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Summary ¶Trends and low frequency fluctuations relying on 14 observed temperature and precipitation series 1901?1998 from Hungarian sites are presented. The statistical significances of systematic changes are calculated by the t-test for the linear trends and the Mann-Kendall test. Characteristics of long-term fluctuations are investigated by spectrum analysis (Fisher-test), fitting optimum-ranked polynomials as well as illustrated by smoothed curves of 15-point Gauss-filter application. While the increase of mean temperature in Hungary during the 20 th century is not significant, the annual precipitation totals have substantially decreased. In the first half of the century mainly the precipitation totals in the transitional seasons decreased. By the second half of the century the seasonal structure of the precipitation trends has altered significantly: there was practically no systematic change in the transitional seasons, but winter precipitation decreased dramatically. The paper makes some comparisons with the same type climatic characteristics of the surrounding geographical regions, the temperature changes of the Northern Hemisphere, as well as discusses the relationship between winter precipitation in Hungary and the North Atlantic oscillation. A significant 50-year oscillation was found in the summer mean temperatures and the annual sums of extreme positive daily temperature anomalies in Hungary. This oscillation seems to be in tune with other processes over the Euro-Atlantic region. A cycle of 3.6 years in the annual precipitation totals was found to be significant at the 0.10 level. [ABSTRACT FROM AUTHOR]

Investigation of diurnal temperature data series in Hungary indicates that extreme anomalies often occur in groups. Periods which includeat least 3-6 extreme anomalous days with 3-5 times higher frequency relative to the climatological average are referred to as periods of extremity (PE). Although PEs cover only 5-12% of the whole time-series (1901-1993), they include 40-90% of all days with extreme temperatures. This refers both to the positive and negative anomalies. This paper shows a method for delimitation technique of PEs which is more suitable for the revelation of time-sequence structure of extreme temperature value occurrences, than traditional investigations of daily ormonthly values. As it was checked by Monte-Carlo simulations, a one step autoregressive model, exhibiting nearly normal distribution gives a fairly good approach of extreme temperature occurrences. However,significant differences between the statistical characteristics of real and simulated PEs are also experienced. Statistical connections between PEs and macrocirculation are also investigated. [ABSTRACT FROM AUTHOR]

Homogenized monthly and annual mean temperatures for ten locations in Hungary from 1901 to 1999 are analyzed. A principal component analysis was performed and the first new component containing 94.5% of the total variance has been retained. A linear regression of this variable on a sea level pressure NAO index results in relatively weak correlations. In order to consider the trends in both data series, a polynomial of years is added to the regression. After a selection of the optimal polynomial orders by Akaike's criteria the correlation coefficients are significantly increased. The Southern Oscillation Index (SO index) characterizing the El Ni?o - Southern Oscillation (ENSO) is then incorporated in the relationship via a nonlinear, threshold model. The threshold model consists of the above linear regressions but is conditioned on the SO index threshold variable. The rationale behind this approach is to allow a change of model performance according to ENSO phase. The thresholds are not pre-specified but are estimated from the data, while the number of thresholds is chosen by Akaike's criteria. A likelihood ratio test shows an improvement of these models over the linear model with very strong significance levels, except in June. [ABSTRACT FROM AUTHOR]