Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Gridded climate fields for Europe since 1500 AD

For the time period 1500-2000 a large number of high-quality climate proxy information and early instrumental station data exist for the European continent. This allows the reconstruction of time series of past climate variability and gridded climate information. Casty et al. (2005) reconstructed independent monthly European temperatures, precipitation and 500 hPa geopotential height fields back to 1766. Pauling et al. reconstructed seasonal European precipitation back to 1500. The approach is based on a Principal Component Regression, where the predictand is the gridded climate field information over Europe and the predictors are instrumental measurements or climate proxy information for the pre-instrumental period. They showed that it is possible to statistically reconstruct gridded climate parameter fields over the North Atlantic and European region for at least the last 500 years.

Precipitation variability over the last half millennium reveals both large interannual and decadal fluctuations. Applying running correlations, major non-stationarities in the relation between large-scale circulation and regional precipitation are found. For several periods during the last 500 years, key atmospheric modes for southern Spain/northern Morocco and central Europe as representations of two precipitation regimes were identified. Using scaled composite analysis, we show that precipitation extremes over central Europe and southern Spain are linked to distinct pressure patterns. Due to its high spatial and temporal resolution, this dataset allows detailed studies of regional precipitation variability for all seasons, impact studies on different time and space scales, comparisons with high-resolution climate models as well as analysis of connections with regional temperature reconstructions.

Casty et al. (2005) presented so-called combined winter climate regimes for the 1766 2000 period over the North Atlantic/European sector. They expand previous studies on recurrent regimes by combining spatially high-resolution independent reconstructions of the 500 hPa geopotential height, land surface air temperature, and precipitation fields. Nonlinear Principal Component Analysis was applied to the data in order to account for the underlying nonlinear dynamics of climate regimes. Three recurrent winter climate regimes are detected. One regime resembles in its pressure, temperature, and precipitation pattern the positive phase of the North Atlantic Oscillation (NAO), whereas the other two regimes are European blocking situations.

Raible et al. (2005) investigated the decadal trend behaviour of the Northern Hemisphere atmospheric circulation using long-term simulations with different state-of-the-art coupled general circulation models (GCMs) for present-day climate conditions (1990), reconstructions of the past 500 years, and instrumental station observations. The multi-model simulations show that strong positive winter NAO trends are connected with the underlying sea surface temperature (SST) and exhibit a SST tripole trend pattern and a northward shift of the storm-track tail. Strong negative winter trends of the Aleutian low are associated with SST changes in the El Niño Southern Oscillation (ENSO) region and a westward shift of the storm track in the North Pacific. The observed simultaneous appearance of strong positive NAO and negative Aleutian low trends is very unlikely to occur by chance in the unforced simulations and reconstructions. The positive winter NAO trend of the last 50 years is not statistically different from the level of internal atmosphere ocean variability. The unforced simulations also show a strong link between positive SST trends in the ENSO region and negative Aleutian low trends. With much larger observed SST trends in the ENSO region, this suggests that the observed negative Aleutian low trend is possibly influenced by external forcing, for example, global warming, volcanism, and/or solar activity change.

The above studies all aim at improving the understanding of the past climate variability of the North Atlantic realm. However, the gridded climate field reconstructions for this region are, until now, restricted to cover the last half millennium. Using the data collected in the project PACLIVA, it should be possible to extend such climate field reconstructions further back in time. It is therefore very important to obtain synthesised and homogenised marine sediment records and ice cores for the North Atlantic region as input variables for the mentioned Principal Component Regression approach to estimate gridded SST of the North Atlantic during the Holocene. Such methods, among others, could pave the way towards new spatial climate reconstructions on much longer time scales than possible today. This is a very challenging task due to difficulties in the dating, temporal resolution, or signal detection of each climate proxy record collected in PACLIVA.

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Climate and Environmental Physics
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