Monitoring climate at Jungfraujoch in the high Swiss Alpine region.

A homogenized temperature record measured at Jungfraujoch, the highest permanently manned meteorological station in Europe at 3580 m asl, is presented based on almost 70 years of record (1937-2005). The observed decadal variability as well as the overall trend (1.8 degrees C/69 years) in the homogenized data is comparable to other homogenized Swiss time series at other altitudes. A detailed analysis of seasonal mean temperature trends revealed no significant height dependence for the period 1961-2005. The dominant trend features are the weaker trends in autumn, significant only at low altitudes. Temperature indices such as thawing days, derived from newly homogenized minimum temperature series, exhibit strong vertical and seasonal trend dependence. Strongest relative trends occur in winter at an altitude around 1000 and 1600 m asl. For the summer season relative trends in thawing days are strongest at the highest stations, as expected. At Jungfraujoch an increase of about 50% is observed for the period 1961-2005 even when the extraordinary warm summer of 2003 is excluded.