COMPUTER PROCESSED LANDSAT LAND COVER MAPS OF HUNGARY

Two studies using LANDSAT imagery are summarized. The urban area study of the city of Budapest uses a statistical classifying method with ground truth to identify eleven land use categories resulting in a 60 to 80% reliability. The rural area study of Komarom County attempts to use LANDSAT to monitor the utilization of farms of agri-ecological research by identifying actual cropland patterns. Translated by the authors and submitted for publication in June, 1984.     

Trends, time-varying and nonlinear time series models for NGRIP and VOSTOK paleoclimate data

In order to gain further insights into stochastic behaviour of paleoclimate data, including timescales at and below Milankovitch forcing, three specific questions are discussed using δ ¹⁸O NGRIP and Vostok Deuterium content data. A comparison of ordinary and time-varying coefficients autoregressive (AR) models shows that both data sets are distinguishable from data generated by suitable low-order AR processes in contrast to earlier conclusions. A harmonic regression analysis clearly distinguishing between discrete and continuous spectra detects cycles corresponding to variations of eccentricity, obliquity and precession. Contribution of eccentricity to the total variance in the last 422,766-year Vostok data is close to, while the variance reduction delivered jointly by obliquity and precession is substantially smaller than a previous recent finding. A harmonic regression analysis with time-varying frequencies and amplitudes is also performed. This approach delivers a gain over the constant frequency model at any reasonable significance level. It is demonstrated that variations of frequencies are at least partly due to real variations and not merely to timescale uncertainties. In order to consider nonlinearity in paleoclimate data, threshold autoregressive (TAR) models are applied to time series examined. A bivariate TAR model describing simultaneous NGRIP and Vostok data exhibits three fix points and one limit cycle related to a part of Dansgaard–Oeschger events. The model selected suggests that Greenland has a primary role in the Greenland–Antarctica climate variation relationship.     

Alpine metamorphic evolution and cooling history of the Veporic basement in northern Hungary: new petrological and geochronological constraints

Petrological and geochronological investigations were carried out on metamorphic rocks of the Veporic unit (Inner Western Carpathians) in northern Hungary. K/Ar and Ar/Ar data on micas and amphibole show only Alpine ages (mostly in the range of 87-95 Ma) in this basement unit. Thermobarometric calculations yield lower amphibolite facies peak conditions (ca. 550냴 °C and 9ǃ kbar) for the Eoalpine metamorphic event. Complex evolution of gneissic rocks is reflected by the presence of discontinuously zoned garnets, the cores of which may represent relics of a pre-Alpine (presumably Variscan) thermal event. Zircon fission track (FT) data in the narrow range of 75-77.5 Ma indicate that this portion of the Veporic unit was emplaced to shallow crustal levels already during the Senonian time. The relative minor difference between zircon FT and K/Ar or Ar/Ar ages suggests very rapid cooling during the Late Cretaceous, most probably related to the extensional unroofing of the Veporic core complex. The obtained cooling ages do not support previous models of Tertiary uplift and exhumation of the Veporic unit along the Hurbanovo-Diósjeni Line.     

Resonant Absorption of Nonlinear Slow MHD Waves in Isotropic Steady Plasmas - I. Theory

This paper considers driven resonant nonlinear slow magnetohydrodynamic (MHD) waves in dissipative steady plasmas. A theory developed by Ruderman, Hollweg, and Goossens (1997) is used and extended to study the effect of steady flows on the nonlinear resonant behaviour of slow MHD waves in slow dissipative layers. The method of matched asymptotic expansions is used to describe the behaviour of the wave variables in the slow dissipative layer. The nonlinear analogue of the connection formulae for slow MHD waves obtained previously by Goossens, Hollweg, and Sakurai (1992) and Erdélyi (1997) in linear MHD, are derived. The effect of an equilibrium flow results partly in a Doppler shift of the available frequency for slow resonance and partly in the modification of the width of the dissipative layer.     

Abrupt temperature changes during the last 1,500 years

We investigate the occurrence of abrupt changes in a total of 35 different proxy records from the extra-tropical Northern Hemisphere for the last ~1,500 years. The proxy records include ice-core δ¹⁸O, speleothem, tree ring width/density, marine sediment and lake sediment records with annual, sub-decadal or decadal resolutions. The aim is to explore the spatio–temporal distribution of abrupt climate changes using a kink point analysis technique. A clustering of warm kink points (the kink points with the highest temperatures) around AD 1000 appears corresponding to the Medieval Warm Period and indicates a geographically widespread temperature peak at that time. Kink points around AD 1000 are somewhat more numerous on higher latitudes than on lower latitudes. There are some tendencies for the coldest kink points (the kink points with the lowest temperatures) to be clustered in the ninetenth century, but they are generally more unevenly spaced in time than the warm peaks around AD 1000. The relative lack of kink points detected during the 1500 s–1700 s, likely the coldest part of the Little Ice Age, implies that this cold period was relatively stable and without abrupt events. A possible cluster of kink points on lower latitudes in the early ninth century is also found. No clear difference in the timing of kink points between the different proxy types can be observed.     

Investigation of the climate-driven periodicity of shallow groundwater level fluctuations in a Central-Eastern European agricultural region

The distribution and amount of groundwater, a crucial source of Earth’s drinking and irrigation water, is changing due to climate-change effects. Therefore, it is important to understand groundwater behavior in extreme scenarios, e.g. drought. Shallow groundwater (SGW) level fluctuation under natural conditions displays periodic behavior, i.e. seasonal variation. Thus, the study aims to investigate (1) the periodic behavior of the SGW level time series of an agriculturally important and drought-sensitive region in Central-Eastern Europe – the Carpathian Basin, in the north-eastern part of the Great Hungarian Plain, and (2) its relationship to the European atmospheric pressure action centers. Data from 216 SGW wells were studied using wavelet spectrum analysis and wavelet coherence analyses for 1961–2010. Locally, a clear relationship exists between the absence of annual periodic behavior in the SGW level and the periodicity of droughts, as indicated by the self-calibrating Palmer Drought Severity Index and the Aridity Index. During the non-periodic intervals, significant drops in groundwater levels (average 0.5 m) were recorded in 89% of the wells. This result links the meteorological variables to the periodic behavior of SGW, and consequently, drought. On a regional scale, Mediterranean cyclones from the Gulf of Genoa (northwest Italy) were found to be a driving factor in the 8-yr periodic behavior of the SGW wells. The research documents an important link between SGW levels and local/regional climate variables or indices, thereby facilitating the necessary adaptation strategies on national and/or regional scales, as these must take into account the predictions of drought-related climatic conditions.