Estimates of the North Atlantic Oscillation back to 1692 using a Paris–London westerly index

Abstract

A westerly index for Europe is developed back to 1692 using newly recovered and corrected Mean Sealevel Pressure (MSLP) data from London and Paris. The index is compared against various instrumental and proxy indices of the North Atlantic Oscillation (NAO). In the winter, the Paris-London index depicts a spatial pattern of atmospheric circulation that is bi-modal, with centres of action that are shifted eastwards compared to the NAO. Owing to asymmetry in the NAO the Paris-London index provides a good depiction of positive NAO conditions as well as extreme negative phases of the NAO that arise from reversals of the pressure centres, but less extreme negative NAO conditions are associated with westerly index values approaching zero. The merit in using the Paris-London index lies with its consistency over time as a measure of westerly wind flow, which may not be the case with other proxy-based indices. In the summer, the Paris-London index bears a close relationship to the reconstructed high-summer NAO series of Folland et al. (2009) et al. (1999) NAO reconstruction. An important finding is that the summer NAO was highly variable during the early nineteenth century but was predominately positive on the decadal time scale during that period. Since circa 1970 the summer index has mostly been negative, indicating reduced westerlies and increased blocking conditions that are exceptional in the context of the last 250 years.as well as the summer Luterbacher

Variations in the difference between mean sea level measured either side of Cape Hatteras and their relation to the North Atlantic Oscillation

“…Before approximately 1780, the amplitude of the reconstructed NAO variability is smaller than in the following two centuries, and there is only approximate similarity with other versions of the NAO record in this earlier period (e.g. see Figure 10 of Cornes et al 2013). The anomalous negative value in 2010 has been discussed by Osborn (2011).…”

A 305-year continuous monthly rainfall series for the island of Ireland (1711–2016)

“…Paris-London (PL) Index: Cornes et al (2013) developed the Paris-London index as an indicator of the state of the NAO index. This index, developed from recovered and corrected mean sea level pressure (MSLP) data from the respective cities, provides a consistent measure of westerly air flow over northwest Europe.…”

“…This index, developed from recovered and corrected mean sea level pressure (MSLP) data from the respective cities, provides a consistent measure of westerly air flow over northwest Europe. Full details of the construction of the PL index, together with a comparison with available NAO reconstructions, are provided by Cornes et al (2013). Only seasons with no missing data in any constituent month were employed.…”

Sea-level changes in Iceland and the influence of the North Atlantic Oscillation during the last half millennium

“…Cornes et al, 2013;Hurrell and van Loon, 1997;Jones et al, 1997;and Luterbacher et al, 1999). We therefore first explore the relationship between the NAO and sea level in instrumental records, and then test the hypothesis that the periods of rapid sea-level rise in our Icelandic salt-marsh proxy record are synchronous with reconstructed changes in NAO.…”