Vol. 105, No. 1 * Pages 1–62 * January - March 2001

The first part of this review paper summarizes the changes in Hungarian temperature and precipitation series during this century. Then, some possible hydrological, agricultural and ecological consequences of a future climate change are outlined, obtained after using empirical downscaling techniques developed for estimation of local effects of a global climate change. Finally, local temperature and precipitation changes corresponding to the doubling of the concentration of atmospheric greenhouse gases obtained with a stochastic downscaling method are presented. Climate of Hungary has become warmer and dryer during this century. The global climate change expected under increasing concentration of atmospheric greenhouse gases further contributes to this tendency.

Seasonal changes in surface-atmosphere heat exchange processes were studied over diverse vegetated surfaces by the synergy of ground observations and satellite measurements over two target areas in Hungary. NOAA Advanced Very High Resolution Radiometer (AVHRR) Global Area Coverage (GAC) data and the NOAA Global Vegetation Index (GVI) weekly data set were combined with conventional ground observations from meteorological stations. Multi-year mean seasonal cycles of satellite-derived parameters were derived and compared. The temporal variation of day- and nighttime temperature difference (DNTD) proved to be directly related to that of latent heat exchange through vegetation conditions and precipitation. Sensible heat flux was characterized by the air-skin temperature difference. The observed differences over the two target areas can be attributed to differences in the dominant vegetation. Time series of DNTD, derived from daytime GVI temperature data and nighttime minimum soil temperature, exhibited significant interannual variability also.

The paper describes a visibility and fog forecasting model developed and used at the Hungarian Meteorological Service (HMS) for last 3 years. The investigated model is a perfect prognostical model (PP). Characteristics of the model, such as input data, statistical approach, decision trees and threshold numbers are described in this paper. The model was tested for both measured sounding and predicted data. Verification of the model led to very good results, so it was applied to aeronautical forecasting as well as to nowcasting. Information and short review about different types of other visibility models are also given.

The problems concerning the numerical solution of the chemistry-transport equations — the basis of all air pollution models — and the operator splitting procedure are discussed. The main aim of the paper is to clarify the mathematical background of operator splitting. The connection between Lie-algebra and the splitting procedure with its error (the so-called splitting error) is studied. Two important examples of the splitting technique are introduced (DEM splitting, physical splitting).