Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension to R. and H.H. Collier for lumber accompanied by an itemized list, May 11, 1857

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension to R. and H.H. Collier for lumber accompanied by an itemized list, May 11, 1857.

Pay roll voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension for repairs to fences and cattle guards etc. in the months of April and May. This document is attached to a time sheet, May 11, 1857

Pay roll voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension for repairs to fences and cattle guards etc. in the months of April and May. This document is attached to a time sheet, May 11, 1857.

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension for April and May, paid to James and Benson Co. for fence repairs, May 11, 1857

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension for April and May, paid to James and Benson Co. for fence repairs, May 11, 1857.

Pay roll voucher # 17 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Northern Division for the month of May, 1857, approved by F. Shanly, chief engineer and W.G. Thompson, assistant engineer, May 27, 1857

Pay roll voucher # 17 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Northern Division for the month of May, 1857, approved by F. Shanly, chief engineer and W.G. Thompson, assistant engineer, May 27, 1857.

Pay roll voucher #16 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the office approved by F. Shanly, chief engineer, May 30, 1857

Pay roll voucher #16 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the office approved by F. Shanly, chief engineer, May 30, 1857.

Pay roll voucher #18 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Southern Division approved by F. Shanly, chief engineer and F.A. Doyle assistant engineer, May 31, 1857

Pay roll voucher #18 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Southern Division approved by F. Shanly, chief engineer and F.A. Doyle assistant engineer, May 31, 1857.

Pay roll voucher #21 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Southern Division approved by F. Shanly, chief engineer and Francis A. Doyle, assistant engineer (copy) June 29, 1857

Pay roll voucher #21 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Southern Division approved by F. Shanly, chief engineer and Francis A. Doyle, assistant engineer (copy) June 29, 1857.

Pay roll voucher #19 from the Port Dalhousie and Thorold Railway Extension, for the office approved by F. Shanly, chief engineer (copy), July 1, 1857

Pay roll voucher #19 from the Port Dalhousie and Thorold Railway Extension, for the office approved by F. Shanly, chief engineer (copy), July 1, 1857.

Pay roll voucher #26 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Southern Division, for the month of July, 1857 approved by F. Shanly, chief engineer and Francis A. Doyle (copy), July 28, 1857

Pay roll voucher #26 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Southern Division, for the month of July, 1857 approved by F. Shanly, chief engineer and Francis A. Doyle (copy), July 28, 1857.

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension to Francis A. Doyle for fees at the Fonthill Registry Office (copy), July 28, 1857

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension to Francis A. Doyle for fees at the Fonthill Registry Office (copy), July 28, 1857.

Pay roll voucher #24 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the office, for the month of July, 1857 approved by F. Shanly, chief engineer (copy), July 31, 1857

Pay roll voucher #24 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the office, for the month of July, 1857 approved by F. Shanly, chief engineer (copy), July 31, 1857.

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension to W.G. Thompson regarding horse hire (copy), Jul. 30, 1857

Voucher from the Engineer Department of Port Dalhousie and Thorold Railway Extension to W.G. Thompson regarding horse hire (copy), Jul. 30, 1857.

Pay roll voucher #25 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Northern Division, for the month of July, 1857 approved by F. Shanly, chief engineer and W. G. Thompson (copy), July 30, 1857

Pay roll voucher #25 from the Engineer Department of Port Dalhousie and Thorold Railway Extension, for the Northern Division, for the month of July, 1857 approved by F. Shanly, chief engineer and W. G. Thompson (copy), July 30, 1857.

Past and recent changes in the North Atlantic oscillation

The North Atlantic oscillation (NAO) is under current climate conditions the leading mode of atmospheric circulation variability over the North Atlantic region. While the pattern is present during the entire year, it is most important during winter, explaining a large part of the variability of the large-scale pressure field, being thus largely determinant for the weather conditions over the North Atlantic basin and over Western Europe. In this study, a review of recent literature on the basic understanding of the NAO, its variability on different time scales and driving physical mechanisms is presented. In particular, the observed NAO variations and long-term trends are put into a long term perspective by considering paleo-proxy evidence. A representative number of recently released NAO reconstructions are discussed. While the reconstructions agree reasonably well with observations during the instrumental overlapping period, there is a rather high uncertainty between the different reconstructions for the pre-instrumental period, which leads to partially incoherent results, that is, periods where the NAO reconstructions do not agree even in sign. Finally, we highlight the future need of a broader definition of the NAO, the assessment of the stability of the teleconnection centers over time, the analysis of the relations to other relevant variables like temperature and precipitation, as well as on the relevant processes involved