенос энергии от синоптических истчников зимой до суточных бризов и северо-западных пассатных ветров летом.

Research paper thumbnail of Estimation of sunrise and sunset hours for locations on flat and complex terrain: review and advancement

Renewable Energy, 1997

This work concerns the calculation of sunrise and sunset hours at a location on complex terrain. ... more This work concerns the calculation of sunrise and sunset hours at a location on complex terrain. This is particularly important to all solar irradiance and illuminance codes that estimate solar irradiance or illuminance on horizontal or inclined surfaces on a specific day at a location on non-fiat terrain. Specific formulas are given.

Research paper thumbnail of Mapping Atmospheric Corrosion on Materials of Archaeological Importance in Athens

Water, Air, & Soil Pollution, 2011

Atmospheric pollution is known to induce corrosion effects on various materials. For Greece, ston... more Atmospheric pollution is known to induce corrosion effects on various materials. For Greece, stone deterioration could emerge severe costs in the case of damaging cultural monuments. This work aims to investigate the corrosion process on materials of archaeological importance (marble, limestone, and sandstone) in the Greater Athens Area (GAA) by using sophisticated geoanalytical methods together with dose–response functions for selected materials, in order to derive corrosion maps for GAA in the period 2000–2009. Also, a corrosion trend analysis is performed, which can be a very helpful tool for the prediction of potential risks to monuments of cultural heritage due to atmospheric pollution. The corrosion effects on the selected materials are generally weak. Nevertheless, increasing corrosion trends are found in the eastern regions of GAA for all sheltered materials and in the northern parts of GAA for unsheltered marble. The technique is finally applied to 12 locations in GAA, which include some of the most important archaeological monuments of Athens, and provides comprehensive results for the estimation of the impact of atmospheric corrosion on the structural materials of these archaeological sites.

Research paper thumbnail of Mapping Atmospheric Corrosion on Modern Materials in the Greater Athens Area

Water, Air, & Soil Pollution, 2013

In this study, we investigate the corrosion effects on modern materials at various sheltered and ... more In this study, we investigate the corrosion effects on modern materials at various sheltered and unsheltered locations in the Greater Athens Area (GAA) due to atmospheric pollution, since materials deterioration could emerge severe economic costs in the near future. The preselected materials are weathering steel, copper, bronze, zinc, and aluminum, which are mainly used in modern constructions in the GAA. The method applied in this study leads in the production of corrosion maps for GAA in the period 2000–2009 by using sophisticated geoanalytical methods together with dose–response functions for the selected materials. The corrosion effects are significant for weathering steel, moderate for copper and bronze and weak for zinc and aluminum. Also, a corrosion trend analysis is performed, which can be a very helpful tool for future protection of such materials from atmospheric pollution. The results show increasing corrosion trends for weathering steel and copper in the eastern regions of GAA, probably caused by the recent operation of the Athens International Airport at Spata, while no corrosion trends were observed to the other materials. The method applied in this work provides comprehensive results for the estimation of the impact of atmospheric corrosion on various construction materials.

Research paper thumbnail of Diffuse solar irradiation model evaluation in the North Mediterranean Belt area

Solar Energy, 2001

The performance of daily and hourly diffuse horizontal solar irradiation models and correlations ... more The performance of daily and hourly diffuse horizontal solar irradiation models and correlations is examined using an assembled data set of multivariate meteorological time series from countries in the North Mediterranean Belt area. The correlations reviewed use only daily global, hourly global or daily diffuse irradiation as input, for the daily or hourly time scale. The best overall performance was presented by the Frutos correlation for the estimation of the daily diffuse radiation by an adapted version of the Liu and Jordan correlation for the mean daily diffuse radiation profile, and by the Hollands and Crha model for estimation of hourly diffuse values from the corresponding global values. The results show that the best correlation for each site varies. Two empirical piecewise correlations were also developed by the authors with the help of the data bank available, yielding models that showed even better fits to the data. The results show some seasonal and location dependence.

Research paper thumbnail of Solar position and right ascension

Solar Energy, 1993

Abstract A new correction of right ascension, proposed by the authors, permits smooth SUNAE algor... more Abstract A new correction of right ascension, proposed by the authors, permits smooth SUNAE algorithm runs, minute by minute, for a period of a year.

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

Meteorology and Atmospheric Physics, 2000

This work studies the variability of the Linke (T L) and Unsworth-Monteith (T U) turbidity parame... more 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.

Research paper thumbnail of Air Temperature Model Evaluation in the North Mediterranean Belt Area

Journal of Applied Meteorology, 2002

A comparative assessment of air temperature models, using hourly and daily air temperature measur... more A comparative assessment of air temperature models, using hourly and daily air temperature measurements in 34 different stations in the north Mediterranean belt, is presented. Four air temperature models were used to estimate hourly and daily mean air temperature from daily maximum, daily minimum, and monthly mean air temperature. Root-mean-square error (rmse), scatter graphs, and cumulative frequency curves were used to determine the performance of each model. The best overall performance for estimating hourly air temperature from monthly mean values was presented by Erbs's model; the ''standard'' model gave the best performance for estimating daily mean air temperature from daily minimum and maximum air temperature values. The results show that the Erbs and standard models are the best for all stations used. A new Climatic Synthetic Time Series for the Mediterranean Belt Temperature Model (CLIMEDTEM) for estimating daily air temperature was developed by the authors with the help of available data banks, yielding a stochastic model that showed fits to the data with rmse values of 14%.

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

Climatic Change, 1989

In this paper, the characteristics of the long-term precipitation series at Athens (1858-1985) ha... more 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 chmatxc fluctuations and tendencies. The series of precipitation at Athens is one of the longest in southeastern Europe.

Research paper thumbnail of Comments on an analytical-empirical method for determining the roughness length and zero-plane displacement by A. K. Lo

Boundary-Layer Meteorology, 1995

Research paper thumbnail of Atmospheric Aerosol Climatology over the Globe: Emphasis on Dust Storms

Springer, 2012

Atmospheric aerosols play a major role in climate change science debate. These can infl uence cli... more Atmospheric aerosols play a major role in climate change science debate. These can infl uence climate in two ways, directly and indirectly. Since the concentration and composition of atmospheric aerosols are very variable in time and space, their characteristics cannot be studied individually, but in terms of their climatological effects. This study gives some of the main features that characterize atmospheric aerosols. Four locations in the world are selected due to their different environments (weather and atmospheric conditions). The aerosol optical depth and the Ångström-exponent are examined at these sites for the period 2002-2004. Emphasis is given on the atmospheric aerosols in the form of dust. The aerosol optical depth and the aerosol index are presented for a dust storm that occurred over Greece in April 2005.