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Anastasia Poupkou Prodromos Zanis Panagiotis Nastos Dimitrios Papanastasiou Dimitrios Melas Kleareti Tourpali Christos Zerefos 《Theoretical and Applied Climatology》2011,104(3-4):459-472
Wildfires are a common experience in Alaska where, on average, 3,775?km2 burn annually. More than 90% of the area consumed occurs in Interior Alaska, where the summers are relatively warm and dry, and the vegetation consists predominantly of spruce, birch, and cottonwood. Summers with above normal temperatures generate an increased amount of convection, resulting in more thunderstorm development and an amplified number of lightning strikes. The resulting dry conditions facilitate the spread of wildfires started by the lightning. Working with a 55-year dataset of wildfires for Alaska, an increase in the annual area burned was observed. Due to climate change, the last three decades have shown to be warmer than the previous decades. Hence, in the first 28?years of the data, two fires were observed with an area burned greater than 10,000?km2, while there were four in the last 27?years. Correlations between the Palmer Drought Severity Index and the Canadian Drought Code, against both the number of wildfires and the area burned, gave relatively low but in some cases significant correlation values. Special emphasis is given to the fire season of 2004, in which a record of 27,200?km2 burned. These widespread fires were due in large part to the unusual weather situation. Owing to the anticyclonic conditions of the summer of 2004, the composite anomaly of the 500?mb geopotential height showed above normal values. The dominance of a ridge pattern during summer resulted in generally clear skies, high temperatures, and below normal precipitation. Surface observations confirmed this; the summer of 2004 was the warmest and third driest for Interior Alaska in a century of climate observations. The fires lasted throughout the summer and only the snowfalls in September terminated them (at least one regenerated in spring 2005). Smoke from the forest fires affected the air quality. This could be demonstrated by measurements of visibility, fine particle matter, transmissivity of the atmosphere, and CO concentration. 相似文献
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Katsirakis Manolis Tsompanakis Yiannis Psarropoulos Prodromos N. 《Geotechnical and Geological Engineering》2022,40(6):3325-3341
Geotechnical and Geological Engineering - The seismic design of new retaining structures is usually performed following modern seismic norms. Nonetheless, there are various monumental retaining... 相似文献
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Recent past and future patterns of the Etesian winds based on regional scale climate model simulations 总被引：1，自引：0，他引：1
Christina Anagnostopoulou Prodromos Zanis Eleni Katragkou Ioannis Tegoulias Konstantia Tolika 《Climate Dynamics》2014,42(7-8):1819-1836
The aim of this work is to investigate the recent past and future patterns of the Etesian winds, one of the most persistent localized wind systems in the world, which dominates the wind regime during warm period over the Aegean Sea and eastern Mediterranean. An objective classification method, the Two Step Cluster Analysis (TSCA), is applied on daily data from regional climate model simulations carried out with RegCM3 for the recent past (1961–1990) and future periods (2021–2050 and 2071–2100) constrained at lateral boundaries either by ERA-40 reanalysis fields or the global circulation model (GCM) ECHAM5. Three distinct Etesian patterns are identified by TSCA with the location and strength of the anticyclonic action center dominating the differences among the patterns. In case of the first Etesian pattern there is a ridge located over western and central Europe while for the other two Etesian patterns the location of the ridge moves eastward indicating a strong anticyclonic center over the Balkans. The horizontal and vertical spatial structure of geopotential height and the vertical velocity indicates that in all three Etesian patterns the anticyclonic action center over central Europe or Balkan Peninsula cannot be considered as an extension of the Azores high. The future projections for the late 21st century under SRES A1B scenario indicate a strengthening of the Etesian winds associated with the strengthening of the anticyclonic action center, and the deepening of Asian thermal Low over eastern Mediterranean. Furthermore the future projections indicate a weakening of the subsidence over eastern Mediterranean which is rather controlled by the deepening of the south Asian thermal Low in line with the projected in future weakening of South Asian monsoon and Hadley cell circulations. 相似文献
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P. Zanis P. S. Monks E. Schuepbach S. A. Penkett 《Journal of Atmospheric Chemistry》2000,37(3):331-332
Volume Contents
Contents to Volume 37 相似文献6.
