C. Cartalis

Modifications in energy demand in urban areas as a result of climate changes: an assessment for the southeast Mediterranean region

Abstract The impact of climate changes on the urban environment may be assessed by calculating the modifications in energy production and consumption for such daily operations as heating and cooling. In this study climate changes in the southeastern Mediterranean (the area of Greece) were simulated for the year 2030 on the basis of specially constructed climatic scenarios which describe potential reductions in the emissions of greenhouse gases, and were, thereafter, used to calculate the heating and cooling degree days for the same year. The results show that the cumulative amount of heating and cooling degree days will decrease and increase, respectively, as compared to the respective amounts for the year 1990. In terms of the cooling degree days, it was found that the areas most affected were the Attica and central Macedonia regions, the Aegean islands and Crete, whereas in terms of the heating degree days, it was found that a large part of the country will require less energy for heating.

The Long-Term Coupling between Column Ozone and Tropopause Properties

Abstract The observational data of the vertical temperature distribution and column ozone, obtained from 10 main stations in the Northern Hemisphere, are analyzed in order to explore the tropopause variations in conjunction with the dynamical variability in column ozone. From the analysis presented, it is evident that the summer distribution of the frequency of occurrence of the tropopause over Greece, apart from its main maximum (around 12 km), is also characterized by a secondary one around 16 km. It is proposed that this elevated maximum possibly originates from the height variation of the tropopause from 12 to 16 km depending on whether the Athens station is located below the cyclonic shear side or below the anticyclonic shear side of the subtropical jet stream. It is also suggested that the transport in the upper troposphere and lower stratosphere that originated in the equatorial region forces the appearance of the multiple tropopauses above Greece. Furthermore, the observational analysis of the ver...

Surface ozone in Athens, Greece, at the beginning and at the end of the twentieth century

Abstract Atmospheric ozone at the surface was monitored in Athens, Greece during the first four decades of the twentieth century using De James colometric papers. This historic record is analysed in conjunction with present ozone measurements in Athens (1987–1990) to show an increase of the ozone mixing ratio from 28.2 to 57.4 ppb for daytime, and from 26.6 to 48.5 ppb for nighttime. The annual cycle of surface ozone contains one maximum for the daytime data and two maxima for the nighttime data, the situation being reversed when a subperiod (1901–1907) of the historic record is considered. Comparison of this subperiod to the Montsouris data show higher ozone levels in Athens, and in phase annual cycles. Finally, harmonic analysis of the historic and present records for Athens, shows—in addition to the well known 12-month and 6-month waves—a relatively strong 4-month wave in surface ozone, and a shift in the tiome of ozone maximum for both daytime and nighttime ozone data.

Mapping micro-urban heat islands using NOAA/AVHRR images and CORINE Land Cover: an application to coastal cities of Greece

Land Surface Temperature (LST) is a significant parameter for identifying micro-climatic changes, their spatial distribution and intensities in relation to the urban environment. In this study, LST is estimated using thermal infrared data as acquired by the Advanced Very High Resolution Radiometer (AVHRR) instrument onboard the National Oceanic and Atmospheric Administration (NOAA) satellite and by using a split window algorithm that is adjusted to account for the region of Greece. For the assignment of the surface emissivity, a new methodology based on the Coordination of Information on the Environment (CORINE) Land Cover database for Greece is used. The algorithm is applied to a night-time series of NOAA/AVHRR images of Greece in order to produce surface temperature maps of an enhanced spatial resolution of 250 m for the cities of Thessaloniki, Patra, Volos and Iraklion, which are the most significant harbour cities of Greece. Results indicate the presence of urban heat islands (UHIs) in each case study, with highest temperatures detected along the coastal zone of the harbour cities resulting from denser urban fabric and road network as well as intense human activity.

Integrating Corine Land Cover data and Landsat TM for surface emissivity definition: application to the urban area of Athens, Greece

This study examines the potential of the combined use of the land cover/land use information provided by the Corine Land Cover (CLC) database with Landsat satellite data for the definition and quantitative correlation of emissivity with various land covers and land uses that describe a certain territory. Surface emissivity in the 10.5–12.5 µm wavelength range is derived using Landsat data and the Normalized Difference Vegetation Index Thresholds method (NDVITHM), whereas mean emissivity values for selected urban/non‐urban land cover types are estimated by integrating the emissivity image with the land cover vector data. The method is applied to the greater Athens area, Greece, in order to estimate the emissivity of various land cover types found within the urban setting. Analysis of variance (ANOVA) indicates statistically significant differences in emissivity associated with different land cover types. Furthermore, statistical results demonstrate that the method is very effective and can provide emissivity values of different land cover types with good accuracy and therefore can quantitatively link emissivity with surface type.

