Extended Abstract (664K)P4.3
The Atmosphere and the Spatial and Temporal Variability of Phenological Observations in Central Europe
Helfried Scheifinger, Central Institute for Meteorology and Geodynamics, Vienna, Austria; and E. Koch, C. Peter, A. Menzel, and R. Ahas
A data set of 17 phenological phases from Germany, Austria, Switzerland and Slovenia spanning the time period from 1951 to 1998 has been available for analysis together with a gridded temperature data set (1x1 deg grid) and the North Atlantic Oscillation (NAO) index time series. The disturbances of the westerlies constitute the main atmospheric source for the temporal variability of phenological events in Europe. The trend, the standard deviation and the discontinuity of the phenological time series at the end of the eighties can to a great extent be explained by the NAO. A number of factors modulate the influence of the NAO in time and space. The seasonal shift of the westerlies oerlaps with the sequence of phenological spring phases, thereby gradually reducing its influence on the temporal variability of the phenological events with progressing spring (temporal loss of influence). This temporal process is reflected by a pronouncerd decrease in trend and standard deviation values and common variability with the NAO with increasing yearday. The reduction in influence of the NAO with increasing distance from the Atlantic coast is not only appearent in studies based on the data set of the International Phenological Gardens, but also in the data set of this study with its smaller spatial extent (large scale loss of influence). The common variance between phenological and NAO time series displays a discontinuous drop from the European Atlantic coast towards the Alps. On a local and regional scale mountainous terrain reduces the influence of the large scale atmospheric flow from the Atlantic via a proposed 'decoupling mechanism'. Valleys in mountainous terrain have the inclination to harbour temperature inversions over extended periods of time during the cold season, which isolate the valley climate from the large scale atmospheric flow at higher altitudes. Most phenological stations reside at valley bottoms and are thus over such time periodes decoupled from the influence of the westerly flow regime (local scale loss of influence). This study corroborates with an increasing number of similar investigations that vegetation does react in a sensitive way to variations of its atmospheric environment across various temporal and spatial scales.
Poster Session 4, Poster Session: Plants, Phenology, and Drought
Thursday, 31 October 2002, 12:30 PM-1:30 PM
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