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Anticyclonic atmospheric circulation as an analogue for the warm and dry mid-Holocene summer climate in central Scandinavia
1Department of Earth Sciences, Uppsala University, Villavägen 16, 752 36 Uppsala, Sweden
2Earth Sciences Centre, University of Gothenburg, P.O. Box 460, 405 30, Göteborg, Sweden
3Department of Geology, P.O. Box 64, 00014, University of Helsinki, Helsinki, Finland
Abstract. Climate reconstructions from central Scandinavia suggest that annual and summer temperatures were rising during the early Holocene and reached their maximum after 8000 cal yr BP. The period with highest temperatures was characterized by increasingly low lake-levels and dry climate, with driest and warmest conditions at about 7000 to 5000 cal yr BP. We compare the reconstructed climate pattern with simulations of a climate model for the last 9000 yr and show that the model, which is predominantly driven by solar insolation patterns, fails to produce the reconstructed mid-Holocene dry and warm period in Scandinavia. As an alternative explanation for the reconstructed climate, we hypothesize that the trend from the moist early Holocene towards dry and warm mid-Holocene was caused by a changing atmospheric circulation pattern with a mid-Holocene dominance of summer-time anticyclonic circulation. An extreme case of the anticyclonic conditions is the persistent blocking high, an atmospheric pressure pattern that at present often causes long spells of particularly dry and warm summer weather, or "Indian summers". The hypothesis is tested with daily instrumental temperature and precipitation records in central Sweden and an objective circulation classification based on surface air pressure over the period 1900–2002. It is concluded that the differences between the precipitation and temperature climates under anticyclonic and non-anticyclonic conditions are significant. Further, warm and dry combination, as indicated by mid-Holocene reconstructions, is a typical pattern under anticyclonic conditions. These results indicate that the presented hypothesis for the mid-Holocene climate is likely valid.
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Citation: Antonsson, K., Chen, D., and Seppä, H.: Anticyclonic atmospheric circulation as an analogue for the warm and dry mid-Holocene summer climate in central Scandinavia, Clim. Past Discuss., 4, 585-610, 2008. Bibtex EndNote Reference Manager
