Abstract. Potential effects of the E1 Nifio-Southern Oscillation (ENSO) warm extreme on the Turkish monthly precipitation totals between 1931 and 1990 were investigated using precipitation data from more than one hundred and eight Turkish meteorological stations. The data were normalized by using the annual total precipitation to minimize the probable topographical effects. A quiet standard annual variation was determined by month-by-month averaging for each annual month of the Neutral years. The anomalies in percent of the Turkish precipitation data were then calculated by subtracting E1 Nifio-year monthly percent precipitation from the corresponding quiet standard value. The obtained anomalies were sorted after the E1 Nifio high ENSO index month and analyzed by superposed epoch method. Distract effects of high ENSO index months were found so that a large part of the month-to-month variability may be attributed to E1 Nifio event. Spatially coherent and statistically significant precipitation responses to E1Nifio were shown in some regions of Turkey.

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The correlation between sulfur dioxide (SO 2 ) concentrations measured at the European and Asian sides of Istanbul and meteorological parameters is investigated using principal component analysis (PCA) and multiple regression analysis techniques. Several meteorological parameters are selected to represent the atmospheric conditions during two winter periods: 1993-1994 and 1994-1995. Six principal components are found to explain the majority of the observed meteorological variability. Surface pressure, 850-mb temperature, and surface zonal (east-west) and meridional (north-south) winds show high loadings on separate factors identified by PCA. We seek dominant meteorological parameters that control the SO 2 levels at each monitoring station. Several multiple regression analysis models are fitted to the data from each monitoring station using six principal components and previous-day SO 2 concentrations as independent variables.Results suggest that the most important parameters, highly correlated with SO 2 concentrations in the Istanbul metropolitan area, are atmospheric pressure and surface zonal and meridional winds. These components have more influence on the determination of the air pollution levels at the Asian side than at the European side. IMPLICATIONSReleased pollutants during the warming season are the main factors in determining the persistent air pollution level in Istanbul. Uncontrolled expansion of the city also causes severe air pollution problems in certain areas. City regulations banning usage of less efficient, poor-quality lignite for heating purposes and supporting usage of natural gas instead decreased air pollution levels. The municipality must expand the ambient air monitoring network, especially in the problem areas mentioned in this study, to protect public health. In Istanbul, sulfur-containing fuels used by building and industry should be controlled to prevent emissions of large amounts of both gaseous and particulate pollutants into the atmosphere. Stringent programs and measures are needed to select the cleanest fuels that will protect air quality and human health.