Variations and Trends in Annual and Seasonal Air Temperatures in Greece Determined from Ground and Satellite Measurements

SummaryThe variations and trends in annual and seasonal air temperatures in Greece were examined on the basis of ground measurements for 25 stations during the period 1951–1993, and satellite measurements for the south eastern Mediterranean during the period 1979–1991. Data were smoothed using a 5-year running mean and were thereafter examined by regression analysis to define trends in the long duration time series. Data were also examined to detect abrupt changes and trends in the long duration annual, winter and summer series of mean maximum, mean minimum and mean temperatures. An overall cooling trend was detected for the majority of stations in winter over the entire period; the same cooling trend was also recognised for the annual and summer mean values, although a reverse warming trend was detected around the mid-70s at several stations. Satellite measurements indicate a slight warming trend, although this is not statistically significant. Considering the results of the regression analysis and the statistical tests applied to the 25 stations, it may be concluded that annual mean temperatures are dominated by an overall cooling trend, with the exception of stations in urban areas where urbanisation effects may have resulted in a warming trend. Summer temperatures, however, exhibit a warming trend roughly after 1975 at most stations.

A new algorithm for the detection of plumes caused by industrial accidents, based on NOAA/AVHRR imagery

The Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA satellites may be used for detecting plumes caused by industrial accidents through the combined use of the visible (0.58-0.68 @m), near infrared (0.72-1.10 @m) and thermal infrared (11.5-12.5 µm) channels of the AVHRR. In this study a model algorithm is developed to identify pixels which correspond to plumes caused by industrial accidents. The novelty of the algorithm is that it combines the visible, the near infrared and the thermal infrared AVHRR channels in order to produce a two-dimensional feature space image in which the plumes can be detected and monitored. The algorithm was evaluated for four industrial accidents: in Enschede, the Netherlands on 13 May 2000; in Genoa, Italy on 13 April 1991; in Lyon, France on 2 June 1987 and in Kalohori, Greece on 24 February 1986. The effectiveness and reliability of the algorithm was found to be satisfactory in all case studies.

Summertime Measurements of Benzene and Toluene in Athens Using a Differential Optical Absorption Spectroscopy System

Abstract In this paper, measurements of benzene, toluene, p, mxylene, ozone (O3), nitrogen dioxide (NO2), and sulfur dioxide (SO2) made using the differential optical absorption spectroscopy (DOAS) technique during a 4-month period of summer 2000 (June–September) in Athens, Greece, are presented. An assessment of benzene mean value concentrations during this 4-month period exceeded 10 µg/m3, which is 2 times greater than the average yearly limit proposed by European authorities. Toluene measurements present mean values of approximately 33 µg/m3. Benzene and especially toluene measurements are highly correlated with NO2 and anticorrelated with O3. High values of benzene, NO2, and toluene are also correlated with winds from the southeast section, an area of industrial activity where emissions of volatile organic compounds (VOCs) have been recorded in previous studies. O3 is correlated with winds from the south-southwest section affected by the sea breeze circulation. Diurnal variations of O3, NO2, and SO2 concentrations are compatible with measurements from the stations of the Ministry of Environment’s network. Outliers are combined with weak winds from the south-southwest. As far as p, m-xylene measurements are concerned, there is a poor correlation between gas chromatography (GC) and DOAS Opsis measurements, also observed in previous relevant campaigns and eventually a criticism in the use of the DOAS Opsis model for the measurement of p, m-xylene.

Application of an automated cloud‐tracking algorithm on satellite imagery for tracking and monitoring small mesoscale convective cloud systems

In this study, an automatic algorithm for tracking convective cloud cells, on the basis of infrared and water vapour Meteosat images, is applied in the case of intense precipitation events of 26 and 27 January 1996 in Greece, and the results are presented. The case presented in this study has the particularity of consisting of several localized maximum precipitation events that resulted from small mesoscale convective systems. The ability of the algorithm to detect and track in Meteosat images, in real mode, propagating cloud systems of this size, through the monitoring of several cloud parameters that express cloud development and movement, is examined. It was found that the algorithm was capable of identifying small mesoscale cloud cells and tracking them consistently to the point of dissipation. Moreover, the introduction in the algorithm of new cloud parameters, which are directly related to the cloud‐top structure, has proved very valuable in providing additional information on the convective potential of the detected cloud cells. Finally, an empirical nowcasting of convective cloud movement and evolution could be carried out in many cases to support the forecasters decisions by using information on cloud speed, direction and development in conjunction with synoptic analysis.

Use of Meteosat imagery to define clouds linked with floods in Greece

A cloud classification scheme has been developed with the aim of defining and monitoring clouds cells associated with heavy rain. In the first stage of the scheme, Meteosat images in the visible were corrected to account for varying illumination times and angles. In the second stage, analysis of Meteosat images in the visible, infrared and water vapour channels resulted in the assignment of spectral signatures to seven categories of cloud class. The analysis was supported by temperature and humidity profiles from radiosondes in the wider geographical area as well as by synoptic maps of the area. Finally, Meteosat images reflecting two flood incidents which occurred in Greece on 21 October 1994 and 12 January 1997 were classified on the basis of the defined cloud categories; cloud cells associated with heavy rain were clearly depicted on the classified images through the category of thick opaque convective clouds.