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M. Varvayanni C. G. Helmis G. T. Amanatidis D. N. Asimakopoulos J. G. Bartzis A. Soilemes K. H. Papadopoulos H. D. Kambezidis 《Pure and Applied Geophysics》1993,140(4):681-720
Field measurements of wind, air temperature and humidity were taken at the eastern part of the Attika district in June 1991, to examine the topographic influences exerted on the local sea breezes. These influences are due either to the elongated Evia island, faced by the northern half of Attica coastline some tens of kilometers offshore, or to the coast-parallel range of Hymettos mountain, rising steeply 12 km onshore. The instrumentation consisted mainly of three tethered meteorological balloons released at characteristic sires (i.e., the coast, a location between shoreline and mountain foot and the mountain top) and three autographic ground-based anemometers operating at selected locations. Data from the ground-based and upper air stations of the Hellenic National Meteorological Service, as well as the diurnal weather maps were also obtained and analyzed. Observations were made under different synoptic wind and the latter was found to determine remarkably the significance of the topographic effects. A preliminary two-dimensional numerical approach was also made concerning the sea breeze capability to reach the Hymettos mountain top in the case of a weak opposing geostrophic flow. 相似文献
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H. A. Flocas C. G. Helmis S. N. Blikas D. N. Asimakopoulos J. G. Bartzis D. G. Deligiorgi 《Theoretical and Applied Climatology》1998,59(3-4):237-249
Summary In this study an attempt is made to examine and analyse the mean characteristics of the katabatic flows at the western slope
foot of a 1024 m high knife edge mountain using a meteorological tower and three surface meteorological stations. In addition,
the frequency distribution of the occurrence of the katabatic flow over one year period is studied along the characteristics
of the flow arriving in the neighbouring urban area at a distance of 1.5 km. It was found that the katabatic flow occurs mainly
in autumn and spring with the highest frequency in April. The flow is generally characterised by small depth as it is affected
substantially by the background flow. The expected direction of the katabatic wind dominates mainly at the level of 7 m, where
the influence of the background flow is minimised. At the level of 18 m the wind direction shifts, due to the interaction
of the katabatic wind with the background flow. The katabatic flow can penetrate at a distance of 1.5 km being substantially
weakened.
Received September 18, 1996 Revised August 4, 1997 相似文献
3.
A new algebraic turbulent length scale model is developed, based on previous one-equation turbulence modelling experience in atmospheric flow and dispersion calculations. The model is applied to the neutral Ekman layer, as well as to fully-developed pipe and channel flows. For the pipe and channel flows examined the present model results can be considered as nearly equivalent to the results obtained using the standard k– model. For the neutral Ekman layer, the model predicts satisfactorily the near-neutral Cabauw friction velocities and a dependence of the drag coefficient versus Rossby number very close to that derived from published (G. N. Coleman) direct numerical simulations. The model underestimates the Cabauw cross-isobaric angles, but to a less degree than the cross-isobar angle versus Rossby dependence derived from the Coleman simulation. Finally, for the Cabauw data, with a geostrophic wind magnitude of 10 ms–1, the model predicts an eddy diffusivity distribution in good agreement with semi-empirical distributions used in current operational practice. 相似文献
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G. C. Efthimiou D. Hertwig S. Andronopoulos J. G. Bartzis O. Coceal 《Boundary-Layer Meteorology》2017,163(2):179-201
Wind fields in the atmospheric surface layer (ASL) are highly three-dimensional and characterized by strong spatial and temporal variability. For various applications such as wind-comfort assessments and structural design, an understanding of potentially hazardous wind extremes is important. Statistical models are designed to facilitate conclusions about the occurrence probability of wind speeds based on the knowledge of low-order flow statistics. Being particularly interested in the upper tail regions we show that the statistical behaviour of near-surface wind speeds is adequately represented by the Beta distribution. By using the properties of the Beta probability density function in combination with a model for estimating extreme values based on readily available turbulence statistics, it is demonstrated that this novel modelling approach reliably predicts the upper margins of encountered wind speeds. The model’s basic parameter is derived from three substantially different calibrating datasets of flow in the ASL originating from boundary-layer wind-tunnel measurements and direct numerical simulation. Evaluating the model based on independent field observations of near-surface wind speeds shows a high level of agreement between the statistically modelled horizontal wind speeds and measurements. The results show that, based on knowledge of only a few simple flow statistics (mean wind speed, wind-speed fluctuations and integral time scales), the occurrence probability of velocity magnitudes at arbitrary flow locations in the ASL can be estimated with a high degree of confidence. 相似文献
5.
