Abstract : O.4
Reconstruction and climatological analysis of the temperature series of Verona (1741 2006)

Michele Andrighetti, Gabriele Rampanelli, Dino Zardi
Department of Civil and Environmental Engineering, University of Trento, Trento, Italy

A long series of air temperature measurements in Verona has been obtained after careful search of both published and unpublished data in various archives, libraries and academies. Data covering almost uniformly the period 1741-2006 have been collected, along with single observations, the most ancient dating back to 1709.

The series provides a remarkable sample of temperature variations in a transition region between the Alps and the foreland of the Po Plain.

A preliminary assessment about quality and reliability has been performed, also on the basis of metadata and historical information. Gaps have been filled by means of a linear regression line between data of the original nonhomogenised series of Verona and data of a reference series. The latter has been obtained as a weighted mean of the homogeneous series of Milano (1763-1998) and Padova (1725-1997). The weights were the correlation coefficients between the nonhomogeneous series of Verona and the homogeneous ones.

Then the homogeneous series has been normalized to the reference series in order to detect and remove outliers. It turned out that 90% of the outliers were located before 1900, as expected for the better quality of recent instruments against older ones.

Finally the Standard Normal Homogeneity Test has been applied. The corrections applied to the various discontinuity sum up to a total of 1.21 C, with a mean value of the corrections being 0.31 C.

After application of a recursive low-pass filter, highest frequencies of the climatic signal have been filtered out and possible trends evaluated. An overall tendency of increasing temperature on the whole 1741-2006 period has been estimated in 0.40 0.06 C/century, rising to 5.99 0.73 in the last three decades.

Spectral analysis pointed out components amenable to global patterns such as El Nio Southern Oscillation, the North Atlantic Oscillation, the Mediterranea Oscillation and the Sunspot series.