A group of researchers found out that stratospheric processes improve the quality of winter climate forecasts in the Northern Hemisphere.
"In our research we found out that the best forecasts are produced by models which reproduce stratospheric processes well. However, the forecasts in some other stratosphere-resolving models were not better than forecasts by models having artificially simplified stratosphere", says researcher Alexey Karpechko from the Finnish Meteorological Institute.
One of the reasons improving the forecasts by stratosphere-resolving models was that they better forecast global impacts of El Niño on winter climate, including its impacts on European climate. The study concluded that in order to further improve the quality of seasonal forecasts the models have to better simulate the stratospheric coupling with the surface climate.
Predictability of the day-to-day evolution of weather systems in most parts of the world is limited to a period of approximately 10 days ahead. Beyond this limit, only statistical properties of atmospheric conditions can be predicted, for example the mean air temperatures over some period of time. Such predictability is possible because atmospheric conditions are sensitive to other components of the climate system which vary at slower time scales than weather and can push the evolution of the atmosphere towards some preferred states. One of these components is the stratosphere, which is a highly stratified, stable, and dry atmospheric layer found between 10 and 50 km above the surface, i.e. above the layer where the weather systems form. Although the stratosphere is not directly involved in the development of daily weather, stratospheric conditions influence weather and climate variability.
Traditionally forecast models included only a simplified representation of the stratospheric processes; however scientists currently believe that further improvements of long-range forecasts, such as forecasts of seasonal climate, require better modelling of the stratosphere. The study is published in the Quarterly Journal of the Royal Meteorological Society.
Researcher Alexey Karpechko, tel. +358 50 361 3901, email@example.com
Butler A. H., O. Alves, A. Arribas, M. Athanassiadou, J. Baehr, N. Calvo, A. Charlton-Perez, M. Déqué, Daniela I.V.Domeisen, H. Hendon, Y. Imada, M. Ishii, M. Iza, A. Yu. Karpechko, A. Kumar, C. MacLachlan, W. J. Merryfield, W. A. Müller, A. O'Neill, A. A. Scaife, J. Scinocca, M. Sigmond, T. N. Stockdale, and T. Yasuda (2016), The Climate-system Historical Forecast Project: Do stratosphere-resolving models make better seasonal climate predictions in boreal winter? QJRMS, doi:10.1002/qj.2743
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