2017. március 28. kedd
IDŐJÁRÁS - OMSZ angol nyelvű folyóirat

Vol. 120, No. 2 * Pages 127–266 * April - June 2016

Quarterly journal of the Hungarian Meteorological Service

Effect of weather conditions on annual and intra-annual basal area increments of a beech stand in the Sopron Mountains in Hungary
Ernő Führer, Márton Edelényi, László Horváth, Anikó Jagodics, László Jereb, Zoltán Kern, Andrea Móring, Ildikó Szabados, and Zoltán Pödör
 PDF (3338 KB)   |   Abstract

We studied the effect of meteorological parameters such as average monthly temperature and sum of precipitation on basal area increment (BAI) of a beech stand in the Sopron Mountains in subalpine climate in Hungary between 1985 and 2007. The applied multivariate regression analysis takes into account the influence of the weather conditions on increments also in the previous two years. Results indicated that precipitation generally stimulated the BAI in the studied stand, while above average temperature during the growing season depressed it. One of the dominant periods for growing of basal area is the autumn of the penultimate year when precipitation and temperature has positive and negative effect on increment, respectively. In the main growing period (spring-early summer) the previous year’s precipitation has positive, while autumn temperature has negative effect. Current spring to early summer precipitation enhances the beech growth, and in contrary, the mean temperature in June-July has negative effect on the BAI. There is a breakpoint in the trend of meteorological variables at about 1999. A significant decrease was observed in the growth of beech in the summer months in the period of 2000–2007 compared to growth between 1985 and 1999 probably caused by the changed meteorological conditions. The maximum growth shifted from June to May, and the relative share of spring months in the BAI has increased since 2000. Drastic loss in increments can be observed in July and August, which was partly compensated in autumn. The long-term trend of annual BAI is continuously decreasing; comparing the two periods, the average yearly increments decreased from 21 cm2 to 12 cm2. According to forecasted climate change, not only further loss in growth but also drastic decay in vitality and tolerance can be expected for beech at this site over the 21st century.

A closure study on aerosol extinction in urban air in Hungary
Ágnes Molnár, Dénes Párkányi, Kornélia Imre, Vera Gácser, and Edit Czágler
 PDF (2512 KB)   |   Abstract

In this study, we present our results from an investigation into the use of visibility data as a viable tool for the survey of long-term variations in air quality. We found that visibility data in general can be used to estimate atmospheric aerosol extinction coefficients, and that PM10 can be successfully estimated from aerosol chemical composition. Our results indicate that PM10 concentrations provide a good basis for the reconstruction of aerosol extinction coefficients. It was also shown that both derived (from visibility) and reconstructed aerosol extinction coefficients were in good accordance with each other, mainly in the case of dry aerosols. Ambient values can be determined if an adequate hygroscopic growth rate for aerosol extinction is considered. We also found that a rather precise estimation of extinction coefficient can be reached if a modified version of the widely used IMPROVE formula is applied.

Analysis of annual and seasonal temperature trends using the Mann-Kendall test in Vojvodina, Serbia
Milivoj B. Gavrilov, Ivana Tošić, Slobodan B. Marković, Miroslava Unkašević, and Predrag Petrović
 PDF (1269 KB)   |   Abstract

The annual and seasonal trends of mean, maximum, and minimum temperatures were analyzed on the territory of Vojvodina, north Serbia. We used observed, quality controlled, homogenized, and spatially averaged data from 9 meteorological stations during two periods: 1949–2013 and 1979–2013. Positive trends were found in 29 out of the 30 analyzed time series using a linear tendency (trend) equation, while negative trends were found in only 1 case. After the application of the classical Mann-Kendall (MK) test, statistically significant positive trends were confirmed in 15 series, while in remaining cases, statistically significant trends were not confirmed. After applying the modified MK test, positive trends were found in 26 series, and 4 cases were with no trend. We find that significant positive trends are dominated during the year, spring and summer; and they are most numerous in the time series of monthly mean temperatures. In accordance with the behavior of analyzed trends, the increase of temperatures is dominant in Vojvodina.