The three-dimensional compressible non-hydrostatic mesoscale model ADREA, developed at NCSR Demokritos for wind field and dispersion predictions in complex terrain, is used to perform two-dimensional simulations of orographically induced precipitation. The model makes use of a simple cartesian grid by allowing blocked areas in the grid volumes and grid faces which are crossed by the irregular topography (the so-called porous-medium concept). Additionally, since we are seeking both simplicity and low computational requirements, only one prognostic equation for the whole of the water substance is implemented. The model equations are based on the theory developed for multicom-ponent/multiphase mixtures and give full account of the effects arising from the relative motion between water particles and moist air. The evaluation of the feasibility of this approach is obtained by comparing model predictions with measurements and analytical results concerning orographic precipitation episodes in the mountain barrier of Sierra Nevada. 相似文献
6.
Ch.?VasilakosEmail author Th.?Maggos J.?G.?Bartzis P.?Papagiannakopoulos 《Journal of Atmospheric Chemistry》2005,52(2):101-116
Volcanoes have been identified as an important natural source of sulfur compounds such as H2S, CS2, SO2 and COS. The emission of volcanic sulfur compounds lead to the formation of sulfate aerosol and contribute to the acidity
of precipitation.
Two weekly measuring campaigns have been performed in the non-erupting volcanic area of Sousaki, Korinthou, to determine the
concentration levels of the above-mentioned compounds in the region, while meteorological parameters were also recorded.
The samplings have been performed during in a 24 h basis, covering two seasons of the year, a week in August 1998 and a week
in January 1999. Reduced sulfur compounds were determined by a simple method of gas chromatography. Quality assurance procedure
showed a very good precision and accuracy of the method utilized for the sulfur compounds determination.
In accordance with literature, H2S was the dominant sulfur compound at the volcano area, while COS, and CS2 didn't present significantly high values. Nevertheless, the concentration levels of the above pollutants are varying depending
on the volcano magnitude and status (active, extinct). 相似文献
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G. T. Amanatidis K. H. Papadopoulos J. G. Bartzis C. G. Helmis 《Boundary-Layer Meteorology》1992,58(1-2):117-132
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. 相似文献
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Marie-Cecile Chalbot Ino-Christina Vei Ilias G. Kavouras Ioannis Bartzis 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(5):731-738
Occupational exposures to aromatic hydrocarbons may be overwhelmed by mainstream and secondary smoking exposures. The objective of this study was to evaluate the influence of occupational exposures and smoking on benzene and toluene urinary metabolites. The metabolites were measured in pre and post-work shift urine specimens in oil refinery workers by gas chromatography/mass spectrometry techniques. Post-shift concentration differences between non-smokers and smokers were statistically significant (at p-value?<?0.05). Pre- and post-shift concentrations of urinary phenol (benzene biomarker) did not vary significantly for both non-smokers and smokers. Occupational exposures to toluene triggered an increase of post-shift levels (compared to pre-shift levels) of urinary cresol for non-smokers and workers who had less than 10 cigarettes during the work shift. For these groups, non-occupational exposures before and during the work shift did not vary. For smokers who did not smoke during the work shift and for those who had more than ten cigarettes during the shift, the post-shift levels of both cresol and hippuric acid were reduced approximately 30% lower than pre-shift levels. This is due to increased exposures to tobacco smoke before the work shift. The relationships between phenol and (cresol?+?hippuric acid) levels for non-smokers and smokers indicated that elevated co-exposures due to smoking result in the reduction of all metabolites levels in urine. These findings demonstrated that exposures to tobacco smoke may stochastically interfere with occupational exposures when biological monitoring is used to assess occupational health risks. Factors influencing the magnitude of the interference were specimen collection time (in relation to the timing of occupational exposures and excretion rates of biomarkers), smoking intensity and timing before and during the work shift. 相似文献
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