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Abstract:
To investigate relationships between large-scale circulation and regional-scale temperatures during the
last (Eemian) interglacial, a simulation with a general circulation model (GCM) under orbital forcing
conditions of 125 kyr BP is compared with a simulation forced with the Late Holocene preindustrial
conditions. Consistent with previous GCM simulations for the Eemian, higher northern summer 2-m temperatures
are found, which are directly related to the different insolation. Differences in the mean circulation
are evident such as, for instance, stronger northern winter westerlies toward Europe, which are
associated with warmer temperatures in central and northeastern Europe in the Eemian simulation, while
the circulation variability, analyzed by means of a principal component analysis of the sea level pressure
(SLP) field, is very similar in both periods.
As a consequence of the differences in the mean circulation the simulated Arctic Oscillation (AO)
temperature signal in the northern winter, on interannual-to-multidecadal time scales, is weaker during the
Eemian than today over large parts of the Northern Hemisphere. Correlations between the AO index and
the central European temperature (CET) decrease by about 0.2. The winter and spring SLP anomalies over
the North Atlantic/European domain that are most strongly linearly linked to the CET cover a smaller area
and are shifted westward over the North Atlantic during the Eemian. However, the strength of the connection
between CET and these SLP anomalies is similar in both simulations.
The simulated differences in the AO temperature signal and in the SLP anomaly, which is linearly linked
to the CET, suggest that during the Eemian the link between the large-scale circulation and temperaturesensitive
proxy data from Europe may differ from present-day conditions and that this difference should be
taken into account when inferring large-scale climate from temperature-sensitive proxy data.
