Shifts in early spring wind regime in North-East Europe (1955–2007)

Abstract. Changes to the winter-to-spring switch-time of the upper air flow regime at the 850 and 500 hPa levels over the north-eastern Baltic Sea are analyzed based on a data set extending from 1955 to 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 and using 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.