andreas.hoy@ioez.tu-freiberg.de

1. Extremes in Surface Climate Parameters and Atmospheric Circulation Patterns in Eastern Germany and Estonia Andreas Hoy1, Jaak Jaagus2, Jörg Matschullat1 2: Tartu Ülikool Institute ofGeography Vanemuise 46, 51014 Tartu, Estonia 1: TU Bergakademie FreibergInterdisciplinary Environmental Research Centre, Brennhausgasse 5, 09599 Freiberg, Germany andreas.hoy@ioez.tu-freiberg.de Research Approach Various studies on climate extremes show that their variations are largely caused by fluctuations in atmospheric circulation patterns. To what extend extreme conditions of surface climate parameters can be explained by manual circulation classifications is tested for two European regions. There are only two long time series of fundamentally different classification approaches available in continental Europe: one focussed on Central Europe (Classification of Grosswetterlagen; time series since 1881) and one centred to St. Petersburg (Classification of Vangengeim/Girs;time series since 1891). Relations of both classifications with monthly anomalies of temperature, precipitation, relative humidity, air pressure and sunshine duration were studied for the period 1901-2009 (compared to 1961-1990) for the winter (October-March) and summer half year (April-September). Two stations (with long and reliable meteorological time series) near the centre of the classification approach were chosen – Tartu (Estonia) and Potsdam (East Germany). The performance of both circulation classifications is tested for each region. • Data and Methods • Circulation data were taken from Gerstengarbe/Werner (2005, Grosswetterlagen) and Sepp (2005, Vangengeim/Girs). Meteorological data were retrieved from the national weather services of Germany (DWD) for Potsdam and Estonia (EMHI) for Tartu. The Potsdam climate series are complete, the Tartu ones include negligible gaps for precipitation (08/09 1944) and air pressure (08/09 1944, 12 1945), while relative humidity data are still in demand and thus could not be included here. • Two approaches were used: • For each end of the probability spectrum ten years with the most extreme conditions were determined for individual surface climate parameters. According average deviations of circulation patterns were identified and analysed for those years to reveal relations during extreme conditions. • Correlation coefficients of surface climate and atmospheric circulation time series were calculated and tested for significance (Student´s t-test) to identify connections between the full time series. Extreme values Winter Half Year Classification of Grosswetterlagen (centred above Middle Europe) - Direction of Inflow Classification of Vangengeim & Girs(centred above St. Petersburg) Summer Half Year Figures: Average occurrence anomalies of circulation patterns during the ten highest/ lowest values of five different surface climate parameters in Potsdam and Tartu within 1901-2009 Grosswetterlagen: HME = Anticyclone over Central Europe; West/ North/ East/ South = direction of inflow Vangengeim/ Girs: W = maritime, westerly inflow; E = continental, easterly/ southerly inflow; C = continental, northerly inflow Discussion Assumptions: It is characteristic for European climate that directions of circulation pattern anomalies for extreme values and full time series correlations are opposite between time series of precipitation/ relative humidity and those of sunshine duration/ air pressure. Temperature series show a seasonal behaviour being warmer during maritime conditions in winter while colder in summer and vice versa for continental inflow Extreme values are frequently connected to air masses approaching from either west or east. For Grosswetterlagen in Potsdam this is particularly true for temperature and, to a smaller extent, precipitation in winter, while additionally in summer anticyclonal conditions over Central Europe show a distinct behaviour. Tartu, being some 1.500 km away from the focus region, gets extreme values within all four elements (temperature, precipitation, sunshine duration, air pressure) for western/ eastern inflow especially in winter. Deviations in Vangengeim/ Girs classification are more pronounced (three instead of five groups in Grosswetterlagen). Predominantly maritime conditions (W) are clearly differentiated from continental ones (E and C) in Tartu for all elements particularly in winter. In summary, Grosswetterlagen classification performs well in identifying pattern underlying climate extremes in both locations, whereas Vangengeim/ Girs suit well for Tartu, but is not sufficient enough for Potsdam. Correlation coefficients: Full time series (109 years) are used instead of just a selection of 20 extreme years. Despite most correlations are weak and insignificant, strong correlations were found for basically maritime and continental inflow in both locations for temperature in winter. For Tartu this is also true for precipitation, sunshine duration and air pressure, while in Potsdam HME and C-conditions reveal good correlations for those elements. Conclusions: For both approaches stronger relationships between atmospheric circulation and climatic variables are typical for winter half year, the Vangengeim-Girs classification as well as for air temperature, precipitation and (only Tartu) pressure. Surface climate elements in Tartu seem to be more closely connected to large scale circulation than in Potsdam. Correlations Figures: Correlation of time series of five surface climate parameters in Potsdam and Tartu with circulation patterns of two different classifications within 1901-2009 (winter and summer half year) Significant correlations with p≤0,05 are showed in strong, weak and insignificant correlations in light colours References Gerstengarbe FW, Werner PC (2005) Katalog der Grosswetterlagen Europas (1881-2004) nach Paul Hess und Helmuth Brezowsky. 6th ed., Selbstverlag des Deutschen Wetterdienstes, Potsdam/Offenbach (in German), 153 pp. Sepp M (2005) Influence of atmospheric circulation on environmental variables in Estonia. Dissertation, Institute of Geography, Tartu Ülikool, 155 pp.