A European pattern climatology 1766-2000
Casty, Carlo ; Raible, Christoph ; Stocker, Thomas ; Wanner, Heinz ; Luterbacher, Jürg
In: Climate Dynamics, 2007, vol. 29, no. 7-8, p. 791-805
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- Using monthly independently reconstructed gridded European fields for the 500hPa geopotential height, temperature, and precipitation covering the last 235years we investigate the temporal and spatial evolution of these key climate variables and assess the leading combined patterns of climate variability. Seasonal European temperatures show a positive trend mainly over the last 40years with absolute highest values since 1766. Precipitation indicates no clear trend. Spatial correlation technique reveals that winter, spring, and autumn covariability between European temperature and precipitation is mainly influenced by advective processes, whereas during summer convection plays the dominant role. Empirical Orthogonal Function analysis is applied to the combined fields of pressure, temperature, and precipitation. The dominant patterns of climate variability for winter, spring, and autumn resemble the North Atlantic Oscillation and show a distinct positive trend during the past 40years for winter and spring. A positive trend is also detected for summer pattern 2, which reflects an increased influence of the Azores High towards central Europe and the Mediterranean coinciding with warm and dry conditions. The question to which extent these recent trends in European climate patterns can be explained by internal variability or are a result of radiative forcing is answered using cross wavelets on an annual basis. Natural radiative forcing (solar and volcanic) has no imprint on annual European climate patterns. Connections to CO2 forcing are only detected at the margins of the wavelets where edge effects are apparent and hence one has to be cautious in a further interpretation