Variability in surface atmospheric circulation over Europe from early instrumental records.
The variability of atmospheric circulation is reconstructed over the last two centuries
from surface pressure observations extending into the 18th and 19th centuries at 51 locations
across Europe. Daily observations from London and Paris exist for 1697-1706; these are
analyzed and compared to modem data.
The monthly pressure data have been rigorously checked to ensure compatibility with
modem observational standards. The pressure series have undergone relative homogeneity
tests using a technique developed to deal specifically with these data, and the results
compared to those obtained using well-established homogeneity methods. The method
developed here was shown to be the most appropriate, particularly for the earlier data.
Empirical orthogonal function (BOF) analysis was used to test the stability of
circulation patterns over different periods. The three most important modes of variation were
found: EOF 1) describing the overall covariance of pressure; EOF 2) the strength of the zonal
flow over Europe; and EOF 3) the degree of cycloncity or anti-cyclonicity in the eastern
North Atlantic. The ability of the sparser network of 20 stations available from the early 19th
century to adequately recover the patterns and variability of the full network is demonstrated.
Time series of the North Atlantic Oscillation, the mid-latitude westerly winds, and an index
representing the strength of the westerly air flow between London and Paris have been
constructed and extend back to the 18th century, as well as the period 1697-1706 for Paris and
Correlations between eight temperature series from western and central Europe and the
circulation indices demonstrate the importance of the atmospheric circulation in determining
European temperatures. Running correlations calculated over windows of 25 years reveal
striking non-stationarity in circulation-climate relationships. Spectral analyses of the
circulation indices suggest a shift from high-frequency oscillatory behaviour in the 19th
century to lower frequency behaviour in the 20th