Joint effects of large scale circulation and atmospheric oscillations (ENSO, NAO) on regional climate parameters

Rita Pongrácz

Ph.D. School on Earth Sciences, coordinator: Dr. Péter Márton
Ph.D. Program on Geography - Meteorology, coordinator: Dr. Gyula Gábris
Supervisor: Dr. Judit Bartholy, head, professor, C.Sc.
Research institute: Eötvös Loránd University, Department of Meteorology. Budapest, 2003.


In the dissertation joint effects of large scale circulation and climatic oscillation phenomena (ENSO: El Niño / Southern Oscillation, NAO: North Atlantic Oscillation) on the Northern mid-latitudes have been analysed. Two selected regions have been investigated: (1) the Carpathian Basin in the Atlantic-European area, (2) the Midwest in North America. Our main goal was to determine the statistical relationships, and then considering these findings, to build models that are able to estimate regional climate parameters.

In the presented studies traditional mathematical statistical techniques (teleconnection analysis, EOF analysis, multivariate linear regression) and an alternate technique (fuzzy rule-based models) have been applied. Fuzzy logic is considered a new approach in the meteorology literature in Hungary. In order to reveal statistical linkages between distant regions teleconnection analysis is used, namely, anomaly maps of height and temperature of several geopotential levels are compared during different phases of atmospheric oscillation phenomena. Furthermore, monthly relative frequency of large scale macrocirculation patterns and regional climate parameters is evaluated in case of these phases. EOF analysis uses empirical orthogonal functions to map spatial patterns of a given field possessing the largest variances during different ENSO phases. Regions with the largest positive and negative values in the spatial patterns of EOF modes show the action centers of the given field. Multivariate linear regression (MLR) and fuzzy rule-based (FRB) models determine the regional climate parameters using predictor variables. Fuzzy logic is able to consider several contradictory responses, which may be true to varying degrees. In the dissertation sensitivity analysis of FRB models is carried out, furthermore, model outputs are compared to results from the MLR models using the same conditions (i.e., input variables, datasets).

Based on the results besides the more direct effect of large scale macrocirculation, teleconnection of climatic oscillation phenomena (ENSO and NAO) is considerably present in the selected regions of the Northern mid-latitudes. Regional climate information obtained from the FRB models using both the relative frequency of MCP types and the climatic oscillation phenomena as input variables are able to reproduce the statistical characteristics of the observed regional climate parameters. The best results can be achieved if (1) both zonality and cyclonic/anticyclonic dominancy are considered at MCP classification, (2) time lag of the climatic oscillation is taken into account. Simulated time series much better represent the observed time series if FRB models presented in the dissertation are used instead of MLR models. Based on the comparison of different model error terms the same conclusion can be drawn: errors of the FRB models are smaller than those of the MLR models.

Main advantage of applying fuzzy rule-based models includes long range estimation of climate parameters when regional climatological information is needed for a long period.