Wind tunnel and computational fluid dynamics study of wind conditions in an urban square
Márton Balczó and András Tomor
 PDF (13872 KB)   |   Abstract

Recognizing the role of urban squares in city life, the paper focuses on wind conditions at squares, with the objective to understand the building-scale flow phenomena influencing the wind comfort of pedestrians and the dispersion of pollutants. Wind tunnel testing of a selected square has been carried out at two wind directions, as well as accompanying computational fluid dynamics (CFD) simulations were performed using the MISKAM microscale model. The high spatial resolution experimental and CFD data allowed the identification of flow structures, like separation bubbles, vortices, high-speed zones in and around the square. Based on the analysis of numerical and experimental data obtained, the MISKAM model is able to resolve the flow field in a complex urban setting with some limitations. In a second step, the model was then used to run further numerical simulations, to compare fully built-up areas to an area with a square, and to assess the influence of tree plantings on the square. Results regarding the latter indicate that below tree crown height, flow velocity and turbulent kinetic energy are both decreased by about one fourth due to the vegetation. It is also shown that the presence of the square increases wind speed in connecting streets and induces longitudinal flows even in streets perpendicular to the approaching wind direction. The time-resolved wind tunnel measurements also allowed presenting the local velocity statistics as wind roses. Using these, we identified locations with non-isotropic turbulence and alternating wind directions.

Implementation and validation of a bulk microphysical model of moisture transport in a pressure based CFD solver
Norbert Rácz and Gergely Kristóf
 PDF (3753 KB)   |   Abstract

We study wet cooling tower plume formation involving mesoscale meteorological effects (such as stratification or compressibility). This was achieved by incorporating transformations and volume source terms into a pressure based computational fluid dynamics (CFD) solver (ANSYS-FLUENT). Moisture dynamics is taken into account with a bulk microphysical model that was recently implemented into the solver.
This model has been validated against known numerical solutions of idealized two-dimensional dry and wet thermals. In particular, the overall thermal profile and the liquid water concentration field indicated good model performance. Model performance has also been compared with measurements for the formation of a large wet cooling tower plume. Simulations are encouraging with regard to the predictability of cumulus like plume structures with complex thermal stratification, the overall liquid water content along the plume axis, and also the turbulent fluctuations caused by the vertical movements in the plume.
The advantage of this approach is that a uniform physical description can be used for close- and far-field flow by using a single unstructured mesh with local refinements. This allows for investigating the finely structured microscale flow phenomena around complex orographic features in a single framework.

Correlation analysis of tilted and horizontal photovoltaic panel’s electricity generation and horizontal global radiation
Miklós Horváth and Tamás Csoknyai
 PDF (2044 KB)   |   Abstract

Present paper aims at analyzing the correlation between global radiation and electricity production of photovoltaic (PV) panels. In case of high correlation, the electricity production can be estimated by the measured or predicted global radiation. Such solution can be applied for forecast purposes if global radiation data are available. On the other hand, global radiation can be measured based on the performance of a small and cheap PV system, which can be a reasonable solution if global radiation data is not available and a high precision monitoring system is too expensive.
The study is based on on-site measurements for the period of four months. At the station, seven PV panels are installed with different orientation and tilt angle and their electricity production is registered. The solar radiation is measured with a pyranometer. In the first group, there are four PV panels. One is placed horizontally and the other three are placed with a tilt angle of 45°. In the second, three-panel group the panels are placed with 90° tilt angle. The station is located in Debrecen, Hungary and the paper focuses on the Hungarian climatic conditions.
The research proves that the correlation strongly depends on the orientation and the tilt angle of the panel, and for prediction and estimation purposes the 45° tilted, south oriented surface is the most recommended option.

Judit Batholy

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