Climate of the Past Discussions www.clim-past-discuss.net 1814-9340 1814-9359 4 2 2008 10.5194/cpd-4-271-2008 http://www.clim-past-discuss.net/4/271/2008/ http://www.clim-past-discuss.net/4/271/2008/cpd-4-271-2008.html http://www.clim-past-discuss.net/4/271/2008/cpd-4-271-2008.pdf 271 287 2008-03-04 Shifts in early spring wind regime in North-East Europe (1955–2007) S. Keevallik T. Soomere soomere@cs.ioc.ee Marine Systems Institute at Tallinn University of Technology, Estonia Institute of Cybernetics at Tallinn University of Technology, Estonia Changes of the winter-to-spring switch-time of the upper air flow regime at 850 and 500 hPa levels over the north-eastern Baltic Sea are analyzed based on a data set extending until 2007. The long-term variation of the air flow in early spring (March) exhibits multiple regime shifts. The shifts are extracted by means of a vector analysis of the monthly mean air flow as well as the statistical shift detection technology. In the middle of the 1960s the average air flow turned from NW (WNW) to W (WSW) at the 500 (850) hPa level. The original regime was restored in the mid-1990s. The regime shifts in the average air flow in March can be interpreted as changes in the transition time from winter to summer circulation type. The BACC Author Team: Assessment of Climate Change for the Baltic Sea Basin. Springer, 2008. Broman, B., Hammarklint, T., Rannat, K., Soomere, T., and Valdmann, A.: Trends and extremes of wave fields in the north-eastern part of the Baltic Proper, Oceanologia, 48(S), 165–184, 2006. Jaagus, J.: Climatic changes in Estonia during the second half of the 20th century in relationship with changes in large-scale atmospheric circulation, Theor. Appl. Climatol., 83, 77–88, 2006. Järvet, A.: Influence of hydrological factors and human impact on the ecological state of shallow Lake Võrtsjärv in Estonia, Dissertationes Geographicae Universitatis Tartuensis, Tartu, Estonia, 2004. Keevallik, S. and Russak, V.: Changes in the amount of low clouds in Estonia (1955–1995), Int. J. Climatol., 21, 389–397, 2001. Keevallik, S. and Rajasalu, R.: Winds on the 500 hPa isobaric level over Estonia (1953–1998), Phys. Chem. Earth PTB, 26, 425–429, 2001. Keevallik, S.: Changes in spring weather conditions and atmospheric circulation in Estonia (1955–1995), Int. J. Climatol., 23, 263–270, 2003. Keevallik, S., Soomere, T., Pärg, R., and Žukova, V.: Outlook for wind measurement at Estonian automatic weather stations, Proc. Estonian Acad. Sci. Engineering, 13, 234–251, 2007. Kysely, J.: Implications of enhanced persistence of atmospheric circulation for the occurrence and severity of temperature extremes, Int. J. Climatol., 27, 689–695, 2007. Kysely, J., and Huth, R.:~Changes in atmospheric circulation over Europe detected by objective and subjective methods, Theor. Appl. Climatol., 85, 19–36, 2006. Kysely, J., and Domonkos, P.: Recent increase in persistence of atmospheric circulation over Europe: Comparison with long-term variations since 1881, Int. J. Climatol., 26, 461–483, 2006. Pryor, S. C. and Barthelmie, R. J.: Long-term trends in near-surface flow over the Baltic, Int. J. Climatol., 23, 271–289, 2003. Rodionov, S. N.: A sequential algorithm for testing climate regime shifts, Geophys. Res. Lett., 31, L09204, doi: 10.1029/2004GL019448, 2004. Rodionov, S. and Overland, J. E.: Application of a sequential regime shift detection method to the Bering Sea ecosystem, ICES J. Mar. Sci., 62, 328–332, 2005. Soomere, T. and Keevallik, S.: Anisotropy of moderate and strong winds in the Baltic Proper, Proc. Estonian Acad. Sci. Engineering, 7, 35–49, 2001. Soomere, T. and Zaitseva, I.: Estimates of wave climate in the northern Baltic Proper derived from visual wave observations at Vilsandi, Proc. Estonian Acad. Sci. Engineering, 13, 48–64, 2007. Soomere, T., Behrens, A., Tuomi, L., and Nielsen, J. W.: Wave conditions in the Baltic Proper and in the Gulf of Finland during windstorm Gudrun, Natural Hazards and Earth System Sciences, 8, 37–46, 2008. Sooäär~J. and Jaagus, J.: Long-term variability and changes in the sea ice regime in the Baltic Sea near the Estonian coast, Proc. Estonian Acad. Sci. Engineering, 13, 189–200, 2007. Suursaar Ü., Kullas, T., Otsmann, M, Saaremäe, I., Kuik, J., and Merilain, M.: Hurricane Gudrun and modelling its hydrodynamic consequences in the Estonian coastal waters, Boreal Environ. Res., 11, 143–159, 2006. Tooming, H. and Kadaja, J.: Snow cover and surface albedo in Estonia, Meteorol. Z., N.F. 9, 97–102, 2000.