The current study proposes an analytical closed-form solution for the dynamic distress of rigid fixed-base retaining systems aiming at evaluating the main assumptions and limitations of the pertinent available elasticity-based methods. The new solution is actually an extension of the well-known model of Wood and is capable of evaluating the dynamic distress of either a single or a pair of rigid fixed-base walls interacting with each other, in the case of harmonic base loading. Wall distress is mainly evaluated in terms of dynamic earth pressures, shear forces and bending moments, while the original concept of a “distress spectrum” is introduced as a potential new tool for the seismic design of retaining structures. Distress and wall deformation are interrelated in a number of three-dimensional graphs, where dynamic interaction phenomena are evident. Finally, given the rigorous nature of the new solution, its results verify qualitatively and quantitatively the negligible amplitude of the computational errors of the approximate elasticity-based solutions proposed in the literature. 相似文献
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D. Founda H. D. Kambezidis M. Petrakis P. Zanis C. Zerefos 《Theoretical and Applied Climatology》2009,97(3-4):385-389
Two discontinuities were detected in the air-temperature time series at the meteorological station of the National Observatory of Athens. The first discontinuity reflects the instrumental change, which took place in June 1995 and the second discontinuity (and most pronounced) the application of a correction factor to the temperature values (in January 1997), after a calibration of the new thermometers. As a result, a cooling bias was observed after June 1995 and a warming bias after January 1997. The magnitude of bias exhibited a seasonal variability being more pronounced and reaching up to 0.67°C during the warm period of the year. The common period of operation of the ‘old’ and ‘new’ instrumentation was used for the estimation of monthly correction factors and the removal of the bias. The application of the new correction factors, restore the continuity in the air temperature record after June 1995. 相似文献
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D. Akritidis P. Zanis I. Pytharoulis A. Mavrakis Th. Karacostas 《Meteorology and Atmospheric Physics》2010,109(1-2):9-18
This case study investigates a stratospheric intrusion event down to the earth’s surface (near sea-level pressure) of the greater area of Athens (23.43°E 37.58°N), which occurred on 9 October 2003 and caused a remarkable increase in surface ozone concentrations not related to photochemical production. This event is among the rare case studies investigating, on the one hand, a deep stratospheric intrusion down to the earth’s surface at near sea-level pressure and, on the other, an event affecting the near surface ozone of a megacity such as Athens. The synoptic situation is described by a deep upper lever trough at 300 and 500 hPa extending over Greece, which is related to a deep tropopause fold as revealed by vertical cross sections of potential vorticity, relative humidity, divergence and vertical velocity. The analysis of potential vorticity at several isentropic levels indicates a hook-shaped streamer of high PV values (greater than 4 pvu at the 315 K isentropic level) over southeast Europe, which coincides with a streamer of dry air as observed from satellite images of water vapor. The aforementioned structure characterizes a textbook case study of stratosphere-to-troposphere transport. The Lagrangian particle dispersion model FLEXPART was used to calculate the trajectories of air particles reaching the receptor site and the fraction of particles with stratospheric origin. It reveals an important direct stratospheric impact within 1 day related to the tropopause fold described in this study with the fraction of stratospheric particles reaching maximum values of 1.9 and 4.5% for threshold values of the dynamical tropopause 2 and 1.5 pvu, respectively. Furthermore, a larger indirect aged stratospheric contribution is also revealed 4 to 5 days prior to the release, related to stratospheric intrusion events at the western Atlantic Ocean, reaching maximum values of 2.5 and 6.9% of particles crossing the 2 and 1.5 pvu potential vorticity surfaces, respectively. 相似文献
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P. Zanis C. Douvis I. Kapsomenakis I. Kioutsioukis D. Melas J. S. Pal 《Theoretical and Applied Climatology》2009,97(3-4):327-337
Regional climate simulations have been performed over the greater European area for 3 years using three convective parameterizations: (a) the Grell scheme with Arakawa-Schubert (AS) closure assumption, (b) the Grell scheme with Fritsch-Chappell (FC) closure assumption and (c) the MIT scheme. The comparison of the model results of near-surface temperature with near-surface temperature observations indicates a cold bias with both Grell scheme configurations. This bias is significantly reduced when the MIT convective scheme is introduced, even during months of low convective activity. The temperature differences between the Grell (with either AS or FC closure schemes) and the MIT scheme are largest in the lower troposphere, extending up to 700 hPa. In terms of total precipitation, no systematical differences between Grell and MIT schemes are observed throughout the year for the European domain but the convective portion of total precipitation is greater in the MIT scheme simulations. For the central Eastern Europe region, MIT scheme simulations generally produce more precipitation during the warm season than Grell simulations, while for the southern Eastern Europe region, the MIT precipitation enhancement is small and not systematically positive. It is evident that the cause of the differences between the convective schemes is the more intense convection in the MIT scheme configuration, which in turn imposes a more effective drying of the atmosphere, less low-level clouds, more short-wave solar radiation absorbed from the ground and hence warmer low level temperatures. 相似文献