Vol. 105, No. 2 * Pages 63–134 * April - June 2001

The aim of this paper is to summarize the history of Hungarian research carried out during the last forty years to study the atmospheric aerosol. This period can be divided in three parts. In the first part (between 1960 and 1980) the water soluble inorganic ions were investigated to understand the role of aerosol particles in the cloud formation The studies showed that water soluble particles are composed mainly of ammonium sulfate and about the half of the mass of this compound can be identified in the size range of particles with a diameter below 0.2 mm. The sampling program done over the remote ocean indicated that sulfate particles give the major part of the number of aerosol particles even under oceanic conditions, far from the continents. Sulfur budget calculations made it evident that sulfate particles in the continental air are of anthropogenic origin. This meant that human activities control in a great measure the formation of cloud condensation nuclei. Research in the second part (between 1981 and 1995) was devoted to the study of elemental composition of aerosol particles including some toxic metals like lead, zinc and vanadium. Since about 1995, in the third part, one of our main aims has been the investigation of organic species in the atmospheric aerosol. These studies demonstrated that an important fraction of organic matter consists of macromolecules like humic substances in the soils. A non negligible part of these macromolecules are soluble in water. The second goal after 1995 has been to study the effects of the optical properties of aerosol particles on the solar radiation transfer for understanding the role of aerosol particles in visibility control and climatic variation.

The importance of agrometeorological models and their application to improve cultivation techniques are growing day after day. This is mainly due to the need of an integrated agriculture, in which expensive and polluting input has to be substituted by more sustainable agronomic practices. Unfortunately, weather data used as input for these models are not always available, so methods to estimate the missing data have high importance. Starting from these considerations, some models to calculate hourly temperature from maximum and minimum daily values were used to simulate thermal pattern during seven different years (from 1994 to 2000). The obtained results were first compared with the measured values of hourly temperature to control the accuracy of the models. Then, calculated temperatures were used as input of an agrometeorological model simulating the development of Plasmopara viticola on grapevine (Vitis vini­fera). Simulations, using measured and predicted temperatures, were compared to evaluate the possibility of applying temperature models to generate input data of biological systems. The Parton model showed the higher accuracy, while the Ephrath, Wcalc and Goudriaan models presented a decreasing precision in the simulation of thermal pattern. However, all the methods allowed a good substitution of measured temperatures for the application of agrometeorological models.

The Great Hungarian Plain, which is the most important agricultural area of the country, is often stricken by drought. Dry years were particularly frequent in the last fifth of the 20th century. Tendencies of seasonal and annual precipitation totals during the 20th century were analysed using data series of monthly precipitation amounts from 14 Hungarian observing stations. Efficiencies of PDSI and SPI were investigated focusing the examples of unusual large changes in water supply anomalies between November 1999 and October 2000.
Our results show that precipitation has clearly decreased during the 20th century, particularly in early spring and early autumn. The decrease of annual totals is significant at the 0.95 level in all parts of Hungary. Frequency of severe drought events has markedly increased, although very wet periods also occurred in the recent years. PDSI and SPI are widely applied tools to characterise natural water supply. The various indices have different advantages and disadvantages. For example, while SPI for 6 months seems to be the best indicator of natural water supply for an average plant, SPI for 3 months is the better tool for sensitive, shallow-rooted plants.

Several authors investigated Hungarian wind characteristics in the last few decades. For instance, Tar (1980, 1983) analyzed the entire country. The European Wind Atlas was published in 1989 in Risø, Denmark for the Commission of the European Communities. Shortly after the need of a similar publication for the non-EU member countries emerged and only eight years later just partly satisfied with the Wind Atlas for the Central European Countries (ZAMG, 1997). Responding partly for these initiatives, and partly perceiving the increased prosperity of renewable energy resources in this region, in the middle of the 90’s a research program started to study and map the wind climate of Hungary to aid on wind energy usage. Within this project, supplementary wind characteristics have been calculated for 13 Hungarian climate stations. Wind measuring field experiments have been performed and analyzed to determine the possible wind energy resources of Hungary. Temporarily operating climate stations have been installed for automated data collection and quality control. Vertical extrapolation of wind potential and calculation of the Weibull parameters have been completed in order to compare available and extractable wind potential. Mean power outputs and errors of using different averaging periods have been estimated. Using the European Digital Terrain Model, the WAsP model have been adapted. Errors of the model have been analyzed by comparing complex (valley of Lake Akkajaure, Sweden) and simple (Hegyhátsál area, Hungary) terrains.